Paleocene Vertebrates from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

U.S. GEOLOGICAL SURVEY BULLETIN 2093 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 
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Paleocene Vertebrates from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

Edited by Frank C. Whitmore, Jr., and Cary T. Madden 

U.S. GEOLOGICAL SURVEY BULLETIN 2093 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government. 

Published in the Eastern Region, Reston, Va. 

Manuscript approved for publication Aprill4, 1994. 

Library of Congress Cataloging in Publication Data 

Paleocene vertebrates from Jabal Umm Himar, kingdom of Saudi Arabia I edited by 

Frank C. Whitmore, Jr., and Cary T. Madden. 

p. em.- (U.S. Geological Survey bulletin; 2093A-F) 

"Prepared in cooperation with the Ministry of Petroleum and Mineral Resources, Kingdom 

of Saudi Arabia." 

Includes bibliographical references. 

Supt. ofDocs. no.: Ul9.3:2093A-F 

1. Vertebrates, Fossil-Saudi Arabia. 2. Paleontology-Paleocene. I. Whitmore, 

Frank C., Jr. II. Madden, Cary T. III. Geological Survey (U.S.). IV. Saudi Arabia. 

Wizarat al-Batriil wa-al-Tharwah al-Ma' diniyah. V. Series. 

QE75.B9 no. 2093A-F 

[QE841] 

557.3 s-dc20 94-32990 

[566'.09538] CIP 
CONTENTS 

[Letters indicate the chapter.] 

A. The Umm Himar Formation (Paleocene) of Saudi Arabia and Associated Strata: 

Stratigraphy, Vertebrate Fauna, and Paleoenvironment 

By Cary T. Madden, Frank C. Whitmore, Jr., Dwight L. Schmidt, and Ibne 

Mohammed Naqvi 

B. A Paleocene Percoid Fish, Tentatively Referred to the Family Serranidae, from Jabal 

Umm Himar, Kingdom of Saudi Arabia 

By P.H. Greenwood 

C. Paleocene Amiid Fish from Jabal Umm Himar, Kingdom of Saudi Arabia 

By Mark VH. Wilson 

D. A Paleocene Lungfish, Ceratodus humei Priem 1914, from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

By Frank C. Whitmore, Jr. 

E. Paleocene Pelomedusid Turtles from Jabal Umm Himar, Kingdom of Saudi Arabia 

By Roger C. Wood 

F. Dyrosaurs (Crocodilia, Mesosuchia) from the Paleocene Umm Himar Formation, 

Kingdom of Saudi Arabia 

By Wann Langston, Jr. 

III 

The Umm Himar Formation (Paleocene) of Saudi 

Arabia and Associated Strata: Stratigraphy, 

Vertebrate Fauna, and Paleoenvironment 

By Cary T. Madden, Frank C. Whitmore, Jr., Dwight L. Schmidt, and 

Ibne Mohammed Naqvi 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

U.S. GEOLOGICAL SURVEY BULLETIN 2093-A 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
CONTENTS 

Abstract.......................................................................................................................... A 1 

Introduction . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 1 

Previous Investigations.......................................................................................... 4 

Acknowledgments................................................................................................. 4 

Stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Khurma Formation .. . . . . .. . . . . . .......... ... . . ... .. . . . . . . . .. . . . .. . . . . .. . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . ... . .. . . . . . 4 

U mm Himar Formation......................................................................................... 4 

Chert...................................................................................................................... 5 

Laterite................................................................................................................... 7 

Harrat Hadan Basalt.............................................................................................. 7 

Fauna............................................................................................................................. 9 

Age................................................................................................................................ 13 

Environment . .. . . . . . . . . . . .. . . . .. . . . . .. . . . . .. . . . . . . . .. .. . . . . .. .. .... . . . . . . . . .. .. . . . . . . . . .. . . . .. . . . . .. . .. . .. .. . .. . . . . . . . . . .. . . .. 14 

Other Vertebrate Fossils from the Arabian Peninsula ............ ........... ... .. ..... .... .. .. .. .. ...... 15 

Geologic History........................................................................................................... 16 

References . . . . .. . . . . . . . . . . .. . . . .. . . . . .. . . . . .. . . . . . . . . . .. . . . . . . . .. .. .. . .. . . . . .. .. . . .. . . . . .. . .. .. . . . . . . . . . . .. . . . .. . . . . . . . . . .. .. . . 17 

FIGURES 

AI. Map of western Saudi Arabia, showing location of Jabal Umm Himar area.............................................................. A2 

A2. Geologic map of Jabal Umm Himar area, showing fossil localities........................................................................... 3 

A3. Stratigraphic sections measured at vertebrate fossil localities in the Jabal Umm Himar area.................................... 6 

A4. Composite stratigraphic columnar section of Umm Himar Formation and overlying and underlying rocks in 

Jabal U mm Hi mar area................................................................................................................................................ 8 

A5. Tertiary diagram showing composition of dolomitic limestone from the upper member of the Umm Himar 

Formation . . . . . . .. . . . . . . . . . . .. . . . . . . . . . .. . .. . .. . . . . . . . . .. .. . . . . . . . . .. . . . .. . . . . .. . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . .. . . . . .. . . . . .. . . . . . . . . . .. . .. .. . . . . . . . . . . .. .. ... . . . .. . . . . . .. . . . 11 

A6. Diagram showing isotopic age plotted against K20 content for basaltic rocks from Harrat Hadan and other 

areas............................................................................................................................................................................. 11 

TABLES 

AI. Chemical analyses for Fe20 3 and FeO and semiquantitative spectrographic analyses for other elements in 

iron-oxide materials from the Jabal Umm Himar area ................................................................................................ A9 

A2. Partial chemical analyses, in percent, for major elements of samples from the dolomitic limestone member of 

the Umm Himar Formation, Jabal Umm Himar area. The average of five samples of pisolitic laterite from nearby 

Jabal Saq is also given................................................................................................................................................. 10 

A3. List of vertebrate fossils from the localiJies at Jabal Umm Himar. ............................................................................. 12 

All 
The Umm Himar Formation (Paleocene) of Saudi Arabia 

and Associated Strata: Stratigraphy, Vertebrate Fauna, 

and Paleoenvironment 

By Cary T. Madden, 1 Frank C. Whitmore, Jr.,2 Dwight L. Schmidt,3 and Ibne Mohammed Naqvi4 

ABSTRACT 

The first Paleocene vertebrate fauna known from the 

Arabian Peninsula is represented by fossils collected from 

21 localities at Jabal Umm Himar, near Turabah, Southern 

Hijaz Province, Saudi Arabia. The fossils are from a mudstone, 2-3 meters thick, in the Umm Himar Formation. This 

formation, about 20 meters thick, consists of three members: (1) a basal ferruginous mudstone, (2) an interbedded 

mudstone and shale, from which the fossils were recovered, 

and (3) an upper dolomitic limestone. The Umm Himar Formation is underlain by Nubian-like quartzose sandstone, 

which overlies Precambrian rocks. The formation is overlain by the Harrat Hadan Basalt of late Oligocene and early 

Miocene age. 

The vertebrates include sand sharks (Odontaspis substriata); nurse sharks (Ginglymostoma maghrebianum and 

G. sokotoense); eagle rays (Myliobatis dixoni); torpedos 

(Eotorpedo hilgendorfi); pycnodont fish (Pychodus); perch 

(Parapercichthys arabis); bowfins (Amiidae); catfish (Siluriformes); lungfish ( Ceratodus humei); very large sidenecked turtles (Pelomedusidae); and archaic crocodilians 

(Rhabdognathus spp., Hyposaurus nopcsai, and Phosphatosaurus sp.). The Paleocene age determination for the fauna 

is based upon the stratigraphic ranges of the lungfish Ceratodus humei, the dyrosaurid crocodilians Rhabdognathus 

compressus and Hyposaurus nopcsai, and catfish (Siluriformes). Although not conclusive evidence of a Paleocene 

age, the sharks are consistent with this interpretation. The 

most nearly comparable fauna is that of the Dange Formation of Sokoto Province, Nigeria, whose age has been determined, on the basis of Foraminifera, to be late Paleocene. 

1

P.O. Box lin, El Prado, NM 87529. 

2l).S. Geological Survey, Rm. E-308, NHB 137, Smithsonian Institution, Washington, D.C. 20560. 3U .S. Geological Survey, MS 913, Box 25046, Denver Federal Center, 

Denver, CO 80225-0046. 

4U.S. Geological Survey Saudi Arabian Mission, P.O. Box 1488, 

Jiddah , Saudi Arabia. 

The paleoenvironment of Jabal Umm Himar was estuarine. The presence of a coastal environment indicates that 

at least a shallow sea must have existed in the At Taif region 

during the earliest Tertiary. 

INTRODUCTION 

Jabal U mm Hi mar ("hill of the mother of the donkey") 

is a large hill at lat 21°10'N., long 41°25'E., 100 km east of 

At Taif and 26 km west of Turabah, in the central western 

part of Saudi Arabia (fig. A 1 ). An unimproved desert road 

connecting At Taif and Turabah crosses the Jabal Umm 

Hi mar area (fig. A2) in the Jabal In quadrangle (Gonzalez, 

1973). All parts of the area are readily accessible by fourwheel-drive vehicle over the desert plain. The plain is at an 

altitude of about 1,200 m and small hills rise 10- 50 m above 

it. The conspicuous basalt plateau of Harrat Hadan rises 

nearly 200 m above the desert plain in the northern part of 

the Jabal U mm Hi mar area. 

In 1971 two fossil vertebrates were collected by 

Schmidt and Louis Gonzalez from a small wadi at locality 1 

(fig. A2), 3.5 km northeast of Jabal Umm Himar. In 1974, 

the fossils were identified by Whitmore as representing a 

large member of the Mesosuchia, a widely distributed 

(Africa, Europe, Asia, North America, and South America) 

suborder of archaic crocodilians that originated in the Early 

Jurassic and became extinct in the late Eocene. Additional 

surface material was collected during October 1974 by 

Schmidt, T.H. Kiilsgaard, R.H. Blank, and N.E. Gettings. 

The present report records the Paleocene vertebrates, 

stratigraphy, and environment of deposition in the Jabal 

Umm Himar area. This report is based upon paleontologic 

and geologic field investigations undertaken during JulyAugust 1976 and December- January 1978- 79 (Madden and 

others, 1979). The fossils described in this bulletin constitute the first Paleocene vertebrate fauna known from the 

Arabian Peninsula. 

Specimens discussed in this Bulletin have been 

assigned numbers with the prefix SAP (for Saudi Arabian 

Project) that identify them as to locality, higher taxon, and 

AI 
A2 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Figure Al. Index map of western Saudi Arabia, showing location of the Jabal Umm Himar area relative to the Hail Arch, the 

Sirhan-Turayf Basin, and other geologic features. 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA 

QUATERNARY 

TERTIARY 

PRECAMBRIAN 

4 KILOMETERS 

EXPLANATION 

Holocene ~ ALLUVIUM-Sand, gravel, and silt in wadis 

Miocene 

Paleocene 

~ TERRACE ALLUVIUM 

OLIVINE BASALT 

i=fUl UMM HIMAR FORMATION-Ferruginous mudstone, 

~ mudstone, shale, dolomitic limestone 

~ QUARTZ MONZONITE 

~ META VOLCANIC GREENSTONE 

4 MILES 

• 

Ota 

Geology by lbne Mohammed 

Naqvi July 1976 

Fossil localities 

Line of stratigraphic sections 

x 71288 Sample localities 

Road 

Figure A2. Geologic map of Jabal Umm Himar area, showing fossil sample localities and line of stratigraphic sections 

(fig. A3). 

A3 
A4 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

specimen number within the taxon from a given locality. 

For example, SAP 33-CR-9 signifies the ninth crocodilian 

specimen from locality 33. 

PREVIOUS INVESTIGATIONS 

Brown and others (1963) mapped the region, including 

the Jabal Umm Himar area, as a part of the 1 :500,000-scale 

map of the Southern Hijaz quadrangle. Baghanem (1972) 

described the geology of the Jabal Umm Himar area in a 

master's thesis for the South Dakota School of Mines and 

Technology. In 1970, Baghanem, then a geologist with the 

Directorate General of Mineral Resources (DGMR), Kingdom of Saudi Arabia, collected fossils including remains of 

turtles (order Chelonia) from the Jabal Umm Himar area. 

His fossils were the first collected from the area. 

Gonzalez (1973) mapped and described the Umm 

Himar deposits as a part of the 1: 1 00,000-scale map and 

report of the Jabal In quadrangle. 

ACKNOWLEDGMENTS 

Our field investigations were sponsored by the Directorate General of Mineral Resources, Ministry of Petroleum 

and Mineral Resources, Kingdom of Saudi Arabia, under an 

agreement with the U.S. Geological Survey (USGS). We 

had helpful discussions about the paleontology and geology 

of Jabal Umm Himar with A.H. Baghanem, W.A. Berggren, 

Eric Buffetaut, G.F. Brown, Richard Estes, the late F.J. 

Fitch, L.B. Halstead, D.G. Hadley, the late J.H. Hanley, the 

late W.R. Hamilton, Nicholas Botton III, Roman Karpoff, 

G.E. Mayer, T.H. Kiilsgaard, M.J. Novacek, R.W. Purdy, 

L.F. Rooney, F.S. Simons, N.F. Sohl, I.G. Sohn, V.A. 

Springer, R.K. Stucky, W.R. Taylor, J.A.H. Van Couvering, 

D.J. Ward, S.H. Weitzman, P.J. Whybrow, and G.R. Zug. 

Participants in our various field parties were J.R. Matzko, 

T.H. Kiilsgaard, Farah Warsama, Mohammed Mellah, and 

Mohammed Ali. Wann Langston, Jr., Mark V.H. Wilson, 

and Roger C. Wood contributed stratigraphic and paleoecologic data concerning crocodilians, fishes, and turtles, 

respectively. Their detailed observations appear in succeeding chapters. 

STRATIGRAPHY 

The vertebrate fossils were collected at 21 localities in 

the Jabal Umm Himar area (fig. A2). Fossil bone fragments 

lie on slopes below-and within-a 2-3-m-thick fossiliferous mudstone of the Umm Himar Formation, herein named 

for Jabal Umm Himar. Stratigraphic sections were measured at each fossil locality and 12 of these sections are 

shown in figure A3. The type section for the Umm Himar 

Formation is at locality 3 (figs. A2 and A3). Tentative correlations between sedimentary units are shown on the diagram, figure A3. A composite columnar section, figure A4, 

shows the subdivision of the formation and characteristic 

thicknesses of its members. North of the Jabal Umm Himar 

area, parts of the Umm Himar Formation are exposed discontinuously over about 7,500 km2 around the Harrat 

Hadan plateau (Brown and others, 1963; Gonzalez, ' 1973; 

Baghdadi, 1977). 

The Umm Himar Formation consists of three members: a basal ferruginous mudstone, a middle fossiliferous 

interbedded mudstone and shale, and an upper dolomitic 

limestone. The formation is flat lying and about 22m thick. 

It is underlain by Precambrian rocks consisting of highly 

deformed metavolcanic greenstones and quartz monzonite 

(Gonzalez, 1973). In a few places, thin remnants of a 

quartzitic sandstone of the Khurma Formation (Brown and 

others, 1963) lie between the Umm Himar Formation and 

the Precambrian basement rocks. 

The top of the Umm Himar Formation is a slightly 

undulating erosional surface of possible Eocene age covered by locally derived erosional debris less than 1 m thick. 

In many places this debris is a silicified breccia. Floodbasalt flows of middle Tertiary age overlie the erosion surface and Umm Himar Formation (Gonzalez, 1973). 

KHURMA FORMATION 

Erosional remnants of white to tan, fluviatile quartzitic 

sandstone and quartz-pebble conglomerate, from 2 to 4 m 

thick, are exposed at several places in the Jabal U mm Himar 

area; such a remnant, not mapped on figure A3, occurs at 

locality 41 (fig. A4 ). The conglomerate lies directly on 

saprolitic quartz monzonite. Conspicuous crossbedding 

suggests a generally northerly transport direction (Baghanem, 1972). The rocks are commonly friable but locally are 

well cemented by silica and iron oxide. The conglomerate 

contains rounded to subrounded pebbles that are as large as 

1.2 em in diameter and that average 0.6 em across (Baghanem, 1972, p. 17). The sandstone appears to have been gently deformed and to lie with slight angular unconformity 

beneath the Umm Himar Formation. The quartzitic facies 

contrasts sharply with the overlying mudstone of the Umm 

Himar Formation. The sandstone is tentatively correlated 

with the Khurma Formation that Brown and others (1963) 

mapped on the northeastern side of the Harrat Hadan 

plateau. 

UMM HIMAR FORMATION 

The basal member of the Umm Himar Formation consists of red-brown oolitic iron oxide and mudstone from 2 to 

4 m thick (figs. A3 and A4). In most places the ferruginous 

mudstone member lies on saprolitic quartz monzonite of 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA AS 

Precambrian age, but in a few places, it lies unconformably 

on the Khurma Formation. 

The ferruginous mudstone is massive to poorly bedded, its lower part is characterized by oolitic iron oxide and 

irregular, fist-sized lumps of massive iron oxide, or bog 

iron. The oolites are from 0.3 to 2 mm in diameter and have 

nuclei of broken oolites, detrital grains, and fossil fragments 

(Baghanem, 1972). A bog iron specimen (no. 71242) from 

locality 3 contains about 6S .S percent total iron as Fe20 3 

and FeO. A vertical channel sample (no. 71244) through 

50 em of oolitic iron oxide contains about 61 percent total 

iron as Fe20 3 and FeO, whereas a vertical channel sample 

(no. 71243) through 1 m contains about 4S percent total iron 

as Fe20 3 and FeO (table AI). Interstitial quartz, calcite, 

chlorite, and goethite fill the space between the goethitic 

oolites (Baghanem, 1972, p. 21 ). The upper part of the 

member is ferruginous mudstone containing abundant root 

casts, as much as 3 em in diameter, filled with iron-oxide 

oolites. 

The middle member of the Umm Himar Formation is 

greenish-gray mudstone and tan shale from S to 10m thick. 

The lower half is massive, thick-bedded mudstone, containing detritus, abundant montmorillonite, illite, and subordinate gypsum (Baghanem, 1972, p. 24 ). Fossil bones are 

locally abundant in the lower 2-3 m. Most of the bones are 

disoriented fragments, but a few are articulated. 

Carbonate fluorapatite and montmorillonite, according 

to x-ray diffraction analyses, make up one or more conspicuously white beds, from 3 to 10 em thick, in the lower half 

of the member. The P20 5 content of one bed is S.96 percent 

(chemical analysis by DGMR-USGS Chemical Laboratory, 

Jiddah). Detrital grains, largely quartz, are sparse. Dispersed oolites, about 1 mm in diameter, have well developed concentric structure and make up to 20 percent of the 

sample. They consist largely of montmorillonite and carbonate fluorapatite. The upper part of the middle member 

and the shaly (low~r) part of the upper member, in total a 

dolomitic shale, contain 1.37 percent P20 5 (vertical channel 

sample through 7 m, no. 116218, table A2), which suggests 

that the entire shale part of the section is slightly 

phosphatic. 

The upper half of the middle member consists largely 

of interbedded siltstone and shale. Bedding becomes well 

developed to laminated near the top where the shale is commonly highly fissile. 

The upper member of the Umm Himar Formation consists of gray, fine-grained dolomitic limestone that weathers 

yellowish tan; the rock is mostly well indurated but locally 

is chalky and white. The top is a greatly undulating erosion 

surface. The preserved thickness of the member is commonly about 6 m, and the maximum thickness is about 11 

m. Bedding ranges from thick bedded to laminar. At most 

places the lower contact with the shale is abrupt, but in 

some places the lower few meters consist of impure to silty 

limestone, or of interbedded limestone and shale. Fossil 

invertebrates and shell debris are present locally. At least 

one bed of gastropod coquina, from 10 to 20 em thick, lies 

near the upper part of the stratigraphic section. Baghanem 

(1972, p. 28) reports well-preserved pelecypods and gastropods, as well as scattered quartz grains, carbonate oolites, 

and cross laminae. The composition of the carbonate rock is 

highly variable (table A2, fig. AS) and all samples but one 

are highly siliceous. 

Small sills of basalt intrude the mudstone and shale 

(middle) member and the dolomitic limestone (upper) 

member at two localities (localities 3 and 34, fig. A3). The 

basalt is related to the Oligocene and Miocene Harrat 

Hadan Basalt. The intrusive basalt locally deforms the bedding of the Umm Himar Formation. This deformation and 

associated contact metamorphism are intense in places outside the Jabal Umm Himar area of figure A2 where larger 

sills and plugs of basalt intrude the formation. The intrusion 

causes local silicification and minor iron oxide replacement 

of the carbonate rock. One irregular pod of replacement iron 

oxide, 3m long and 2m wide, at locality 3, contains about 

63 percent total iron as Fe20 3 (712S2, table AI). The Fe20 3 

content of the carbonate rock is from 1.S to 4.1 percent 

(table A2). The replacement iron contains 1.37 percent FeO, 

which is proportionately 1.5 to 19 times more abundant than 

the FeO content of the oolitic iron (table AI). The replacement iron was probably hydrothermally reworked from the 

sedimentary iron in the section during the emplacement of 

the intrusive basalt. 

CHERT 

A siliceous breccia commonly forms a resistant, nonconformable top on the dolomitic limestone member of the 

Umm Himar Formation (fig. A3). This cap rock of silicified 

chert has protected and preserved the Umm Himar Formation. The white cherty breccia weathers dark brown and is 

commonly from O.S to 1.S m thick. It consists of silicified, 

angular fragments, from O.S to 3 em across, of former carbonate including locally abundant shell debris, as well as 

other detritus. The siliceous breccia is probably silicified 

colluvium developed on a low-relief erosional surface cut 

on the dolomitic limestone of the Umm Himar. Remnants of 

iron oxide overlie the siliceous breccia ih many places, 

especially where nearby outcrops of basalt have protected 

the iron oxide from erosion. Silicification extends downward into the dolomitic limestone of the U mm Himar; 

the gastropod coquina bed is especially well silicified. 

Baghanem (1972) describes two beds containing abundant 

gastropods and pelecypods that are replaced by silica near 

the top of the dolomitic limestone member. Brown and others (1963) mention a "silicified coquina of 'Melanoides'-

like freshwater snails." It is unlikely that the chert is sedimentary silica related to the deposition of the U mm Hi mar 

Formation. It is more probable that the silica is a product of 
METERS 

161; 

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Locality 27 

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tc 

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r 

c 

:: 

:: 

::c: 

~ ;J> 

~ 

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a 

0 

0 

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"'1 

en 

;J> 

c 

S2 

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:;:zj 

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tc 

> 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA A7 

soil processes and laterization following deposition of the 

Umm Himar Formation. 

LATERITE 

A pisolitic iron-oxide layer, in places several meters 

thick, lies above a jaspery substratum. This layer is always 

adjacent to, and overlain by, basalt, in such a way that 

abundant basalt talus obscures the stratigraphic relations. In 

places it is inferred to overlie the dolomitic limestone member of the Umm Himar Formation and hence probably lies 

on the silicified upper part of the formation. At Javbal Saq, 

10 km west of the northwestern corner of the geologic map 

(fig. A2), a pisolitic iron-oxide layer of laterite (Martin, 

1969, p. 11), about 5 m thick, lies on sandstone and quartzpebble conglomerate (Khurma Formation?) and is overlain 

by Tertiary basalt. The average composition of five samples 

from the Jabal Saq locality (Martin, 1969, p. 8) is given in 

table A2. Baghanem (1972, p. 36) refers to similar ironoxide layers as "reworked ferric oxide deposits," some 

about 2 m thick. They rest on Precambrian rocks or on sandstone and are overlain by Tertiary basalt. A calcic phase in 

the "reworked deposits" (Baghanem, 1972, p. 37) is probably a carbonate cement deposited in the laterite by carbonate waters associated with the basalt eruptions. 

The pisolitic iron-oxide layers are lateritic deposits 

formed prior to the deposition of the Tertiary basalt as 

described in the As Sarat area, 350 km south of Harrat 

Hadan (Overstreet and others, 1977). In the As Sarat area, 

the laterite formed during Eocene and early Oligocene time 

and was covered by upper Oligocene to lower Miocene 

basalt. A thick saprolite underlies the lateritic and silicic 

paleosoil zones in both the As Sarat and the Harrat Hadan 

areas. 

HARRAT HADAN BASALT 

Alkalic olivine basalt underlies the Harrat Hadan plateau, which rises nearly 200m above the surrounding plain. 

Numerous buttes are erosional outliers of basalt flows 

whereas other buttes and conical hills are necks of basalt 

feeders. The outliers of basalt rest upon the Umm Himar 

Formation on all sides of the basalt plateau. The steep basalt 

scarps of the plateau and butte landforms are perpetuated by 

the underlying, less resistant Umm Himar beds. However, 

the basalt itself is highly saprolitic beneath its own erosionally resistant outcrop and basalt talus, and this soft, deeply 

weathered basalt also, in part, accounts for the steep basalt 

scarps. 

The Harrat Hadan Basalt has been dated (fig. A6) by 

whole-rock K-Ar method at 27.8 ± 1.4 and 26.6 ± 1.3 Ma 

(lower basalt, olivine tholeiite; Arno and others, 1980); 17.7 

± 0.9, 16.0 ± 0.8, and 15.2 ± 3.0 Ma (upper basalt, basanite; 

Arno and others, 1980); and 16.6 ± 1.5 and 16.2 ± 1.8 Ma 
AS PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

(]) 

c 

(]) 

u 

0 

·;§ 

"0 

@ 

METERS 

1--+----Unconformity 

Upper member 

Middle member 

Lower member 

Erosion surface 

BASALT-Flows 

BASALT -Flows 

CHERT-White. weathers dark-brown; commonly 

silicified limestone detritus (colluvium); top grades 

into pisolitic iron oxide of laterite. 

DOLOMITIC LIMESTONE-Gray, weathers yellow, 

well-bedded, thick-bedded to laminated; top commonly 

grades to chert, in places pink to red, partly silicified 

(about 10 percent). Upper to middle parts in places are 

white and chalky. Lower half, in places 10-60 percent 

interbedded fissile shale and siltstone. In places silicified 

and ferruginous pods are associated with basalt sills, 

to 4 m thick. 

MUDSTONE AND SHALE-Greenish-gray. Upper half 

grades upward to moderately to well-bedded, gray and 

yellow siltstone and fissile shale. Lower half is massive 

mudstone. Lower 2-3 m contains petrified bones and 

white phosphatic clay layer, 0.1 m thick. 

FERRUGINOUS MUDSTONE-Brown, massive- to thickbedded. Upper part contains abundant root casts to 3 em ' 

diameter. Lower 50 em consists of oolitic iron and irregular 

lumps of bog-iron oxide; iron oxide to 60 percent Fe20 3. 

J..!.-.:~....,...:-.!. •:,..... ~-. :;:::::.."? •• '"". -- Unconformity 

QUARTZOSE SANDSTONE AND CONGLOMERATEThin-bedded to laminated, white, fine- to medium-grained, 

friable. soft-sediment deformation, locally silicified. Some 

shale and sandy shale, yellow and friable. Turritella (?)-like 

fossils and wood-fragment casts. 

~--------1- Unconformity 

X 

X 

X 

X 

X 

QUARTZ MONZONITE AND GREENSTONE-Saprolitic; 

bleached and iron stained at contact. 

Figure A4. Composite stratigraphic columnar section of the Umm Himar Formation and overlying and underlying rocks in the Jabal 

Umm Himar area. 

(Brown and others, 1989). A "hornblende phonolite" at 

Jabal 'In, 18 km west of the northwest corner of figure A2, 

has been dated at 22.2 ± 3.5 Ma (Brown and others, 1989) 

and is probably a late fractionation product of the parent 

magma of the Harrat Had an Bas alt. 

Basalt from the Harrat As Sarat, which is a high basalt 

plateau geomorphically similar to Harrat Hadan, has been 

dated 30.3 ± 0.5 and 25.3 ± 0.5 Ma. The Harrat As Sarat 

contains a late fractionated trachyte dated at 22.3 ± 0.2 Ma 

(Brown and others, 1989; Coleman and others, 1975). 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA A9 

Table Al. Chemical analyses for Fe203 and FeO and semiquantitative spectrographk analyses for other elements in iron-oxide materials 

from the Jabal Umm Himar area. See figures A2 and A3 for sample localities. 

[Iron analyses by Masoud Shah, H. Karam, and M. Calcalttawy, DGMR-USGS Chemistry Laboratory, Jiddah, May 23, 1977. 0.0 indicates element looked 

for but not found; other elements also looked for but not found are Ag, As, Au, Bi, Cd, Mo, Nb, Pb, Sb, Sn, and W. All samples are grab samples except as 

noted] 

Sample no. 

Stratigraphic section 

Type of sample 1 

Percent 

Parts per 

million 

Mg 

Ca 

Ti 

B 

Ba 

Be 

Co 

Cr 

Cu 

La 

Mn 

Ni 

Sc 

Sr 

v 

y 

Zn 

Zr 

71242 

B 

64.51 

.86 

.3 

.07 

.15 

150 

70 

7 

15 

150 

70 

50 

300 

30 

50 

0.0 

700 

15 

200 

30 

0 

44.71 

.14 

.3 

.7 

.03 

70 

70 

30 

15 

100 

20 

70 

1,500 

30 

20 

300 

150 

150 

300 

30 

0 

60.04 

.86 

.3 

1.5 

.07 

150 

70 

30 

30 

150 

15 

70 

1,500 

30 

15 

0.0 

500 

70 

300 

70 

71252 

R 

62.59 

1.37 

.07 

. 7 

.15 

70 

300 

15 

50 

150 

15 

150 

700 

70 

7 

300 

300 

100 

300 

150 

71260 

28 

0 

61.32 

.29 

.3 

2 . 

.03 

150 

70 

20 

30 

150 

15 

70 

700 

30 

15 

300 

300 

100 

300 

70 

71261 

28 

0 

49.82 

.36 

.3 

3. 

.07 

150 

70 

20 

70 

150 

15 

70 

1,500 

30 

7 

300 

300 

100 

300 

150 

71265 

2 

0 

63.87 

.07 

.15 

3. 

.07 

70 

500 

15 

30 

150 

15 

50 

1,000 

30 

5 

0.0 

300 

50 

300 

30 

71275 

37 

0 

37.68 

.22 

.15 

3. 

.05 

70 

150 

20 

30 

150 

20 

50 

1,500 

30 

5 

0.0 

300 

50 

300 

20 

1

0, oolitic iron oxide-sedimentary origin in ferruginous mudstone (lower) member of the Umm Hi mar Formation. 

B, bog iron oxide-massive lumps in ferruginous mudstone (lower) member of the Umm Himar Formation. 

R, iron oxide in massive pods replacing dolomitic limestone (upper) member of the Umm Himar Formation. 

P, pisolitic iron oxide in laterite overlying the Umm Himar Formation. 2Channel sample through 1 m, lower part of ferruginous mudstone (lower) member of the Umm Himar Formation. 

3Channel sample through 0.5 m, lower part of ferruginous mudstone (lower) member of the Umm Himar Formation. 

71283 

41 

0 

48.54 

.14 

.07 

5. 

.03 

70 

300 

30 

70 

150 

15 

70 

1,500 

50 

15 

150 

300 

150 

300 

70 

FAUNA 

71288 71289 

See fig. A2 See fig. A2 

p 

44.71 

.07 

.15 

5. 

.15 

50 

150 

20 

30 

150 

20 

50 

700 

70 

15 

0.0 

300 

70 

200 

70 

0 

73.45 

.07 

.07 

1.5 

.07 

150 

500 

30 

30 

150 

15 

70 

300 

70 

15 

200 

700 

150 

300 

50 

The lower part of the Harrat Hadan Basalt and the 

whole of the Harrat As Sarat basalt appear to be of similar 

age between about 30 and 22 Ma, whereas the upper part of 

the Harrat Hadan Basalt above about 20 m of intercalated 

lime,stone appears to range between about 18 and 15 Ma. 

The intercalated uppermost lower Miocene limestone is 

chemically very different from the dolomite and dolomitic 

limestone of the Paleocene Umm Himar Formation (fig. 

A5). We interpret the upper basalt at Harrat Hadan as resting disconformably on the lower basalt. 

The Paleocene vertebrates from the 21 localities have 

been named the Umm Himar local fauna (Madden and 

others, 1979). These vertebrates include sand sharks 

(Odontaspis substriata); nurse sharks (Ginglymostoma 

maghrebianum, G. sokotoense); early torpedos (Eotorpedo 

hilgendorfi); eagle rays (Myliobatis dixoni); three species of 

pycnodont fish (Pycodus spp.); a large amiid (Amiidae gen. 

et sp. indet.), the first Tertiary member of this family from 
A10 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Table A2. Partial chemical analyses, in percent, for major elements of samples from the dolomitic limestone member of the Umm Himar 

Formation, Jabal Umm Himar area. The average of five samples of pisolitic laterite from nearby Jabal Saq is also given. 

[Samples 116216-116221 analyzed by I. Baraja, Masoud Shah, Aziz Khan, and H. Karam, DGMR-USGS Chemistry Laboratory, Jiddah, February 26, 

1978; symbol(-) indicates no determination] 

Dolomitic limestone member 1 Laterite2 

Plot number (fig. AS) 34 43 52 

Sample no. 116221 116219 116217 

Type of sample Dolomite Dolomite Limestone 

Si02 15.50 20.50 .90 

Al203 .76 4.36 .40 

Fe203 1.59 2.55 4.14 

CaO 27.29 24.73 50.60 

MgO 16.75 13.90 3.27 

P205 .01 .17 .04 

C02 37.60 32.80 39.88 

Ignition loss 

61 

116218 

Siliceous 

dolomitic shale 

39.50 

9.90 

9.52 

12.54 

7.67 

1.37 

14.93 

75 

116216 

Dolomitic 

limestone 

12.40 

.94 

3.19 

32.16 

12.84 

.02 

37.41 

Siliceous 

dolomite 

39.20 

18.20 

12.7 

42121-42125 

Pisolitic 

ironstone 

23.8 

.75 

43.1 

2.9 

0.4 

12.6 

1Samples collected near locality 3 (fig. A2) by L.F. Rooney and D.G. Hadley. 

2Data from Martin, 1969, p. 8. Average of five analyses of five representative grab samples from Jabal Saq, 10 km west of the northwest corner of 

figure A2; analyses were made in DGMR-USGS laboratory, Jiddah, 1968. 

3Chip sample through 5.5 m of upper part of member (section no. 3) including silicified top. 

4Chip sample through 4 m of middle and upper part of member (section no. 3). 

5Chip sample through 1.2 m of lower part of member (section no. 3 ). 

6Chip sample through 7 m of lower part of member and shale part of underlying mudstone and shale member (section no. 3). 

7 Grab sample, representative limestone (from near station no. 44, fig. A2). 

8Data from Baghdadi, 1977, p. 11. 

the African continental plate; catfishes (Siluriformes); 

perch (Parapercichthys arabis); a large lungfish (Ceratodus 

humei); large side-necked turtles (Pelomedusidae gen. et sp. 

indet.); and medium to large dyrosaurid crocodilians (Rhabdognathus spp., Hyposaurus nopscai, and Phosphatosaurus 

sp. (table A3). The most notable feature of this fauna is the 

association of taxa that originated during the Mesozoic but 

survived into the early Tertiary: Amiidae, Pycnodontiformes, Ceratodus, Pelomedusidae, and Dyros.auridae. This 

association is characteristic of the earliest Tertiary (Paleocene to middle Eocene) faunas of Africa (Swinton, 1930; 

White, 1934; Arambourg, 1952; Arambourg and Joleaud, 

1943; Priem, 1897). The Umm Himar local fauna has affinities with the Paleocene faunas of Africa because Arabia 

was a contiguous part of that continent until the early 

Miocene (Brown, 1970); since then, as a result of the opening of the Red Sea and other plate movements, Arabia has 

been attached to Eurasia. 

Sharks are represented by Odontaspis substriata, 

Ginglymostoma maghrebianum, and G. sokotoense. The 

genera Odontaspis and Ginglymostoma first appeared in the 

geologic record in rocks of Cretaceous age in Europe, 

Africa, and Asia, and both occupy nearshore or estuarine 

habitats in coastal waters (Bigelow and Schroeder, 1948). 

0. substriata is the most common shark at Jabal Umm 

Himar, and apparently also at most other African localities 

during the Paleocene (Arambourg, 1952). The rarest shark 

is G. maghrebianum, which is represented by only one 

tooth, from locality 37. Another Ginglymostoma, G. sokotoense, is sympatric with G. maghrebianum at that locality 

and is known also from locality 36W. 

Torpedos and eagle rays are represented by Eotorpedo 

hilgendorfi and Myliobatis dixoni, respectively. Remains of 

eagle rays were collected from 10 of the 21 localities, 

whereas those of torpedos were collected from only 3 localities. Eotorpedo hilgendorfi is, however, the most common 

species of torpedo known from the earliest Tertiary of 

Africa (White, 1934; Arambourg, 1952; Cappetta, 1972; 

Jaekel, 1904). 

The extinct pycnodont fishes belong to the holostean 

order Pycnodontiformes and are represented by one jaw 

fragment from locality 1 collected in 197 4 by Schmidt, as 

well as by teeth from seven other localities (table 3; Madden, 1983). Pycnodonts were widely distributed during the 

Mesozoic, for they are known from Europe, Asia, Madagascar, Africa, and North and South America. However, only in 

Europe and Africa were these holosteans hitherto known to 

have survived into the Tertiary; they are known from the 

Eocene of Europe·and from the lower Paleocene to middle 

Eocene (Danian to Lutetian) of West Africa. The only genus 
c 4 

Q) 

(.) 

Cii 

a. 

+-' 

..c 

C) 

"Qj 

~ 

0 

N 

~ 

UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA All 

EXPLANATION 

Miocene Limestone 

D L.F. Rooney and D.G. Hadley 

(written commun., 1982) 

+ Martin. 1969 

x Baghdadi, 1977 

Paleocene Dolomitic Limestone 

0 L.F. Rooney and D.G. Hadley 

(written commun., 1982) 

o Martin, 1969 

• Baghdadi. 1977 

X 

CaO 

19 analyses, Miocene limestone 

~ +. (17 Baghdadi, 1977; 2 Martin, 1969) 

02 [] 

+ ' 

+ X 

+ 

MgOL-------------------------------------------------------------------~Si02 

Figure AS. Tertiary diagram (Ca0-Mg0-Si02) showing composition of dolomitic limestone from the upper 

member of the Umm Himar Formation, Jabal Umm Himar area (see table A2), as compared to limestone in the 

overlying Miocene flood basalts. 

~ : 

--- --- _ __,·_~(?,':.. B___; ~: 

• B : B.' 

B • , ___ · ___ · __ · ~~-oO· _j 

' ' 

early Miocene 

20 

AGE (Ma) 

late Oligocene 

25 30 

EXPLANATION 

Harrat Hadan 

• Amo and others, 1980 

0 Brown and others, 1989 

Harrat as Sirat 

D Brown and others, 1989 

!::, Coleman and others. 1977 

\1 Coleman and others, 1975 

Basalt overlying Shumaysi Formation 

(Jiddah area) 

x Brown and others, 1989 

+ Coleman and others, 1979 

P Phonolite 

T Trachyte 

B Basanite 

OT Olivine tholeiite 

Figure A6. Diagram showing isotopic age plotted against K20 content for basaltic rocks from Harrat Hadan and from correlative 

basaltic rocks from other areas. 
Al2 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Table A3. List of vertebrate fossils from the localities at Jabal Umm Himar. 

Locality 

2 4 5 27 28 29 32 33 34 35 36E 36W 37 37E 38 43 58 59 60 

CHONDRICHTHYES (cartilaginous 

fishes) 

SELACHII (sharks)l-3 

Odontaspidae (sand sharks) 

Odontaspis substriata Stromer, 

1910 ······································ X X 

Orectolobidae (nurse and carpet 

sharks) 

Ginglymostoma maghrebianum 

Casier, 1947 .............................. X 

Ginglymostoma sokotoense White, 

1934 ·········································· X X 

BATOIDEA (rays and torpedos) 1•

4 

Torpedininae (torpedos) 

Eotorpedo hilgendorfi (Jaekel, 

1904) ..................................... X X X 

Myliobatidae (eagle rays) 

Myliobatis di.xoni Agassiz, 1843 X X X X X X X X X X 

OSTEICHTHYES (bony fishes) 

PYCNODONTIFORMES I 

Pycnodus sp. (very large) .............. X X X X X 

Pycnodus sp. (medium sized) ........ X X 

Pycnodus sp. (small) 

AMIIFORMES6•

9 ......................................... X X X X 

Amiidae gen. et sp. indet. .............. X 

SILURIFORMES (catfishes)5·6 ............. X X X X 

PERCIFORMES 

Parapercichthys arabis 

Greenwood, 1983. ...................... X 

DIPNOI (lungfishes)4 

Ceratodontidae 

Ce ratodus humei Priem, 1914 ... X 

REPTILIA (reptiles) 

CHELONIA (turtles)7 

Pelomedusidae (side-necked 

turtles) gen. et sp. indet. ............ X X X X X X X 

CROCODILIA I.4.H 

Dyrosauridae (archaic crocodiles) 

Hyposaurus nopcsai ...................... X X 

Rhabdognathus compressus .......... X X 

Rhabdognathus sp ......................... X X X X X 

Phosphatosaurus sp ....................... X 

Dyrosauridae, gen. et sp. indet. ..... X X X X X X X X X X X 

1Identified by C.T. Madden. 6Jdentified by R.K. Stucky. 

2Identified by R.W. Purdy. 7Identified by R.C. Wood. 

3Identified by D.J. Ward. ~Identified by Wann Langston, Jr. 

4Identified by F.C. Whitmore, Jr. 9Identified by M.V.H. Wilson. 

5fdentified by W.R. Taylor. 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA A13 

known from the lower Tertiary is Pycnodus; the fossils from 

Jabal Umm Himar are assigned to that genus. On the basis 

of tooth size we estimate that three species were present. 

The upper jaw bone from locality 1 represents the largest 

pycnodont known from Africa. 

Amiids are represented by a single vertebra from locality 2, interpreted as an anterior caudal centrum of a large 

species, probably not congeneric with any amiid of Tertiary 

age (Wilson, Chap. C, this volume). Until now, only polypterids and lungfishes were known from Paleocene freshwater deposits in Africa (Van Couvering, 1977). Fossil Amia 

species are known from Tertiary freshwater deposits of Eurasia and from Cretaceous and Tertiary freshwater deposits 

of North America (Boreske, 1974). The occurrence of a 

Paleocene amiid in an assemblage that has African affinities 

suggests either incomplete isolation of the African-Arabian 

freshwater fauna or a long prior history for amiids on the 

African plate. 

Catfish spines and vertebrae were recovered from 4 of 

the 21 localities (localities 2, 28, 33, 36W). These remains 

were identified by W.R. Taylor of the U.S. National 

Museum of Natural History and R.K. Stucky, then of the 

University of Colorado Museum. Stucky (written commun., 

1979) has reported that three types of catfishes are represented. Elsewhere in the African plate, catfishes are first 

known from the lower Paleocene (Montian) of the Congo 

(now Zaire; Casier, 1960) and also from the upper Paleocene of Nigeria (White, 1926, 1934; Cappetta, 1972). 

These are the earliest records for the order in the Old World; 

catfish have been reported from the Cretaceous of Bolivia 

(Wenz, 1969) and of Patagonia (Cione and Laffite, 1980) 

and from the Cretaceous of South Dakota (Frizzell, 1965). 

Lungfish are represented by a single tooth of a very 

large Ceratodus from locality 34. This specimen is identified as Ceratodus humei because of its few ridges and large 

size. C. humei is endemic to the African plate. It first 

appeared in the Early Cretaceous and last appeared in the 

Paleocene (Whitmore, Chap. D, this volume). This is one of 

few species of Ceratodus that survived into the Tertiary. C. 

humei was widely distributed; it is known from both North 

and West Africa. 

Turtle remains are known from 15 of the 21 localities, 

but only those from localities 3, 4, 26, 29, 33, 35, and 38 are 

identifiable. These remains represent what is probably a single species of pelomedusid (side-necked) turtles (Wood, 

Chap. E, this volume). The Jabal Umm Himar turtle was 

very large, its shell roughly comparable in size with that of 

the largest living side-necked species, Podocnemis expansa, 

from the Amazon and Orinoco basins of South America; a 

badly fragmented shell from locality 35 measured some 90 

em in length. Modern pelomedusids are confined to South 

America, sub-Saharan Africa, and Madagascar. However, 

this group was much more widely distributed during the 

earliest Tertiary (Wood, 1984): Paleocene side-neckers are 

known from Europe, the Pako-Indian subcontinent, North 

Africa, sub-Saharan Africa, and South America. The Arabian species partly bridges the geographic hiatus between 

the Paleocene pelomedusids known from North Africa and 

those from the Pako-Indian subcontinent. This turtle was 

probably essentially aquatic, judging from its flattened 

shells. 

Crocodilian remains vary in abundance at 15 localities. 

All are recognizable as members of the primitive Suborder 

Mesosuchia, Family Dyrosauridae. Three genera are represented: Rhabdognathus, Hyposaurus, and Phosphatosaurus. 

The Dyrosauridae range from the Late Cretaceous (late 

Maastrichtian) to late Eocene and have been reported from 

North and West Africa, North and South America, and Asia 

(Pakistan and Burma). The Dyrosauridae are thus demonstrated to have had a southern Tethyan distribution (Langston, Chap. F, this volume). The material from Jabal Umm 

Himar includes three partly articulated but incomplete skeletons of the dyrosaur Rhabdognathus sp. This material permits the first attempt at skeletal reconstruction of a 

longirostrine dyrosaur. The Dyrosauridae of the Umm 

Himar Formation strongly resemble those of the Dange Formation, upper Paleocene, of Sokoto Province, Nigeria. 

During excavations at locality 37, large and small 

smooth rounded pebbles and cobbles of quartzite were 

found near the crocodile skeleton. Quartzite rocks are not 

indigenous to the fossil bed, and these were probably transported as gastroliths, or gizzard stones, by the reptile. 

AGE 

The Jabal Umm Himar vertebrate local fauna is 

assigned a Paleocene age on the basis of stratigraphic 

ranges of the lungfish Ceratodus humei, the dyrosaurid 

crocodilians Rhabdognathus compressus and Hyposaurus 

nopcsai, and catfish (Siluriformes ). 

With one questionable exception, C. humei has been 

reported in beds no later than the Paleocene. The two dyrosaur species are known only from the Paleocene of Mali and 

from the Dange Formation (late Paleocene, Thanetian) of 

Sokoto Province, Nigeria, whose age has been determined 

on the basis of Foraminifera (Petters, 1978). Langston 

(Chap. F, this volume) states that the strong resemblance of 

the Umm Himar dyrosaurs to those of the Dange Formation 

suggests a late Paleocene age for the Umm Himar Formation. Ceratodus and the Dyrosauridae are Mesozoic animals 

that survived into the Paleogene of the Tethyan region. 

The catfishes (Siluriformes), on the other hand, are 

typically Tertiary forms. They are unknown in pre-Tertiary 

rocks of Europe, Asia, or Africa, but have recently been 

reported from the Cretaceous of South America. 

The stratigraphic range of the fossil sharks is consistent with a Paleocene age for the Umm Himar Formation. 
A14 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

ENVIRONMENT 

The environment of Jabal Umm Himar in Paleocene 

time was estuarine or lagoonal; the climate was either tropical or subtropical, but probably seasonally arid in the 

nearby interior. These reconstructions are based upon the 

presence of certain vertebrates, their fossilized condition, 

and the type of sediments in which they were deposited. 

All the shark and ray genera identified from Jabal 

Umm Himar occupy salt-water and brackish-water habitats 

in modern seas and oceans. The most notable feature of this 

fauna, from a paleoenvironmental viewpoint, is the presence of nearshore forms. Odontaspis, Ginglymostoma, and 

Myliobatis occupy coastal habitats, either nearshore or estuarine, and are most abundant in shallow waters (Bigelow 

and Schroeder, 1948, 1953). Catfish are also found in both 

fresh and salt water. The presence of Ginglymostoma indicates a tropical or subtropical environment because these 

sharks inhabit only tropical and subtropical seas and oceans 

at present. The dyrosaurs were evidently euryhaline forms 

(Langston, Chap. F, this volume), but like the sharks and 

rays from Jabal Umm Himar, they are most often found in 

shallow marine sediments that indicate nearshore and possibly estuarine environments. 

The lungfish Ceratodus humei indicates a probable 

seasonally arid climate, at least for the nearby interior. Most 

modern lungfish, namely species of African Protopterus 

and South American Lepidosiren, inhabit shallow ephemeral bodies of fresh water in seasonally arid climates. They 

survive in such climates by burrowing into bottom mud and 

aestivating during dry seasons. The single specimen of C. 

humei was probably transported to Jabal Umm Himar from 

a freshwater habitat in the nearby interior. Modern lungfish 

inhabit fresh water exclusively. Assuming that the amiid 

was a freshwater fish that had habits similar to those of 

Holocene Amia, the single vertebra was probably also 

washed into the deposit from a large river or shallow lake 

environment. 

Clams from near the top of the Umm Himar Formation 

were identified by N.F. Sohl and E.G. Kauffman (written 

commun., 1975) and the late J.H. Hanley (written commun., 

1977) as Brachydontes and a Corbicula-like form. The 

association of these two mollusks is indicative of a brackish-water environment. Deposits of this marginal marine 

environment are now exposed over an area of some 60 km 

by 120 krn. 

The fossil bed is composed of shallow-water deposits, 

either lagoonal or estuarine, that are poorly sorted and 

poorly consolidated. Such deposits indicate a low-energy 

environment, one having little or only gentle current action. 

Partly articulated crocodile skeletons at localities 33 and 37 

are consistent with this interpretation. Abundant iron oolites 

and root casts in the bed immediately below the fossil bed 

suggest a lagoonal marsh in which tides provided the agitation for oolitic growth. The deposition of iron oxide in the 

Jabal Umm Himar area also suggests a tropical environment. In the Lake Chad region today, which can be used as 

a modern analog (Lemoalle and Dupont, 1973), iron is 

transported from a tropical zone of lateritic soil to a saline 

environment at Lake Chad where iron is deposited as 

oolites. In Lake Chad the water salinity is a result of an arid 

climate, but at Jabal Umm Himar the depositional salinity 

was provided by the proximity of the sea and aridity need 

not be implied by evidence of the iron oolites. Kaolinite is 

the characteristic product of tropical weathering. Colloidal 

and (or) absorbed iron and kaolinite are transported in acid 

river water. On entering brackish or saline water, the 

solution becomes basic and the kaolinite is converted to 

montmorillonite (the common clay in the Umm Himar 

deposits) and reactive iron is precipitated with silica in the 

form of oolites. 

At Jabal Umm Himar a tropical environment and tropical weathering persisted after the deposition of the Umm 

Himar Formation. This is indicated by the development of a 

laterite upon the Umm Himar deposits. The siliceous part of 

the soil profile is best preserved, but, in places, remnants of 

the pisolitic iron oxide (upper part of the profile) are preserved and overlain by the Harrat Hadan Basalt, which is as 

old as late Oligocene. 

In the southern Arabian Shield, laterite, overlying a siliceous subsoil and thick saprolite, is well preserved beneath 

the basalt flows of the As Sarat; the lowest flows are dated 

about late Oligocene (Coleman and others, 1977). The 

lower basalt flows themselves are partly lateritized (Overstreet and others, 1977, p. 10) and the equivalent Yemen 

Volcanics (formerly Trap Series) to the south contain intercalated paleosols (Overstreet and others, 1977, p. 1 0; Grolier and Overstreet, 1978). 

It is interesting to note that the four types of iron oxide 

deposits in the Jabal Umm Himar area probably have a 

common initial source of iron that is associated with tropical weathering. This is suggested by similar minor-element 

abundances for all the iron types (semiquantitative spectrographic analyses, table AI). The pisolitic iron of the laterite 

was a direct product of tropical weathering of the Umm 

Himar deposits. The oolitic iron and the bog iron, deposited 

in the basal part of the Umm Himar Formation, resulted 

from iron transported from nearby lateritic soils. The 

replacement iron in the dolomitic limestone member probably was hydrothermally reworked iron from the other three 

deposits; the hot intrusive basalt of Harrat Hadan Basalt age 

heated interstitial water in the Umm Himar sediments and, 

through convection, the hot water transported and deposited 

iron in the dolomitic limestone. 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA Al5 

OTHER VERTEBRATE FOSSILS FROM 

THE ARABIAN PENINSULA 

The vertebrate fossils from Jabal Umm Himar represent the first Paleocene vertebrate fauna known from the 

Arabian Peninsula. Fossil vertebrates found elsewhere in 

the peninsula range in age from the Devonian to the late 

Pleistocene. 

Lelieve (1989) reported the first known occurrence of 

Devonian vertebrates in Saudi Arabia. Two dermal plates 

found in the Jawf Formation, northeast of the Arabian 

Shield, seem to indicate an early Emsian age. One plate was 

identified as from an arthrodire, Suborder Brachythoraci, 

and was tentatively referred to the Family Buchanosteidae. 

The other specimen was indeterminate. 

Unidentifiable bones were reported from the Jilh Formation of Triassic age in eastern Saudi Arabia (Powers and 

others, 1966, p. D36). 

F.C. Whitmore, Jr. (written commun., 1976) has identified two vertebrae collected by P.L. Binda (formerly with 

the Saudi Arabian Directorate General of Mineral 

Resources and King Abdulaziz University, Jiddah) from the 

Jurassic Hanifa limestone southeast of Jizan as belonging to 

an archaic (mesosuchian) crocodile. 

Karpoff (1957) reported that fossils collected from the 

Usfan Formation of Eocene age, near Jiddah, include 

sharks; he (written commun., 1977) reports that these forms 

represent galeoids. 

Thomas and others (1989) report terrestrial vertebrates 

of early Oligocene age from the Ashwaq formation at two 

localities in the southern part of the Dhofar (Sultonate of 

Oman). Eleven species of mammal are present, representing 

five orders (Primates, Proboscidea, Embrithopoda, Hyracoidea, and Rodentia). 

R. Meyer (written commun., 1975) has identified a fish 

fauna of modern African or Asian affinities from the lower 

Miocene Baid Formation in the Ad Darb area, Jizan region 

(Schmidt and others, 1982). Dunkle (in Brown, 1970) identified a similar fauna from the same formation and region. 

Powers and others (1966, p. D97) reported the first 

fossil vertebrates from eastern Arabia: indeterminate sharks 

from the Hadrukh Formation of probable early Miocene age 

and indeterminate vertebrates from the Dam Formation of 

early Miocene (Burdigalian) age. Later, Tleel (1973) 

reported fossil mammals from the latter formation, near 

Dhahran; his report is the first published reference to Tertiary mammals from the Dam Formation. Three vertebratebearing lithostratigraphic units of Miocene age have been 

formally named in eastern Saudi Arabia. They are, in 

ascending order of age, the Hadrukh (continental), Dam 

(marine), and Hofuf (continental) Formations (Why brow, 

1984; Whybrow and others, 1987). 

Whybrow and others (1982) described a· fauna from 

the Hadrukh Formation of early Miocene age: rodents, 

including two new genera in the families Zapodidae and 

Cricetidae; antelope; an ochotonid lagomorph; and teeth of 

sharks and teleosts, possibly reworked from lower beds. 

Fossil fruit of the tribe Potamogetoneae (pondweeds and 

ditch grasses) were found. The reports of rodents and plants 

were the first for the Neogene of Saudi Arabia. 

Hamilton and others (1978) recorded two faunas from 

the Dam Formation: (1) the Jabal Midra Ash-Shamali fauna 

includes a fish (Lates), turtle, rabbit, cricetodont rodent (cf. 

Cricetodon atlasi), an indeterminate dipodid rodent, and 

small and medium-sized species of bovids; (2) the Ad 

Dabtiyah fauna consists of fish, turtle, crocodile, two new 

but indeterminate species of dryopithecine apes (see 

also Andrews and others, 1978), an indeterminate carnivore, indeterminate rodents, a geniohyid hyracoid ( cf. 

Pachyhyrax championi), a shovel-tusked gomphotheriid 

proboscidean (Platybelodon [possibly Amebelodon filholi, 

eds.]), two rhinoceroses (Brachypotherium sp. and Dicerorhinus or Aceratherium sp.), two indeterminate species of 

pigs, a chevrotain (Dorcatherium cf. D. libiensis), an indeterminate giraffe, and an indeterminate boselaphine bovid. 

A delphinoid cetacean has also been found in the Dam Formation (Whitmore, 1987). Fossil vertebrates from the Dam 

Formation have also been described by Thomas and others 

(1982) and by Buffetaut (1984). 

Further studies of the Ad Dabtiya local fauna, from the 

continental equivalents of the Dam Formation, have been 

led by P.J. Whybrow (1987). These include a report on a 

new hominoid, Heliopithecus leakyi Andrews and Martin 

1987, separate papers on the mastodons, rhinoceroses and 

ruminants by Gentry (1987), suids (Pickford, 1987) and a 

cyprinid fish (Greenwood, 1987). 

Thomas and others (1978), Sen and Thomas (1979), 

Thomas (1983), and Morales and others (1987) described a 

middle Miocene fauna from the Hofuf Formation near AI 

Jadidah, south of Damman in eastern Saudi Arabia. This 

fauna includes a hyena (Percrocuta sp.), two rodents, a proboscidean (Gomphotherium angustidens), a rhinoceros 

(Dicerorhinus cf. D. primaevus), a pig (cf. Lopholistriodon 

sp.), a giraffe (Palaeotragus sp.), and three species of 

bovids. 

A late Miocene mammalian fauna, including the proboscidean Stegotetrabelodon grandincisivum, occurs at 

Jabal Barakah on the coast of Abu Dhabi in the United Arab 

Emirates (Glennie and Evamy, 1968, p. 81-82; Madden and 

others, 1982; Madden and Whitmore, 1983). Whybrow 

(1989) named the Baynunah Formation, applying the name 

to" ... surface exposures of fossiliferous late Miocene sediments found in the United Arab Emirates and located east 

of 52 degrees, zero minutes east and north of 22 degrees, 30 

minutes north." Jabal Barakah was designated as the type 

section. 

Miocene vertebrates also occur in southwestern Saudi 

Arabia. A fish fauna of early Miocene age was found in the 

Baid Formation at Ad Darb (Madden and Whitmore, 1983) 

and a mammalian fauna including the anthracothere Mas-
AI6 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

ritherium occurs in the same formation at nearby Wadi 

Sabya (Madden and others, I983). 

Brown (oral commun., I977) reports that some years 

ago an advanced horse fossil of late Tertiary age was collected at AI Hufuf Oasis. 

Mammal bones have been found in lake beds of late 

Pleistocene age in the Rub' AI Khali, the Empty Quarter of 

the southern Arabian Peninsula. McClure (1978, p. 261) 

reports Bos primigenius, Bubalus, and Hippopotamus. 

J.W. Whitney collected bones representing a large bovine, 

two species of antelope, Equus sp., and a small canid (F.C. 

Whitmore, Jr., written commun., I980, 198I). 

GEOLOGIC HISTORY 

Vertical movements on the central Arabian arch controlled erosion and sedimentation in central Arabia during 

the Paleozoic and Mesozoic (Powers and others, I966, p. 

DI03). During the Middle Cretaceous, southern Arabia was 

uplifted while northern Arabia continued to subside. The 

Hail Arch first emerged during the Late Cretaceous along 

an axis trending north-northwest through the vicinity of 

Hail (fig. AI). The Aruma Formation, Upper Cretaceous, 

consisting of sandstone and an upper phosphorite bed, 

shows distinct facies changes across the arch. By the Paleocene, during further uplift of the arch and contraction of 

the Tethys Sea, a Mediterranean seaway was separated from 

the eastern seaway of the Arabian Gulf (Powers and others, 

1966, p. DI04). Paleocene deposition is represented by the 

lower part of the Hibr Formation of limestone and phosphorite beds in the Sirhan-Turayf basin of western Saudi Arabia 

on the west side of the arch (Meissner and Ankary, I972) 

and Jordan (Bender, I975) and by the Umm er Radhuma 

Formation (Powers and others, I966) on the east side of the 

arch (fig. AI). 

The Mediterranean seaway transgressed southward 

across Egypt, and Upper Cretaceous ·and Paleocene marine 

beds were deposited; maximum transgression in Egypt was 

during the late Paleocene (Landenian) (Said, I962, p. 144-

I45). Evidence of this marine transgression is not preserved 

in the Sudan (Whiteman, I97I ). Maximum southerly transgression of the seaway reached the vicinity of Jiddah where 

a marine limestone, the Usfan Formation, was deposited 

during the late Paleocene(?) (Karpoff, I957; Brown, I970). 

The Usfan Formation consists of, in ascending order, fossiliferous marine limestone, fine-grained sandstone with 

minor silty sandstone beds, glauconite sandstone (approximately dated at 55 ± 1.2 and 42.8 ± I.O Ma by the whole 

rock K-Ar method), and chert (possibly silicified marl) 

(Brown, I970). Brown and others (1963) report a phosphatic constituent in the Usfan. The maximum southerly 

transgression, the Jiddah embayment, extended more than 

200 km east of Jiddah and east of Taif. A coastal area 

(strand line) existed in the vicinity of Harrat Hadan at the 

Jabal Umm Himar fossil locality. The embayment axis may 

have been in the present location of the Red Sea. 

The eastern boundary of the Jiddah embayment was 

probably along a southern extension of the Hail Arch, and 

the southern embayment perhaps connected with the Paleocene Sirhan-Tirayf basin to the north. At Jabal Umm 

Himar, the Umm Himar Formation, initially_more than 22 m 

thick, was deposited during the Paleocene in a restricted 

lagoonal-estuarine environment. 

In the Harrat Hadan area the Umm Himar Formation is 

underlain by quartzose sandstone and quartz-pebble conglomerate of the Khurma Formation (Brown and others, 

I963). The Khurma Formation is a mature fluviatile deposit 

of Nubian facies. The continental Khurma Formation may 

be correlated with some part of the marine sandstone of the 

Aruma Formation that was deposited in the early SirhanTurayf basin in the northwestern part of Saudi Arabia. In 

Sudan, the youngest Nubian Sandstone is Upper Cretaceous 

(Turonian; Whiteman, 1971, p. 50). In Egypt, the Nubian 

Sandstone underlies Cenomanian deposits (Said, I962, 

p. 3I8). 

After deposition of the Umm Himar Formation, the sea 

receded from the Jiddah embayment. Slight erosion of the 

upper part of the formation resulted in a gently undulating 

surface covered by limestone colluvium. This debris was 

subsequently weathered to a laterite in a semitropical or 

tropical climate both in Saudi Arabia (Overstreet and others, I977) and in Sudan (Delany, 1954). Still later, much of 

the ferriferous part of the lateritic soil was eroded leaving 

the underlying silicic part of the soil profile. This resistant 

silicified soil zone, in addition to a low relief that was near 

sea level, accounts for the preservation of the thin Umm 

Himar Formation for about 30 million years until it was 

covered by the Harrat Hadan Basalt. 

The complete regression of the Paleocene sea by late 

early Eocene is well recorded in the Sinai, Gulf of Suez, and 

northern part of Egypt (Tromp, 1950, p. 386; Said, 1962, p. 

I45). A significant regional unconformity lies at the base of 

the middle Eocene in Egypt (Tromp, 1950). Another broad 

but brief transgression and regression resulted in middle 

Eocene limestone deposition in Egypt. However, in the Gulf 

of Suez, a continuous marine section of late Eocene and 

Oligocene age indicates that some form of narrow seaway 

persisted at least in the Gulf (Tromp, I950). 

In the Jiddah area, the lower and middle parts of the 

Shumaysi Formation were freshwater deposits of early 

Eocene age (Moltzer and Binda, I98I). In contrast, the 

upper part of the Shumaysi contains sparse layers of silicic 

ash that should be correlative to the late Oligocene and 

early Miocene Jizan Group of the southern Red Sea coastal 

plain (Schmidt and others, 1982 ). The uppermost part of the 

Shumaysi consists of siltstone, shale, and limestone containing pelecypods and gastropods of a mixed marine and 

freshwater environment (Al-Shanti, 1966; Moltzer and 
UMM HIMAR FORMATION (PALEOCENE) OF SAUDI ARABIA AND ASSOCIATED STRATA A17 

Binda, 1981), but a marine environment of this age has not 

been reported from anywhere else in the Red Sea region. 

The sedimentary Shumaysi Formation is conformably 

overlain by a thick section of basalt flows dated by the 

whole-rock K-Ar method at 25.9 ± 3.0, 32.6 ± 2.0, 25.8 ± 

5.0 (Brown and others, 1989), and 20.1 ± 0.7 Ma (Coleman 

and others, 1979) and undoubtedly is penecontemporaneous 

to the extension of the lower part of the Harrat Hadan Basalt 

(fig. A6). The Jiddah area rocks were subsequently extensionally block faulted in latest early Miocene time during 

the first-stage seafloor spreading of the Red Sea (Schmidt 

and others, 1982). 

The continental flood basalt of the Harrat Hadan is 

alkalic and of late Oligocene to early Miocene age. The 

earliest alkalic flood basalts from around the Red Sea are 

also of the same age. In Egypt, scattered but widespread 

thin basalt flows overlie fluvio-marine sediments as young 

as late Oligocene and are overlain by lower Miocene marine 

sediments well dated by fossils (Tromp, 1950, p. 390). 

Basal flows of the Ethiopian basalt series in southeastern 

Sudan have been dated at 33 Ma by the K-Ar method 

(Grasty and others, 1963, p. 101) but this date is considered 

too old by Jones and Rex (1974). The basal basalt overlies 

laterite and contains interbeds of mudstone with plant fossils, 0.5 m; limestone with crocodile, catfish, and wrasse 

fossils, 1 m; and dolomite, 0.2 m (Delany, 1954, p. 16; 

Whiteman, 1971, p. 103). The Ethiopian basalt series in 

Ethiopia is dated at 27-23 Ma by Jones and Rex (1974), 

which corresponds well to the As Sarat and lower part of 

the Harrat Hadan ages of 30-22 Ma in southern Saudi Arabia, about 250 km east of the basalts in Sudan and Ethiopia 

(distance with Red Sea closed). Corresponding flood basalts 

in Yemen are between 29 and 20 Ma (Civetta and others, 

1978). In the Afar of Ethiopia, the early volcanics are dated 

from latest Oligocene to early Miocene (Mohr, 1975). 

The Red Sea escarpment was first significantly 

uplifted 5-10 million years after the extensive early continental basalt volcanism and after the initiation of the firststage opening of the Red Sea. This rise of the Red Sea 

escarpment and the resultant elevation of the Harrat Hadan 

plateau started the present erosion cycle there. The erosionally resistant laterite on the Umm Himar Formation formed 

a lagging stripped surface adjacent to the receding basalt 

scarp of the Harrat Hadan plateau. The Harrat Hadan Basalt 

was deeply weathered to saprolite during the Miocene and 

Pliocene, and the low erosional resistance of the saprolitic 

basalt greatly enhanced the stripping process and the development of the plateau landform. Erosion in the Harrat 

Hadan area was augmented by continued uplift of the Red 

Sea escarpment during the second-stage opening of the Red 

Sea after about 5 Ma. The combined uplift has elevated the 

Umm Himar Formation at Harrat Hadan about 1,200 m 

above its probable correlative, the Paleocene marine Usfan 

Formation, near Jiddah. 

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A Paleocene Percoid Fish, Tentatively Referred to 

the Family Serranidae, from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

By P.H. Greenwood 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

U.S. GEOLOGICAL SURVEY BULLETIN 2093-B 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
CONTENTS 

Abstract.......................................................................................................................... B 1 

Introduction .................................................................................................................. . 

Description . .. ... . . . ........... .. . . ............. ... . . . ..... .. . . . . .......... ... . .. . ......... ........ .. . .............. .. . . ....... 1 

Taxonomic Position....................................................................................................... 3 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

FIGURES 

B 1. A, entire specimen (USGS SAP 60-Per-1) in right lateral view. B, outline drawing of identifiable bones 

visible in right lateral view................... ....................................................................................................................... B2 

B2. A, entire specimen (USGS SAP 60-Per-1) in left lateral view. B, outline drawing of identifiable bones 

visible in left lateral view............................................................................................................................................ 2 

B3. A, dorsicranium of entire specimen (USGS SAP 60-Per-1). B, outline drawing of identifiable bones in 

dorsicranium ....... ... . . . . ........ ....... .. ........... .............................. ... .... ....... ... . ................. .. . ................... ....................... ... ..... 3 

BII 
A Paleocene Percoid Fish, Tentatively Referred to the Family 

Serranidae, from Jabal Umm Himar, Kingdom of Saudi Arabia 

By P.H. Greenwood I 

ABSTRACT 

A previously unknown percoid fish, described from the 

Umm Himar Formation, has closest affinities to a family 

now known mostly from marine and brackish water of temperate and tropical regions. Related percoid fishes are 

known from the Paleocene of France, Sweden, and Chile. 

INTRODUCTION 

The holotype and sole example of Palaeopercichthys 

arabis Greenwood (1983, 1987 for a correction to the 

generic name used in 1983) is a somewhat distorted and 

incomplete syncranium (with part of the pectoral girdle) 

from a fish about 18.5 em standard length. It was collected 

as float at the surface of locality 60, Jabal Umm Himar, but 

is from the lower 2-3m of the middle member of the Umm 

Himar Formation (see Madden and others, Chap. A, this 

volume). The specimen (U.S. Geological Survey SAP 

60-Per-1) is temporarily deposited in the U.S. Geological 

Survey's Saudi Arabian collection, Department of Paleobiology, National Museum of Natural History, Washington, 

D.C. 

DESCRIPTION 

Palaeopercichthys arabis is fully described and illustrated below (figs. B l-B3), and its taxonomic affinities 

were discussed in Greenwood (1983). 

Diagnostic features for Palaeopercichthys arabis are 

as follows: 

A serranidlike teleost having the frontal and pterotic 

laterosensory canals in the form of deep and broad gutters 

open except for a short, partially bridged posterior section. 

The frontal canals of each side are separated medially by a 

1

Zoology Department, The Natural History Museum, London SW7 

5BD. 

narrow but prominent wall of bone formed from each frontal. The frontal and parietal bones are without crests, but a 

low, anteromedially directed ridge is present on each parietal. Posteriorly, the frontals are separated by a broad tongue 

of the supraoccipital bone; in dorsal view the outline of the 

supraoccipital is roughly pyriform. 

In lateral view the roof of the occipito-temporal skull 

region rises steeply, and is noticeably domed. The deep 

posttemporal fossa of each side is almost square in outline; 

the supratemporal fossae are shallow and, seemingly, are 

confined to the supraoccipital bone. 

The dentigerous surface of the vomer is heart shaped; 

the existing alveolar scars indicate that the vomerine teeth 

were small and densely arranged. The palatine is a stout 

ploughshare-shaped bone with a deeply grooved lateral 

margin; alveolar scars on its dentigerous region indicate that 

the teeth were probably larger than those on the vomer 

and those situated laterally and posterolaterally on the 

premaxilla. 

The premaxilla is about four-fifths the length of the 

maxilla. It carried a fine felt of small teeth, probably extending the entire length of its lateral dentigerous face; a few, 

somewhat larger, teeth seem to have been present anteriorly. 

There is, apparently, no supramaxilla. The maxilla extends 

to the level of the vertical through the anterior orbital 

margin. 

Regrettably, no elements of the lower jaw are preserved. It is thought, from the orientation of the quadrate 

(after making due allowances for distortion), that the lower 

jaw sloped upwards at an angle of about 30 degrees to the 

horizontal. 

All identifiable elements of the infraorbital series are 

relatively deep bones when compared with those from 

extant serranid and percichthyid taxa. A large suborbital 

shelf is present on the presumed third infraorbital bone. It is 

impossible to determine whether or not any of the infraorbital bones preserved had a serrated ventral margin. 

The outer margins of bones in the opercular series 

apparently are without spines, serrations, or deep indentations, but the operculum probably carried a single, bluntly 

rounded spine on its dorsoposterior border. 

Bl 
B2 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Figure Bl. A, entire specimen (USGS SAP 60-Per-1) in right, 

lateral view. When in situ on vertebral column, dorsal roof of skull 

would slope upwards from vomer at angle of about 40-45 degrees 

to horizontal (and not lie almost horizontally as depicted here). B, 

outline drawing of identifiable bones visible in right lateral view. 

ACH, anterior ceratohyal; ACHL, tip of anterior ceratohyal (left); 

Br, bridge across posttemporal laterosensory canal groove; CL, 

cleithrum; CLH, head of cleithrum; EOC, epioccipital; F, frontal; 

FG, laterosensory canal groove in frontal; FBr, base of bridge 

across frontal laterosensory canal groove; HY, hyomandibula; 

HYPH, hypohyals; lOP, interoperculum; LE, lateral ethmoid; 

MX, maxilla;. MXH, head of maxilla; N, n~sal; OP, operculum; 

PTG 

OPS,? opercular spine; PAL, palatine; PAR, parietal; PMX, 

premaxilla; PMXA, ascending process of premaxilla; POP, 

preoperculum; PR, ridge on parietal; PT, posttemporal; PTF, 

posttemporal fossa; PTG, laterosensory canal groove on 

posttemporal; Pt, pterotic; Ptg, laterosensory canal groove on 

pterotic; Q, quadrate; SE, supraethmoid; SO, suborbital bones; 

S02, 2nd suborbital bone; S03, 3rd suborbital bone; S04, ?4th 

suborbital bone; SOC, supraoccipital bone; SOCC, supraoccipital 

crest (ridgelike portion); SOP, suboperculum; SOS, suborbital 

shelf on 3rd suborbital bone; SPh, sphenotic; UR, urohyal; V, 

vomer; X1, unidentified bone, possibly part of pterygoid arch; and 

X2, unidentified bone, possibly part of hyomandibula. 

?OPS 

Figure B2. A, entire specimen (USGS SAP 60-Per-1) in left lateral view. Matrix-filled orbital region is indicated by stippling. B, o~tline 

drawing of identifiable bones visible in left lateral view. Abbreviations as in fig. B 1. 
A PALEOCENE PERCOID FISH, FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA B3 

Figure B3. A, dorsicranium of entire specimen (USGS SAP 60-

.Per-1 ). B, outline drawing of identifiable bones in dorsicranium. 

Sutures are indicated by dotted lines; the course of frontal and 

pterotic laterosensory canal systems is indicated by dashed lines. 

Abbreviations as in fig. B 1. 

TAXONOMIC POSITION 

Enough diagnostic characters are preserved in the 

holotype to warrant the assignme1,1t of Palaeopercichthys 

arabis to the perciform suborder Percoidei. Its familial 

( assignment is, however, far less certain. On the basis of 

overall similarity, the visible syncranial features seem to 

suggest affinity with certain extant members of the families 

Serranidae and Percichthyidae. Unfortunately the nature 

and condition of the specimen preclude its detailed comparison with the few recorded Paleocene serranids and percichthyids known, for the families respectively, from France, 

Sweden, and Chile (see Arratia 1982). 

Extant percichthyids have a wide distribution in 

marine, brackish, and fresh waters of tropical and temperate 

regions; living serranids, too, are widely distributed in tropical and temperate regions but with only a few taxa occurring in freshwater habitats. Interestingly, Palaeopercichthys 

arabis shares certain derived features with an extant freshwater percichthyid from Australia (Plectroplites ambigua), 

namely the steeply upswept profile to the postorbital skull 

roof and that area's inflated appearance. The fossil shares 

with another extant percichthyid, Perichthys trucha from 

Chilean fresh waters, the apparently derived feature of 

open, gutterlike fronto-pterotic lateral-line canals. The significance, in a phylogenetic sense, of these resemblances 

cannot be evaluated since the only specimen of Palaeopercichthys arabis is both incomplete and damaged, thus not 

revealing any of the diagnostic features that would allow its 

certain placement in either the Percichthyidae or the Serranidae. The visible characteristics that it shares with the 

Serranidae (as currently defined) are its generally plesiomorphic jaw morphology and overall similarity with that 

family in its syncranial organization and morphology. The 

absence from the specimen (either morphologically or 

because of its incompleteness) of features presumed to be 

diagnostic for other basal percoid families adds to the difficulty of assigning the taxon to a definite place in this confused area of percoid taxonomy. 

With this level of uncertainty, and because of the syncranial anatomy having an overall serranidlike facies, the 

taxon is tentatively referred to the Serranidae. 

REFERENCES 

Arratia, G., 1982, A review of freshwater percoids from South 

America (Pisces, Osteichthyes, Perciformes, Percichthyidae 

and Perciliidae): Abhandlungen der Senckenbergischen 

Naturforschenden Gesellschaft, 540, p. 1-52. 

Greenwood, PH., 1983, A new Palaeocene fish from Saudi Arabia: Journal of Natural History, v. 17, no. 3, p. 405-418. 

---1987, A replacement name for Parapercichthys Greenwood (1983), a junior homonym: Copeia, no. 3, p. 787. 

Madden, C.T., Naqvi, I.M., Whitmore, F.C., Jr., Schmidt, D.C., 

Langston, Wann, Jr., and Wood, R.C., 1979, Paleocene vertebrates from coastal deposits in the Harrat Hadan area, At Taif 

region, Kingdom of Saudi. Arabia: U.S. Geological Survey 

Saudi Arabian Project Report 269, 29 p. 

Paleocene Amiid Fish from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

By Mark V.H. Wilson 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

U.S. GEOLOGICAL SURVEY BULLETIN 2093-C 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
CONTENTS 

Abstract.......................................................................................................................... C 1 

Introduction .................................................................................................................. . 

Acknowledgments ................................................................................................ . 

Description of the Specimen ........................................................................................ . 

Discussion...................................................................................................................... 2 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

PLATE 

[Plate follows references] 

C 1. The Saudi Arabian fossil amiid centrum compared with certain other fossil centra. 

FIGURE 

C1. Histological detail of USGS SAP 2-Am-1 in transverse section in the region of neural-arch facets......................... C2 

en 
Paleocene Amiid Fish from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

By Mark V.H. Wilsonl 

ABSTRACT 

A single vertebral centrum from the Paleocene Umm 

Himar Formation near Turabah, Saudi Arabia, represents 

the first Tertiary record of the Amiidae from the Arabian 

Peninsula. The centrum resembles an anterior diplospondylous caudal centrum of Amia or Kindleia in proportions and 

histology, but differs in being much larger, in being more 

circular, and in having hemispherical arch facets. It is probably not congeneric with any described amiid of Tertiary 

age, but with discovery of additional material the Saudi 

Arabian amiid might prove to be closely related to one of 

the genera of large-bodied amiids with ossified vertebrae 

known from Cretaceous formations. 

INTRODUCTION 

Among the Paleocene fossil vertebrates collected from 

Jabal Umm Himar, Kingdom of Saudi Arabia (Greenwood, 

1983; Madden and others, 1979; Chap. A, this volume), is a 

single broken vertebral centrum. This report establishes that 

the centrum represents an amiid fish, and discusses the taxonomic, stratigraphic, and biogeographic significance of this 

identification. 

The fossil, USGS SAP 2-Am 1, was collected in 1974 

from locality 2 of the Jabal Umm Himar local fauna (Madden and others, 1979, Chap. A, this volume, fig. A2). The 

site is in the lower few meters of the middle mudstone and 

shale unit of the Umm Himar Formation, at 21°11.3'N, 

41 °30.8'E, 3 km northeast of Jabal Umm Himar. 

The fossil centrum is probably of Paleocene age and 

almost certainly not older than latest Cretaceous or younger 

than Eocene, based on first and last appearances of taxa 

found at various Umm Himar fossil localities. At locality 2 

the centrum was preserved with remains of torpedos (Turpedininae), eagle rays (Myliobatidae), catfishes (Siluriformes ), and mesosuchian crocodilians (Hyposaurus 

nopcsais, Rhabdognathus compressus, and Rhabdognathus 

1 Department of Zoology and Laboratory for Vertebrate Paleontology, 

The University of Alberta, Edmonton, Alberta T6G 2E9 Canada. 

sp.), an assemblage suggestive of estuarine habitats. The 

taxa found at other Umm Himar sites indicate estuarine or 

lagoonal conditions, with abundant sharks, eagle rays, catfishes, a percoid, side-necked turtles, and crocodilians, 

along with rare pycnodonts, lungfish, and perciforms 

(Greenwood, 1983; Madden and others, 1979, Chap. A, this 

volume). A tropical climate at the time of deposition is suggested by the presence of iron oolites within the Umm 

Himar Formation and by laterite developed on the unconformity that constitutes the top of the formation (Madden 

and others, 1979, Chap. A, this volume). 

ACKNOWLEDGMENTS 

I thank C.T. Madden and F.C. Whitmore, Jr., for 

arranging for my study of the specimen, and Richard Stucky 

and Joseph Nelson for reading a draft of the manuscript. 

Allan Lindoe helped with specimen preparation. This 

research was supported in part by Natural Sciences and 

Engineering Research Council of Canada operating grant 

A9180 to the author. 

DESCRIPTION OF THE SPECIMEN 

The centrum is incomplete, having been broken along 

an oblique plane passing through the middle of the bone (pl. 

C 1, fig. 1). The sagittal plane of the centrum is indicated 

by the presence of two hemispherical excavations that 

are interpreted as neural or haemal arch facets (pl. C 1, 

figs. 2-5). 

It is difficult to orient the centrum correctly because 

there is no reliable indicator of either anterior or dorsal 

directions. However, for the purposes of this description the 

arch facets will be interpreted as neural-arch facets. The 

inferred neural-arch facets are closer to one face of the centrum than to the other, and the face that is more distant from 

the facets is presumed to be the anterior face (pl. C1, fig. 1; 

figs. 2, 3 toward the left). 

The centrum is 15 mm thick (anteroposteriorly), and 

when complete was about 29 mm wide and about 34 mm 

high. It is amphicoelous and imperforate, with the anterior 

Cl 
C2 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Figure Cl. Histological detail of USGS SAP 2-Am-1 in transverse section in the region of neural-arch facets, drawn by camera 

lucida, bone shown in black, pore spaces in white. The section is 

incomplete in the lower right and upper right because of breakage 

of the specimen. 

and posterior faces having conical caps of lamellar bone 

that are thicker at their rims than at their centers. These caps 

show concentric growth rings externally (pl. C 1, fig. 1) and 

definite growth layers in cross section (pl. C1, fig. 2). The 

external surface of the centrum, apart from the anterior and 

posterior faces, has a porous, incomplete (partly eroded) 

layer of lamellar bone that covers porous bone beneath. 

In transverse section the centrum consists of porous 

bone (pl. C 1, figs. 4, 5). The porosity is greatest beneath the 

arch facets and decreases toward the middle of the centrum 

(fig. C1). The less porous parts have been secondarily filled 

by additional bone. 

A distinctive feature is the histology of the bone 

between the arch facets, where layers result from the alternation of bony lamellae and intervening spaces. The bony 

lamellae and other bony partitions throughout the centrum 

are themselves layered on a small scale. These small-scale 

layers are interpreted as growth increments, and are parallel 

to the walls of the pore spaces. 

DISCUSSION 

The centrum is assigned to the Amiidae on the basis of 

external proportions and histology in transverse section. 

The list of taxa with which the centrum has been compared 

includes both freshwater and marine fishes known to have 

been extant during latest Cretaceous to early Tertiary times. 

Late Cretaceous and early Tertiary freshwater and 

marine fishes of Africa and the Arabian peninsula (including fauna from Israel and Lebanon) consist of Elasmobranchii, Polypteridae, Lepidosirenidae, Ceratodontidae, 

Lepisosteidae, Pycnodontidae, Amiidae, and various Teleostei (Chap. A, this volume; Chalifa, 1989; Chalifa and Tchernov, 1982; de Brain and others, 1974; Greenwood, 1974, 

1983; Van Couvering, 1977; Wiley, 1976). The Polypteridae 

and Lepisosteidae have vertebrae with distinctive shapes 

not at all similar to the fossil centrum in question. The Ceratodontidae, Lepidosirenidae and Pycnodontidae lack ossified centra, although some Devonian lungfish have them 

(Schultze, 1970). The calcified centra of elasmobranchs 

have a variety of shapes (Applegate, 1967), including 

spool-shaped forms with hemispherical arch facets, but all 

are concentrically laminated and radially fibrous in transverse section (pl. C1, fig. 9). 

Teleostean vertebral centra are for the most part longer 

and more constricted, having prominent longitudinal ridges. 

However, some teleostean centra, such as those of primitive 

salmoniforms, approach the Saudi Arabian centrum in 

shape, including the possession of hemispherical arch facets. The similarity does not extend to histological features 

seen in transverse section; prominent radiating struts of 

dense bone characterize the teleostean centra (Schaeffer, 

1967; pl. C1, fig. 6), but are not seen in the Saudi Arabian 

fossil. 

The Saudi Arabian fossil centrum is, however, closely 

approximated in external form and histology by centra of 

the Amiidae, a family with a long fossil history but a single 

extant freshwater species in North America (Schultze and 

Wiley, 1984 ). I have compared the Saudi Arabian fossil 

with centra of Amia and with the Late Cretaceous to early 

Tertiary genus Kindleia, included within Amia by some 

authors (Janot, 1967; Boreske, 1974; Gaudant, 1980), and 

synonymized with Cyclurus Agassiz by Gaudant (1987). 

Centra of these genera are imperforate, amphicoelous, 

higher and wider than long, and have a slightly porous 

appearance externally. In transverse section the centra of 

Amia and Kindleia are composed of spongy bone (Schaeffer, 1967), resembling that of the Saudi Arabian fossil in 

detail (pl. Cl, figs. 4, 5, 7, 8). Among the striking similarities are the greater porosity of bone beneath the arch facets, 

and the layered appearance of bony lamellae and intervening spaces between the arch bases (pl. C 1, figs. 5, 7). I 

therefore conclude that the Saudi Arabian fossil belongs 

within the Amiidae. 

In Amia and Kindleia the shape of the centrum differs 

markedly from one end of the vertebral column to the other 

(Boreske, 197 4 ). Trunk vertebrae are wider than they are 

high, and relatively longer than are caudal centra. Diplospondylous caudal centra are in turn shorter than monospondylous caudal centra (Boreske, 1974, fig. 14). The 

proportions of the Saudi Arabian fossil are closest to those 

of diplospondylous caudal centra of Amia or Kindleia near 

the front of the diplospondylous series. 

However, there are important differences between the 

Saudi Arabian fossil and the known species of Amia and 

Kindleia: size and shape of the centrum, and shape of neural 

facets. The fossil is large compared to all known Kindleia 

and almost all known Amia. Although data are not available 

for all species, the estimated height and width of the Saudi 

Arabian fossil are approached only by the largest specimens 

of Amia uintaensis, a Late Cretaceous to early Tertiary 
PALEOCENE AMIID FISH FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA C3 

species from North America (Boreske, 1974), and by Amia? 

chauliodeia Hall and Walberg 1989, a Late Cretaceous species from North America. Second, in Amia and Kindleia, 

caudal centra approach a rectangular shape and neural and 

haemal arch facets are elongated anteroposteriorly and 

often subrectangular or hourglass shaped (Janot, 1967, pl. 

xi, fig. 5; Boreske, 1974, fig. 11) rather than hemispherical. 

It seems clear from these differences that the Saudi 

Arabian amiid is not congeneric with either Amia or 

Kindleia, both of which occur in Cretaceous and early Tertiary freshwater deposits in North America (Hall and Walberg, 1989; Wilson, 1982) and Eurasia (Boreske, 1974; 

Janot, 1967). Late Cretaceous forms other than Amia and 

Kindleia include disarticulated skull bones and vertebrae 

reported by de Brain and others (1974) from lower Senonian continental deposits of Nigeria and said to be similar to 

Amia; Pachyamia, a genus with ossified centra and diplospondyly, reported by Chalifa and Tchernov (1982) from 

Cenomanian lagoonal or marine deposits of Israel; and 

Melvius, a large-bodied amiid described by Bryant (1987) 

from disarticulated but associated remains in the fluvial 

uppermost Cretaceous Hell Creek Formation of North 

America. Another genus in the family is Urocles, from the 

Jurassic and Lower Cretaceous of Europe (Lange, 1968) 

and the Cretaceous of Brazil (Santos, 1960). The amiid 

Enneles is also known from Brazil (Santos, 1960), from the 

Santana Formation of Ceara, and is probably of Early 

Cretaceous (Aptian) age (Forey, 1977). Also often included 

within the Amiidae (Patterson, 1973; Chalifa and Tchernov, 

1982) are the Jurassic and (or) Early Cretaceous genera 

Amiopsis, Ikechaoamia, Liodesmus, Sinamia, and 

Vidalamia, all of which occur in the Northern Hemisphere: 

North America, Europe, northern China and Mongolia 

(Chalifa and Tchernov, 1982; Zhang and Zhang, 1980; Li, 

1984; Liu and Su, 1983). All of these taxa are older than 

Tertiary. 

According to Patterson (1973) and Chalifa and Tchernov (1982), ossified centra arose within the Amiidae-if the 

Late Jurassic Liodesmus, which lacks centra, is correctly 

interpreted as an amiid. Further, most Jurassic and Cretaceous amiids had diplospondyly in the caudal region 

(Schaeffer, 1960; Chalifa and Tchernov, 1982 ), as did Atacamichthys, a Jurassic teleost from Chile not classified as an 

amiid or even as a halecomorph (Arratia and Schultze, 

1987). 

Although most or all of these genera had ossified centra, too little is known about details of their vertebral anatomy to permit meaningful comparisons with the Saudi 

Arabian fossil. A partial exception is Melvius, which had 

caudal centra very similar to but much larger than those of 

Amia, that is, comparable in size to the Saudi Arabian fossil 

but more like Amia in shape. Atacamichthys centra have 

been studied in transverse section (Arratia and Schultze, 

1987), and do not resemble the Saudi Arabian fossil. Any of 

the other genera with ossified centra could be relatives of 

the Saudi Arabian amiid. 

To summarize the above discussion, the fossil represents an amiid with vertebral anatomy similar in histology 

and proportions to Amia, Kindleia, and Melvius, comparable in size to Melvius and some species of Amia but differing from all three in overall shape and in shape of arch 

facets. In view of the anatomical differences between the 

new fossil and Amia, Kindleia, and Melvius, and the geologic age differences between the new fossil and all other 

known amiids, it is unlikely that the Saudi Arabian fossil 

represents a species that has been named. However, I have 

refrained from describing a new taxon on the basis of the 

single fossil centrum because it has been shown that many 

previous descriptions of amiid species, based on vertebral 

characters, are not specifically distinct (Boreske, 1974 ). 

Although all previously reported latest Cretaceous, 

Tertiary, and Holocene amiids are freshwater fish, there is 

some doubt about whether earlier amiids are all freshwater 

fish, as stated by Chalifa and Tchernov (1982), or whether 

some were marine. Although some appear to be in continental deposits (Maisey, 1990), the freshwater status of other 

deposits is doubtful. 

There is also doubt about the habitat of the Saudi Arabian amiid, a fact that restricts its usefulness for interpreting 

the biogeographic history of the family. The fossil locality 

is thought to represent an estuary at the southern extremity 

of a marine transgression from the Tethys Sea to the north 

(Madden and others, 1979; Chap. A, this volume). 

Although some marine taxa are included in the assemblage, 

several others are more probably of freshwater origin. If the 

Saudi Arabian amiid proves to be marine, it would be the 

geologically youngest marine amiid known. 

Although separated from Africa by shallow seaways 

during various parts of its Mesozoic history, the Arabian 

Peninsula is usually considered to be part of or connected to 

the African plate (Smith and others, 1981; Lillegraven and 

others, 1979). If, as seems likely, the Saudi Arabian amiid 

was a freshwater fish, it represents the most recent occurrence of freshwater amiids on the African land mass. The 

family is otherwise missing from the African Tertiary 

record (Greenwood, 1974; Van Couvering, 1977). Because 

amiids have been reported from the lower Senonian of 

Nigeria (de Broin and others, 197 4 ), it is possible that they 

have a long independent history in Africa similar to that 

inferred for gars by Wiley (1976). However, in view of the 

post-Early Jurassic breakup of Pangea and the earliest 

records of the family in the Jurassic, it is possible that the 

Saudi Arabian fossil amiid represents a lineage that survived on the African plate and its connected fragments after 

isolation from its sister group in either Eurasia or South 

America. 

A further possibility is that amiids gained access to 

Africa-Arabia at a time significantly later than the early 

divergence of the family, perhaps from Eurasia, after the 
C4 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

last continental connections between South America and 

Africa were broken in about the late Albian to Turonian 

time interval (Lillegraven and others, 1979). Some terrestrial fossil vertebrates have a distribution that suggests 

Laurasian-African connections during the Cretaceous, as 

for example the occurrence of a pachycephalosaurid dinosaur in the Upper Cretaceous of Madagascar (Sues, 1980). 

The question of amiid history in Africa and the Arabian 

Peninsula cannot be confidently answered on present evidence, although a better understanding of the phylogenetic 

relationships of the Saudi Arabian amiid would help, as 

would efforts to find additional amiid fossils in African and 

Arabian deposits of Cretaceous and early Tertiary age. 

REFERENCES 

Applegate, S.P, 1967, A survey of shark hard parts, in Gilbert, P, 

Mathewson, R.F., and Rail, D.P, eds., Sharks, skates and 

rays: Johns Hopkins Press, p. 36-67. 

Arratia, G., and Schultze, H.P, 1987, A new halecostome fish 

(Actinopterygii, Osteichthyes) from the Late Jurassic of Chile 

and its relationships, in Martin, J.E., and Ostrander, G.E., 

eds., Papers in Vertebrate Paleontology in Honor of Morton 

Green: Dakoterra, v. 3, p. 1-13. 

Boreske, J.R., Jr., 1974, A review of the North American fossil 

amiid fishes: Museum of Comparative Zoology, Harvard 

University, Bulletin, v. 146, no. 1, p. 1-87. 

Bryant, L.J., 1987, A new genus and species of Amiidae (Holostei; 

Osteichthyes) from the Late Cretaceous of North America, 

with comments on the phylogeny of the Amiidae: Journal of 

Vertebrate Paleontology, v. 7, no. 4, p. 349-361. 

de Broin, F., Buffetaut, E., Koeniger, J.C., Rage, J.C., Russell, D., 

Taquet, P, Vergnaud-Grazzini, C., and Wenz, S., 1974, La 

faune de vertebres continentaux du gisement d'In Beceten 

(Senonien du Niger): I' Academie des Sciences (Paris), 

Comptes Rendus, v. 279D, p. 469-472. 

Chalifa, Y, 1989, Two new species oflongirostrine fishes from the 

lower Cenomanian (Late Cretaceous) of Ein-Yabrud, Israel, 

with comments on the phylogeny· of the Dercetidae: Journal 

of Vertebrate Paleontology, v. 9, no. 3, p. 314--328. 

Chalifa, Y, and Tchernov, E., 1982, Pachyamia latimaxillaris, new 

genus and species (Actinopterygii: Amiidae), from the Cenomanian of Jerusalem: Journal of Vertebrate Paleontology, v. 

2,no. 3,p. 269-285. 

Forey, PL., 1977, The osteology of Notelops Woodward, Rhacolepis Agassiz and Pachyrhizodus Dixon (Pisces: Teleostei): 

British Museum (Natural History) Geology, Bulletin, v. 28, 

no. 2, p. 123-204. 

Gaudant, J., 1980, Sur Amia kehreri (Poisson Amiidae du Lutetien 

de Messel, Allemagne) et sa signification paleogeographique: 

I' Academie des Sciences (Paris), Comptes Rendus, v. 290D, 

p. 1107-1110. 

---1987, Mise au point sur certains poissons Amiidae du 

Cenozo1que europeen: le genre Cyclurus Agassiz (=Kindleia 

Jordan): PaHiontologische Zeitschrift, v. 61, p. 321-330. 

Greenwood, P.H., 1974, Review of Cenozoic freshwater fish faunas in Africa: Geological Survey of Egypt, Annals, v. 4, 

p. 211-231. 

---1983, A new Palaeocene fish from Saudi Arabia: Journal 

of Natural History, v. 17, no. 3, p. 405-418. 

Hall, J.P, and Wolberg, D.L., 1989, A new Late Cretaceous 

(Campanian-Maastrichtian) amiid (Halecomorphi; Actinopterygii) from the Fruitland Formation, San Juan Basin, New 

Mexico: Journal of Paleontology, v. 63, no. 1, p. 108-115. 

Janot, C., 1967, A propos des amiides actuels et fossiles: Colloques Internationales du Centre National de Ia Recherche 

Scientifique, v. 163, p. 139-153. 

Lange, S.P, 1968, Zur morphologie und taxonomie der fischgattung Urocles aus Jura und Kreide Europas: Palaeontographica, v. 131A, p. 1-78. 

Lillegraven, J.A., Kraus, M.A.J., and Bown, T.M., 1979, Paleogeography of the world of the Mesozoic, in Lillegraven, J.A., 

Kielan-Jaworowska, Z., and Clemens, W.A., eds., Mesozoic 

mammals: the first two-thirds of mammalian history: University of California Press, p. 277-308. 

Li Guo-qing, 1984, Discovery of Sinamia from East Jilin: Vertebrata Palasiatica, v. 22, p. 145-150. 

Liu Hsien-ting, and Su De-zao, 1983, Fossil ami ids (Pisces) of 

China and their biostratigraphic significance: Palaeontologica 

Polonica, v. 28, p. 181-194. 

Madden, C.T., Naqvi, I.M., Whitmore, F.C., Jr., Schmidt, D.L., 

Langston, Wann, Jr., and Wood, R.C., 1979, Paleocene vertebrates from coastal deposits in the Harrat Hadan area, At Taif 

region, Kingdom of Saudi Arabia: U.S. Geological Survey 

Saudi Arabian Project Report 269, 29 p. 

Maisey, J.G., 1990, Stratigraphy and depositional environment of 

the Crato Member (Santana Formation, Lower Cretaceous of 

N.E. Brazil), in Grimaldi, D.A., ed., Insects from the Santana 

Formation, Lower Cretaceous, of Brazil: Bulletin of the 

American Museum of Natural History, no. 195, p. 15-19. 

Patterson, C., 1973, Interrelationships of holosteans, in Greenwood, P.H., Miles, R.S., and Patterson, C., eds., Interrelationships of fishes: Zoological Journal of the Linnean Society, v. 

53, suppl. 1, p. 233-305. 

Santos, R.S., 1960, A posi<;ao sistematica de Enneles audax Jordan 

e Branner da Chapada do Araripe, Brasil: Divisao de Geologia e Mineralogia, Monografia, v. 17, p. 1-25. 

Schaeffer, B., 1960, The Cretaceous holostean fish Macrepistius: 

American Museum Novitates, no. 2011, 18 p. 

---1967, Osteichthyan vertebrae, in Patterson, C., and Greenwood, P.H., eds., Fossil vertebrates: Journal of the Linnaean 

Society of London (Zoology), v. 47, no. 311, p. 185-195. 

Schultze, H.P, 1970, Die Histologie der Wirbelkorper der Dipnoer 

(The histological structure of the centra of dipnoans): Neues 

Jahrbuch fiir Geologie und PaUiontologie, Abhandlungen, v. 

135,no. 3,p. 311-336. 

Schultze, H.P, and Wiley, E.O., 1984, The neopterygianAmia as a 

living fossil, in Eldredge, N., and Stanley, S.M., eds., Living 

fossils: New York, Springer Verlag, p. 153-159. 

Smith, A.G., Hurley, A.M., and Briden, J.C., 1981, Phanerozoic 

paleocontinental world maps: Cambridge, Cambridge University Press, 102 p. 

Sues, H.D., 1980, A pachycephalosaurid dinosaur from the Upper 

Cretaceous of Madagascar and its paleobiogeographical 

implications: Journal of Paleontology, v. 54, no. 5, 

p. 954--962. 

Van Couvering, J.A.H., 1977, Early records of freshwater fishes in 

Africa: Copeia, 1977, no. 1, p. 163-166. 
PALEOCENE AMIID FISH FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA C5 

Wiley, E.O., 1976, The phylogeny and biogeography of fossil and 

Recent gars (Actinopterygii: Lepisosteidae): University of 

Kansas Museum of Natural History, Miscellaneous Publication, no. 64, p. 1-111. 

Wilson, M.V.H., 1982, A new species of the fish Amia from the 

Middle Eocene of British Columbia: Palaeontology, v. 25, no. 

2, p. 413-424. 

Zhang, Mi-man, and Zhang, Hong, 1980, Discovery of lkechaoamia from South China: Vertebrata Palasiatica, v. 18, no. 2, 

p. 89-93. 

PLATE 
Plate Cl 

[The Saudi Arabian fossil amiid centrum compared with certain other fossil centra] 

Figures 1-5. Fossil amiid centrum from Jabal Umm Himar, USGS SAP 2-Am-1. 

1. Anterior view, showing growth rings on anterior face. 

2. Lateral view, showing left neural facet (arrow). 

3. Dorsolateral view, showing right (upper arrow) and left (lower arrow) neural facets. 

4. Entire specimen in transverse section. 

5. Detail of transverse section showing circular profile of the neural facets, porosity beneath 

facets, and alternating bony lamellae and planar pore spaces between facets. 

6-9. Comparative fossil centra in transverse section. 

6. UALVP (University of Alberta, Laboratory for Vertebrate Paleontology) 15488, probable 

salmoniform centrum from Upper Cretaceous Vermilion River Formation, Manitoba, 

Canada, showing radiating bony struts. 

7. UALVP 10833, caudal centrum of Kindleiafragosa Jordan, from Paleocene Paskapoo 

Formation, Alberta, Canada. 

8. UALVP 13862, trunk centrum of a large Kindleiafragosa, from Paleocene Paskapoo 

Formation, Alberta, Canada. 

9. UALVP 70, a spool-shaped centrum possibly of the ray Myledaphus sp., from Upper 

Cretaceous Horseshoe Canyon Formation, Alberta, Canada, showing concentric rings 

typical of chondrichthyan centra. 
j______J 

5mm 

4 

j______J 

5mm 

5mm 

L__j 

5mm 

AMIID CENTRA 

5mm 

5mm 

A Paleocene Lungfish, Ceratodus humei 

Priem 1914, from Jabal U mm Himar, 

Kingdom of Saudi Arabia 

By Frank C. Whitmore, Jr. 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

U.S. GEOLOGICAL SURVEY BULLETIN 2093-D 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
CONTENTS 

Abstract.......................................................................................................................... D 1 

Introduction . . .. . . . . . . . . . . . . . . . .. . . . . .. . . . . .. . . . .. . . . . . . . . . .. . . . . . . ... . .. . . . . . . . . . .. . . . . . . . . . .. . . . . .. . . . . . .. . ............ .. . . . . 1 

Acknowledgments................................................................................................. 1 

Description ... .. . .. . .. . . . . . . . . . .. . . . . .. . . . . .. . . . .. . . . . . . . . . .. . . . . . . . . . ... . ........ .. . . . . .. . . . . . . .. . ... . ... . . . . .. . . . . .. . . . . . . . . . 1 

Comparison with Other African Species of Ceratodus.... .. . . . . .. . . . . . . . . . .. ... .. . . . . .. . . . . .. . . . . .. .. . 4 

Geographic Distribution and Stratigraphic Range of Ceratodus humei. .. . . . . .... .. .. ... .. . . . . 4 

Paleoecology.................................................................................................................. 5 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

FIGURES 

Dl. Index map of western Saudi Arabia showing location of the Jabal Umm Himar area .............................................. D2 

D2. Right pterygo-palatine tooth of Ceratodus humei ........................................... .... ........................................................ 3 

DII 
A Paleocene Lungfish, Ceratodus humei Priem 1914, 

from Jabal Umm Himar, Kingdom of Saudi Arabia 

By Frank C. Whitmore, Jr. 1 

ABSTRACT 

A single pterygo-palatine tooth of a large lungfish, 

identified as Ceratodus humei Priem 1914, was collected 

from the U mm Hi mar Formation of Paleocene age in the 

Harrat Hadan area, At Taif region, in the western part of the 

Kingdom of Saudi Arabia. It was associated with crocodilian remains in a fauna that also includes sharks, rays, bony 

fishes, and turtles. The fauna indicates an estuarine or 

lagoonal environment. The presence of a single lungfish 

specimen, in contrast to the large numbers of lungfish found 

in probable lake beds of Cretaceous and Paleocene age in 

the Sahara, points to the probability that the Saudi Arabian 

specimen was transported, before burial, from a nearby 

body of fresh water. 

The geographic range of Ceratodus humei extends 

from Morocco to western Saudi Arabia; the geologic range 

of C. humei sensu stricto is from Lower Cretaceous to 

Paleocene. 

INTRODUCTION 

A single right pterygo-palatine tooth of a large lungfish 

was collected by Cary T. Madden on July 31, 1976, from the 

Umm Himar Formation of Paleocene age in the Harrat 

Hadan area, At Taif region, Kingdom of Saudi Arabia (fig. 

D1). The specimen was found at locality 34, about 2 km 

north-northeast of Jabal Umm Himar, at lat 21°1l'N., long 

41 °24.3'E. (Madden and others, 1979, fig. 2). The tooth was 

associated with crocodilian remains belonging to the extinct 

suborder Mesosuchia (see Langston, Chap. F, this volume). 

Elsewhere in the Harrat Hadan area, the Umm Himar Formation has yielded sharks ( Odontaspis mac rota, cf. Scapanorhynchus sp., Ginglymostoma maghrebianum, G. 

blackenhorni, and Squatina sp.); rays (Mylobatidae); bony 

fishes (Pycnodontiformes, Amiiformes, Siluriformes, and 

Perciformes); and turtles (Pelomedusidae) (Madden and 

1 U.S. Geological Survey, National Museum of Natural History, Washington, DC 20560 

others, Chap. A, this volume). Of the fossil vertebrates, the 

rays, Crocodilia, and turtles are the most widespread components of the U mm Himar fauna; the single tooth reported 

here is the only lungfish specimen that was found while collecting at 21 vertebrate-bearing localities in the U mm 

Himar Formation. At all the localities "fossil bone fragments lie on slopes below-and within-a 2-3-m-thick fossiliferous mudstone" at the base of the Umm Himar 

Formation (Madden and others, Chap. A, this volume). The 

mudstone is brown and massive to thick-bedded; its upper 

part contains abundant root casts up to 3 em in diameter. 

The lower 50 em consists of oolitic iron and irregular lumps 

of bog-iron oxide (Madden and others, Chap. A, this 

volume). 

ACKNOWLEDGMENTS 

Field investigations and subsequent laboratory studies 

were sponsored by the Directorate General of Mineral 

Resources (DGMR), Ministry of Petroleum and Mineral 

Resources, Kingdom of Saudi Arabia, under an agreement 

with the U.S. Geological Survey (USGS). Participants in the 

field parties were D.L. Schmidt, C.T. Madden, Ibne 

Mohammed Naqvi, J.J. Matzko, T.H. Kiilsgaard, Farah 

Warsama, Mohammed Mellah, and Mohammed Ali. 

I thank Robert W. Purdy and Hans-Peter Schultze for 

reviewing the manuscript, and P.H. Greenwood for furnishing locality data. 

The photographs of the lungfish tooth were taken by 

Robert H. McKinney of the USGS. 

DESCRIPTION 

Class Osteichthyes 

Subclass Sarcopterygii 

Order Dipnoi 

Family Ceratodontidae2 

2Martin (1984, p. 266) assigns C. humei to the Lepidosirenidae, stating that it is an archaic member of that family. 

Dl 
D2 

go ' 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

\ I I 

\' •Tabuk I 

--'l \ 

' ..... , 

' ' 'i, 

·y 

',, 

I 

I 

I 

(' ,--.t i '\ 

Abha•~ t - As SarafFJt- - ""-,~, 

I } ,' ' .. ___ _ \ 

----.. --~·-

, I 

I YEMENi -~---·-·- -----~~--

31 

Figure Dl. Index map of western Saudi Arabia showing location of the Jabal Umm Himar area relative to the Hail Arch, the SirhanTurayf Basin, and other geologic features. ' 
A PALEOCENE LUNGFISH, CERATODUS HUMEIPRIEM 1914, FROM JABAL UMM HIMAR D3 

8 

c 

Figure D2. Right pterygo-palatine tooth of Ceratodus humei, USGS SAP 34-LNG-1. A, occlusal view; B, external view; C, medial 

view; D, dorsal view. xi. 

Ceratodus humei Priem 1914 

Figure D2 

A single right pterygo-palatine tooth (USGS SAP 

34-LNG-1) of a large lungfish was collected at locality 34. 

The occlusal surface (fig. D2A) measures 72.4 mm anteroposteriorly; its width, from the second crest to the mesialointernal angle, is 46.3 mm. These are the measurements 

used by Tabaste (1963). The antero-internal border of the 

tooth, which lies on the midline of the palate, is almost 

straight for a distance of 45 mm posterior to the anterior 

apex of the tooth. The postero-internal border, which is 35 

mm long, is at an angle of 55 degrees to the antero-internal 

border. The postero-external border, gently curved and 29 

mm long, lies at approximately a right angle to the posterointernal border. The antero-external border is 66 mm long; it 

lies approximately parallel to the postero-internal border. 

On the antero-external border of the tooth are four 

crests (figs. D2A, B). The first three are sharply pointed and 

prominent; the fourth is much lower and forms the external 

termination of a low sharp ridge that runs about halfway 

across the tooth and blends with the reticulate occlusal 

surface. The height of the crests decreases from front to 

back: The first and third crests rise prominently above the 

general occlusal surface and have no medially trending 

ridges. A low ridge runs posteromedially from the second 

crest about halfway across the tooth, where it blends with 

the reticulated occlusal surface. 

These characters match the emended diagnosis of the 

species presented by Tabaste (1963, p. 443; translated from 

French by F.C.W.): "Masticating surface of the teeth, both 

upper and lower, almost plane, without crest. Crests reduced 

to 4 strong denticulations of the labial border. Mesial border 

rectilinear. Internal border curved." The Saudi Arabian 

specimen closely resembles one from the Maastrichtian of 

In Afarag, Algeria, figured by Tabaste (1963, pl. II, fig. 2). 

It differs from the Algerian specimen in having the mesialointernal angle slightly farther posterior, between the second and third crests. The difference may be due partly to 

abrasion of the internal border of the Saudi Arabian tooth. 

Several wear facets are visible on the crown of the 

tooth. The largest is on the posterolateral side of the first 

crest. It measures 16.8 mm dorsoventrally and 8.6 mm 
D4 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

transversely and is so extensive that it may have removed 

the crown of the crest, altering the outline of the tooth as 

seen in occlusal view. In other palatine teeth of Ceratodus 

humei the first crest curves anterolaterally (compare Arambourg and Joleaud, 1943, pl. III, figs. 7 and 8); this may 

have been true of the tooth from Saudi Arabia when it was 

unworn. 

There is a small facet, 6.1 mm anteroposterior and 3.4 

mm wide, on the tip and anterior face of the fourth crest. No 

wear facets are visible on the second and third crests. A single facet runs along almost the entire width of the posterior 

edge of the tooth crown. It begins at the lateral edge of the 

crown and extends medially for 23 mm. Its maximum 

anteroposterior width is 5.8 mm. There is a round facet, 3.5 

mm in diameter, at the posterior end of the anterointernal 

border. It is at the posterior end of an indistinct discontinuous ridge that runs posteriorly from the first crest. 

The tooth plate is attached dorsally to the heavy pterygoid bone (figs. D2C, D), which has a maximum dorsoventral thickness of 20.7 mm at the midline of the skull, over 

the anterior end of the tooth (fig. D2C). The ascending process of the pterygoid projects posterolaterally above the 

tooth plate, at an angle of 25 degrees with the midline of the 

skull. Its origin lies above the area between the third and 

fourth crests of the tooth plate. The process, which is broken, projects posterodorsally to the posterior edge of the 

tooth plate. At its broken (posterior) end, the process is 19.2 

mm high and 10.1 mm wide. 

Above the tooth plate the pterygoid surface is dorsally 

concave, having a deep anteroposterior trough medial to the 

origin of the ascending process (fig. D2D). 

COMPARISON WITH OTHER AFRICAN 

SPECIES OF CERATODUS 

Ceratodus is a form genus for Mesozoic and Tertiary 

dipnoan tooth plates; skull roofs of Mesozoic lungfishes 

with ceratodontid tooth plates are so distinct from each 

other that they have been assigned to at least four different 

genera (Schultze, 1981, p. 188). Nevertheless, given the 

limitations of available material, it appears that specific distinctions within the form genus are valid and useful (see 

also Schultze, 1981 ). 

The type specimen of C. humei is 34 mm long and 20 

mm wide, much smaller than the Saudi Arabian specimen 

discussed there. Authors after Priem (1914) have assigned 

much larger teeth to the species: Stromer and Weiler (1930) 

report a mandibular tooth 53 mm long and 29 mm wide at 

the second crest; Arambourg and Joleaud (1943) state that 

the largest tooth in their collection is 60 mm long and 50 

mm wide, with the largest mandibular tooth being 45 mm 

long and 35 mm wide; Tabaste (1963) reports the largest 

tooth from her Paleocene collection as being 94 mm long. 

On the occlusal surface of the tooth plate of Ceratodus 

humei the crests are not produced medially as well-defined 

ridges. This is in contrast to the pterygo-palatine teeth of 

other African species of Ceratodus: Ceratodus africanus 

Haug 1905 (Peyer, 1925, pl. 1 and 2; Arambourg and 

Joleaud, 1943, pl. 2 and 3; Tabaste, 1963, pl. 1); C. tuberculatus Tabaste 1963 (pl. 2 and 3); C. tiguidiensis Tabaste 

1963 (pl. 5); C. pectinatus Tabaste 1963 (pl. 6); and C. protopteroides Tabaste 1963 (pl. 6). 

In Ceratodus africanus, the tooth crests are directed 

posteriorly beginning with the third crest (Tabaste, 1963, p. 

442). In the Saudi Arabian specimen, all four crests are 

directed anteriorly, the angle with the sagittal plane increasing from the first crest (parallel to the plane) to the fourth 

(almost at right angles to it). 

In the Saudi Arabian specimen, the ascending process 

of the pterygoid originates above the area between the second and third crests; in C. africanus, it originates between 

the third and fourth crests (Peyer, 1925, p. 5). 

GEOGRAPHIC DISTRIBUTION AND 

STRATIGRAPHIC RANGE 

OF CERATODUS HUMEI 

Ceratodus humei has been reported from the Lower 

Cretaceous of the Djoua Depression on the northeast border 

of the Hoggar, Algeria; southern Morocco; and in Niger 

(Tabaste, 1963, p. 439, 443). Martin (1981, p. 73) identified 

as Ceratodus humei a tooth plate from the lower Cenomanian of Baharija, Upper Egypt, which was referred to C. 

africanus by Peyer (1925). The species is known from the 

Campanian (upper Senonian) of Quft, Upper Egypt (Priem, 

1914, p. 368); of Mahamid, Upper Egypt (Stromer and 

Weiler, 1930, p. 25; Arambourg and Joleaud, 1943, p. 47); 

and of Damergou, Niger (Arambourg and Joleaud, 1943, p. 

47). Greigert and others (1954) placed the Damergou material in the Turonian. Maastrichtian occurrences are at In 

Afarag, Algeria, and at Mt. Igadman and Termeuth, Niger 

(Tabaste, 1963, p. 439--440). 

Tabaste (1963, p. 444) first reported Ceratodus from 

the Tertiary outside Australia. She (1963, table IV) listed C. 

humei from the Paleocene at Cheik Keini and In Fargas, 

Mali. Martin (1984, p. 268) states that C. humei or a closely 

related species persists into the Lutetian (middle Eocene) at 

Tamaguilelt in east central Mali. Savage (1969, p. 169) 

reported Ceratodus sp. indet. from beds of probable late 

Eocene age at Dor el Taha in southern Libya. 

The presence of Ceratodus humei in Saudi Arabia is 

the easternmost occurrence in the geographical range for 

the species that covers almost the entire width of North 

Africa. Its range in Paleocene time, from the eastern Mali to 

Saudi Arabia, almost equals the maximum extent of the species. The geologic range of C. humei sensu stricto was from 

Lower Cretaceous into Paleocene. 
A PALEOCENE LUNGFISH, CERATODUS HUMEI PRIEM 1914, FROM JABAL UMM HIMAR D5 

PALEOECOLOGY 

Tabaste (1963, p. 458) reports that, according to A.F. 

de Lapparent, lungfish teeth are found in large concentrations at widely scattered points in the Sahara. Tabaste interprets these concentrations as perhaps traces of temporary 

lakes where lungfish could survive droughts because of 

their ability to aestivate. 

In contrast to the large numbers of teeth found at 

Saharan localities, the presence of only one lungfish tooth 

in the collections from Jabal Umm Himar suggests that the 

specimen was transported to its place of burial. Its association with crocodilians, in a fauna that also includes sharks, 

rays, bony fishes and turtles, is best explained by interpreting the fauna as estuarine or lagoonal, having lived near the 

mouths of streams in whose drainage system the lungfish 

lived. 

The presence of iron oolites and root casts in the fossilbearing horizon suggests deposition in an estuarine or 

lagoonal marsh (see Madden and others, Chap. A, this 

volume). 

REFERENCES 

Arambourg, Camille, and Joleaud, L., 1943, Vertebre fossiles du 

Bassin du Niger: West French Africa, Direction des Mines, 

Bulletin 7, p. 33-70. 

Greigert, J., Joulia, F., and de Lapparent, A.F., 1954, Repartition 

stratigraphique des gisements de Vertebres dans le Cretace du 

Niger: Comptes Rendus de 1' Academie des Sciences, Paris, v. 

239, p. 433-439. 

Hauf, Emile, 1905, Paleontologie. Documents scientifiques de la 

Mission saharienne (Mission Fureau-Lamy). Publication de 

la Societe de Geographie, Paris, p. 751-832. 

Madden, C.T., Nagvi, I.M., Whitmore, F.C., Jr., Schmidt, D.L., 

Langston, Wann, Jr., and Wood, R.C., 1979, Paleocene vertebrates from coastal deposits in the Harrat Hadan area, At Taif 

region, Kingdom of Saudi Arabia: U.S. Geological Survey 

Saudi Arabian Project Report 269, 29 p. 

Martin, Michel, 1981, Uber drei Zahnplatten von Ceratodus aus 

der Agyptischen Kreide: Mitteilungen der Bayerischen 

Staatssammlung fiir PaHiontologie und historische Geologie, 

Heft 21, p. 73-80. 

---1984, Deux Lepidosirenidae (Dipnoi) Cretaces du Sahara, 

Protopterus humei (Priem) et Protopterus protopteroides 

(Tabaste): Palaontologische Zeitschrift, Bd. 58, Heft 3/4, 

p. 265-277. 

Peyer, B., 1925, Ergebnisse der Forschungsreisen Prof. E. 

Stromers in den Wiistem Agyptens. II. Wirbeltier-Reste der 

Baharije-Stufe (unterstes Cenoman). 6. Die CeratodusFunde: Abhandlungen der Bayerischen Akademie der Wissenschaften, Band 30, Abhandlung 5, 23 p. 

Priem, M.F., 1914, Sur les vertebres du Cretace et de l'Eocene 

d'Egypte: Societe Geologique de France Bulletin, v. 14, 

p. 366-382. 

Savage, R.J.G., 1969, Early Tertiary mamma1locality in southern 

Libya: Proceedings of the Geological Society of London, no. 

1657, p. 167-171. 

Schultze, Hans-Peter, 1981, A dipnoan tooth plate from the Lower 

Cretaceous of Kansas, USA: Transactions of the Kansas 

Academy of Sciences, v. 84, no. 3, p. 187-195. 

Stromer, E., and Weiler, W., 1930, Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wiistem Agyptens. VI. 

Beschreibung von Wirbeltier-Resten aus dem nubischen 

Sandsteine Ober-agyptens und aus agyptischen Phosphaten 

nebst Bemerkungen tiber die Geologie der Umgegend 

von Mahamid in Ober-agypten: Abhandlungen der 

Bayerischen Akademie der Wissenschaften, MathematisheNaturwissenschaftliche Abteilung, Neue Folge 7, p. 1-42. 

Tabaste, Nicole, 1963, Etude des restes de poissons du Cretace 

saharienne: Institut fran~ais d' Afrique noire Memoires, v. 68, 

p. 436-499. 

Paleocene Pelomedusid Turtles from Jabal U mm 

Himar, Kingdom of Saudi Arabia 

By Roger C. Wood 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

U.S. GEOLOGICAL SURVEY BULLETIN 2093-E 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
CONTENTS 

Abstract.......................................................................................................................... E 1 

Introduction .................................................................................................................. . 

Acknowledgments ................................................................................................ . 

Systematic Paleontology .............................................................................................. . 

Material Available ................................................................................................ . 

Taxonomic Status . . .. . . . . . . . . . . .. . . . .. . . . . .. . . . .. . . . . . . . . . . .. . . . . . . . . . .. . . . .... .. . . . . . . .. . . . . .. . . . .. . . . . . . . . . .. . . . . 2 

Discussion...................................................................................................................... 3 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

FIGURES 

El. Posterior half, anterior half, and composite drawings of xiphiplastron ...................................................................... E2 

E2. Ventral and dorsal view of proximal end of pelomedusid humerus . . . .. . . . . .. . . . . . . . . . .. . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 2 

E3. Dorsal and posterior views of isolated neural bones of Arabian pelomedusid ........................................................... 3 

Ell 
Paleocene Pelomedusid Turtles from Jabal Umm Himar, 

Kingdom of Saudi Arabia 

By Roger C. Wood I 

ABSTRACT 

Fragmentary chelonian remains collected from Jabal 

Umm Himar, near Turabah, Saudi Arabia, appear to represent a single type of pelomedusid (side-necked) turtle. Too 

little of this taxon has been preserved to permit diagnosis 

below the familial level. However, it was clearly a large species and almost certainly primarily aquatic. This occurrence 

is the first record of pelomedusid turtles, either living or fossil, from the Arabian Peninsula. Comparison with both African and Asiatic fossil pelomedusids provides no definite 

insights regarding the Arabian turtle's relationships to other 

members of the family from either continent. 

INTRODUCTION 

Fossil turtle remains are relatively common among the 

Paleocene fossil vertebrates collected from 21 localities at 

Jabal Umm Himar, near Turabah, in the Harrat Hadan area, 

At Taif region, Kingdom of Saudi Arabia (Madden and others, 1979). Despite their fragmentary nature, these remains 

are of particular interest because they provide the first adequate documentation for the presence of this reptilian order 

from the Arabian Peninsula. These specimens form the 

basis for the description in the present report. 

ACKNOWLEDGMENTS 

I am grateful to C.T. Madden and F.C. Whitmore, Jr., 

for their invitation to study this material. I thank L. Cahen 

and A.J. Charig for permission to examine African fossil 

turtles in their care from Zaire and Nigeria, respectively. 

Thanks are also due to C.T. Madden and C.A. Walker for 

unpublished information. The line illustrations were drawn 

by Laszlo Meszoly. Funding for the line drawings was provided by a grant from Stockton State College's Research 

and Professional Development Committee. A postdoctoral 

1Faculty of Science and Mathematics, Stockton State College, 

Pomona, N.J. 08240. 

fellowship from the National Science Foundation provided 

the time necessary to complete my research, while a grant 

from the National Geographic Society made it possible for 

me to examine comparative material in several European 

museums during the summer of 1978. 

The pelomedusid turtle fossils were collected during 

field investigations sponsored by the Directorate General of 

Mineral Resources (DGMR), Kingdom of Saudi Arabia 

under an agreement with the U.S. Geological Survey 

(USGS). 

C.T. Madden and F.C. Whitmore, Jr., edited and 

reviewed the original manuscript. 

SYSTEMATIC PALEONTOLOGY 

Order Testudines 

Suborder Pleurodira 

Family Pelomedusidae 

MATERIAL AVAILABLE 

Turtle remains are known from 15 of the 21 localities 

(Madden and others, 1979). Most of these are amorphous 

shell fragments of no taxonomic value. Nevertheless, their 

abundance suggests that turtles must have been a relatively 

common component of the U mm Himar local fauna. 

A partial shell was found at locality 33, but it was 

severely eroded, badly fractured, and collected as unassociated pieces rather than in a plaster jacket. Efforts to reassemble these fragments proved unsuccessful; however, 

given the shell's wretched state of preservation, it seems 

unlikely that much in the way of useful taxonomic information would have been discernible in any event. 

Only seven localities (3, 4, 28, 29, 33, 35, and 38) 

yielded identifiable material, all isolated specimens. Anatomically recognizable bones of the shell include several 

neurals and a few peripherals from the carapace as well as a 

nearly complete right hypoplastron and three partial xiphiplastra from the plastron. The remainder of the skeleton is 

represented only by the proximal end of a humerus and several pelvic fragments. 

El 
E2 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

B 

3cm 

L..L....!__j 

Figure El. A, Posterior half of left xi phi plastron (USGS SAP 

NO-Pel-1 ); B, anterior half of right xi phi plastron (USGS SAP 

38-Pel-1 ); C, composite drawing of left and right xiphiplastron 

based upon specimens shown in A and B, with the latter projected 

in mirror image. The internal surface is shown on the left, the 

external surface on the right. Stippled areas represent pelvic scars, 

diagonally shaded areas are broken surfaces. The dashed line in C 

marks .the anterior border of specimen A; the dotted line marks the 

posterior border of specimen B. 

TAXONOMIC STATUS 

The available evidence indicates that only a single type 

of chelonian is represented in the Umm Himar local fauna. 

The species represented appears to have been a pelomedusid or side-necked turtle. This identification is based 

upon the following typical characters: (1) presence of a laterally placed, subcircular mesoplastron on the underside 

(plastron) of the shell; (2) fusion of the pelvic girdle to the 

shell (fig. El); (3) proportions of the head of the humerus 

(fig. E2); and (4) the shape and presumed arrangement of 

the neural bones (fig. E3) along the midline of the top part 

of the shell (carapace). 

Of these four characters, the last is the most tenuous 

and requires some clarification. In typical pelomedusids, 

the first neural abuts directly against the rear of the nuchal 

bone and is relatively long and narrow, forming an elongate 

oval. The successive neurals are all hexagonal (often appropriately described as coffin shaped) and follow in uninterrupted sequence, their proportions toward the rear of the 

series becoming increasingly short anteroposteriorly and 

3cm 

Figure E2. Proximal end of pelomedusid humerus (USGS SAP 

3-Pel-1), in A, ventral and B, dorsal views. Diagonally shaded 

areas are broken bone surfaces. 

broad transversely. Pelomedusids usually have six to seven 

neurals. 

One of the identifiable Umm Himar shell fragments is 

clearly a first neural (fig. E3A). Because they are both hexagonal in outline and relatively elongate anteroposteriorly, 

several other isolated neural specimens (figs. E3B, C, D) 

undoubtedly were situated close to or immediately behind 

the first one. Although the total number of neurals in a typical Umm Himar shell cannot be determined from present 

evidence, what has been preserved accords well with the 

widely prevalent pelomedusid pattern and suggests that the 

Arabian form's shell probably was characterized by six to 

seven neurals arranged along the midline of the carapace in 

unbroken sequence. 

Despite the fragmentary and disarticulated nature. of 

the material, several features can be discerned that might be 

of taxonomic value below the familial level. For example, 

cross-sectional views of the neural bones (figs. E3F, G, H) 

indicate that a rather pronounced ridge extending along 

much of the length of the carapace's midline. This ridge, or 

keel, was apparently continuous and characterized by gently 

sloping sides in contrast, for instance, to the abruptly projecting and discontinuous keels of some turtles, perhaps 

best exemplified by certain populations of the living North 

American emydines Graptemys and Malaclemys. 

Even discounting the presence of the median ridge on 

the external surface of the neurals, these bones appear to be 

disproportionately thick in relation to their surface areas 

(see especially fig. E3H). Because bones in turtles do not 

apparently become progressively thicker as shell size 

increases, the massiveness of the Arabian neurals cannot 

legitimately be ascribed simply to their large size. Therefore, the thickness of this turtle's bones might, as part of a 

suite of characters, perhaps be perceived as a distinctive 

feature of taxonomic value. 

While size alone is insufficient for diagnosing any turtle species,. it might (again, with other characters) contribute 

to such a diagnosis. Adult specimens of the Arabian pelomedusid clearly attained a rather large size, their shells being 
PALEOCENE PELOMEDUSID TURTLES FROM JUBAL UMM HIMAR, KINGDOM OF SAUDI ARABIA E3 

c 

3cm 

I 

E F G H 

Figure E3. Isolated neural bones of Arabian pelomedusid (USGS SAP 33r-Pel-1, USGS SAP 33-Pel-2, USGS SAP 33r-Pel- 3, USGS 

SAP 29-Pel-1): A-D, dorsal views, anterior ends facing top of page; E-H, views of posterior ends showing thickness and median ridge. A 

is a first neural, the others are probably second or third neurals. . 

roughly comparable in length to those of the largest living 

pelomedusid, Podocnemis expansa from the Amazon and 

Orinoco River basins of South America. The badly fragmented shell from locality 33 measured roughly 90 em in 

length (C.T. Madden, personal commun., 1978). The largest 

known shells of P. expansa are reported to attain a length of 

87.5 em (Pritchard, 1979, p. 751). A few other fossil pelomedusids were comparable in size to the Arabian form 

("Podocnemis" indica Lydekker, 1887) or even larger (Stupendemys geographicus Wood, 1976). 

Several other features can be discerned that, however, 

are unlikely to be taxonomically useful. The external shell 

surfaces are covered with a lightly inscribed network of 

anastomosing vermiculations. This sculpture is typical of 

many, but by no means all, pelomedusids. 'Moreover, judg~ 

ing from a single specimen composed of an associated hexagonal neural and the medial portion of an· adjacent 

peripheral, shells of the Arabian pelomedusid appear to 

have been moderately flattened dorsoventrally, suggesting 

that this was a highly aquatic species. Finally, the shape of 

the anal notch at the posterior end of the plastron seems to 

have been somewhat variable. In at least some extant species of pelomedusids (Podocnemis unifilis), anal notch 

shape varies considerably and is not apparently correlated 

with either sex or size. 

In summary, it is possible that the Umm Himar pelomedusid may represent' a previously undescribed taxon 

characterized by rather large size, very thickly boned shell, 

and a continuous keel along the midline of the carapace 

(rather than the usually flat transverse arch). However, the 

available material does not really permit a definitive diagnosis. For the present, therefore, the Gtnm Himar chelonian 

is best simply named "Pelomedusidae gen. et sp. ident." 

DISCUSSION 

This section describes the first record of pelomedusid 

turtles, either fossil or living, from the Arabian Peninsula. 

The occurrence is not particularly surprising, however. Fossil pelomedusids are known from both east and west of the · 

Arabian locality. In Africa, they are relatively abundant 

(Wood, 1971), whereas in the Indian subcontinent they are 

known so far from only a few specimens (Wood, 1970). The 

most similar of the asiatic fossil pelomedusids appears to be 

"Poddcnemis" indica (Lydekker, 1887) from the Paleocene 

or Eocene of Pakistan. It is likely that this taxon 'represents a 

pelomedusid; although this unfortunately cannot be conclusively shown. Its carapace is large (nearly 90 em long), the 

neural pattern is similar (although nothing is known about 
E4 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

the relative thickness of the neurals ), and, like the Arabian 

shell material " ... the median line is much elevated, with 

the [pleurals] sloping rapidly away on either side" (Lydekker, 1887, p. 64). The sediments from which "P. indica" 

was recovered were described as " ... either of marine or 

estuarine origin [which] is confirmed by the Chelonians, 

one of which is covered with the 'spat' of oysters while 

sharks' teeth are embedded in the matrix of the other" 

(Lydekker, 1887, p. 59-60). 

In Africa, the geographically closest fossil pelomedusid is Podocnemis somaliensis from the middle Eocene of 

Somalia (Walker, 1966). A variety of morphological details 

militates against any particularly close relationship between 

the Somalian and Arabian pelomedusids. Abundant nautiloids were collected along with the single known shell of P. 

somaliensis, which suggests that this fossil pelomedusid, 

like "P." indica, may have been salt tolerant. 

Shweboemys antiqua (Andrews) from upper Eocene 

deltaic or nearshore IT.J.arine deposits of northern Egypt is in 

some respects similar to the Arabian turtle. Although 

smaller, its carapace had a similar neural bone pattern and 

its pleurals slope flatly to either side of a midline peak. Its 

neurals, however, are not disproportionately thick. 

Fragments from Sokoto Province, Nigeria, originally 

described by Swinton (1930) as "Podocnemis-like," almost 

certainly represent a very large pelomedusid and are 

roughly contemporaneous with the Arabian material. Several isolated neural bones (R5661, R5665, R5685) examined in the paleontological collections of the British 

Museum (Natural History) are roughly comparable in size 

and shape to the hexagonal Umm Himar neurals, but they 

are proportionately much thinner and lack any signs of a 

midline ridge. Swinton also described and figured (Swinton, 1930, pl. 14, fig. 2) the ventral surface of a first neural 

bone and said that its dorsal surface is " ... devoid of ornamentation." Complete shells and even skulls of very large 

pelomedusids recently have been discovered in northern 

Nigeria (C.A. Walker, personal commun., 1980); this discovery should soon permit a very full characterization of 

this taxon. Only when similar good fortune results in the 

recovery of comparably preserved specimens from the Arabian Peninsula will adequate comparisons be possible. 

Of all the African fossil pelomedusids, the most similar to the Arabian turtle in terms of both age and morphology appears to be Taphrosphys congolensis (Wood, 1975). 

Remains referable to this species range in age from Late 

Cretaceous through Eocene, but the best preserved and most 

abundant specimens are Paleocene in age. Undescribed 

material now under study permits fairly complete reconstruction of the entire carapace of T. congolensis. It was 

rather large (perhaps 80 em in length) and had seven neurals 

shaped and arranged according to the typical pelomedusid 

pattern. Rather deeply inscribed anastomosing vermiculations covered its external surface. Conceivably there may 

have been a continuous ridge along the midline of the 

carapace, but this possibility cannot be verified from those 

portions of the carapace that have been preserved, nearly all 

of which have been squashed flat; in some cases, the dorsal 

surface of the carapace is actually somewhat concave. 

Unlike the Arabian pelomedusid shell with its markedly 

thickened bone, however, the shell of T. congolensis tends 

to be thinner than one might ordinarily expect for a turtle of 

its size. 

Given the similarities between the Umm Himar pelomedusid and T. congolensis, it is tempting to speculate, 

despite their geographic separation, that they might be particularly closely related to each other. Again, however, until 

such time as better preserved specimens of the Arabian turtle become known, such speculations cannot be confirmed. 

One nonanatomical commonality worth noting concerns habitat. The environment represented by the deposits 

in which the Umm Himar fauna occurs was estuarine or 

lagoonal (Madden and others, 1979; and Chap. A, this volume). Likewise, the sediments from which T. congolensis 

was recovered also accumulated in a littoral marine environment (Cahen, 1954 ). Although pelomedusids are all 

freshwater forms at present, the family's fossil record indicates that they were not always so narrowly adapted in the 

past. Two tortoiselike and therefore presumably terrestrial 

forms (both from the middle Tertiary of Africa and neither 

yet reported formally in the published literature) have been 

recognized. More directly relevant to interpretation of the 

turtles from Jabal Umm Himar are a variety of other fossil 

pelomedusids (especially of Late Cretaceous and early Tertiary age) that seem to have inhabited brackish and perhaps 

even marine waters. The nearshore or deltaic marine habitat 

apparently common to both T. congolensis and the Umm 

Himar pelomedusid raises the possibility that uninterrupted 

gene flow may have been possible between these two contemporaneous forms on opposite sides of the African continent through intermediate populations around its periphery. 

Such distributional continuity as postulated here woul,d in 

turn help to account for the morphological similarities noted 

above. 

Why some fossil turtles had exceptionally thick shells 

is not at all understood nor has the question received much 

attention. Some authors (Fichter, 1969; Jackson, 1978) have 

suggested, without either much conviction or enthusiasm, 

that the thicker shells of some North American fossil turtles 

may be correlated with cooler climates. Such an explanation 

would seem to have little, if any, relevance to the Arabian 

turtles, which are believed to have lived in a tropical or subtropical climate (Madden and others, 1979; and Chap. A, 

this volume). Convincing evidence, however, cannot at 

present be readily marshalled in support of some alternative 

explanation. The problem, therefore, remains unsolved. 
PALEOCENE PELOMEDUSID TURTLES FROM JUBAL UMM HIMAR, KINGDOM OF SAUDI ARABIA E5 

REFERENCES 

Cahen, L., 1954, Geologie du Congo Beige: Liege, Imprimerie H. 

Vaillant-Carmanne, 577 p. 

Fichter, L.S., 1969, Geographical distribution and osteological 

variation in fossil and recent specimens of two species of 

Kinosternon (Testudines): Journal of Herpetology, v. 3, nos. 

3-4, p. 113-119. 

Jackson, D.R., 1978, Evolution and fossil record of the chicken 

turtle Deirochelys, with a re-evaluation of the genus: Tulane 

Studies in Zoology and Botany, v. 20, nos. 1-2, p. 35-55. 

Lydekker, R., 1887, Eocene chelonians from the Salt-Range: 

Memoirs of the Geological Survey of India, Paleontologia 

Indica, Series 10: Indian Tertiary and Post-Tertiary Vertebrata, v. 4, pt. 3, p. 59-65. 

Madden, C.T., Naqvi, I.M., Whitmore, F.C., Jr., Schmidt, D.L., 

Langston, Wann, Jr., and Wood, R.C., 1979, Paleocene 

vertebrates from coastal deposits in the Harrat Hadan area, At 

Taif region, Kingdom of Saudi Arabia: U.S. Geological Survey Saudi Arabian Project Report 269, 29 p. 

Pritchard, P.C.H., 1979, Encyclopedia of turtles: Neptune, N.J., 

T.F.H. Publications, 895 p. 

Swinton, W.E., 1930, On fossil Reptilia from Sokoto Province: 

Geological Survey of Nigeria, Bulletin no. 13, p. 15-60. 

Walker, C.A., 1966, Podocnemis somaliensis, a new pleurodiran 

turtle from the middle Eoc~ne of Somalia: Palaeontology, v. 

9, pt. 3, p. 511-516. 

Wood, R.C., 1970, A review of the fossil Pelomedusidae 

(Testudines, Pleurodira) of Asia: Brevi ora, no. 357, p. 1-24. 

---1971, The fossil Pelomedusidae (Testudines, Pleurodira) of 

Africa: Ph.D. thesis, Harvard University. 

---1975, Redescription of "Bantuchelys" congolensis, a fossil 

pelomedusid turtle from the Paleocene of Africa: Revue de 

Zoologie Africaine, v. 89, fasc. 1, p. 127-144. 

---1976, Stupendemys geographicus, the world's largest 

turtle: Breviora, no. 436, p. 1-31. 

Dyrosaurs ( Crocodilia, Mesosuchia) 

from the Paleocene Umm Himar Formation, 

Kingdom of Saudi Arabia 

By Wann Langston, Jr. 

PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

U.S. GEOLOGICAL SURVEY BULLETIN 2093-F 

Prepared in cooperation with the Ministry of 

Petroleum and Mineral Resources, Jiddah, 

Kingdom of Saudi Arabia 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
CONTENTS 

Abstract.......................................................................................................................... Fl 

Introduction . . . . . . . . .. . . . . . . . . . .. . . . . .. . . . . .. . . . .. . . . . . . . . . .. . . . . .. . . . . .. . . . .. . . . . .. . . . . . . . . . .. .. . . . . . . . . .. . . . .. . . . . . . . . . .. . . . . 1 

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

Occurrence..................................................................................................................... 2 

Identifications................................................................................................................ 2 

Osteological Notes......................................................................................................... 7 

Pathology....................................................................................................................... 30 

Gastroliths...................................................................................................................... 32 

Coprolites .. . . . .. . . . . .. . . . . .. . . . . . . . . . ... . . . . . . . . .. . . ....... .. .. .. .. . . . . .. . . . .. . . . . . .. .. . .. . . . . . . . . . .. . . . . .. . . . . . . . . . .. . . . .. . . . . 32 

Size, Skeletal Reconstruction, and Interpretation.......................................................... 32 

Stratigraphic Implications . . . .... .. . . . . . .. . . . . .. . . . . .. .. ... . . . . .. . . . .. . . . . . ................ ..... ... . . . . . . . . . .. . . . .. . . . . 34 

Paleogeographic Implications ... .. . . . .. . . . . .. . . . . . . . . . .. . . . . ..... .. . .. . . .. .. . ........... ..... ... . . . . . . . . . .. . . . .. . .. . 34 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

FIGURES 

Fl. Geologic map of Jabal Umm Himar area, showing fossil localities.......................................................................... F3 

F2. Mandibular rostra of dyrosaurs from Saudi Arabia.................................................................................................... 4 

F3. Cross-sections of dyrosaurian mandibular rostra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

F4. Mandible of Rhabdognathus compress us................................................................................................................... 6 

F5. Frontal bones of dyrosaurs ......................................................................................................................................... 6 

F6. Rhabdognathus sp., no. 35-CR-9. End of interlocked cranial and mandibular rostra................................................ 8 

F7. Rhabdognathus sp. Reconstruction of post-rostral skull, from above........................................................................ 8 

F8. Rhabdognathus sp. Quadrate bones from above........................................................................................................ 9 

F9. Rhabdognathus sp., no. 37A-CR-1. Distal (articular) end ofleft quadrate................................................................ 9 

FlO. Rhabdognathus sp., no. 33-CR-10. Braincase from the right side............................................................................. 10 

Fll. Rhabdognathus sp., no. 37-CR-1. Articular region of left mandible, from above..................................................... 11 

F12. Rhabdognathus sp., no. 37-CR-1. First and second mandibular teeth showing. recumbency and overlapping 

roots............................................................................................................................................................................. 12 

F13. Rhabdognathus sp., no. 37-CR-1. Atlas and axis, right lateral view......................................................................... 13 

F14. Rhabdognathus sp., no. 57-CR-1. Opposing articular ends of the atlanta! and axial centra...................................... 13 

F15. Rhabdognathus sp. Variation in the ventral ridge system on axial vertebrae............................................................. 14 

F16. Rhabdognathus sp., no. 37-CR-1. Vertebrae.............................................................................................................. 16 

F17. Rhabdognathus sp., no. 37-CR-1. Articulated seventh cervical to ninth thoracic vertebrae, ventral aspect............. 16 

Fl8. Rhabdognathus sp., no. 37-CR-1. Caudal vertebrae.................................................................................................. 18 

F19. Rhabdognathus sp., no. 37-CR-1. Proximal ends of thoracic ribs............................................................................. 19 

F20. Rhabdognathus sp., no. 37-CR-1. Sacral vertebrae and ribs, dorsal aspect............................................................... 19 

F21. Dyrosaur and eusuchian sacra, left lateral aspect....................................................................................................... 20 

F22. Rhabdognathus sp., no. 37-CR-1. Haemapophyses ................................................................................................... 21 

F23. Rhabdognathus sp. Pectoral girdle............................................................................................................................. 22 

F24. Rhabdognathus sp. Humeri ........................................................................................................................................ 23 

F25. Rhabdognathus sp. Articular ends of the humerus of large individuals ..................................................................... 23 

F26. Rhabdognathus sp., no. 58-CR-1. Right pubis, ventral aspect................................................................................... 24 

F27. Rhabdognathus sp. Tibia............................................................................................................................................ 25 

F28. Rhabdognathus sp. Fibulae ..... ................................................................................................................................... 26 

F29. Rhabdognathus sp. Reconstruction of right pes . . . . .. . . ... . . . . .. .... .. . . . . . . . . . .. .. . . . . . . . .. . . . . ..... ...... .. . . . . .. . . . . . . . . . ... .. . .. . . . . . . . . . ...... .. . . . 27 

FII 
CONTENTS FIII 

F30. Rhabdognathus sp., no. 37-CR-2. Left astragalus and calcaneum ............................................................................. F28 

F31. Rhabdognathus sp., no. 58-CR-1. Costal cartilages................................................................................................... 29 

F32. Rhabdognathus sp. Reconstruction of dorsal armor................................................................................................... 30 

F33. Crocodilian osteoscutes from Saudi Arabia................................................................................................................ 31 

F34. Rhabdognathus sp., no. 3-CR-3. Pathological left femur........................................................................................... 31 

F35. Hyposaurine dyrosaur skeleton based primarily on Rhabdognathus sp. from Saudi Arabia..................................... 33 

TABLES 

Fl. Interdental distances measured from the centers of the alveoli ................................................................................... F12 

F2. Anteroposterior diameters of alveoli............................................................................................................................ 12 

F3. Measurements of atlas-axis.......................................................................................................................................... 14 

F4. Measurements of vertebrae, specimen no. 37-CR-1 ............................................................................... ,.................... 15 

F5. Measurements of selected humeri................................................................................................................................ 23 

F6. Comparative measurements of dyrosaurian femora..................................................................................................... 25 

F7. Measurements of tibiae................................................................................................................................................ 26 

Dyrosaurs (Crocodilia, Mesosuchia) from the Paleocene Umm Himar 

Formation, Kingdom of Saudi Arabia 

By Wann Langston, Jr. 1 

ABSTRACT 

Dyrosaur remains from western Saudi Arabia support 

the view that sediments of the Umm Himar Formation are 

of Paleocene age and represent lagoonal and estuarine environments. Bones and teeth of at least 45 individuals, from 

15 localities, vary considerably in size. Three partly articulated but incomplete skeletons assigned to Rhabdognathus 

sp. shed new light on the osteology and permit a first 

attempt at skeletal reconstruction of a longirostrine 

dyrosaur. Three hyposaurines (Hyposaurus nopcsai, Rhabdognathus compressus, Rhabdognathus sp.) and one phosphatosaurine (Phosphatosaurus sp.) are recognized from 

rostral fragments and frontal bones. Such diversity, noted in 

other occurrences, may reflect ecological segregation manifested in specialized rostral and dental characters and by 

individual size. 

The braincase of Rhabdognathus sp. is exceptionally 

well ossified and is greatly attenuated anteriorly by prolongation of the laterosphenoids and the basicranial axis. 

Olfactory and optic nerves passed forward through separate 

tunnels formed by these bones. The structure probably 

increased the strength of the cranial axis otherwise lessened 

by the long temporal fossae and slender temporal arcades. 

Hyposaurine dyrosaurs possessed relatively powerful 

forelimbs, suggesting derivation from terrestrial ancestors. 

Extremely high neural spines in the posterior trunk and tail 

may have enhanced swimming capability, and also limited 

vertical flexion of the body. The cranio-cervical joint and 

shape of the cervical vertebrae confirm Buffetaut's interpretation of restricted lateral but increased vertical ranges of 

motion in the neck. Massive and broadly overlapping dorsal 

osteoscutes lack anterolateral peg and socket articulations. 

The Saudi Arabian material shows little evidence of 

disease, but injury during life is evinced by an amputated 

and partly healed femur. Gastroliths are associated with 

some specimens. 

1

Vertebrate Paleontology Laboratory, The University of Texas at Austin, Balcone Research Center, Austin, Texas 78712. 

INTRODUCTION 

Many remains of dyrosaurs were found by joint U.S. 

Geological Survey-Saudi Arabia field parties in 1976-78. 

No fewer than 45 individuals of varying sizes are represented in the collection. Most of the material consists of 

incomplete vertebrae, limb bones, and other fragments collected on the surface, but three incomplete skeletons were 

also found in situ. 

Whereas the Dyrosauridae are well defined on both 

cranial and postcranial features, effective generic and specific discrimination within the family is as yet restricted to 

cranial and mandibular characters, which reflect differing 

feeding adaptations (Moody and Buffetaut, 1981; Buffetaut, 

1982). A number of descriptive accounts of dyrosaur 

remains have been published since Owen first recognized 

Hyposaurus rogersii in 1849 (for a taxonomic history of the 

Dyrosauridae, see Buffetaut, 1976a,b, 1982). The most 

comprehensive description of a dyrosaur skeleton is that of 

the North American Maastrichtian Hyposaurus natator 

(Troxell, 1925). Troxell's study was augmented by a 

description of an incomplete skeleton of Hyposaurus 

(=Congosaurus) bequaerti (Dollo) by Swinton (1950). 

Interestingly, neither species was recognized as dyrosaurian 

at the time (see Buffetaut, 1976b). Arambourg (1952) provided additional data on Dyrosaurus phosphaticus (Thomas), and descriptions of the skull of D. phosphaticus by 

Thevenin (1911), by Piveteau (1935), and lately by Buffetaut (1982) have furnished most of our knowledge about the 

cranial anatomy of the slender-snouted dyrosaurs. Of 

massive-headed forms, Buffetaut (1978a; 1979) has 

described the skulls of Sokotosuchus ianwilsoni Halstead 

and Phosphatosaurus gavialoides Bergounioux. Storrs 

( 1986) has recently described an incomplete dyrosaur skeleton from the Paleocene of Pakistan. Nevertheless, many 

aspects of dyrosaurian osteology remain to be seen. The 

Saudi Arabian material sheds additional light on some questions, and permits for the first time a tentative skeletal 

reconstruction of this unusual crocodilian taxon. 

Fl 
F2 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

ACKNOWLEDGMENTS 

I am indebted to C.T. Madden and F.C. Whitmore, Jr., 

for allowing me to study the Saudi Arabian dyrosaur material collected by Madden and his associates. I am also 

indebted to A.B. Busbey III, for his comments and careful 

criticism. 

All specimens described herein are the property of the 

Kingdom of Saudi Arabia. They are numbered according to 

the localities of Madden and consecutively within each 

locality: no. 37-CR-1 means the first numbered crocodilian 

specimen from Madden's locality 37. All locality numbers 

bear the prefix USGS SAP indicating the U.S. Geological 

Survey-Saudi Arabian collection, but the acronym has been 

omitted in the text in the interest of brevity. 

OCCURRENCE 

The specime~s described below were derived from 15 

of 21 vertebrate-producing sites in the vicinity of Jabal 

Umm Himar, a large hill 100 km east of At Taif and 26 km 

west of Turabah, in southern Hijaz Province, Kingdom of 

Saudi Arabia (fig. Fl). 

All of the material was recovered from a well-defined 

2-3-m-thick, massive, thick-bedded, green-gray mudstone 

at the base of the middle member of the Umm Himar Formation of Paleocene age. The source of these sediments has 

been interpreted as a lagoonal or estuarine environment 

subject to little or only gentle current action (Madden and 

others, 1979, Chap. A, this volume). It is significant that all 

fossils occurred roughly on strike over a distance of only 

4.5 km. This fact increases the likelihood that they represent 

nearly coeval events. 

Most localities produced only weathered and fragmentary material of little importance except to demonstrate the 

presence of dyrosaurs in the Umm Himar Formation at 

those places, and to provide data on the size range of the 

individuals. 

IDENTIFICATIONS 

Taxonomically useful specimens in the collection are: 

Number Description Identification 

2-CR-2 Posterior end of mandibular Hyposaurus 

symphysis. nopcsai 

(Swinton, 

1930) 

2-CR-4 Section of mandibular rostrum, Rhabdo gnathus 

including anterior end of splenial compress us 

symphysis. (Buffetaut, 

1980) 

2-CR-5 Fragment of mandibular rostrum. Rhabdognathus 

sp. 

Number Description 

3-CR-2 Short piece of mandibular rostrum 

anterior to splenia symphysis. 

27-CR-1 Frontal plate. 

27-CR-2 Section of mandibular rostrum. 

33-CR-9 Incomplete skeleton, including braincase, temporal arch fragments, parts 

of the rostrum and postcranial 

elements. 

37-CR-1 Partly articulated skeleton, including 

posterior part of braincase, postorbital bone, parts of the rostrum, 

quadrate, and articular region of the 

mandible, and a large part of the 

postcranial skeleton. 

37E-CR-2 Fragment of mandibular rostrum. 

43-CR-1 Incomplete mandibular symphysis. 

58-CR-1 Partly articulated skeleton, including 

posterior part of braincase, segment 

of the mandibular rostrum and postcranial elements, and a large part of 

the postcranial skeleton. 

60-CR-4 Fragment of rostrum. 

Identification 

Rhabdognathus 

compressus 

Hyposaurus 

nopcsai 

Hyposaurus 

nopcsai 

Rhabdognathus 

sp. 

Rhabdognathus 

sp. 

Dyrosauridae 

Rhabdognathus 

sp. 

Rhabdognathus 

sp. 

Phosphatosaurus sp. 

Numbers 2-CR-5, 3-CR-2, 37E-CR-2, and 58-CR-1 

display the reduced seventh tooth that is distinctive of the 

family Dyrosauridae (Buffetaut, 1976a). An incomplete left 

postorbital bone associated with no. 37-CR-1, but not certainly belonging to the skeleton from locality 37, retains the 

broken base of the characteristic dyrosaurid postorbital spur 

(see Buffetaut, 1976a). Temporal arch bones with no. 

33-CR-9 indicate the presence of a distinctively huge elongate supratemporal fenestra of dyrosaurid proportions. 

Braincases belonging to nos. 33-CR-9, 37-CR-1, and 

58-CR-1 are uniquely dyrosaurian. All other material in the 

collection is morphologically consistent with what is currently known about the dyrosaurid skeleton. 

All rostral fragments except no. 60-CR-4 are evidently 

from slender-snouted dyrosaurs of the subfamily Hyposaurinae Buffetaut (1980). These specimens differ considerably 

in size and shape and represent different segments of the 

snouts (fig. F2). The variety of these specimens brings to 

mind a curious phenomenon within the Dyrosauridae: several closely similar species often occur in the same deposits. 

Swinton ( 1930), for example, described an assemblage of 

17 rostral fragments from Paleocene rocks at Wurno, in 

northwestern Nigeria. Among them he recognized three 

new genera and species: Wurnosaurus wilsoni, Rhabdognathus rarus, and Sokotosaurus nopcsai; and, on the basis 

of the occipital end of a skull, he named a new species of 

Dyrosaurus, D. minor. Although the existence of three or 

four closely similar longirostrine forms in such close 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F3 

QUATERNARY 

TERTIARY 

PRECAMBRIAN 

4 KILOMETERS 

EXPLANATION 

Holocene ~ ALLUVIUM-Sand, gravel, and silt in wadis 

Miocene 

Paleocene 

~ TERRACE ALLUVIUM 

OLIVINE BASALT 

~ UMM HIMAR FORMATION-Ferruginous mudstone, 

~ mudstone, shale, dolomitic limestone 

~ QUARTZ MONZONITE 

~ META VOLCANIC GREENSTONE 

4 MILES Geology by lbne Mohammed 

Naqvi July 1976 

• Fossillocalities 

Line of stratigraphic sections 

x 71288 Sample localities 

Road 

Figure Fl. Geologic map of Jabal Umm Himar area, showing fossil sample localities and line of stratigraphic sections (fig. A3). 
F4 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

43-CR-1 

A 

0 

I 

em 

5 

I 

58-CR-1 

8 

37-CR-10 

c 

2-CR-2 

D 

Figure F2. Mandibular rostra of dyrosaurs from Saudi Arabia. A-C, Rhabdognathus sp.; D-E, Hyposaurus nopcsai. 

proximity as implied in Swinton's study is suspect on ecological grounds, his specimens are different, and most 

recent writers (Steel, 1973; Halstead and Middleton, 1976; 

Buffetaut, 1979, 1980) accept the validity of the species. 

Buffetaut (1980), however, reassigned Wurnosaurus and 

Sokotosaurus to the genus Hyposaurus, and Halstead and 

Middleton (1976) synonymized D. minor with Rhabdognathus rarus. Similar assemblages are reported from Mali 

and elsewhere (Buffetaut, 1980). 

Swinton, among others, emphasized the cross-sectional shape of dyrosaur rostra as a taxonomic tool (fig. F3). 

The outline, however, may be expected to vary somewhat 

with size of the individual and the positions of the sections 

along the rostrum. Sections may vary radically when taken 

through the alveoli and the adjacent interalveolar spaces 

(figs. F3H,J), so cross sections of rostra must be used with 

some caution. 

Rostra associated with the incomplt?te skeletons of nos. 

33-CR-9, 37-CR-1, and 58-CR-1, and isolated specimens 

37-CR-7, 37-CR-10, 43-CR-1, and 37-CR-12 conform 

fairly well to Buffetaut's (1980) revised definition of Rhabdognathus. In most of the specimens it is impossible to tell 

where the splenial symphysis ends in relation to the dental 

sequence, but in no. 58-CR-1 this point is at the level of the 

tenth tooth, as in Rhabdognathus. The transverse separation 

between alveoli is, however, greater than in known species 

of this genus, and the alveolar salients are less marked than 

in R. rarus. The uniform occurrence of these differences 

throughout the Saudi Arabian sample is suggestive, but the 

taxonomic value of such features standing alone seems 

doubtful to me. Rather than add another ill-defined taxon to 

the literature I will refer these specimens to Rhabdognathus 

sp. 

Two rostral fragments, nos. 2-CR-4 and 3-CR-2 (figs. 

F3G-/; F4), are strikingly different from the others in the 

collection. They are about as high as wide in cross section, 

but their sides are flatter than in Rhabdognathus sp., the 

teeth are more widely spaced, and the distance between 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION 

8 0 

E 0 

H 

K 0 

____ , 

' .. 

N 

c 

F 

L 

0 

0 

0 

0 

(') 

\ I \ , .... " , __ , 

Figure F3. Cross sections of dyrosaurian mandibular rostra, drawn to the same scale. All sections 

except I are through alveoli. A, Hyposaurus (= Wurnosaurus) wilsoni (Swinton), section near tip of 

splenial symphysis; B, Hyposaurus nopcsai (no. 27-CR-2), section forward of the tip of the splenial 

symphysis; C, H. nopcsai (no. 2-CR-2), section near end of symphysis; D, Hyposaurus (= Sokotosaurus) nopcsai (Swinton), holotype, section near anterior tip of splenial symphysis; E, H. nopcsai 

from Swinton, 1930; F, Dyrosaurus phosphaticus Thomas; G, Rhabdognathus compressus (no. 

3-CR-2), section at level of 9th tooth; H, R. compressus (no. 2-CR-4); /, the same drawn through 

inter-alveolar space; J, R. rarus Swinton (lectotype, Halstead and Middleton, 1976), section at level 

of 6th tooth; K, R. rarus (syntype of Swinton, 1930), section near anterior end of rostrum, possibly at 

3rd tooth; L, Rhabdognathus sp. (no. 37-CR-1), section at level of ?4th tooth; M, Rhabdognathus sp. 

(no. 43-CR-1 ), section near end of splenial symphysis; N, Rhabdognathus sp. (no. 33-:..:R-9), section 

at level of 4th tooth; 0, Rhabdognathus sp. (no. 58-CR-1) section at level of lOth tooth. Sections of 

Swinton's specimens (C,D,J,K) are new, drawn from casts; F, redrawn from Buffetaut and others. 

F5 

opposite alveoli is as much as two times the width of the 

alveoli. Alveolar salients are not strongly developed. The 

alveoli are narrowly oval, with the width equal to about 64 

percent of the length. The long axis of the alveoli slants 

diagonally outward behind. The broken crowns of teeth are 

strongly compressed laterally, a little thicker anteriorly than 

posteriorly, and the thickly enameled outer surface bears 

strong longitudinal ribbing (the condition of the lingual side 

of the crown is undetermined). The teeth have remarkably 

long roots. Although in cross section these rostral fragments 

are perhaps less elevated and more rounded than implied in 

Buffetaut's definition of Rhabdognathus compressus, the 

dental characters of these specimens are sufficient to place 

them in that species. 

The posterior part of a mandibular symphysis (no. 

2-CR-2) is transversely oval in section, similar to Hyposaurus wilsoni, but the alveoli are larger and closer together 

than in that species. The buccal surface is concave transversely, instead of arched as in H. wilsoni. This specimen 

and no. 27-CR-2, a short segment of another rostrum from 
F6 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

farther forward (figs. F2D,E; F3B,C), are best assigned to 

H. nopcsai. This disposition appears to be confirmed by a 

frontal plate (no. 27 -CR-1; fig. F5B), which resembles the 

frontals referred to Sokotosaurus by Halstead and Middleton (1976, fig. 7j). While those authors' argument for this 

assignment is not completely convincing, this solution 

seems preferable to regarding the pitted frontals as an atypical (?atavistic) Rhabdognathus. 

A well-preserved frontal plate (no. 2-CR-3) is very 

similar in outline to no. 27 -CR-1, but differs in lacking pitted sculpture and in the slight transverse depression of the 

interorbital plate (fig. F5C). It may belong to Rhabdognathus sp. The anteromedial edge of the supratemporal 

fenestra is more angular than in H. nopcsai. 

3-CR-2 

A 

0 5 

I I 

em 

2-CR-4 

Figure F4. Rhabdognathus compressus. A, lateral view of mandibular segment with tooth root exposed; B, dorsal view of mandibular rostrum showing laterally compressed teeth in section and 

oval alveoli. 

0 5 0 

em 

I 

\. 

' \ 

\ 

\ 

\ 

I 

\ 8 .... , I 

\1"\ ./ 

\I 

27-GR-1 

em 

5 0 

Specimen no. 60-CR-4 consists of several weathered 

large and massive rostral fragments. Some vertebrae and 

limb segments associated with them in the field are not 

unusually large, so no. 60-CR-4 clearly represents more 

than one individual. One large piece, evidently from the cranial rostrum, contains one nearly complete subround alveolus with a transverse diameter of 29 mm, and behind this is 

part of another alveolus of similar proportions. The teeth 

were curved but not so strongly bent as the teeth in Rhabdognathus sp. The two alveoli are separated by an interdental space of only 9 mm and neither of them is surrounded by 

an elevated rim. A large tooth (no. 60-CR-6) is poorly preserved, being little more than a matrix cast of the pulp cavity with patches of dentine adhering near the tip and the 

root. Surface features are not preserved. The specimen is 

thick and although possessing a small nipple at the tip is 

clearly blunter than teeth in most dyrosaurs. It is slightly 

bent transversely but shows no anteroposterior curvature. It 

is broadly oval in cross section with transverse and fore and 

aft diameters of 18 and 25 mm, respectively, at the base. 

The specimen is 57 mm high, but the intact tooth was, of 

course, larger than this. 

Also from locality 60 is a small part of the anterior end 

of a mandibular rostrum probably belonging to no. 

60-CR-4. This rostrum contains part of the side of a large 

recumbent tooth, probably the first. Only the inner side of 

the root is visible~ but this contains a pulp cavity exceeding 

20 mm in diameter. The preserved segment of the root is 78 

mm long, and it is broken off at both ends. Dorsolateral to 

this tooth is the crown of a second recumbent tooth missing 

the outer surface. It is about 15 mm in diameter where broken off at the base and is 45 mm long as preserved. This 

. tooth has not yet erupted, but its pointed tip is directed into 

what was evidently an alveolus with raised edges. Lacking 

the tip of this tooth, it is impossible to say how widely separated the first two teeth would have been. It is clear, 

2-GR-3 

em 

5 

Figure FS. Frontal bones of 

dyrosaurs. A, frontal plate 

assigned to cf. Sokotosaurus 

Swinton(= Hyposaurus) by Halstead and Middleton, from the 

Dange Formation in Nigeria; B, 

H. nopcsai, referred specimen; 

C, frontal plate possibly belonging to Rhabdognathus sp. A 

redrawn from Halstead and Middleton, 1976. 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F7 

however, that the end of the rostrum was not expanded 

transversely. 

A second, smaller, but more complete rostral end (no. 

60-CR-5) confirms the interpretation of the larger fragment 

and appears to represent a smaller individual of the same 

species. It is clearly dyrosaurian. A third, less complete, tip 

agrees with the second. 

Whether the diverse fragments from locality 60 belong 

to the same species is not clear, but I believe all the rostral 

parts at least are attributable to one species. The close spacing of the teeth and the lack of elevated alveolar rims in no. 

60-CR-4 suggest they are from the posterior part of the 

snout. The characters noted agree with Phosphatosaurus 

gavialoides Bergounioux (1955), previously known from 

the Paleocene of Mali and Niger and the lower Eocene of 

Tunisia (for a description and illustrations of P. gavialoides, 

see Buffetaut, 1978a). But scant basis exists for distinguishing the large form from locality 60 from the Late Cretaceous Sokotosuchus ianwilsoni Halstead, from Niger, which 

resembles Phosphatosaurus in those features preserved in 

no. 60-CR-4. Nevertheless, I shall tentatively assign the 

Saudi Arabian material to Phosphatosaurus sp., because, , 

other things being equal, its geological age is more in 

accord with Phosphatosaurus than with Sokotosuchus. 

A thick, bent tooth crown (no. 28-CR-1) may belong to 

Phosphatosaurus, but it is much smaller than the specimens 

from locality 60. The crown is almost smooth, but it has a 

sharp carmina on its anterior edge. It is curved both anteroposteriorly and medially. 

Thus, as at Wurno and in Mali, several species of dyrosaurs seem to occur in close association at Jabal Umm 

Hi mar. 

Such diversity may have been an accident of taphonomy; however, the phenomenon now evident in at least 

three widely separated localities may reflect natural associations. Ecological segregation was perhaps affected by differing habits reflected in disparate head and tooth forms and 

body size. 

OSTEOLOGICAL NOTES 

There is a considerable body of literature dealing with 

the osteology of dyrosaurs. The most recent comprehensive 

contribution is by Buffetaut (1982), but no complete 

account of the skeleton has yet been published. The following notes emphasize certain aspects observed for the first 

time in the Saudi Arabian material. The most useful specimens are the three skeletons nos. 33-CR-9 and -10, 

37-CR-1, and 58-CR-1, of which the last two were found 

partly articulated and are more complete than the first. 

Material from other localities will be discussed as appropriate. I presume that most if not all of the specimens are 

attributable to Rhabdognathus sp., but I suspect that for 

postcranial elements these notes are generally applicable to 

any of the more advanced Hyposaurinae. 

Skull.-The dyrosaur head skeleton is fairly well 

known through descriptions of D. phosphaticus by Thevenin (1911), Arambourg (1952), and Piveteau (1935), of 

Hyposaurus natator by Troxell (1925), and of Phosphatosaurus gavialoides and Sokotosuchus ianwilsoni by Buffetaut (1978a; 1979). Although illustrations of almost 

complete hyposaurine skulls and jaws exist-D. phosphaticus (Thevenin, 1911, pl. 1), Rhabdognathus rarus, and 

(Buffetaut, 1980, pl. 2)-these have not been described 

fully. The Saudi Arabian material adds little more to existing knowledge, but the anterior part of the braincase in no. 

33-CR-10 and well preserved occipital segments of this 

specimen and nos. 37-CR-1 and 58-CR-1 provide some new 

data of importance. 

Most of the skull and jaw material in the Saudi Arabian collection is badly shattered and concerted attempts to 

reassemble the specimens have not been very successful. In 

addition to the braincase, material from locality 33 includes 

the tip of the rostrum, with upper and lower jaws tightly 

interlocked when found (a frequent occurrence in slendersnouted dyrosaurs); the left postorbital and squamosal 

bones; and several fragments of the temporal arcades. Many 

fragments of the rostrum contain teeth. It is presumed that 

all these parts are derived from one individual (no. 

33-CR -1 0): Specimen no. 37 -CR -1 includes the anterior 

end and about the posterior half of the mandibular rostrum, 

with the palatal part of the cranial rostrum attached when 

discovered; the occiput; the right quadrate; and various 

fragments. The articular part of the left mandible is also 

present. However, locality 37, like locality 33, has yielded 

cranial remains of other individuals, including the anterior 

end of a left mandible (no. 37-CR-7), a basicranium (no. 

37-CR-9), a tip of a very small mandibular rostrum (no. 

37-CR-20), a fragmentary left postorbital (no. 37-CR-11), 

and other fragments. Specimen no. 58-CR-1 contains the 

middle third of the mandibular rostrum, with the opposing 

palatal bones attached in matrix; a badly crushed posterior 

segment of the rostrum; the well-preserved occipital and 

otic region of the skull; and several teeth. 

As in other long-snouted dyrosaurs, the cranial bones 

are lightly sculptured, the dominant feature being long 

grooves and ridges, with pitting largely confined to the temporal arches and the angular and surangular bones. 

The external nares, surrounded by the premaxillae, are 

undivided, but posteriorly they are entered by a short narial 

spine formed exclusively of the premaxillae (fig. F6A). In 

outline they are broadly pear shaped, a little wider in front 

than behind, and about five-sixths as wide as they are long. 

The narial opening is higher posteriorly than anteriorly, so it 

is directed forward as well as upward (fig. F6B). The incisive foramen, seen through the nares, is slitlike, a little 

wider in front than behind, and rises anteriorly between the 

premaxillae. An attempted reconstruction of the postrostral 
F8 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

8 

0 5 I I 

A em 

Figure F6. Rhabdognathus sp., no. 33-CR-9. End of interlocked 

cranial and mandibular rostra. A, from above; B, from the side. 

skull (fig. F7) shows that the supratemporal fenestra of 

Rhabdognathus sp. had ~he same proportions seen in Dyrosaurus and the orbits were correspondingly small. The parietal space between supratemporal fenestrae is reduced to a 

narrow ridge. 

The frontal participated extensively in the supratemporal fenestrae, sending back a distinct sagittal crest between 

them. This crest, which is 7 mm wide, rises slightly toward 

the rear. The least interorbital distance in no. 2-CR-3 is 20 

mm, and the greatest transverse diameter (across the postorbital processes) is 46 mm. The parietal ramus of the frontal 

is l<()nger than in other crocodilians and posteriorly it 

divides, overlapping the sides of the parietal with long posteriorly acute processes. This arrangement is altogether different from the transverse and usually blunt fronto-parietal 

contact in eusuchians. 

The frontals are supported anterolaterally by the 

extremely elongated laterosphenoids (fig. F1 0). The parietals, best seen in no. 33-CR-10, display the same relationships to adjoining bones as in eusuchians, due allowance 

being made for the longitudinal attenuation of all the elements. As in a specimen of Dyrosaurus figured by Lavocat 

(1955) and Buffetaut (1982), the parietal plate descends in a 

broad V-shaped pattern onto the posterior face of the 

occiput, thus excluding the supraoccipital from the skull 

roof. 

The rostrum is elevated, a feature noted elsewhere in 

D. phosphaticus by several authors. At the level of the fifth 

upper tooth (MX 1), the rostrum, including the mandible, is 

33 mm wide and 64 mm high in no. 33-CR-9. The sutural 

relationships between the premaxilla and maxillae are as 

depicted in D. phosphaticus by Piveteau (1935, fig. 7). The 

coalesced nasal bones do not reach the nares. 

The right quadrate of no. 37-CR-1 lacks its proximal 

end and part of the medial condyle, but the distal end is perfectly preserved in no. 37 A-CR-1 (fig. F8). What remains of 

the quadrate in no. 37-CR-1 is an oblong piece 91 mm long 

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Figure F7. Rhabdognathus sp. Reconstruction of the post-rostral 

skull, from above, based on no. 33-CR-10. 

and 40 mm wide at the condylar end. That part which 

extends beyond the end of the paroccipital process seems 

much longer in relation to its width than in living crocodilians. Whether this resulted in an attenuated suspensorium as 

is suggested in some published illustrations (Piveteau, 

1935, fig. 9; Buffetaut, 1980, pl. 2-2) or is merely an illusion owing to a wider contribution by the quadratojugal, is 

unknown. The articular condyle (fig. F9) is more broadly 

exposed dorsally than below. The lateral part is well 

rounded dorsoventrally and curves around onto the dorsal 

surface to a greater extent than in eusuchians, The medial 

condyle is larger than the lateral condyle, but it was 

extended more onto the posteroventral side of the quadrate. 

The intercondylar notch is broad and shallow:. The lateral 

condyle is sharply truncated where it joined the quadratojugal to complete the cranial articulation. A small notch on 

the medial edge near the posterior end is located where one 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F9 

37 A-CR-1 

A 

0 I . 

em 

5 

37-CR-1 

8 

Figure F8. Rhabdognathus sp. Quadrate bones from 

above. A, left; B, right. 

would normally expect the aeriferous foramen, but an actual 

opening in the bone is not apparent. A fragment of the left 

quadrate bears a strong rounded tendon scar adjacent to its 

quadratojugal edge. This probably corresponds to crest A of 

Iordansky (1973) and is situated in about the same position 

as this crest in Crocodylus acutus. In no. 37 A-CR-1 the 

crest occurs a little more medially. A piece of what may be 

part of the united quadratojugal and jugal is preserved, but 

the condylar part of the quadratojugal is missing. In Hyposaurus natator, the quadratojugal is said to compose about 

one-fourth of the cranial jaw hinge (Troxell, 1925), and 

Buffetaut (1975) has pointed to this as a fairly common feature of long-snouted mesosuchians. 

The occipital region of the dyrosaurian skull is a massive structure that is frequently found more or less intact. 

Several of these have been figured (Swinton, 1930, pl. 4, 5; 

Piveteau, 1935, fig. 9; Lavocat, 1955, fig. 1; Buffetaut, 

1980, pl. 2-2, 1982, figs. 17, 18). Occipital masses belonging to nos. 33-CR-10, 37-CR-1 , and 58-CR-1 are present in 

the Saudi Arabian collection, and no. 33-CR -10 is attached 

to the anterior end of the braincase. These specimens, which 

await further preparation, should provide new data on the 

endocranial cavity and otic structures. The posttemporal 

fenestra occurs on the posterodorsal edge of the occipital 

face as a wide but slitlike opening. It passes inward beneath 

the roof of the parietal and the medial branch of the squamosal. Its path slants downward through the occipital mass 

and emerges in a transversely oval foramen on the posterior 

wall of the supratemporal fossa (fig. FlO, posterior-most 

arrow). The foramen magnum is subtriangular in outline 

with the apex downward. It is bounded largely by the exoccipitals with a minor contribution from the basioccipital in 

an arrangement not unlike that seen in many eusuchians. 

Such features as the huge occipital tuberosities and greatly 

Figure F9. Rhabdognathus sp., 

no. 37A-CR-1. Distal (articular) 

end of left quadrate (superior surface at top). 

expanded penotlc bullae are well described by Swinton 

(1930), Lavocat (1955), and Buffetaut (1982), and require 

no further elaboration. The virtual median contact achieved 

between opposite periotic bullae within the endocranial 

chamber must have resulted in a curious separation of the 

longitudinal head sinus from the dorsal surface of the hindbrain. The sinus must have risen up through an oval passageway posterodorsal to the bullae, thence passing forward 

above them through a restricted channel, and then rejoined 

the brain, so to speak, near the cerebellum in a large vaulted 

area of the endocranial roof. Foramina, which transmitted 

various branches of the longitudinal sinus, can be seen in 

the walls of this space. 

A striking feature of the braincase is its forward attenuation (fig. Fl 0). The laterosphenoids unite in the midline 

beneath the forebrain, and join the parietals and frontals 

dorsolaterally. This produces an elongate bony tunnel 

through which passed the olfactory peduncles (in all other 

mesosuchians and eusuchians the corresponding area is 

mostly cartilaginous, Hopson, 1979). Below this olfactory 

tunnel is another enclosed passageway, which carried the 

optic nerves forward. This passageway is formed by upward 

and forward expansion of the basisphenoidal rostrum, 

which, unlike the condition in other crocodilians, unites 

suturally with ventrolaterally expanded ridges of laterosphenoid. At its anterior end, this optic tunnel has about 

the same diameter as the exit of the olfactory tunnel, but the 

olfactory tunnel expands greatly posteriorly into a vertically 

oval space, whereas the optic tunnel remains about the same 

diameter throughout its length. The optic tunnel is shorter 

than the olfactory tunnel, ending anteriorly about 27 mm 

from the end of the fused laterosphenoids in no. 33-CR-10. 

Paired channels on the ventral surfaces of the combined laterosphenoids lodged the optic nerves for a short distance 

beyond their exit from the optic tunnel. Here, the basisphenoidal rostrum probably separated from the laterosphenoids 

and projected a short distance forward as a process. This 

process, however, appears to have been slender and rod 

shaped, and not a vertically expanded, laterally compressed 

basisphenoidal rostrum as seen in other crocodilians. 

The hypertrophy and other structural modifications in 

the anterior part of the braincase and basicranial axis may 

have strengthened the axis in a region otherwise weakened 
FlO PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

0 2 

em Is 

Figure FlO. Rhabdognathus sp., no. 33-CR-10. Braincase from the right side. Lower right, transverse section at ~; bs, basisphenoid; fpt, 

posttemporal fenestra; fr, frontal; ls, laterosphenoid; pa, parietal; qu, quadrate; sq, squamosal; I-V, paths of cranial nerves. Passages 

through bones indicated by arrows (see text). 

by attenuation of the temporal region and its relatively narrow lateral bony arcades. 

Except for those just described, cranial foramina are 

not visible in the specimens. A large lateral excavation posteriorly on the laterosphenoid probably housed part of the 

trigeminal ganglion. Farther forward, on the ventrolateral 

surfaces of the laterosphenoid-parasphenoid complex, are 

various longitudinal channels that probably lodged the ophthalmic ramus and the motor branch of the trigeminal nerve 

to the levator bulbi muscle (see Hopson, 1979). 

Foramina associated with the eustachian system are as 

discussed by Lavocat (1955). 

Although the proportions of the braincase are unusual, 

it must be stressed that all structures except the dorsal longitudinal sinus retain the usual crocodilian interrelationships. 

The unique features are owing to proportional differences 

and not to deviations from the crocodile plan of 

organization. The braincase has simply been stretched forward, or backward, as the case may be, in conjunction with 

the elongation of the temporal fossae. The tubular construction of the anterior braincase is no doubt related to a need to 

strengthen this part of a long slender head against the 

stresses generated by very powerful jaw muscles. While 

such attenuated braincases may be expected in crocodilians 

with elongated temporal fossae, I am unaware of any 

detailed description of such. Somewhat similar conditions 

are described in Metriorhynchus, but according to Wenz 

( 1968) the extent and relationships of the laterosphenoid are 

comparable to those in existing crocodilians. Nothing is 

said about a tunnel for the optic nerves as occurs in the 

dyrosaur neurocranium. The condition appears analogous to 

that which produced the closing of the secondary palate in 

crocodilians (see Langston, 1973). 
DYROSA URS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION Fll 

Interestingly, the braincase of the recently described 

Late Triassic protosuchian, Eopneumatosuchus, which does 

not have excessively elongate supratemporal fenestrae, nevertheless possesses an attenuated laterosphenoid and various longitudinal lateral sulci for cranial nerves on the side 

of the braincase somewhat evocative of the dyrosaur conditions (Crompton and Smith, 1980). 

Mandible.-Some features of the anterior end of the 

mandible have already been noted. The rostrum is not 

expanded anteriorly. The seventh tooth is reduced in size. 

The rostrum widens gradually posteriorly. The splenial 

symphysis ends anteriorly at the level of the tenth dentary 

tooth, on the dorsal side of the rostrum in no. 58-CR-1. On 

this basis the length of the presplenial rostrum of no. 

37 -CR -1 is estimated at about 215 mm. Ventrally, the splenial appears to end in a point somewhere near the level of 

the 11th tooth; however, in the specimens where sutures can 

be seen there is a certain asymmetry in their arrangement, 

which gives the impression that one splenial bone extends 

much farther forward than the other. In no. 37-CR-1 this is 

the left splenial, whereas in no. 2-CR-2 it is the right. The 

tip of the shorter splenial is not visible in either specimen. 

Swinton (1930) speaks of splenials being visible on the ventral side of the jaw, but not on the oral side in a specimen 

referred to Sokotosaurus nopcsai, and of splenials in the 

same species, which lack any trace of a midline suture. A 

well preserved segment of rostrum no. 43-CR-1 shows no 

trace of either splenial in the ventral side at the level of the 

12th tooth. The splenials in Hyposaurus bequaerti are regular in development (Swinton, 1950, pis. 2--4); however, 

aberrations in very long and slender splenials are not surprising. Thevenin (1911) believed that the angular and not 

the splenial formed the posterior part of the symphysis on 

the ventral side of the mandible in Dyrosaurus, but this has 

not been confirmed and is almost certainly in error. 

A large part of the left articular bone and some of the 

adjacent surangular (fig. Fll) are present in no. 37-CR-1. A 

small piece of the angular is attached. The dyrosaur surangular is unique in its large contribution to the glenoid fossa 

(Buffetaut, 1975). In the present specimen it forms almost 

half of the glenoid fossa and is thus even more extensive 

than in a dyrosaurid from the Paleocene of Mali figured by 

Buffetaut (1975, fig. 2a). The fossa is about 56 mm wide. It 

is limited behind by a low transverse elevation. A massive 

blunt process on the medial side projects forward to a 

greater degree than in any nondyrosaurian crocodile known 

to me. A comparable feature is evident in the jaw of Hyposaurus bequaerti (see Swinton, 1950, pl. 4) and in an 

unnamed dyrosaur from Mali (Buffetaut, 1975, fig. 2a). 

Buffetaut's drawing indicates that the medial condylar basin 

occupies only part of this projection, but no. 37 -CR -1 has a 

smooth articular surface extending over its entirety. The 

anteroventral process of the articular, which ended in cartilage, was a thick plate of bone that descended more vertically into the adductor fossa than in existing crocodilians. 

ar 

ang 

Figure Fll. Rhabdognathus sp., no. 37-CR-1. Articular region 

of left mandible, from above. Art, articular; sang, surangular. 

The articular forms the posterior side of this fossa, which is 

relatively much wider than in C. acutus, for example. Laterally, at the posterior edge of the glenoid fossa, is a large 

anteriorly directed foramen. This probably corresponds to a 

small foramen, which in existing crocodilians may enter the 

jaw from farther down in the adductor fossa, often in the 

suture between the surangular and the articular. It is far 

removed from this suture in no. 37-CR-1, however. Swinton 

(1950) reports a large , foramen in the surangular of H. 

bequaerti, but says that it lies behind the hinder rim of the 

glenoid fossa. He compares it to the aeriferous foramen in 

other crocodilians. The opening cannot be the foramen for 

the siphoneum because its presence in the surangular and 

within the glenoid fossa makes no sense embryologically or 

functionally. On the other hand, no foramen for the siphoneum is evident on the preserved part of the articular in no. 

37 -CR -1. Behind the transverse posterior rim of the glenoid 

fossa, the articular expands diagonally across the base of the 

retroarticular process and no doubt took · over most of the 

surangular's usual role in that process. The . process is 

formed by the articular medially, the surangular dorsolaterally, and the angular ventrolaterally. It is evidently longer in 

dyrosaurs than in any other crocodilian (Swinton, 1950). 

The lateral surfaces of the surangular arid angular bones are 

much more deeply pitted than other dermal bones of the 

head. 

The mandibular alveoli are borne in salients that are 

formed by wide intervening notches in the dorsolateral edge 

of the dentary. The salients are often visible in ventral 

aspect, especially toward the front of the jaw. 

The oral surface of the mandibular rostrum is arched 

transversely, and the alveoli open below the top of the jaw. 
F12 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Table Fl. Interdental distances measured from the centers of the alveoli 

[In millimeters] 

Alveolus 2 3 4 5 6 

33-CR-9 ............... 17 23 21 26 23 

37-CR-1 ............... 29 

59-CR-1 ............... 

37-CR-10 ............. 9 20 

37-CR-7 ............... 25 

Table F2. Anteroposterior diameters of alveoli 

[In millimeters] 

Alveolus 2 3 4 5 6 7 

33-CR-9 ...... .... 9 7 9 12 8 9 

137-CR-1 ........ 13 10 11 

58-CR-1 .......... 9.5 6 9.5 

37-CR-10 ........ 7.5 6 6.7 8.5 

37-CR-7 .......... 16 10 

27 

17 

8 9 

11 9.5 

1

The tip of this rostrum may be pathologically deformed and the second alveoli 

appear somewhat hypertrophied. 

10 

9 

The lateral edges of the alveoli are lower than the medial 

edges, so the openings are widely exposed in lateral aspect. 

The rims of the alveoli are higher anterolaterally than 

posteriorly. 

The spacing of the teeth in the rostrum is fairly regular 

except for the relatively narrow spaces between the first and 

second and the seventh and eighth teeth (see table F1). The 

diameters of the alveoli vary, but except for the small seventh alveolus, the differences are not great (table F2). 

The mandibular teeth are very long, slender, and 

curved. The crowns have a rounded to slightly oval cross 

section. They project forward and but little outward and 

interlock tightly with the upper teeth when the jaws are 

closed. The crowns are striated and some have weak anterior and posterior carinae, of which the anterior one is 

always the stronger, and often is the only edge present. The 

roots of the teeth are very long and extend diagonally downward through the jaw to rest on the bottom of the dentary 

(fig. F12). In cross section, the root of one tooth may be 

superimposed upon that of the next forward tooth. There 

appears to be a good deal of variability in the surface configuration and the cross section of the teeth, a tendency also 

noted in Dyrosaurus by Thevenin (1911). 

Vertebral column.-The complete dyrosaurian vertebral column has not been described, but Storrs (1986) has 

reported an almost complete articulated presacral column 

from Pakistan. This series consists of 23 presacral 

7 8 9 10 11 12 13 14 

31 31 31 31 31 

19 12 24 23 31 32 

Figure F12. Rhabdognathus sp., no. 37-CR-1. First and second 

mandibular teeth showing recumbency and overlapping roots. 

vertebrae, but it is not certain that the last vertebra preserved is the last presacral. Troxell (1925) reported 22 presacral vertebrae in a disarticulated skeleton of Hyposaurus 

natator, but he b~lieved that some elements were missing. 

Swinton (1950) described selected vertebrae of H. 

bequaerti from an incomplete series, and Buffetaut (1980) 

has discussed regional variations in the column of Dyrosaurus from a functional point of view. 

Most of the vertebral column of no. 37-CR-1 was 

found articulated, and I believe that all presacrals are represented. There is evidence for 25 vertebrae, but what is probably the ninth postcranial vertebra is very fragmentary and 

the third vertebra in front of the sacrum is represented only 

by the tip of a transverse process. Neural spines and zygapophyses are usually separated from their respective centra 

in this and other specimens in the collection, owing to loss 

of the more delicate parts of the neural arches. It has been 

possible, however, to reestablish contact between many of 

the transverse processes and their respective arches. 

Lacking ribs, it is impossible to recognize the first thoracic vertebra in most crocodilians because the morphological changes between cervical and thoracic vertebrae are 

gradual. The eighth postcranial vertebra in no. 37-CR-1, 

however, bears a robust diapophysis confined to the side of 

the pedicle, the parapophysis is a distinct backwardly projecting process arising near the middle of the centrum. I 

take this to be the first thoracic. 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F13 

' ' 

Figure F13. Rhabdognathus sp., no. 37-CR-1. Atlas and axis, 

right lateral view. Cl, nal , ic, centrum, neural arch and intercentrum, respectively, of atlas; C2, na2, centrum and neural arch (broken off) of axis; rl, facet for first rib; r2 cap, capitular facet for 

second rib; r2 tub, facet for tuberculum of second rib. 

There are probably three lumbar vertebrae. The first of 

these bears a winglike transverse process without any rib 

articulation, whereas the first well-preserved vertebra anterior to this has stronger transverse processes that clearly 

bore ribs. Among the associated fragments is the end of a 

transverse process that seems intermediate in shape 

between that of the lumbars and the rib-bearing thoracics; 

this probably represents the middle lumbar because a gap is 

clearly present between the other two lumbars preserved. If 

my interpretation is correct, the vertebral count for Rhabdognathus sp. is C-8, T-14, L-3, S-2. The first 6 caudal vertebrae were found articulated in no. 37-CR-1, and 15 others 

were collected with the specimen. Obvious gaps exist, however, and the total number of caudals in the dyrosaur tail 

remains unknown. 

The atlas-axis complex of Hyposaurus bequaerti has 

been described, but not figured, by Swinton (1950). Troxell 

(1925) describes the central structures in H. natator, and 

provides a small illustration. Parris (1986) figures the 

proatlas of H. rogersii. The atlas-axis complex is present in 

no. 37-CR-1 (fig. F13), and the atlas and axis pleurocentra 

are preserved in no. 58-CR-1. Other atlas and axis centra 

are present in the collection, but no neural arches are 

preserved. 

The intercentrum and the anterior part of the pleurocentrum of the atlas show every sign of having been embedded in cartilage. A deep, round notochordal pit is seen near 

the top of the anterior surface of the intercentrum. Correlated with a relatively huge occipital condyle, the atlanta} 

pleurocentrum appears more massive in relation to the axial 

pleurocentrum than in extant crocodilians-its greatest 

transverse diameter (anterior) exceeds that of the axis (posterior) by about 30 percent. The pleurocentra of the atlas 

and axis are suturally united, as described in H. natator. In 

no. 58-CR-1 these bones have separated, revealing wellformed opposing tongue-and-groove surfaces (fig. F14). 

em 

5 

Figure F14. Rhabdognathus sp., no. 58-CR-1. Opposing articular ends of the atlanta! and axial centra. A, posterior end of atlas; B, 

anterior end of axis. 

Specimen no. 58-CR-1 is only a little smaller than no. 

37 -CR -1 where the bones are united, so their separation in 

no. 58-CR-1 may be owing to fortuitous preservation or 

individual variation. The atlas pleurocentrum is a blocky 

structure with a roughly equilateral wedge-shaped lateral 

profile. Its superior surface is largely occupied by the flat 

bottom of the neural canal. The canal narrows rapidly posteriorly where the dorso-lateral edges of the centrum are 

expanded to receive the anterior ends of the neural arch 

pedicles of the axis. Laterally, above midheight of the pleurocentrum, the robust diapophysis for the axial rib projects 

backward and downward as a discrete process. It is separated from the pleurocentrum distally by a deep pleurocentra! depression that also separates the diapophysis from the 

ventro-lateral parapophysis below. The articular surface of 

the parapophysis is concave in ventral profile and is about 

twice as long as it is high. More than half of this parapophysis is on the pleurocentrum of the axis. Its posterior edge 

stands out sharply from the ventrolateral edge of the axis 

intercentrum. 

The anterior face of the atlanta} pleurocentrum is concave, and, with the neural demi-arches and the atlanta} 

intercentrum, forms a deep, transversely oval cup for the 

occipital condyle. The right demi-arch is preserved in no. 

37 -CR-1, but its superior process and postzygapophysis 

have been broken off. It is mainly a wedge-shaped block 

excavated above by the neural canal. It appears to have been 

lower than the corresponding arch in existing crocodilians. 

The pleurocentrum of the axis is sharply truncated 

anteriorly where it joins the pleurocentrum of the atlas and 

is much wider posteriorly than in front. Anteriorly, its sides 

are almost vertical and its bottom is flat. A system of strong 

ridges is developed on the ventral surface (fig. F15). A low 

tuberous hypapophysis occurs near the posterior end and 

extends forward for about one-third of the length of the 

pleurocentrum. A hypophyseal ridge, reported in H. 
F14 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

A 8 c 

Figure FlS. Rhabdognathus sp. Variation in the ventral ridge system on axial vertebrae. A, no. 37-CR-1; B, no. 58-CR-1; C, no. 3-CR-4. 

Table F3. Measurements of atlas-axis 

[In millimeters] 

Atlas 

Transverse diameter, dorsally, of intercentrum 

Transverse diameter, ventrally, of intercentrum 

Height of intercentrum 

Length of intercentrum 

Transverse diameter, dorsally, of anterior end of 

pleurocentrum 

Height of anterior end of pleurocentrum 

Length, dorsally, of pleurocentrum 

Height of posterior end of pleurocentrum 

Axis 

Transverse diameter, dorsally, of posterior end of 

pleurocentrum 

Height, posterior end of pleurocentrum 

Least transverse diameter of pleurocentrum 

Length of pleurocentrum 

Greatest length of atlas-axis complex 

37-CR-1 58-CR-1 

44 

27 

34 

18 

74 57+ 

45 46 

40 41 

47 43 

47 44 

46 45 

26 28 

63 60 

101 94 

bequaerti by Swinton (1950), is not present in either no. 

37-CR-1 or 58-CR-1 where the hypapophyseal tuberosity is 

bounded anteriorly by a median triangular depression. A 

median ridge is present, however, in a detached pleurocentrum (no. 3-CR-1). The posterior end of the pleurocentrum 

is amphiplatyan, with a shallow central excavation surrounded by a thickened discoid rim that occupies about onequarter of the surface. The floor of the neural canal is 

greatly constricted at midlength, but it flares out posteriorly, 

reflecting the configuration of the pleurocentrum. At 

midlength, the bottom of the canal is pierced by paired longitudinally oval foramina. 

Swinton (1950, p. 19) describes the axis neural arch of 

H. bequaerti as being low anteriorly, but rising posteriorly, 

" ... though the spine itself is nowhere high." For measurements of the atlas and axis see table F3. 

Platycoelous centra are the most frequently found 

dyrosaurian remains. Several authors have noted the wedgeshaped lateral profile in which the cervical centra are longer 

at the bottom than above (table F4 ). The difference is particularly noticeable in the seventh cervical of no. 37-CR-1. 

The dimensions are about equal in the anterior thoracic vertebrae, but farther back the ventral edge becomes shorter 

than the dorsal edge (fig. F16). In the anterior caudals the 

dimensions are again about equal, but from the middle of 

the tail backward the wedging downward condition reappears and increases in the more distal vertebrae. One such 

centrum is 52 mm long ventrally and 55 mm long dorsally. 

The sides of the cervical centra are excavated between 

the dia- and parapophyses. These pleurocentrous depressions are absent in the anterior thoracic vertebrae, but they 

reappear at about thoracic number 9 and thence become 

progressively larger back to the last lumbar. Here the 

depression is about the size of the end of one's thumb and is 

shared about equally by the centrum and the neural arch. 

The ends of the centra consist of a thickened peripheral 

disc surrounding a central depression (figs. F16, F18). The 

thickness of the disc is greatest at the bottom of the centrum, and the central depression is deepest on the posterior 

face. The area of the disc may be as much as two-thirds of 

the area of the distal end in some anterior caudals. The exterior of the bone near the edges of the central disc is marked 

by many short parallel longitudinal ridges. 
Table F4. Measurements of vertebrae, specimen no. 37-CR-1 0 

-< :::0 

[In millimeters] 0 

C/:l 

~ Cervical Thoracic Lumbar Sacral Caudal c 

:::0 

2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 C/:l 

n 

Total height of vertebra 187 182 :::0 

(less hypapophysis) 0 

n 

Centrum 0 

0 

Length, ventral edge 66 73 67 63 66 73 74 72 71 68 63 63 63 57 58 55 55 57 60 59 62 64 70 67 151 160 1

59 158 157 155 t= 

Length, dorsal edge 57 68 63 59 58 64 71 71 72 68 65 66 65 63 62 62 62 62 65 64 65 65 80 70 57 57 58 58 56 54 ?= 

Greatest width, anterior 36 45 48 51 49 254 59 57 58 58 58 57 55 52 53 52 59 58 258 57 76 66 52 56 51 46 44 43 $; 

m 

end C/:l 

0 

Height, anterior end 44 50 51 51 52 53 52 55 52 52 53 256 57 57 59 60 60 58 56 55 54 52 49 45 46 48 46 44 43 41 C/:l 

c 

37 41 52 52 249 245 39 39 37 36 36 36 42 

n 

Least width, midheight 25 30 33 33 49 43 45 44 47 51 55 45 39 36 32 30 30 ::t 

at mid1ength E 

Neural Arch 'Tl 

:::0 

Height, including spine 280 295 281 121 133 0 

from neurocentra! $; 

...., suture ::t 

Greatest width across 268 278 268 269 256 49 52 m 

'"0 

prezygapophyses ~ 

r 

Greatest width across 288 284 296 2118 2116 257 255 250 248 250 48 238 33 m 

0 postzygapophyses n 

2140 2126 2148 2184 194 189 2198 2190 2184 2130 

m 

Width across 98 z 

diapophyses m 

c 

Height of neural spine 33 43 41+ 100 115 166 $; 

from top of canal $; 

Length of neural spine 10 46 250 255 52 246 39 ::t 

at base ~ ~ 

Length of neural spine 248 249 32 :::0 

'Tl at top 0 

:::0 1In caudals greatest length toward bottom of centrum is used to avoid chevron facets. $; 

2 ~ Estimates are given only when small pieces are missing. ...., 

0 

z 

'TI 

...... 

VI 
F16 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

A B 

0 5 

em 

0 

Figure F17. Rhabdognathus sp., no. 37~CR-l. Articulated 

7th cervical to 9th thoracic vertebrae, ventral aspect, showing extent of hypapophyses (anterior is to the left). All hypapophyses are broken off at the base except those of thoracics 

Caudal centra are distinctive in their square-cut, boxlike proportions, noted by Swinton (1950). It was such vertebrae, from the Eocene of Nigeria that Nopcsa (1925) 

mistook for hadrosaurian caudals. Widely beveled edges for 

insertion of chevrons appear first on the posterior ends of 

the second and third caudal centra. Beveling and the formation of facets first takes place on the fourth centrum, and 

continues posteriorly into the distal caudals. 

em 

5 

Figure F16. Rhabdognathus 

sp., no. 37-CR-1. A, centrum of 

the 3rd cervical vertebra, left lateral aspect; B, the same, posterior 

aspect; C, incomplete 12th thoracic vertebra, left lateral aspect; 

D, 9th thoracic vertebra, anterior 

aspect. 

8 and 9, which are represented only by slight swellings in the 

ventral midline. Hypapophysis of the 7th cervical is 

deformed and the right diapophysis is underdeveloped in this 

vertebra. 

Hypapophyses-the root of the name Hyposaurus 

(Owen, 1849)-are more strongly developed in dyrosaurs 

than in any other group of crocodilians. Interestingly, however, as in other marine mesosuchians, the processes are 

less developed in the cervicals than they are in eusuchian 

crocodiles (fig. F17). In no. 37-CR-1 only low tuberosities 

are present at the posterior end of the axis, anteriorly and 

posteriorly on cervicals 3 and 4, and are virtually lacking on 

cervicals 5 and 6. Judging from its broken base, which 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F17 

extends about one-third of the length of the centrum, the 

first strong hypapophysis occurs at the anterior end of cervical 7. This is apparently one vertebra earlier than in the 

articulated series described by Storrs (1986). From here 

posteriorly to the fourth thoracic vertebra, the processes 

extend almost the full length of their respective centra. The 

centrum of the fourth thoracic is 51 mm long at its base. But 

then, in the sixth and seventh, the basal lengths decrease, 

and in the eighth thoracic, one later than in Storrs' specimen, the hypapophysis reverts to a small tuberosity about 

23 mm long on the anterior third of the centrum. The 

remaining presacral vertebrae lack ventral projections and 

the bottoms of the centra become transversely angular, producing the ogival cross section noted by Arambourg (1952). 

Troxell (1925) reported a moderate ventral keel on 

what he believed to be the sixth cervical vertebra in Hyposaurus natator. Keels are said to be present in the vicinity of 

the last cervical and the following four or five thoracic centra, with the hypapophyses increasing in size posteriorly. On 

the fifth thoracic the process is prominent and extends 

nearly the length of the centrum, but the hypapophysis is 

suddenly reduced to only half the length of the centrum on 

the sixth. Apparently hypapophyses do not exist posterior to 

the sixth thoracic vertebra in H. natator. This sequence 

agrees reasonably well with that of Rhabdognathus sp. and 

tends to confirm Troxell's arrangement of the incomplete 

vertebral column in H. natator. 

The hypapophysis of the atlas is described as a slight 

ridge in H. bequaerti, that on the preserved fifth or sixth 

cervical as "slight. .. a little in advance of the middle length" 

(Swinton, 1950, p. 20). The conditions described by Swinton in the ?fourth dorsal and a middorsal are comparable to 

those in no. 37-CR-1. 

Noting the crosslike impression of neurocentra} surfaces, The venin ( 1911) was impressed by the lack of fusion 

between the neural arches and the centra in Dyrosaurus 

phosphaticus. This is now known to be the normal state in 

marine mesosuchians, including large dyrosaurs. Even the 

biggest centra in the Saudi Arabian collection have thus 

become separated from their arches. Only in the caudals 

does the neural arch regularly fuse with the centrum, a tendency shared with eusuchian crocodilians. The pedicles are 

long throughout the column and are broadly attached to the 

centra except in the caudals where their sides are thinwalled. The neural canal is wider than high and is largest in 

the anterior part of the column, but the difference is not 

great. The pedicles are more deeply notched posteriorly 

than anteriorly, where the prezygapophyses restrict the 

intervertebral channels. 

Diapophyses and parapophyses are robust, especially 

on the cervicals and anterior thoracic vertebrae. Diapophyses spring from the centrum in the anterior cervicals, but in 

the fifth cervical a little more than half of the process is 

borne by the neural arch (it is near this vertebra that the 

resemblance of the neuro-central surface to that of Champsosaurus and nothosaurs, noted by early workers, is most 

striking). The parapophyses arise close to the ventral edges 

of the centra on the cervicals. They project outward, forward, and downward below the general plane of the bottom 

of the centra in the anterior vertebrae, rising a little above 

the baseline in the last two cervicals. There follows in the 

first thoracic an abrupt shift upward in the position of the 

parapophysis, to mid-height of the centrum. This shift is 

more pronounced than in Crocodylus. On the third thoracic, 

the parapophysis is partly divided by the neurocentra} 

suture, and on the fifth it is almost completely transferred to 

the neural arch. On the eighth, the parapophysis lies almost 

in the same plane as the diapophysis, and this relationship is 

maintained caudad to the end of the series. 

The diapophysis is completely on the side of the arch 

in the first thoracic vertebra. In the anterior part of the column these processes project outward, downward, and 

slightly forward, but on the first thoracic vertebra the diapophysis slants backward and only a little downward. The 

backward slant increases through thoracics 2-5, but with 

number 7, an angle of about 90 degrees to the sagittal plane 

is achieved and is maintained throughout the rest of the 

series. 

Where united dia- and parapophyses form a transverse 

process, from thoracic 7 to 13, this is broad and platelike. 

When these vertebrae are articulated, the space between 

succeeding transverse processes is only about 5 mm. During 

dorsal or lateral flexion of the trunk, contact between adjacent processes is avoided because their planes are inclined a 

few degrees forward, so the trailing edge (diapophysis) 

always is higher than the leading edge (parapophysis) of the 

succeeding vertebra. The transverse processes seem 

remarkably short, the greatest transverse diameter across 

any of them being about 198 mm, on thoracic number 10. 

Transverse processes on the lumbar vertebrae are broad and 

blade-like and are roughly horizontal. 

Transverse processes are absent on the anterior caudals, where ribs are inserted into facets on the sides of the 

centra and neural arches. The most posterior caudal centrum 

preserved in no. 37-CR-1 has a sharp longitudinal ridge in 

place of the caudal rib. 

The zygapophyses seem less robust than in existing 

crocodilians. Toward the back of the neck, the angle 

between opposite articular faces is more acute than in Crocodylus acutus, for example. The processes are largest and 

most widely spread in the cervical-thoracic transition. They 

diminish in size from the first thoracic posteriorly. The 

articular surfaces are less expanded than in the posterior 

thoracic and lumbar vertebrae of existing crocodilians. The 

prezygapophyses in the posterior part of the trunk are 

inclined at an angle of only about 53 degrees to the sagittal 

plane, compared to a corresponding angle of 70 degrees in 

Alligator mississippiensis. Zygapophyses are not present in 

the distal caudals, but at what point they disappear is 

unknown. What remains of some neural arches, however, 
F18 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

G 

0 5 

em 

D E F 

Figure F18. Rhabdognathus sp., no. 37-CR-1. Caudal vertebrae. A, first; B, fifth; C, medial centra, left lateral aspect; D-F, the 

same, posterior aspect; G, distal caudal centrum and neural spine. 

suggests that prezygapophyses remain for a while after contact with their opposing postzygapophysis has been lost. 

Although most of the spines in the presacral column 

appear to be represented in no. 37 -CR-1, only the first and 

third thoracic and third lumbar spines are attached to their 

respective vertebrae. The anterior presacral spines were evidently similar to those figured for H. natator (Troxell, 1925, 

fig. 4) and for D. paucidens (Arambourg, 1952, fig. 60). 

The anterior cervical spines were low and triangular in lateral profile. The fifth or sixth cervical spine is bent slightly 

backward with the leading edge exceeding the trailing edge 

somewhat in length. The anterior thoracic spines were probably higher, wide and inclined backward as described in H. 

natator and H. bequaerti, but the best preserved spine, that 

of the third thoracic vertebra, is more upright and the leading edge is straighter than in the so-called eighth vertebra of 

H. natator figured by Troxell (1925, fig. 4C). The spine of 

the 3rd lumbar vertebra is, however, much higher in relation 

to the length of the centrum than in the approximately 15th 

vertebra figured by Troxell (1925, fig. 4D). The height of 

the caudal spines is most remarkable. Swinton (1950) figures an anterior caudal of H. bequaerti in which the spine is 

five times as high as its centrum. The spine associated with 

caudal 4 in no. 37 -CR -1 is a little more than three times the 

height of its centrum. The spine of a posterior caudal which 

corresponds in shape to the "late" caudal figured by Swinton (1950, pl. 8B) has a rodlike spine which, when complete, was probably similar to that of H. bequaerti. The 

main part of the spine is a pencillike rod with a thin median 

lamina on the anterior and posterior edges near its base (fig. 

Fl8G). The posterior lamina divides downward to form the 

postzygapophyses, but the forward lamina ends below in 

the roof of the neural canal. Retention of these extremely 

long slender neural spines far distally in the tail is unique to 

the dyrosaurs. 

The sacral centra were apparently separated by a thin 

cartilage disc. The anterior articular face of the first sacral is 

almost round, but the sacral rib heads are expanded anteriorly and are inserted into posterolateral facets on the last 

lumbar centrum. This greatly increases the transverse articulating surface of the first sacral so that while it is 50 mm 

high, it is about 80 mm wide. A similar arrangement exists 

between the second sacral and the first caudal, with the sacral centrum having principal diameters of 46 mm high and 

about 56 mm wide. The intersacral articular surface is transversely oval. The bottoms of the centra are broadly rounded 

transversely, that of the first bearing a low rounded median 

ridge. 

The detached neural arch of the second sacral is partly 

preserved in no. 37-CR-1. As in eusuchians, the prezygapophyses are slender and closer together than those of the 

lumbar vertebrae, and, contrary to conditions in the trunk 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F19 

vertebrae, their articular surfaces are horizontal and slightly 

concave along the axis of articulation. Postzygapophyses 

are larger but are closer together and their articular surfaces 

are somewhat more steeply inclined than in Crocodylus. 

The spinal column of no. 58-CR-1 was partly articulated. Present are 7 cervicals, 14 thoracics, 2 lumbars, 1 sacral and 9 caudals. I find no significant differences between 

these vertebrae and those of no. 37-CR-1; however, the 

hypapophyseal tuberosity is less developed on the seventh 

thoracic centrum, and the bottoms of the succeeding centra 

seem a little more angular than in no. 37-CR-1. 

0 5 

Figure F19. Rhabdognathus sp., no. 37-CR-1. Proximal ends of 

thoracic ribs. 

Ribs.-Except for two cervical ribs, only fragments of 

ribs are available. One cervical rib (no. 33-CR-1) is not significantly different from midcervical ribs in Crocodylus, but 

it seems a little more robust. Judging from the disposition of 

the dia- and parapophyses, the last rib with a bifurcated 

head occurred at about the fourth thoracic vertebra. When 

the tubercular and capitular processes coalesce, the resulting rib head appears broader than in eusuchians and, as 

would be expected from the short transverse processes, the 

capitular process is much abbreviated (fig. F19). There is 

no evidence of uncinate processes. The thoracic ribs are 

expanded distally as in existing crocodilians. 

It is clear from the attachment surfaces on the atlas 

intercentrum that the first cervical rib was single headed as 

in all mesosuchian and eusuchian crocodiles. Its head must 

have been largely imbedded in the cartilage that surrounded 

the atlas as no distinct facets are developed. The second cervical rib was double headed and, to judge from the strength 

of the diapophysis on the atlanta} pleurocentrum, both the 

capitular and tubercular processes were much better 

developed than in existing crocodilians, where the tubercular articulation is often ligamentous (Wettstein, 1937). 

Indeed, I can find no example among mesosuchians or 

eusuchians in which the atlantal diapophysis is so strong as 

in no. 37-CR-1. 

The sacral ribs appear almost as mirror images of one 

another from above, except that the second rib is smaller 

than the first (fig. F20). Their heads are firmly inserted into 

Figure F20. Rhabdognathus sp., no. 37-CR-1. Sacral vertebrae and ribs, dorsal aspect. Anterior at top. 
F20 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

A 

0 

8 

5 

em 

Figure F21. Dyrosaur and eusuchian sacra, left lateral aspect. A, Rhabdognathus sp., no. 37-CR-1; B, Crocodylus acutus, 

drawn to the same scale to contrast shapes of the first sacral ribs. Position of neural arch in A is conjectural. 

sockets on the sides of the centra and the neural arch pedicles. Nevertheless, the bones readily separated in most 

specimens after death. The first sacral rib is distinctively 

different from that of Crocodylus; its iliac end is roughly triangular, with its antero-dorsal corner projecting both anteriorly and laterally far out beyond the level of its ventral 

angle (fig. F21). The iliac surface of the second rib resembles that of Crocodylus. The anterior part of the articular 

surface is convex and was inserted into a corresponding 

excavation on the medial side of the ilium. The rib end is 

drawn out posterodorsally into a long process whose iliac 

surface is broadly excavated. This excavation received a 

correspondingly rounded diagonal ridge of the ilium. 

Caudal ribs, best seen in no. 37-CR-1, are thick and 

wide. Their heads occupy almost the full length of the centrum in the anterior caudals. They are suturally attached to 

excavations in the sides of the centrum and neural arch. The 

last vestiges of the suture are seen in the fourth caudal, after 

which the ribs appear as transverse processes. No caudal rib 

or transverse process is complete, but the thickness of the 

bases of the anterior ribs suggests that these structures were 

of substantial size as far back as the midcaudals. 

Haemapophyses.-Several fairly complete haemapophyses are preserved in no. 37-CR-1 (fig. F22). What is 

probably the second chevron is slender and tapers to a point 

distally. It possesses vertebral facets only on the posterior 

side of the arch. This chevron, lacking the distal tip, is 150 

mm long. The haemal canal has principal maximum diameters of 33 and 9 mm. Farther down the tail the chevrons 

become shorter and broader, flaring ·out distally into an 

asymmetrical spatulate blade. All chevrons preserved have 

the haemal canals closed above, but in at least some the two 

halves of the arch are not coalesced. Proximal ends of the 

arches are robust and, except for the first few chevrons, 

have well-developed facets both fore and aft. Viewed from 

the side, the broadly triangular proximal ends are inserted 

into the correspondingly wide intervertebral spaces. In the 

more distal chevrons the distal end becomes paddle shaped. 

One such bone from no. 37-CR-1 is 70+ mm high with 

anteroposterior diameters at the top, midheight, and bottom 

of 24, 13, and 27 mm, respectively. Far distal chevrons are 

not represented, and it is not known at what position chevrons disappear. 

Gastralia.-One almost complete gastral rib was 

found with no. 58-CR-1. It is thick and on one side, presumably posterior, displays two deep grooves. I believe it is t~e 

l'!lteral segment of the last gastral rib and the larger of the 

two grooves lodged the anterior cartilaginous edge of the 

pubis. The second, smaller, and more medial groove 

received the posterolateral end of the medial segment of the 

rib. The thickest part of the bone occurs in the short space 

between the opposing ends of the two grooves. Here its 

maximum diameter is 9.5 mm. The preserved segment, 

lacking both ends, is 134 mm long. 

Pectoral arch.-The pectoral arch of dyrosaurs is 

impressively massive and is relatively much larger and better ossified than in the other marine mesosuchians. The 

scapula and coracoid display some unique features. 

No complete pectoral elements are available in the 

Saudi Arabian collection. Either a badly weathered proxi-
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F21 

0 

em 

5 

8 

c E 

F 

A D 

Figure F22. Rhabdognathus sp., no. 37-CR-1. Haemapophyses. A, proximal, possibly second chevron; B, mid-caudal chevron; C, 

distal mid-caudal chevron, posterior aspect; D-F, the same, right lateral aspect. 

mal end of a large scapula (no. 37-CR-3) or a slightly 

smaller proximal end of a coracoid (no. 37-CR-2) may 

belong to the skeleton no. 37 -CR -1. Better preserved, but 

probably too small to belong to no. 37-CR-1, is the proximal end of a left scapula (no. 37-CR-4). The proximal end 

of a very small left scapula (no. 37-CR-5) is also present. A 

left coracoid (no. 37E-CR-1) lacks only the anteroproximal 

lobe. Also present is the sternal end of a larger coracoid (no. 

36W-CR-1), and a fragment of a proximal end (no. 

2-CR-1). 

The coracoid (no. 37E-CR-1) resembles that of H. 

natator and confirms Troxell's reconstruction (fig. F23A). It 

is also similar to the coracoid of H. bequaerti. It is much 

more slender, has a straighter shaft, and the distal end is less 

expanded than in eusuchians. When oriented in life position, the shaft projects posteromedially and, curving away 

from the glenoid cavity, becomes almost recumbent distally. 

Seen from the side (fig. F23B), less of the coracoid is visible than in existing crocodiles. Specimen no. 37E-CR-1 is 

205 mm long, but is incomplete. The greatest diameter of 

the distal end is 52 mm, and the least diameter of the shaft 

near midlength is 20 mm. The somewhat larger coracoid 

(no. 37-CR-2) has a greatest proximal diameter of 122 mm. 

Enough is preserved of the scapulae (nos. 37 -CR-4 and 

-5) is preserved to indicate a close resemblance to the peculiar bone of H. nat at or figured by Troxell (1925, fig. 7 A). 

Evidence of the exceptionally developed coracoid lobe is 

seen in no. 37-CR-5 (fig. F23B). It is likely that in adult 

individuals this process was even more accentuated, as indicated in Troxell's illustration. The scapular spine is short, 

lies posterior to the leading edge of the scapula, and is 

largely confined to the coracoid lobe. The beginning of the 

great dorsal expansion of the scapular blade is also evident, 

and between the blade and the coracoid lobe the bone is 

deeply emarginated, as in H. natator. 

The glenoid cavity is formed by subequal parts of the 

scapula and coracoid. It has the usual saddle-shaped character, but is somewhat hourglass-shaped owing to a considerable narrowing of the middle (fig. F23C). The glenoid, 

formed by uniting nos. 37E-CR-1 and 37-CR-4, which are 

about the same size, has a dorsoventral diameter of 60 mm. 

Forelimb.-Massive ends of humeri are frequently 

preserved, but there is not one complete humerus in the collection. The most nearly complete example is a small isolated right humerus, no. 3-CR-1 (fig. F24B). Its proximal 

end is missing, but there is an end from a humerus of similar 

size from locality 33 (no. 33-CR-3) (fig. F24A). Large right 

proximal and distal ends of differing size were collected at 

locality 37, but whether either of them belongs to no. 

37-CR-1 is unknown. Specimen no. 3-CR-1 is a little longer 

than the humerus of H. natator figured by Troxell (1925, 

fig. 8), but it is nevertheless more slender in the shaft and 

the distal end is less expanded. However, the head (no. 

33-CR-3) seems almost identical to the Hyposaurus 

humerus. The only difference I can see between the Saudi 

Arabian specimens and the humerus of H. bequaerti (Swinton, 1950, pl. 6) is that the shaft of no. 3-CR-1 is straighter 

and the distal end is less expanded on the posterior (medial) 
F22 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

,.--- / ', 

I ' 

I ' 

I 

I 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

A 8 

./ r--

f 

I 

\ 

' ' ' /--....-:, 

/ 

I 

I 

I 

I 

I 

I 

I 

I 

\ 

' ' ' ' ,_, / 

,..-

., ....... ----............. ........_. 

,,.. - ' ' ,,.. I 

/,.. I 

/ I 

/ I 

/ / 

', I 

\ I 

\ I 

\ I 

\ I 

\ I 

\ I 

I 

I 

I 

c 

0 

em 

9 

Figure F23. Rhabdognathus sp., pectoral girdle. A, left coracoid, no. 37E-CR-1, anteroventral aspect to show shape of sternal ramus; B, 

left scapula and coracoid, lateral aspect, reconstructed from nos. 37E-CR-1, 37-CR-4, 37-CR-5, and the scapula of Hyposaurus natator; C, 

glenoid surface showing pronounced hourglass outline. 

side. Expansion of the ends and the resulting curvature of 

the sides of the shaft evidently increase with size, as the 

larger specimens in the collection agree better with the 

Hyposaurus humerus in these regards. 

Both Troxell and Swinton remarked upon the long and 

low delto-pectoral ridge in Hyposaurus as compared to the 

ridge in Crocodylus. Their comments apply as well to the 

humerus of Rhabdognathus sp. Those authors were, however, impressed with the general similarities between the 

Hyposaurus and Crocodylus humerus. These similarities are 

less apparent to me. The humerus of H. bequaerti as well as 

the specimens from Saudi Arabia are longer, straighter, and 

more slender than in the crocodile. The distal end is also 

less expanded. 

The proximal end of the humerus no. 37-CR-7 is evocative of that in some ornithopod dinosaurs (fig. F25B). The 

large smoothly rounded caput is more distinct on the dorsal 

surface. The posterior tuberosity, which in eusuchians slants 

sharply away from the caput posterolaterally, forms a 

rounded mass only a little smaller than the caput at the posterior corner of the head. The anterior tuberosity is not differentiated from the caput, so all three elements are 

confluent and lie roughly in a single plane. Thus, when 

viewed from above or below, the proximal end of the 

humerus has the squared-off appearance noted in Hyposaurus by Troxell (1925) and Swinton (1950). 

A distal end of a right humerus (no. 37-CR-6) is especially well preserved (fig. F25A). The smooth-surfaced 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F23 

Table FS. Measurements of selected humeri 

[In millimeters] 

Anteroposterior diameter, proximal end 

Greatest dorsoventral diameter of caput 

Greatest dorsoventral diameter of posterior tuberosity 

Greatest height of deltopectoral crest (including shaft) 

Least diameter of shaft 

Greatest anteroposterio~ diameter, distal end 

Greatest dorsoventral diameter of capitulum 

Greatest dorsoventral diameter of ulnar condyle 

33-CR-3 

A 

0 

I 

em 

5 

I 

3-CR-1 

8 

2-CR-1 

Ill 

57 

49 

Figure F24. Rhabdognathus sp. A, proximal erid of right 

humerus; B, right humerus lacking head. Both specimens are from 

small and relatively immature individuals. 

condyles are better rounded than in Crocodylus. They are 

separated by a broad and shallow intercondylar sulcus that 

extends onto the dorsal surface of the bone instead of ending in a depression half way up on the distal end as in Crocodylus. The ulnar condyle is relatively smaller, and the 

radial condyle (capitulum) relatively larger than in Crocodylus. The ulnar condyle projects beyond the end of the 

radial condyle. 

Measurements of various humeri are given in table F5. 

Of forearm bones, only the proximal end of a very 

large ?left ulna (no. 33-CR-4), the distal end of a much 

smaller left ulna (no. 33-CR-3), and the distal half of a 

?radius (no. 58-CR-1) have been identified. 

33-CR-3 3~CR-l 

57 

27 

22 

27 

22 

40 

26 

24 

0 

37-CR-6 

85 

64 

50 

em . 

37-CR-8 36W-CR-2 

110 72 

65 40 

38 36 

5 

I 

54 

45 

31 

Figure F25. Rhabdognathus sp., articular ends of the humerus of 

large individuals. A, no. 37-CR-6, distal end; B, no. 37-CR-6, 

proximal end; c, caput; r, radial condyle; t, posterior tuberosity. 
F24 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Swinton (1950) stated that the ulna of H. bequaerti 

was so typically crocodilian that it required no detailed 

description. Parris (1986) figures an ulna of Hyposaurus 

rogersii that confirms Swinton's appraisal. The distal end of 

the ulna no. 33-CR-3 differs from that of C. acutus only in 

the stronger development of the anterior part of the ulnare 

surface. This bone is 47 mm in its quasi-transverse diameter 

and from 20 to 30 mm in the direction normal to this 

measurement. 

No manual elements have been recognized in the collection. 

Pelvic arch.-Like the pectoral arch, the pelvis in 

dyrosaurs is more robust than that of other marine mesosuchians and more like the pelvis in eusuchians. Remains of 

the pelvic bones are available from several localities, but 

except for the iliac of no. 37 -CR-1 none of them is complete. Both sides of the pelvis of no. 37-CR-1 were found 

semiarticulated with the sacrum. The left ilium is better preserved than the right. It is a thick and massive bone, having 

the general proportions seen in eusuchians. It differs from 

the bone of H. natator figured by Troxell (1925, fig. 13) 

mainly in the lesser anterior development of the costalis 

process, which appears much blunter in no. 37-CR-1. Noteworthy is the depth and narrowness of the acetabulum, 

which in the right ilium of no. 37-CR-1 is 75 mm high, 70 

mm anteroposteriorly at the ventral edge of the ilium, and 

about 45 mm deep. The acetabular notch on the ventral edge 

of the ilium is, however, relatively wider than in Crocodylus. The lateral edge of the strong posterior ischiadic peduncle projects outward forming a broad posterior wall for the 

acetabulum. The articular end of this peduncle contains, laterally, a mammillary process and, medially, a depression, 

which fit closely the corresponding features of the ischium. 

The anterior peduncle is similar, but it is more distinctly 

divided between convex and concave parts by a narrow and 

shallow channel. The opposing surface on the anterior process of the ischium has an unfinished roughened end 

without a corresponding pit or mammillary process. This 

area was, as in existing crocodilians, deeply imbedded in 

cartilage. The posterior end of the iliac blade resembles in 

lateral profile that of a C. acutus ilium at hand, but its posterior end is a little more broadly rounded. The whole iliac 

blade is more expanded vertically and is not so thick as in 

the crocodile. It is broadly excavated laterally. On the 

medial side, the scars for attachment to the sacral ribs 

reflect the shape of the ends of those ribs. The area for the 

second sacral rib resembles that in C. acutus, but the facet 

for the first rib is shallow and higher than wide. In agreement with the configuration of the end of the first sacral rib, 

it is completely unlike the first sacral rib facet in the crocodile. The left ilium of no. 37-CR-1 is 187 mm long and 116 

mm high at the level of the posterior ischiadic peduncle. 

The proximal end of the ischium resembles that in C. 

acutus, but the area for articulation· of the pubis is a low 

rounded knob at the anteroventral corner of the pubic proem 

' ' 

5 

Figure F26. Rhabdognathus sp., no. 58-CR-1, right pubis, 

ventral aspect. 

cess, whereas in C. acutus it is a wide V-shaped facet. The 

distal part of the ischium is not preserved on any specimen. 

The ischium surrounds the lower two-thirds of the vertically 

ovate acetabular foramen. The opening in the right half of 

the pelvis is 44 mm high and 25 mm long. According to 

Troxell (1925, p. 510), this part of the ischium in H. natator 

is" ... narrow and pointed and not broad as in the true crocodiles, and, having a sharp edge and an acute termination: it 

appears never to have actually joined its fellows on the midline." Swinton (1950), on the other hand, describes the distal end of the ischium in H. bequaerti as much expanded, 

the more usual crocodilian condition. 

Parts of several pubes are available, including proximal ends of opposite elements and the distal end of one 

belonging to no. 37-CR-1. The most complete pubis in the 

collection is the right element of no. 58-CR-1, which is 

missing only a little from around the distal end (fig. F26). 

The pubis is spatulate with a thick round shaft and a slightly 

enlarged blunt proximal end, which is excavated in the center of the articular surface to receive the corresponding low 

rounded knob on the ischium. Distally, the bone flares out to 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F25 

Table F6. Comparative measurements of dyrosaurian femora 

[In millimeters] 

Length 

Antero-posterior diameter of head 

Greatest dorso-ventral diameter of head 

Greatest diameter across condyles 

Least diameter of shaft 

Distance from proximal end to highest point of fourth trochanter 

Distance from distal end to highest point of fourth trochanter 

1

Estimate. 

Figure F27. Rhabdognathus sp., tibia. A, no. 37-CR-1, right -)-

tibia, anterior aspect; B, outline of distal end of left tibia 

(reversed) drawn to same scale as A. Ant., anterior. 

a greater degree than indicated in H. natator (see Troxell, 

1925, fig. 12), and the distal edge, seen in the left pubis of 

no. 37-CR-1, is not so square cut as there. I find no evidence 

that opposite pubes touched each other in the midline distally as shown by Troxell. The pubis of no. 58-CR-1, lacking its distal edge, is 200 mm long as preserved. Its 

proximal end has principal diameters of 34 and 37 mm, and 

the least transverse diameter of the shaft is 23 mm. Its distal 

end is 95 mm across, that of no. 37-CR-1, which is incomplete, is 114 mm. 

Hind limb.-The hind limb is best represented by both 

femora, one complete and one incomplete tibia, and an 

incomplete fibula of no. 37-CR-1. Specimen no. 58-CR-1 

includes the proximal and distal ends of the right femur and 

the distal end of the left, as well as various pieces of the tibiae. Other incomplete hind limb bones from other localities, 

including many pieces of tibiae, are also present. 

Dyrosaurian femora have been described by several 

authors (Arambourg, 1952; Troxell, 1925; Swinton, 1950). 

Arambourg notes a number of features that distinguish the 

femur of Dyrosaurus paucidens from those of nondyrosaurian crocodiles. These features include an almost circular 

cross section of the shaft (I believe of questionable significance); the strong anterior projection of the head, and backward curvature of the distal end; and the oblique twisting of 

the axial plane of the head. The last feature has been 

reported frequently by other authors as well. 

The femora of Rhabdognathus sp. conform to Arambourg's description and resemble the femora of H. 

bequaerti (see Swinton 1950, pl. 7), and H. natator (Troxell 

1925, fig. 9). Although the Rhabdognathus bones appear 

more slender than those mentioned above, this is not borne 

out by comparative measurements (table F6). 

The dyrosaur tibia and fibula have not been usefully 

described. The right tibia of no. 37-CR-1 (fig. F27A) is the 

only complete tibia in the collection, but the ends of the left 

37-CR-1 

right 

349 

84 

50 

170 

40 

118 

231 

37-CR-1 

left 

351 

51 

41 

119 

232 

58-CR-1 

77 

47 

67 

35 

108 

H. bequaerti D. paucidens 

from from Swinton 

Arambourg 

300 339 

75 81 

48 49 

70 73 

40 

105 

195 

ant 

8 

0 5 I I I 

em 
F26 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

Table F7. Measurements of tibiae 

[In millimeters] 

37-CR-1 37-CR-1 

right left 

Length 281 

Antero-posterior diameter proximal end 72 73 

Transverse diameter proximal end 

Least diameter of shaft 23 

Transverse diameter distal end 35 35 

Antero-posterior diameter distal end 62 61 

0 

em 

5 

A B 

Figure F28. Rhabdognathus sp., A, no. 37-CR-1, proximal end 

of left fibula, left lateral aspect; B, no. 60-CR-3, distal end of right 

fibula, posterior aspect. 

tibia are better preserved. There are, in addition, ends of 

several tibiae from other localities. The tibia of no. 37 -CR-1 

is four-fifths th~ length of the femur and is thus relatively a 

little shorter than the tibia in most existing eusuchians (see 

data in Knusel, 1944). The shaft is transversely oval 

throughout and appears gracile when compared to the 

femur. The proximal end is as in eusuchian crocodiles. The 

articular head, thickly capped by cartilage in life, shows the 

characteristic hummocky surface with a central depression. 

The cnemial crest, as usual in crocodiles, is ill defined, but 

the anterolateral edge of the bone is thickened proximally. 

The expansion of the head, rising from the shaft, is more 

gradual than in Crocodylus. The distal end of the tibia is 

thicker, and the fibular crest is sharper and straighter than in 

C. acutus. This condition is accentuated distally by the 

broad excavation of the posterior side of the shaft. In the 

crocodile tibia there is here a limited triangular pit proximal 

to the astragalar articulation, but this is lacking in Rhabdognathus sp. The distal articular surface is broader and shows 

considerably more relief than in the crocodile (fig. F27 B), 

but it resembles Alligator mississippiensis somewhat more. 

That part of the bone which lodges in the dorsomedial facet 

of the astragalus is very broad relative to the rest of the 

58-CR-1 31-CR-1 33-CR-5 60-CR-1 60-CR-2 33-CR-8 

56 59 73+ 43+ 

55 66+ 56 

22 

30 40 44 30 

47 65 60+ 47 

articular surface. This part is set off from the ventro-medial 

angle of the distal end by shallow longitudinal sulci on the 

anterior and posterior faces of the diaphysis. The anterior 

groove dies out shortly above the end, whereas the posterior 

one is confluent upward with the broad posterior excavation 

mentioned above. The two grooves do not extend across the 

ventral end of the bone, however. Ventromedially, and composing about one-quarter of the area of the distal end, is a 

convex triangular surface. This surface is bounded laterally 

by a rounded triangular prominence that extends below the 

level of the rest of the bone. Medial to this prominence, the 

area is traversed by a broad but shallow channel that carried 

the flexor tendon of the hallux. For measurements of tibiae 

see table F7. 

The fibula of Dyrosaurus paucidens was described and 

figured by Arambourg (1952). This bone is remarkably 

stout and bears an obtuse ridge proximally on its lateral 

surface. 

Proximal and distal ends of the left fibula are preserved in no. 37-CR-1, and there is also a perfectly preserved distal end of a left fibula, no. 60-CR-3. Viewed from 

the side (fig. F28A), the expanded proximal end of the 

fibula has the same oblique top seen in existing crocodilians, but this grades downward more gradually into the 

shaft than in a C. acutus fibula. The facet that receives the 

posterior condyle of the femur is less deeply excavated than 

in the crocodile. What remains of the shaft is irregularly 

oval in cross section. The bone appears to have been relatively stout, as in D. paucidens, but there is no trace laterally of the obtuse ridge that occurs in D. paucidens near the 

proximal end of the bone. The surface here is flat and featureless in Rhabdognathus sp. The distal end of the fibula is 

less flattened anteroposteriorly, and the astragalar condyle 

is much better developed than in eusuchians. The whole distal end possesses more relief and in some respects is evocative of the head of a mammalian humerus (fig. F28B). The 

astragalar condyle is large and well rounded and stands out 

from the shaft at an angle of 90 degrees. The surface that 

rests on the calcaneum is slightly concave, and posterolaterally there is a slight ventral projection that overlaps the lat-
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F27 

era! edge of the fibular head of the calcaneum. This process 

is ill defined in the Crocodylus fibula. 

The diameters of the proximal end of no. 37-CR-1 are 

46 mm (anteroposterior) and 15 mm (transverse); those of 

the distal end of no. 60-CR-3, which is about the same size 

as no. 37-CR-1, are 29 mm (anteroposterior) and 38 mm 

(transverse). 

Pes.-Foot bones of Rhabdognathus sp. are well represented. Most of the tarsal elements of both feet are present 

in no. 37-CR-1, which also includes a number of incomplete metatarsals (fig. F29). The right astragalus, calcaneum 

and tarsal IV, and some incomplete metatarsals are also preserved in no. 58-CR-1. Isolated foot bones were encountered at several other localities. 

The pedal skeleton of fossil crocodiles has been largely 

neglected until recent years, one suspects, because of the 

very complicated geometry of the tarsus. Cruickshank 

(1979), Brinkman (1981 ), and Hecht and Tarsitano (1983) 

have furnished useful descriptions of the tarsus in crocodilians and related archosaurs. In this description I shall follow 

the terminology used by Hecht and Tarsitano, which is 

modified from Cruickshank. 

The tarsals of Rhabdognathus sp. are massive and well 

ossified. The astragalus and calcaneum are illustrated in fig. 

F30. The calcaneum does not differ much from that of a 

large Crocodylus or Alligator, but the tuber (fig. F30, Tc) is 

thicker and a little shorter than in those genera. A low, 

rounded ridge connects the tuber with the fibular condyle 

(fig. F30, Fe) laterally; this ridge is much more pronounced 

in the fossil than in either of the existing taxa, but the difference may be owing to the large size of the Rhabdognathus 

specimens. The distal end of the tuber is irregularly teardrop 

shaped when viewed from behind. The usual deep dorsoventral groove for the long flexor tendons of the foot is 

represented by an oval excavation surrounded by .a tumid 

rim, much as in existing eusuchians. The root of the tuber 

gives the impression of being much flatter dorsoventrally 

and broader transversely than in Crocodylus or Alliga_tor, 

owing to the dorso-lateral hypertrophy of the abovementioned ridge. The surface of the fibular condyle is, of 

course, convex; however, it is narrower than in the existing 

taxa, whereas the astragalar surface (which adjoins the surface for the fibula) is relatively broader and slants diagonally away mesad from the fibular condyle at an angle of 

about 45 degrees. The flattened anteroventral facet for the 

fourth distal tarsal (fig. F30, Dt4f) is broad and subreniform 

in outline. It does not display the irregular configuration 

sometimes seen in existing forms. 

The astragalus displays several differences from the 

eusuchian condition. Most important is the broad, helical 

saddle-shaped tibial facet (fig. F30, Tf), which contrasts 

sharply with the narrow and irregularly band-shaped articular surface in eusuchians (see Hecht and Tarsitano, 1983-

their U-shaped tibial facet). The backwardly hooked posteromedial arm of the U and the deep astragalar fossa present 

A 

0 

8 

Figure F29. Rhabdognathus sp., right pes, reconstruction based 

largely on right and left elements of nos. 37-CR-1 and 58-CR-1. A, 

tarsus and incomplete metatarsus, dorsal aspect; B, articular ends 

of metatarsals. Ast, astragalus; Cal, calcaneum; TIV, .fourth distal 

tarsal; 1-V, metatarsals. 

in eusuchians are lacking in Rhabdognathus sp. T~e fossa is 

represented by only a small, shallow, oval pit from which a 

narrow and very shallow diagonal sulcus issues in a posterolateral direction. The area of the tibial facet, which in 

eusuchians forms the slightly elevated posterior arm of the 

U, curves smoothly over the anterodorsal surface of the 

bone. This arrangement should have permitted a greater 

degree of extension at the ankle joint than is usual in eusuchians. The fibular facet (fig. F30, Ff) is more regularly 

rectangular than in either Alligator or Crocodylus. 
F28 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

A 

0 

c Tc 

Figure F30. Rhabdognathus sp., no. 37-CR-1, left 

astragalus and calcaneum. A, proximal; B, lateral; C, distal, 

D, medial surfaces. Ah, anterior hollow of astragalus; Dr, 

distal roller of astragalus; Dt4f, facet for distal tarsal 4; Fe, 

Distally, the so-called distal roller (fig. F30, Dr) surface, which articulates with metatarsals 1 and 2, resembles 

the roller in C. acutus, but it appears. to project more 

strongly anteromedially in Rhabdognathus sp. This may be 

illusory, however, owing to the somewhat less expanded 

tongue of the calcaneum that abuts against the astragalar 

trochlea. The astragalar peg (fig. F30, P) is stouter than in 

either Crocodylus or Alligator and projects a little more 

strongly into the corresponding socket of the calcaneum. In 

eusuchians an articular surface on the astragalar trochlea is 

continuous from the fibular facet-from which it is set off 

by an obtuse angle-to the astragalar peg. This surface is in 

sliding contact with the tongue of the calcaneum. But in 

Rhabdognathus sp. the articulation between the calcaneum 

and astragalus appears to have permitted a greater range of 

motion and to have allowed more rotation around the trochlea and peg than in the eusuchians. 

Dr 

Dt4f 

8 

5 

em 

D 

fibular condyle; Ff, fibular facet; Lc, lateral channel of calcaneum; Me, medial channel of calcaneum; P, astragalar 

peg; Tf, tibial facet of astragalus; Tc, calcaneal tuber. 

The condition of the ankle joint suggests more freedom of motion of the foot in the fore and aft direction than 

occurs in existing crocodiles. At the same time, however, 

side-wise movement was evidently even more restricted in 

the dyrosaur than in eusuchians. 

The fourth tarsal (fig. F29, TIV) is expanded in two 

planes at approximately right angles to each other. It articulates with the calcaneum along a flattened, roughly triangular posterior surface that curves slightly forward above. The 

dorsal surface onto which this curvature passes is mostly 

nonarticular. In contrast to the eusuchian state, this surface 

is extensive, higher in front than behind, and about twice as 

wide as it is long. Curiously, it does not extend completely 

to the anterodorsal edge of the opposing facet on the calcaneum. One would suppose that this allowed for some sliding of the fourth tarsal up and down against the calcaneum; 

however, movement in this direction is inhibited by a poste-
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F29 

riorly developed hooklike process on the ventral side of the 

fourth tarsal. This arrangement is puzzling because the 

articular surface on the calcaneum is well developed and the 

unopposed part does not differ from the area that is in 

contact with the fourth tarsal. The condition is natural and is 

also present in no. 58-CR-1. The ventral (plantar) part of the 

fourth tarsal is expanded anteroposteriorly and is narrow 

transversely, thus forming a blunt heellike edge quite different from the transversely expanded quadrangular surface in 

Crocodylus. Anterolaterally, a broad semilunar facet is 

present for attachment of the fifth metatarsal. In Crocodylus, on the other hand, the proximal end of this metatarsal is 

inserted into a wide groove which occupies virtually the 

entire side of the tarsal. The anterior surface of the fourth 

tarsal, which articulates with the fourth metatarsal, is 

curved upward allowing for a considerable arc of vertical 

rotation at this point. Laterally, the anterior half of the tarsal 

is set off from the posterior, anteroposteriorly-expanded 

part of the bone by an obtuse angle. This side of the bone 

carries a facet, shaped roughly like a figure 8, that opposed 

the medial surface of the third tarsal (in no. 58-CR-1 the figure 8 is interrupted in the middle; thus, there are two facets). 

The third tarsal is an irregularly shaped block of bone 

whose orientation in the tarsus is uncertain. As in existing 

crocodilians, it was no doubt surrounded by a considerable 

mass of cartilage. 

Most of the metatarsals, lacking varying amounts of 

the distal ends, are preserved in no. 37-CR-1 (fig. F29). A 

distal end of one metatarsal of undetermined position is also 

present. The bones of the left side are less distorted than 

those of the right side. The first four metatarsals are massive 

bones with thick proximal ends. They do not differ much 

from the corresponding bones in eusuchians in their articular relationships to each other and in the outlines of the 

proximal ends (fig. F29B). The same may be said of the 

fifth metatarsal except that its proximal end is not inserted 

into a medial depression on the fourth tarsal. This metatarsal does not have the ventrolateral hook seen in eusuchians, 

but instead ends bluntly. The lengths of metatarsals one to 

four are unknown. However, the proximal phalanx of the 

fourth toe is complete and is 62 mm long. If the same relationship between metatarsal and phalangeal lengths seen in 

Crocodylus existed in Rhabdognathus sp. the metatarsus of 

no. 37-CR-1 would have been about 190 mm long. 

Right IV -1 of no. 37-CR-1 and left I-1 of no. 45-CR-1 

are the only phalanges in the collection. They are not 

noticeably different from those phalanges in the crocodile, 

but no. 37-CR-1 appears to be a little thicker than would be 

expected in a C. acutus of this size. 

Costal cartilages.-Of unusual occurrence is the preservation of a number of pieces of the costal cartilages in no. 

58-CR-1 (fig. F31). These are mostly flat, bladelike objects, 

expanded proximally to form facets for the ends of the ribs, 

and displaying a characteristic pitted appearance on all surfaces. Their respective positions in the chest wall have not 

0 5 

Figure F31. Rhabdognathus sp., no. 58-CR-1. Costal cartilages. 

been determined. The largest piece, a proximal end, had a 

maximum anteroposterior diameter of more than 48 mm. 

Like all other pieces preserved, this one is thicker toward 

the posterior edge (about 10 mm) and thins to a relatively 

sharp edge anteriorly. 

Osteoscutes.-Osteoscutes are fairly common in the 

collection, but most are fragmentary. The best examples 

belong to no. 58-CR-1. The armor of Rhabdognathus sp. 

consisted of, on either side of the midline, a longitudinal 

row of overlapping quadrangular plates, which were sutured 

laterally to a parallel series of undetermined shape (fig. 

F32). The thoracic scutes (fig. F33A-C) bear no crests or 

peaks. A few of the plates, which are a little thicker and a 

little shorter than others, are slightly arched transversely. 

These may have been more anterior in position than the flatter plates. There is no trace of peg and socket articulations 

laterally. The superior surfaces are strongly pitted with 

fairly regular round to oval excavations on well over half 

the surface area. The fore and aft edges of these plates are 

generally parallel to each other, and the medial side lies at 

right angles to them. The lateral edge, however, forms an 

acute angle with the anterior ~dge and an obtuse angle with 

the edge behind. In cross section, these plates resemble the 

section of an airplane wing. A smooth, beveled transverse 

strip along the anterodorsal edge was overlapped by a thinner, beveled posterior edge of the plate in front. The medial 

edge is pinched off and nonsutural, but the lateral edge 

bears a strong suture. What is probably the medial part of a 

lateral scute, identified by the opposite course of its sutural 

edge, still shows both anterior and posterior beveling. It is 

thickest in the middle with the ventral surface being more 

convex anteroposteriorly than the dorsal side. The lateral 

outline of this plate is unknown, but there is some evidence 

that its posterior edge may have been curved gently forward 

toward the end. Whether a third row of scutes existed laterally is unknown. 
F30 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

0 5 

em 

It is generally believed that dyrosaurs lacked neck 

shields. Fragments of some very massive plates from locality 60 are, however, less regular in outline and are more 

coarsely sculptured (they have relatively fewer and more 

widely spaced pits) than the thoracic plates of no. 58-CR-1. 

They may be neck shields, but they may belong to Phosphatosaurus. One of the fragments is 23 mm thick. Another 

plate, in no. 33-CR-6, has two adjoining sutural edges, and 

its irregular shape suggests that it may have been part of a 

nuchal shield (fig. F33D). 

Ventral armor consists of irregularly hexagonal to quadrangular osteoderms completely bounded by sutural edges 

(fig. F33E, F). These scutes are flat. The radiating pattern of 

the surficial pits is more obvious than in the dorsal scutes. 

An impressively massive scute, no. 36E-CR-l (fig. F33E) is 

22 mm thick. One osteoscute, no. 33-CR-7, (fig. F33G), differs from all the others described. It is subrectangular, 

shows no clear signs of overlapping relationships, and bears 

no sutures. It is slightly arched in the middle, contains a relatively large number of small regular suboval pits, and, for 

its size, is remarkably thin (8 mm). The position of this 

plate is unknown. 

Selected scutes from no. 58-CR-1 have the following 

measurements (in millimeters; e, estimate; the ordering is 

not necessarily sequential). 

Length medial edge 63 65e 66 58 60 

Length lateral edge 64e 65 63 65e 62 

Transverse diameter anterior edge 86 98 93 84 88 

Transverse diameter distal edge 71 89 77 68e 75 

Greatest thickness of scute 13 14 15 15 16 

Figure F32. Rhabdognathus 

sp., reconstruction of dorsal 

armor, based on osteoscutes from 

no. 58-CR-1. The lateral extent 

of the lateral plates is unknown. 

M, midline. 

The venin ( 1911) believed Dyrosaurus lacked dermal 

armor, but Arambourg (1952) showed that this was 

incorrect. Swinton (1950) found nothing unusual about the 

dorsal scutes of Hyposaurus bequaerti. He describes them 

as squarish and biscuitlike (soda crackerlike), with diameters of about 70 mm and 60 mm. They are, therefore, more 

nearly square than any of the scutes preserved with nos. 

58-CR-1 or 37-CR-1, but the description seems to conform 

more nearly to the anomalous osteoscute no. 33-CR-7. 

Dollo's (1914) characterization of the ventral scutes of H. 

bequaerti as quadrangular and arranged in imbricating 

transverse rows is difficult to reconcile with the known 

plates of Rhabdognathus sp. It is possible that differences in 

plate design reflect differing positions in the armor, or they 

may indicate systematic differences as are displayed by the 

scutes of Alligator and Caiman, for example (Ross and 

Mayer, 1983 ). 

PATHOLOGY 

Crocodilians are notorious for their viability in the face 

of massive trauma and pathological conditions. The dyrosaur remains from Saudi Arabia show little evidence of 

pathology. However, a left femur (no. 3-CR-3) is grossly 

deformed in the distal half, which is broken off some distance above the end (fig. F34). What remains of the shaft 

distal to the fourth trochanter is hypertrophied, and a large 

necrotic sinus occupies about one-fourth of the broken end. 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F31 

33-CR-6 

D 

58-CR-1 

A 

36E-CR-1 

E 

0 

58-CR-1 

8 

em 

5 

I 

33-CR-1 

F 

58-CR-1 

c 

33-CR-7 

G 

Figure F33. Crocodilian osteoscutes from Saudi Arabia. A-F, Rhabdognathus sp., G, unidentified taxon. A, medial and lateral thoracic 

plates of the right side (lateral plate incomplete); B, C, right medial plates; D, ? nuchal plate; E, F, ventral scutes; G, osteoscute of uncertain position and taxon, lacking sutures and evidence of overlapping relationships. 

0 5 l I 

em 

Figure F34. Rhabdognathus sp., no. 3-CR-3. Pathological left femur. S, large necrotic sinus in amputated distal shaft. 
F32 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

The remainder of this end exposes the spongy interior of the 

base. It is possible the animal survived for a time after 

amputation occurred. 

Buffetaut (1983) has reported evident lesions in the 

rostrum of a middle Eocene dyrosaur, Tilemsisuchus lavocati, which he attributes to injuries received during intraspecific fighting. The hypertrophy of the distal part of the 

femur suggests, however, that the lesions in no. 3-CR-3 

resulted from a pathological condition of some duration and 

loss of the distal leg was not in this instance a direct result 

of trauma. 

GASTROLITHS 

Several smooth irregular quartzite pebbles were found 

in the pelvic region of the articulated skeleton no. 37-CR-1. 

The largest pebble h~s principal diameters of 97 and 82 mm 

and weighs 380 g. All edges and corners are rounded off 

and some of the faces of the stones carry a dull polish, but 

chatter marks are not evident. Such rocks are not native to 

the Umm Himar Formation or to the surrounding terrain, so 

it is presumed that the pebbles are gastroliths. 

COPROLITES 

About a dozen coprolites were found at locality 37. 

Shapes include oval, discoidal, irregular, and kidney shaped 

(see Hantzschel and others, 1968). Most specimens resemble coprolites of carnivorous mammals. A few show evidence of compaction in the intestinal tract. They range from 

about 12 to 32 mm in diameter. A somewhat larger example 

thought to be from locality 1 is 38 mm in diameter. The 

coprolites vary in color from ivory to dark purple-brown 

and are generally lighter around the exterior than internally. 

The masses are very dense and compact, and they display a 

strong tendency toward conchoidal and flinty fracture into 

flakes, sometimes resembling chert. Faint random striations 

and short gouges on the surface of a number of the specimens are of unknown origin, but some may be evidence of 

arthropod or insect activity. All specimens contain small gas 

vugs, which are most abundant toward the outer surfaces. 

At least three of the coprolites contain quantities of finesand size green clay pellets, and in one these pellets made 

up a significant part of the mass. The pellets are well 

rounded and may represent remnants of pieces of shale 

ingested by accident or as gastroliths. One specimen contains a small localized mass of comminuted fish bones. Otherwise the fecal masses are devoid of recognizable organic 

structures. This is consistent with. their assignment to the 

Crocodilia in which most organic material is destroyed by 

powerful gastric juices during digestion. 

SIZE, SKELETAL RECONSTRUCTION, 

AND INTERPRETATION 

The Saudi Arabian dyrosaurs display a considerable 

range in size. The smallest individuals, represented by isolated fragments of vertebrae, limb bones, and rostra were 

only about half as big as the largest examples in the collection. Buffetaut (1979, 1980) has estimated the lengths of 

various dyrosaurs up to 6- 7 m, based on Wermuth's proportional tables for recent crocodiles (Wermuth, 1964 ). The venin (1911) estimated the average length of Dyrosaurus at 

5-6 m. Such estimates depend on the presumption that the 

body proportions were similar to those in better known fossil and recent longirostrine taxa, presently an uncertain 

proposition. All that can be said of Rhabdognathus sp. from 

Saudi Arabia is that some individuals were near the upper 

limits of size for known dyrosaurs, and they may have 

exceeded the length of R. rarus estimated by Buffetaut 

(1980) as around 4.5 m; the proximal end of a tibia figured 

by Thevenin (1911, pl. XVI, fig. 6) is, however, about 30 

percent larger than the largest tibia from Saudi Arabia (no. 

60-CR-7), and a femur (pl. XVI, fig. 5) is even larger, surpassing the femur of no. 37-CR-1 by at least 40 percent. 

The distal end of a massive humerus (no. 43-CR-2) is about 

20 percent larger than the same part of the humerus of 

Hyposaurus bequaerti figured by Swinton (1950, pl. VI). If 

the proportions were the same, this humerus would have 

been about 355 mm long. 

Figure F35 is a generalized reconstruction based upon 

the Rhabdognathus sp. specimens described above, supplemented by published data from Dyrosaurus, Hyposaurus 

and other Rhabdognathus material. Mistakes, particularly 

in scaling and detail, are inherent in this kind of reconstruction, but I believe the drawing conveys a reasonable 

impression of the slender-snouted (hyposaurine) dyrosaur 

skeleton. Areas of uncertainty include the heights of the 

neural spines, lengths of the ribs, and the proportions of the 

forearm and forefoot (which are virtually unknown). The 

number of caudal vertebrae and arrangement of the c~evrons is conjectural. The superior part of the scapula is drawn 

from Hyposaurus; the skull and jaw are largely from Dyrosaurus after Thevenin, with proportions adjusted to match 

Rhabdognathus, after Buffetaut. 

The skeleton is depicted in semiprone resting pose 

with the head in alert position, a stance no doubt achieved 

either on land or while resting on the bottom of a body of 

water. The piscivorous habits attributed to Dyrosaurus are 

unquestioned, but the body movements involved in swimming and capture of prey can only be surmised. Axial flexibility may have been more restricted in the trunk than in 

their present day analogues Gavialis and Tomistoma owing 

to relatively heavier and more extensive and better articulated dorsal armor, to the amphiplatyan vertebral centra, and 

to the broad and closely spaced transverse processes in the 

thoracic series. Allocation of 14 vertebrae to the thoracic 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F33 

series (6 more than in eusuchians) and reduction of the 

length of the lumbar series are consistent with this interpretation. The neck on the other hand may have been more 

flexible, especially/ in the sagittal plane. This is suggested 

not only by the suspected absence of nuchal shields, the 

wedge-shaped cervical centra, and marked inclination of the 

zygapophyseal articulations, but also by the triangular cervical neural spines and massive but relatively posterior 

hypapophyses. Indeed, the articulated spinal column of a 

dyrosaur from Pakistan (Storrs, 1986) appears to have the 

neck bent more strongly backward than is possible even in a 

dried skeleton of any existing crocodilian. 

Buffetaut (1982), noting the transversely expanded 

occipital condyle and the broad elevated occipital surfaces 

for the cervical flexor muscles, concluded that the head had 

a greater range of motion in the sagittal plane in dyrosaurs 

than in existing eusuchians, which have more hemispherical 

condyles. This is consistent with the above mechanical 

interpretation of the neck. With reduced lateral and torsional 

components it seems less likely that the dyrosaurs could 

indulge the common eusuchian (except gavials) practice of 

picking up objects with the side of the mouth. 

Buffetaut (1982) regarded the mainly vertical rotation 

of the head as evidence of a diving habit analogous perhaps 

to cetaceans, but this is not so obvious to me. Although a 

seemingly less efficient maneuver, it is conceivable that in 

capturing fish the dyrosaurs threw their heads up and down 

rather than striking from side to side as gavials mainly do. 

This could also help in breaking, dismembering, and swallowing prey. 

Although many neural spines are preserved in the 

Saudi Arabian collection, only a few remain attached to 

their respective vertebrae. The heights of the spines in the 

reconstruction are based largely on the articulated presacral 

column described by Storrs (1986), and on data from Swinton (1950) for Hyposaurus bequaerti. Anterior caudal 

spines are, however, somewhat lower than indicated for H. 

bequaerti because it was not possible to reach the two-fold 

increase in height from the known height of the third lumbar spine in no. 37 -CR-1 without creating an unreasonably 

sudden change in the dorsal profile of the pelvic region. 

High neural spines have long been recognized as a distinctive feature of Dyrosaurus and presumably of other 

dyrosaurs. However, only a few spines in the shoulder 

region and in the tail are greatly hypertrophied. Cervical 

spines are a little higher in relation to their respective centra 

than in some existing eusuchians (the seventh neural arch of 

no. 37 -CR-1 is slightly more than 2.5 times as high as its 

centrum compared to about 2.25 times in a large Crocodylus 

acutus). 

It has been assumed that, like existing crocodiles, the 

dyrosaurs propelled themselves in the water by lateral 

undulations of the body and tail. Although I have drawn the 

tail in a conventional fashion, the wedging of the caudal 

centra suggests some downward bending of the tail, though 
F34 PALEOCENE VERTEBRATES FROM JABAL UMM HIMAR, KINGDOM OF SAUDI ARABIA 

nothing approaching the condition in Geosaurus should be 

inferred. The uniquely lengthened spines may have provided support for a vertical finlike structure. The long and 

distinctively broadened tail therefore probably furnished the 

forward thrust in swimming. The relatively inflexible trunk 

was evidently narrower than in living eusuchians, to judge 

from the short thoracic transverse processes. Perhaps this 

served somehow as a vertical stabilizer, opposing the lateral 

torque generated by the swimming tail. 

The limb proportions are puzzling. Usually in amphibious crocodilians and particularly in marine mesosuchians 

the forelimbs are substantially shorter than the hindlimbs. 

Although the relative lengths of the limbs have not been 

recorded in dyrosaurs, the humerus is almost as long as the 

femur in Hyposaurus bequaerti and the humerus to femur 

ratio is 93 in H. rogersii (YPM 985). Among existing crocodilians the ratio ranges from .60 to 104, with the largest 

value occurring only in an immature Crocodylus porosus 

cited by Knusel (1944). Moreover, the humerus in the Saudi 

Arabian Rhabdognathus sp. seems remarkably massive. 

The functional significance of the relatively powerful forelimbs is not clear, but such a departure from the usual conditions in marine crocodiles suggests that dyrosaur 

ancestors should be sought among Jurassic and Early Cretaceous terrestrial mesosuchians, which are but poorly 

known. The massive conditions of the tarsals and metatarsals are consistent with this conclusion. 

STRATIGRAPHIC IMPLICATIONS 

Fossil crocodilians are generally not very helpful in 

stratigraphic correlation because of the relative longevity of 

genera and inadequate definition of most species. The 

Dyrosauridae, however, are known to have existed from late 

Maastrichtian to late Eocene times. Indeed, it was the dyrosaur remains at Jabal Umm Himar that first indicated that 

the rocks of the Umm Himar Formation were older than 

"probable Pliocene," as originally reported by Gonzales 

(1973). Among dyrosaurs most resembling the Saudi Arabian forms, Phosphatosaurus ranges from the upper Maastrichtian into the Ypresian, in which it is best represented. 

Rhabdognathus rarus, which seems very similar to the most 

abundant Saudi Arabian species, is known from the upper 

Paleocene Dange Formation of Sokoto Province in Nigeria 

and from Paleocene beds in Mali. Rhabdognathus compressus and Hyposaurus nopcsai, the only species positively 

identified in the Saudi Arabian collection, are found also in 

Paleocene rocks in Mali and Sokoto Province, most probably from the Dange Formation. It seems likely, therefore, 

that the Umm Himar Formation was deposited at about the 

same time as the Dange Formation, bearing in mind the limited resolution possible from the dyrosaur material present 

in these units. 

There has been some controversy about the age of the 

Dange Formation and the fossil vertebrate remains from the 

Wurno area (Kogbe 1973, 1974, 1981; Halstead, 1979). 

Originally believed to be Eocene (Nopcsa, 1925), the 

deposits were identified as probably Landenian, hence late 

Paleocene, by Swinton (1930) on the basis of the dyrosaur 

fossils themselves, which had all been found in talus near 

the village of Wurno. Petters (1978) assigned the Dange 

Formation to the Thanetian on the basis of contained 

Foraminifera. 

This study of the Saudi Arabian dyrosaurs confirms 

the preliminary findings by Madden and others (1979), that 

vertebrate-bearing deposits of the Umm Himar Formation 

are of Paleocene age. The strong resemblance between the 

dyrosaurs of the Umm Himar and the Dange Formations 

further suggests that the Umm Himar beds may be assigned 

to the upper Paleocene. This conclusion is consistent with 

that based on stratigraphic ranges of Ceratodus humei and 

the siluriform fishes (Madden and others, Chap. A, this 

volume). 

PALEOGEOGRAPHIC IMPLICATIONS 

Until B uffetaut (197 6a) redefined the Dyrosauridae, 

the group was believed to have been restricted to North 

Africa. With the recognition of the Late Cretaceous Hyposaurus as a dyrosaur, however, the range was extended to 

North and South America (Buffetaut, 1976b). With the later 

discovery of dyrosaurs in Pakistan and Burma, the family is 

seen to have had a southern Tethyan distribution. Indeed, 

Buffetaut (1982) has proposed the new infraordinal name 

Tethysuchia for the family Dyrosauridae. 

Dyrosaurs are generally regarded as marine crocodilians whose principal habitats were restricted to coastal and 

estuarine environments. Only recently have dyrosaur 

remains been encountered in nonmarine deposits (Buffetaut, 1978b, 1978c). These occurrences are comparatively 

late in dyrosaurian history (middle to late Eocene) and may 

represent retreat of relict species into fresh water just prior 

to extinction. It is possible, however, that the group was 

more euryhaline than the fossil evidence suggests, because 

Upper Cretaceous and Paleocene continental vertebratebearing deposits that might contain dyrosaur remains are all 

but unknown in Africa, for example (Buffetaut, 1978c). The 

wide variety of shark and pycnodont remains associated 

with the dyrosaur bones around Jabal Umm Himar, however, leaves little doubt that the fossiliferous ferruginous 

claystones here were deposited under marine influences 

(Madden and others, 1979; Chap. A, this volume). But, as 

those authors note, the presence of Ceratodus humei in the 

deposits indicates closeness of fresh water, if only seasonally. The presence of Rhabdognathus, Hyposaurus, and 

?Phosphatosaurus in the Umm Himar Formation seems 

consistent with the conclusion that the paleoenvironment in 
DYROSAURS (CROCODILIA, MESOSUCHIA) FROM THE PALEOCENE UMM HIMAR FORMATION F35 

the Jabal Umm Himar area was estuarine instead of lacustrine as supposed by Gonzales (1973). The lithology of the 

rocks associated with the bone-bearing strata (see Madden 

and others, Chap. A, this volume) suggests a less welldrained environment than is indicated by the gypsum-rich, 

thin-bedded shales of the dyrosaur-bearing Dange Formation in Nigeria-which are interpreted as tidal flat deposits 

(Petters, 1978) and as a "transitional facies equivalent of the 

open marine calcareous Kalambaina Formation" by Kogbe 

(1981). 

Prior to the joint USGS-Saudi Arabian work, the Late 

Cretaceous and early Paleogene sedimentary history of the 

western edge of the Arabian Peninsula was not well known 

(see Powers and others, 1966). Current paleogeographic 

reconstructions of the region appear to show only land here 

during Paleocene time (for example, see Smith, Hurley, and 

Briden, 1981; Barron and others, 1981). The Umm Himar 

fossils may therefore indicate slower than suspected retreat 

of the Maastrichtian Red Sea embayment of the southern 

Tethys (see Sander, 1970), and the persistence of a coastal 

connection along a northern African shelf between western 

Arabia and the West African seaway as recently as the late 

Paleocene. Perhaps this would extend the eastern edge of 

the Paleocene embayment a little farther east and south 

across Egypt than is indicated in Petters' paleogeographic 

reconstruction (Petters, 1978, fig. 9). 

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at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under the conditions indicated below from the U.S. 

Geological Survey, Information Services, Box 25286, Federal 

Center, Denver, CO 80225. (See latest Price and Availability List.) 

"Publications of the Geological Survey, 1879-1961" may 

be purchased by mail and over the counter in paperback book form 

and as a set of microfiche. 

"Publications of the Geological Survey, 1962-1970" may 

be purchased by mail and over the counter in paperback book form 

and as a set of microfiche. 

"Publications of the U.S. Geological Survey, 1971-1981" 

may be purchased by mail and over the counter in paperback book 

form (two volumes, publications listing and index) and as a set of 

microfiche. 

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased 

by mail and over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic 

and Water-Supply Reports and Maps For (State)," may be purchased by mail and over the counter in paperback booklet form 

only. 

"Price and Availability List of U.S. Geological Survey 

Publications," issued annually, is available free of charge in 

paperback booklet form only. 

Selected copies of a monthly catalog ''New Publications of 

the U.S. Geological Survey" are available free of charge by mail 

or may be obtained over the counter in paperback booklet form 

only. Those wishing a free subscription to the monthly catalQg 

"New Publications of the U.S. Geological Survey" should write to 

the U.S. Geological Survey, 582 National Center, Reston, VA 

22092. 

Note-Prices of Government publications listed in older catalogs, announcements, and publications may be incorrect. Therefore, the prices charged may differ from the prices in catalogs, 

announcements, and publications. 
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