FOSSIL PROBOSCIDEA AND EDENTATA OF THE SAN PEDRO VALLEY, ARIZONA 

By JAMES WILLIAMS GIDLEY 

INTRODUCTION 

A preliminary report on the fossil vertebrates of 

the San Pedro Valley, Ariz., collected by Kirk Bryan 

and me in the winter of 1920 and 1921 was published 

in 1922.1 This report includes a brief statement 

regarding the geology of the locali y and a preliminary 

list of fossil vertebrates obtained by the expedition of 

1921, with descriptions of the rodents and rabbits. 

Two additional papers on this interesting fauna have 

also appeared, one on the turtles by C. W. Gilmore 2 

and one on the birds by Alexander Wetmore. 3 The 

present contribution deals with the proboscideans and 

edentates and gives a somewhat fuller discussion of 

the geology of the fossil-bearing beds. 

GEOLOGY AND FAUNAL ASPECT OF THE SAN PEDRO 

VALLEY DEPOSITS 

As stated in the preliminary report, most of the 

material collected came from two localities, which 

seem to be slightly different in age. One of these- is 

on the west side of the valley near the town of Benson; 

the other is on the east side of the valley in the vicinity 

of the Curtis Flats, about 12 miles from the Benson 

locality Stratigraphically and structurally the beds of 

these two localities seem to be equivalent in age. The 

faunas of the two localities, however, seem to belong 

to slightly different time periods. In fact, the collection obtained from one locality differs so widely from 

that of the other-there being no species in commonthat the deposits evidently represent two distinct time 

periods. These faunas, however, contain several 

genera in common, and the species are so nearly related 

as to indicate that the time interval between the two 

periods represented was probably not great. Further study of the material seems to sustain my first 

impression that the fossil-bearing beds near Benson are 

slightly older than the Blanco formatipn of Texas, and 

that the beds near Curtis Flats are somewhat younger. 

It must be admitted, however, that this opinion is not 

based on any very tangible or direct evidence, and more 

comparisons should be made, especially with the Blanco 

faunas. In its favor is the fact that the beds of the 

Benson locality contain remains of a mastodon with 

enamel-banded tu~ks, Neohipparion, Protohippus (or 

Pliohippus), Merycodus, and other forms of distinctly 

Miocene or Pliocene affinities, whereas the Stegoma;-

todon and Glyptotherium of the 9urtis Flats locality 

seem closely related to but slightly more progressive 

t U. 8. Geol. Survey Prof. Paper 131, pp. 119-131, 1922. 

2 U.S. Nat. Mus. Proc., vol. 61, pp. 1-8, pls. 1-5, 1922. 

aU. S. Nat. Mus. Proc., vol. 64, art. 5, pp. 1-18, figs. 1-9, 1924. 

than species of these genera found in the Blanco formation. The presence of true Equus, which was found 

in the Curtis Flats locality and in one place south of 

the Benson locality, will doubtless be considered by 

some as evidence of Pleistocene age. However, the 

fact must be taken into account that the occurrence 

of this genus in the Pleistocene is confined to the earlier 

stages, and also that even there it is represented by 

several well-defined species of diversified character, 

ranging in size from a Shetland .pony to a draft horse. 

It must therefore be admitted that the genus Equus, 

as at present defined, must have had a very considerable period of · development prior to its first general 

appearance in the regions of our best-known collecting 

fields of Pleistocene age, both in America and in Europe. 

If this is true it would not 1 be surprising, and in 

fact it might be expected, that occasional advance 

guards of the later general invasion of t.his genus 

reached America long ·before the beginning of Pleistocene time. In my opinion this is just what happened 

in the San Pedro Valley and other localities of the 

extreme West. 

Even more puzzling than the· question of exact 

correlation of the San Pedro Valley faunas with those 

of other areas is the apparent disagreement. to which 

I have already referred, of the geologic and faunistic 

evidence relative to the respective time pha.ses of the 

two adjacent localities here under discussion. A detailed study of the deposits themselves, however, 

seems to offer a solution. 

As surveyed and reported by Bryan, 4 the deformed 

valley fill, which includes the fossil-bearing beds, 

occurs in a strip lying on both sides of San Pedro 

River· ·from the Mexican boundary north to Gila 

River. This material consists of cemented gravel 

and conglomerate, which generally border the 

mountains, and of finer material, which in general 

occupies the middle and lower parts of the valley. 

The formation as a whole is the result of deposition 

in an arid intermontane valley. It has been deformed 

and faulted by renewed uplift of the bordering 

mountains, but in general the finer-grained beds in 

the center of the valley were .little affected by these 

movements and for the most part are undisturbed and 

horizontal. However, several partial cycles of erosion 

ensued after the period of· uplift, and large parts of 

the formation were removed, the amounts eroded 

varying from place to place. 

t Bryan, Kirk, and Smith, G. E. P ., Geology and water resource~ of San Pedro 

Valley, Ariz.: U.S. Geol. Survey Wat,er-Supply Paper- (in preparation): 

sa 
84 SHOR.TER CONTRIBUTIONS TO GENERAL GEOLOGY, 19'25 

The two localities lie on opposite sides of San 

Pedro River about 12 miles apart but at similar 

altitudes. The beds at both are horizontal and, 

except for evidence of minor faulting in those near 

Benson, apparently undisturbed. A thickness of 

about 250 feet is exposed in this part "of the valley, 

but the total thickness of the formation is much 

greater, as shown by the logs of wells in the vicinity. 

The fossil-bearing layers are somewhat above the 

middle of the eroded section and are hence near the 

top of the formation. The stratified beds of these 

' localities consist principally of red clays, sands, and 

soft limestones that were evidently laid down in salt 

lakes of small extent in the central part of the Pliocene 

basin. 

The bones occur for the most part in relatively 

small patches or layers of greenish tuffaceous clay, 

which, according to Bryan, interfinger on one side 

with arkosic gravel and conglomerate typical of 

deposition on alluvial slopes and on the other with the 

lake beds. This position seems to confirm Bryan's 

view that these bone-bearing patch.es of greenish 

clay represent the marginal _ and fresh-water springs 

that are characteristic of the borders of salt lakes in 

such basins. The localities thus probably constituted 

the chief watering places for the animals of the region, 

and here, naturally, occur their fossil remains. 

That these areas were once boggy water holes is 

supported by the condition and arrangement of the 

bones they contain. For example, the skull of one of 

the mastodons was found completely covered by the 

undisturbed original matrix and lying in a horizontal 

position resting on the lower jaws, but the top portion 

of the skull was crushed and eroded and the tips of · 

the tusks reaching to the same level were broken. 

This damage had evidently been done while the skull 

yet lay partly buried in wet mud. Also the left fore 

leg of this animal was found in-nearly normal position 

relative to the skull, but with the toes directed downward, reaching a level in the clay 2 feet below it. 

This position indicates that the animal came to his 

death by being hopelessly bogged. The' position and 

arrangement of the other bones as found suggest that 

they had been moved about by being more or less 

trampled and disturbed by contemporary animals who 

were so fortunate as. to escape being engulfed in the 

s~ft and sticky mud. A foot of each of the other two 

mastodons collected was found in a like position, 

giving additional evidence of boggy conditions. The 

carapace of Glyptotherium showed evidence of trampiing. The top had been caved in before being completely 'covered and may have been thus crushed 

by the foot of a Stegomastodon arizonae while lying 

partly buried. 

If, then, we accept Bryan's view regarding the 

conditions of deposition, it is plainly eyident that the 

accu~ulation of material in the central portion of the 

San Pedro basin must have taken place comparatively 

slowly, as these lakes, to become thus saline, must have 

required long periods of desiccation. The few inches 

to 2 feet of soft limestone that marks their former 

existence must therefore represent a very considerable 

length of time, at least a few thousand years. The 

· springs that were marginal to the lakes must have had 

similar periods of existence. 

Under these conditions it is quite possible that, 

although the general process of sedimentation in the 

San Pedro basin was continuous, the marginal springs 

of the two localities may have belonged to lakes of 

slightly different levels. Thus the time interval 

between the active existence of the watering_ places on 

the west side of the salt lakes at the Benson locality 

and those on the east side of the lakes at Curtis Flats 

may well have been long. 

During this interval the faunas changed, but it 

does not necessarily follow that this change was greatly 

affected · by evolution in this locality, for, although 

considered long as measured in years, the interval 

was probably in a geologic sense relatively short, and 

it may well be that the entire change was accomplished 

by migration. In fact, a comparison of the faunas 

seems to confirm this supposition. For example, the 

species of mastodon found at the Curtis Flats can 

not be a descendant of the one found at the Benson 

locality, as it belongs to a very different phylum. The 

Equidae, the Carnivora, the Rodentia, and, in fact, 

the species in · general found in one locality present 

nothing indicating their derivation from their relatives 

of the other locality. In other words, though many of 

the species of the Curtis Flats locality are closely related to species found in the Benson locality, the former are not descendant forms of the latter. 

DESCRIPTIONS OF SPECIES 

Order PROBOSCIDEA 

Two distihct phyla of mastodons, referable to two 

or possibly three new species, appear in the collections 

from the San Pedro Valley. One phylum, represented by a single specimen found in the locality 

just south of Benson, belongs to the group of mastodons with tusks possessing a band of enamel and of 

the nearly straight, twisted variety; the other. is 

represented by three specimens from the Curtis 

Flats locality. 

Genus IANANCUS Aymard 

Genotype.-Anancus avernensis (Crozet and Jobert). 

This genus is based on an Old World species which 

is characterized by . long, nearly straight, twisted, 

and enamel-banded tusks and by the fact that the third 

molars have five and one-half cross lophs. The Benson specimen seems "to belong to this genus, but 

the third molars have only four cross lophs. 
FOSSIL PROBOSCIDEA AND EDENTATA OF SAN PEDRO VALLEY, AR-IZ. 85 

Anancus bensonensis Gidley, n. sp. 

Plate XXXII 

Type.-The greater part of the basal portion of a 

skull from the posterior nareal opening forward, 

including the orbital and zygomatic region, and 

portions of the squamosal and paraoccipital of one 

side. The ·cheek teeth, except right m2 , and part of 

the alveolar sockets of the tusks are also preserved. 

Part of this specimen was obtained through exchange 

from the University of Arizona, and. parts w~re collected by Bryan and Gidley. 

. Type locality.-About 2Y2 miles south of Benson, 

Ariz., in sec. 22, T. 17 S., R. 20 E. 

Horizon.-Middle or upper Pliocene. 

Diagnosis:-I\1olars brachyodont, semibutwdont; 

m2 trilophodont, m3 tetralophodont with small heel; 

main cusps of upper molars wearing to trefoil p~ttern in both rows, but this pattern appears earher 

and is better defined in the cusps of the inner side; 

lophs relatively low and set at right angles to the 

long axis of the tooth crown; valleys shallow and 

almost completely blocked medially by the accessory 

buttresses of the inner row of cusps; rostrum long, 

very broad, and but little bent down o~ th~ pl~ne 

of the palate, being nearly continuous In direct~on 

with it, and seemingly correlated with the possessiOn 

of nearly· straight tusks; palate rather broad and 

but slightly arched. 

The following are additional features which may 

be considered more or less distinctive. The posterior 

nares is relatively small and is oblong-elliptical in 

cross section, and its anterior wall slopes forward 

and upward from the nareal notch at an angle of 

about 45°. The glenoid surface is relatively broad 

antero-posteriorly, and its borders are not sharpl! 

defined. This surface is characteristically probosCIdean in being slightly concave transversely and conv~x 

antero-posteriorly. In the Benson mastod<m, as In 

Mastodon americanum, there is a transverse sulcus 

formed behind the glenoid surface by a broad transverse expansion of the paraoccipital. This sulc~s, 

however is much shallower and narrower than In 

the Pleistocene species, because the paraoccipital 

is more closely appressed to the glenoid portion of 

the squamosal. This feature denotes a shortening 

of the skull in this region and seems to affect the 

position of the external auditory meatus, which is 

situated directly above or slightly forward from the 

middle of the glenoid surface.· In the Indiana mastodon 

, this opening is situated distinctly farther backward 

and -is also placed higher above the glenoid surface. 

·The zygomatic process of the squamosal is relatively 

very short . and its anterior articular border rises 

abruptly at a much greater angle than in M. americanum. The orbit is relatively high above the-tooth 

·row and is placed well forward, its· anterior. border 

being directly above the anterior border of m2 • The 

infraorbital foramen is large and is placed high upon 

the face as compared with this foramen in M. americanum. Also the maxillary border of the orbit rises 

abruptly at the point where it ~eets. the j~gal, 

indicating that there still remained In this species. a 

well-defined inferior postorbital process. . 

Another striking peculiarity of the Benson species 

is the fact that in connection with the b:road and 

remarkably long rostrum the anterior extremities of 

the premaxillaries are greatly. thickened. A simil~r 

thickening of the premaxillaries may be observed In 

old individuals·of the present-day African elephant. 

In the present confused state of o~r ~nowledg~ of 

the diversified species of mastodons, It 1s most difficult to define accurately the limits· of the several 

genera that have been proposed. In conseq~e~lCe it 

has long been recognized that a thorough r~vision of 

the group of Proboscidea ·would be most desuable. I 

have not attempted such a revision . in connection 

with my present study, for this important and much 

needed work is already nearing completion under the 

able direction and personal studies of Prof. Henry 

Fairfield Osborn; and the present reference·· of the 

species here described to Anancus ~ay theref~re ~e 

considered only provisional. In this connectiOn It 

should also be noted that the type of A. bensonensis 

seems to combine characters of species usually regarded as belonging to quite distinct genera. In 

Anancus avernensis .of Europe, .in the. S()uth American 

species " Mastodon andium," and in " Tetralophodon 

shepardi edensis," a. California species recently described by Childs Frick, the tusks are appare~tly of 

the long, . nearly straight type, are set rather widely 

apart, are but slightly divergent in .. the sk~ll, and 

apparently have a downward turn as they emerge from 

the alveoli; but fhether or not in Anancus·bensonensis, 

they were twisted and possessed a band of enamel, as 

in the three spbcies just mep.tion.ed, is, not known. 5 

From the form J and length of the rostrum it seems 

reasonable to infer that the Benson species was 

possessed of lower jaws of the elongate and prob~bly 

tusked type; · but this inference can . not be venfied 

until lower jaws have been fou~d. 

6 Since writing the above description I have again visited the San Pedro Valley, 

where I made a seeond collection oUossn ·vertebrates, this time for the American 

Museum of Natural History. Among ot:qer specimens obtained is a mutilated 

tusk from the Benson locality. This tuskseems with little question to,belong to 

the species of mastodon here described. If so, it entirely corrobo~ates the ·statement made above for it is sqfficiently well preserved to show that It was about 4 

feet long and about 4 inches in diameter and thatit.is of the nearly ~traig~t, twisted 

variety and possesses a wide band of enamel extendmg along nearly Its e?tire length. 

This tusk was found at approximately the same level as that from whwh the type 

specimen was taken, and only a few hundred feet distant from i~. Its fo:m agrees 

exactly with that of the alveolus in the type of Anancus bensonensu. In this connection it may be noted that in the same bed at a somewbat lo:wer ~evel,_ only .a few 

feet away from the tusk just described, was another tusk of qmte.dlfierent ~haracter 

giving positive evidence of a second type of mastodon belongmg to the Benson 

phases. This one, however, was too badly shattered and displaced to be pr~erved, 

but it showed by the natural mold left in the matrix which had surrounded It th11-t 

it was of the short,· thick, much_curyed, and rapidly tapering variety; also, the.re 

was no evidence of an enamel band. Two juvenile tusks from these beds, now m 

the 'American Museum of Natural History collection, give further· evidence CJf two 

types of mastodons in the Benson locality. One of these is about 10 inches Ion~ and 

about IY2 inches in diameter and possessses a well-de.veloped en~m~l band, the 

other is somewhat larger, is more cur-ved, and has no enamel band. 
86 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1925 

A specime from the California locality in the 

American M seum of Natural History (No. 24047) 

has been refe red to " Tetralophodon" edensis. This 

specimen has the anterior portion of the rostrum 

preserved, wi h portions of nearly straight, twisted, 

and enamel-b nded tusks in place. It has thickened 

premaxillaries as in Anancus bensonensis, but this 

thickeniug is markedly less pronounced, and the 

rostrum is rei tively shorter. -

Comparati e measurements indicate that Anancus 

bensonensis is latger than either the South American 

or the Califo ia species and is further distinguished 

from the latte by important differences, especially in 

the last uppe molar. M3 of the Benson species has 

the same nu ber of lophs, but it is relatively longer 

crowned, andJ he transverse crests are parallel instead 

of outwardly diverging, as in the California species. 

The lophs ar also less elevated, and the valleys are 

more open; al o, there is a well-developed cingulum on 

the inner bor er of the crown, and the fourth transverse loph, i stead of being small, as in " Tetralophodon" ede is, is nearly as broad and prominent as 

the third lop . The molars of T. edensis are described 

as having no ingula. , 

Measure ents of type skull of A nancus bensonensis 

[C talog No. 10538, U. S. National Museum] 

Millimeters 

Length of m2 __ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 125. 0 

Width of m2 (m asured at middle loph) ______ _______ __ 88. 5 

Length of m3 ___ -------------------------------- -- 191. 0 

Width of m3 (m asured at second loph)_______________ 99. 0 

Diameter of tus (estimated from alveolus) _____ ______ 130. 0 

· Basal length of kull from postnareal notch forward____ 815. 0 

Greatest width of palate (between posterior lophs of 

second molars --------------'--------------------- 120. 0 

Narrowe~t poin of palate · (between posterior lophs of 

last molar) ___ ---------------------------------- 76. 0 

Distance from 2 to anterior end premaxillary_________ 460. 0 

Extension of rna illary anterior to m2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 390. 0 

Width of skull a orbit (computed) ___________________ 750. 0 

Width of rostru at narrowest point (estimated) ______ 550. ·o ,Width of prema illaries at exit oftusks (estimated) ____ 640. 0 

Width of prem xillaries between alveolar borders of 

tusks _______________________________ __ ___ _______ 355. o 

Vertical diamete of premaxillaries at anterior extremity_ 125. 0 ~ Vertical diamet of orbit_ __________________________ 180. 0 

Genus STEGOMASTODON Pohlig 

The genus Stegomastodon was proposed by H. 

Pohlig in 1912 6 and was based on the species Mastodon mirificus Leidy. 

The generic position of the species described below, 

founded on materials from the Curtis Flats locality, 

can be assumed with much more confidence than 

that of the Benson species just described. Its general 

characteristics, which include a short, narrow, spoutlike symphysis of the lower jaw and the reduction of 

the dental series in each jaw to a single six or seven 

a Soc. beige goologie Bull., vol. 26, p. 193, 1912. 

lobed bunodont molar in the older adult stage, mark 

it rather definitely as belonging to the group typified 

by Stegomastodon mirificus (Leidy). Although only 

the characters of the lower jaw are known from the 

type, a nearly complete skull and lower jaws from 

the Blanco formation of Texas, now. in the American 

Museum of Natural History, 'has been ,referred by 

Osborn to this group, and a · comparison of this specimen seems 'to confirm the generic reference of the 

Curtis Flats specimens, although their specific rank 

appears to be quite distinct. 

Stegomastodon arizonae Gidley, n. sp. 

Plates XXXIII-XXXIX 

Type.-Portion of skeleton of a young adult male, 

including the base portion of the skull with tusks and 

cheek teeth in place; the lower jaws; both fore limbs 

(one with nearly complete foot); parts of both hind 

limbs; the pelvis; and several of the more characteristic vertebrae and ribs (catalog No. 10707, U. S. 

National Museum). 

Referred material.-(!) Portions of a skeleton of a 

moderately old male, including the basal portion of 

the skull with teeth and tusks in place; the lower 

jaws; a fore limb and foot lacking only the proximal 

end of the humerus and the greater portion o£ the 

scapular blade; a few ribs and vertebrae·; and the 

sacrum with parts of the pelvis (catalog No . .10556, 

U. S. National Museum). Found at about the same 

level as the type specimen, and about 100 yards 

distant. (2) A complete hind foot and distal end of 

tibia associated with a lower jaw lacking teeth (catalog No. 10917, U. S. National Museum). Found 

about 50 feet from No. 10556 and at the same 

level. 

Type locality.-Curtis Flats, about 14 miles south~ 

east of Benson, Ariz., in sec. 25, T~ 18 S., R. 21 E. 

Diagnosis. -Skull short; rostrum · short and bent 

sharply downward on the plane of the palate; lower 

jaws with short symphysis, spoutlike chin and no tusks; 

a single tooth in each jaw in old individuals, as in 

Stegomastodon mirijicus (Leidy); tusks without 

enamel, large, stout, much curved, and widely spreading so that at the point of exit from the skull they 

diverge at right angles to each other; second molars 

when present, tetralophodont, or nearly so; third 

molars sextalophodont or septalophodont, with heel; 

lophs when unworn relatively high, with summits of 

main cusps closely approached, leaving the shallow 

longitudinal median valley nearly closed; principal , 

cusps of the last lower molar not arranged in straight 

lines antero-posteriorly, as in most species of mastodons, but curving outward posteriorly, giving to the 

tooth crown a twisted appearance. 

The cusps of these molars, above . and below, arise 

one ab.ove the other in the jaw, so that the anterior 
FOSSIL PROBOSCIDEA AND EDENTATA OF SAN PEDRO VALLEY, ARIZ. 87 

lobes, appearing much earlier, are deeply worn before 

the more posterior ones come into use. These last 

two are progressive characters which parallel or ate 

rather tending toward the condition of tooth replacement found in ·the true elephants and which mark this 

species of mastodon as having advanced, at least in 

this respect, much beyond the better-known later 

survivor of this great group ofProboscidea, Jfastodon 

americanum. The tendency toward elephantlike 

development of the last molars of Stegomastodon 

arizonae is an important difference to be noted in 

comparing it with S. mirificus, the latter being a less 

progressive species. In S. mirijicus the summits of 

the lophs are more nearly on the same plane and are 

more evenly worn by use, as in ~Mastodon americanum. 

This progressive feature is also strongly marked in 

certain species of Old World mastodons and is likewise 

present, but to a much less degree, in certain other 

American species, as Megabelodon Zulli Osborn and 

Tetrabelodon campester Cope. 

Comparative measurements of Stegomastodon and Mastodon, in millimeters 

Teeth, skulls, and jaws 

Length of m z _____________________________________________________ _ VVidth of m2 _____________________________________________________ _ 

Length of m3 _________________________ ,_ ___ . _______________________ _ 

VVidth of m3 at second loph ________________________________________ _ 

Length of m2---- _____________ ---------- __ -- __ --------------------- VVidth of m2- ___________________ - _:.. _--- _- _- _---------------------- Lengthofm3 

_____________________________________________________ _ 

VVidth of m 3 a.t second loph _______________________________________ _ 

Diameter of tusk (greatest) _______________________________________ _ 

Diameter of tusk (least) at same point_ _____________________________ _ 

Basal length of skull from condylar notch ___________________________ _ 

Length of m 2 to anterior end premaxillaries _____________ . ____________ _ 

Length of palatal notch to end premaxillaries_.: ______________________ _ VVidth of skull at orbits ___________________________________________ _ 

VVidth at exit of tusks ____________________________________________ _ 

VVidth at narrowest point of ·rostrum _______________________________ _ 

VVidth of maxillaries at posterior end of tooth rows ___________________ _ VVidth of palate at narrowest point _________________________________ _ VVidth of palate at widest point ________________________________ · ____ _ 

Length of lower jaw, condyle to symphysis __________________________ _ 

Length from angle to point of symphysis ____________________________ _ 

Length from cheek-tooth row to point of symphysis __________________ _ Depth of jaw at condyle __________________________________________ _ 

Depth of jaw at coronoid process ___________________________________ _ Depth of jaw at anterior end of rna ____________________ ' ____________ _ 

Antero-posterior diameter of symphysis _________ :.. ___________________ _ Vertical diameter of symphysis _________________________ -:. __________ _ 

Skeleton 

Steqomastodon arizonae 

Type, 

young adult 

(catalog No. 

10707) 

95 

86 

212 

97 

110 

92 

230 

98 

160 

128 

820 

300+ 

580 

605 

600 

340 

230 

49 

70 

740 

662 

200 

345 

300 

150 

140 

75 

Referred, 

aged adult 

(catalog No. 

10556) 

------------

------------ 260 

87 

------------

------------ 258 

77 

192 

162 

------------

--,----------

------------

------------ 500 

400 

260 

85 

98 

800 

670 

210 

410 

335 

200 

121 

121 

Mastodon 

americanum, 

aged adult 

(catalog No. 

8204) 

119 

90 

185 

95 

120 

90 

180 

102 

205 

205 

1,045 

405 

760 

745 

185 

525 

300 

107 

185 

965 

750 

250 

515 

445 

201 

155 

125 

Steqomustodon arizemae 

Type (catalog Referred (catalog 

No. 10707) No. 10556) 

Length of cervical series __________________________________________ ~_____________ a 1, 450 ___________ _ Length of dorsal series_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1, 445 ___________ _ Length of lumbar series _____________________________ -·__________________________ 250 ___________ _ Length of sacral series__________________________________________________________ 1><350 c 285 

Total length of presacral vertebral column________________________________________ a 2, 035 ------------ Length of centrum of first dorsaL_______________________________________________ 45 ___________ _ Length of centrum of second dorsaL_____________________________________________ 55 ___________ _ Length of centrum of twentieth dorsaL _______________ ·- _____________________________________ - ------------

Length of centrum of first lumbar_______________________________________________ 75 · ___________ _ Height of anterior dorsal spines, first_____________________________________________ 225 ___________ _ Height of anterior dorsal spines, second___________________________________________ 385 . ___________ _ Height of anterior dorsal spines, third____________________________________________ 420 ___________ _ Height of anteriordorsalspines,fourth ______________________ ,_____________________ 425 -------~----

Length of scapula, glenoid cavity to top__________________________________________ 765 ___________ _ Distance from top to posterior angle of blade______________________________________ 780 ___________ _ Distance from spine to posterior angle of blade____________________________________ 512 ___________ _ Distance from spine to anterior angle of blade____________________________________ 150 _ -------- __ _ Length of metacromion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 285 315 

Antero-posterior diameter at constriction below spine______________________________ 230 235 

o Restored. b 4 .vertebrae. • 3 vertebrae. 

· Steqomastodon 

miriji.cus, type, aged adult 

(catalog No. 

209) 

________ "!"'" ___ 

------------

------------

-------------

------------

------------ 210 

7.6 

------------

------------

------------

------------

- - - -- - - --.---

------------

------------

------------

------------

------------

------·------

------------

------------ 220 

------------

------------

------------

Mastodon 

americanum 

(catalog No. 

8204) 

73 

70 

480 

1, 650 

360 

b363 

2,490 

70 

80 

80 

80 

405 

550 

550 

' 520 

920 

910 

510 

150 

365 

230 

./ 
88 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1925 

Cornp(uative measurements of Stegomastodon and Mastodon, in miUimeters-Continued 

Skeleton-Continued 

Stegoma$todon arizonae 

Type (catalog Referred (catalog No. 10707) No. 10556) 

Antero-posterior diameter at coracoid..:___________________________________________ 245 

Antero-posterior diameter of glenoid cavity_______________________________________ 195 

Transverse diameter of glenoid cavity____________________________________________ 130 

Height of spine________________________________________________________________ d 145 

185 

125 

175 

------------ Length of humerus, head to inner condyle________________________________________ 850 

Length of supinator ridge, exter:nal condyle to top of rugosity_______________________ 285 

Antero-posterior diameter of head___ ____________________ ________________________ 210 

------------ 325 

------------ Greatest diameter at proximal end_______________________________ __ ______________ .345 240 

Transverse diameter of distal articular surface_____________________________________ 201 705 Greatest length of ulna____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 720 ------------ Length at sigmoid notch________________________________________________________ 660 555 

Sigmoid notch to post extremity of olecranon_____________________________________ 225 

Transverse diameter at distal end________________ _______________________________ 135 

195 

135 

Length of radius_________________________________ _____________________________ 630 635 

Greatest diameter at proximal end ______ -..,-______________________________________ 110 

Transverse diameter at distal end_______________________________________________ 148 

140 

175 

Antero-posterior diameter at distal end___________________________________________ 98 115 Total width of carpus _____________________________________________________________________ _ 255 Depth of carpus between radius and Me IlL ________________________________________________ _ Length of Me Ill _________________________________ _____________________________ ------------ 160 

130 Length of third digit including Me IlL _____________________________________________________ _ 

Greatest width of pelvis________________________________________________________ 1, 475 

Greatest length of ili urn_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 820 

330 

------------

------------ External point of ilium to acetabulum____________________________________________ 440 ------------ Width of sacral end of ilium at narrowest point___________________________________ 335 

Length of pubic symphysis ______________________________ ·________________________ b 440 ------------

------------ Distance from acetabulum to end of ischium ___________________________ :___________ 345 ------------ Trap.sverse diameter of pelvic opening ____________________________________________ , 415 

Transverse diameter of obdurator foramen ____________________________________ --"-_ 100 ------------

------------ Antero-posterior diameter of obdurator foramen____________________________________ 195 ------------ ~ngth of femur, head to internal condyle________________________________________ 1, 010 

Diameter of head_____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 7 ------------

------------ Diameter through head and trochanter___________________________________________ 335 ------------ Transverse diameter at distal end _______ ,.: _______________________________________ b 215 ------------ Antero-posterior diameter at distal end _________ .__________________________________ 240 ------------ Greatest diameter at middle of shaft---------------------~----------------------- 145 ------------ Least diameter at middle of shaft________________________________________________ 65 ------------ Length of tibia________________________________________________________________ 645 ------------ Transverse diameter of proximal end_____________________________________________ 230 ------------ Transverse diameter of distal end________________________________________________ 160 ------------ Total length of hind limb as mounted____________________________________________ J, 890 ------------ Total length 'of fore limb as mounted____________________________________________ 2, 485 ------------

Mastodon 

americanum 

(catalog No. 

8204) 

270 

197 

130 

180 

905 

395 

235 

330 

210 

795 

655 

270 

a 160 

675 

125 

130 

143 

a 283 

145 

145- a 290 

1,800 

1, 030 

545 

240· 545 

310 

505 

140. 

255 

1, 050· 

175- 310· 245 

235- 155 

95-

660. 

250 

170· 2, 150· 2, 670, I 

o Cast from the "Warren" mastodon skeleton mounted in the American Museum of Natural History, New York City, substituted in the National Museum mount •. b Estimated. 

dAbout. 

Additional skull and skeleton characters.-Stegomastodon arizonae is typically proboscidean throughout 

in skull and s~eleton characters, as might be expected, 

and in many respects, therefore, it resembles Mastodon americanum.1 Certain important modifications, 

however, may be noted, which clearly distinguish it 

from this type of mastodon and also from the Gomphotherium group in so far as the osteologic characters of 

that group are known.' 

The skull, above a plane passing through the base 

of the orbits and the upper border of the condyles, 

. is wanting, but the portion preserved, which includes 

the jugal of the left side and carries the cheek teeth 

and both tusks in place, indicates clearly that it is 

· not of the elongate type, like that of Mastodon ameri-

, canum and Gomphother~um, but is much more brachyo7 For convenie~ce, most of the comparisons are made with the nearly complete 

' skeleton of the Indiana mastodon, a male M. americanum, now on exhibition in the 

National Museum (catalog No. 8204), which is essentially like the "Warren" mastodon now mounted in the American Museum of Natural History, well known 

through published descriptions. · · 

cephalic than either. In addition the tusks are relatively short, much curved, and widely divergent; the 

rostrum is short, broad, and bent sharply downward. 

immediately in front of the cheek teeth, much as in. 

the elephants; and the palatal region in the type skull. 

is very narrow and little or not at all arched. 

The lower-jaws are moderately long but have a. 

short, deep symphysis with narrow, spoutlike chin. 

and no tusks. 

The scapula is much like that of M. americanum,. 

being readily distinguished f~om the Elephas type' 

by the relatively broader ·proportions of its posterior 

blade. The metacromion is a long, well-developed 

process, as in M. americanum, extending backward 

from the lower half of the spine to form a wide Vshaped valley with the likewise well-developed acro--

mion. Compared with the Indiana specimen this. 

valley is shallower and the - metacro:r:nion is less 

downwardly directed, being nearly at right angles. 

with the scapular spine. 
FOSSIL PROBOSCIDEA AND EDENTATA OF SAN PEDRO VALLEY, ARIZ. 89 

The humerus is of about the same robust proportions · as that of the Indiana mastodon but differs 

from it in some important respects. The deltoid 

ridge seems to be relatively thinner and higher, is 

less rugose, and is extended distally ·considerably 

farther along the shaft. Likewise the supinator 

ridge, although relatively shorter and less salient in 

its prominent rugose distal portion, extends its 

proximally diminishing portion much farther up the 

shaft. Thus the ends of these two prominent ridges 

overlap each other for a much greater distance than 

in the Indiana mastodon and in consequence form a 

conspicuous longitudinal external sulcus, which in the 

Indiana specimen is not ·present or but weakly defined. 

Also the internal condylar ridge in the Arizona species 

is more prominent and more backwardly extended. 

Compared with that of M. andium, the humerus is relatively robust, and it agrees rather closely in general 

proportions with that of Gomphotherium angustidens. 

Of seemingly less importance is the fact that the relative length ·of the rugose portion of the supinator 

ridge in · S. arizonae is but little less than one-third 

the total length of the humerus; in M. americanum it 

is definitely more than one-third this length; in G. 

angustidens it is shortest, being definitely less than 

one-third; and in · M. andium it is longest, being 

nearly one-half the total length of the humerus. 

The ulna differs from that of the Indiana specimen 

in that the olecranon process is relatively very short. 

This seems to be characteristic also of the true ·elephants. The radius is much like that of M. americanum and seems to differ only in that the head is 

more expanded antero-internally and narrows up to a 

greater degree externally, thus making it more definitely triangular· in cross section. 

The fore foot is in general much like that of M. 

. americanum but is somewhat more slender in proportions. The carpus and metacarpal III are about equal 

in length. In M. americanum the carpus exceeds the 

length of metacarpal III, and the phalanges are relatively longer. 

The pelvis differs from that of M. americanum in 

having the anterior border of the ilium more convexly curved in outline, viewed from behind, and the 

upper or sacral portion is more expanded anteroposteriorly. The pubic symphysis is long, as in 

M. americanum, but its posterior region seems to be 

not so robust nor so conspicuously produced backward and downward as in· that species. The uncertainty of this statement is due to the fact that this 

portion of the pelvis is somewhat crushed and damaged. 

·Crushing also prevents an accurate and detailed com-

··parison· of the femur' and tibia, but these bones have 

·about the same general proportions and modifications 

· as those ·of M. ainericanum. 

The left astragalus is all that was found ·to represent 

-the hind feet 'of the type specimen, but 'there is in the 

collection a n~arly complete hind foot of another 

specimen (No. 1091 7) associ a ted with a portion of a 

· lower jaw showing the alveolus for a · single cheek 

tooth, which seems to warrant its reference to this 

species. This foot was found with the bones all 

articulated, nearly in their normal position but so 

firmly cemented together that they can not be separated for detailed study. The general characteristics, 

however, can be clearly made out. The tarsal elements are relatively thick compared with those of 

the Indiana mastodon, hence the tarsus as a whole is 

longer and narrower than that of M. americanum. 

The toe~, on the ·contrary, are relatively short, and 

the lateral pair, D I and D V, have the phalanges 

much reduced; those on D I being apparently represented by a single shapeless nodule of bone. The 

terminal phalanges of the other toes are also apparently 

wanting. · 

Comparative measurements of the hind feet of Stegomastodon 

arizonae and Mastodon americanum,a in millimeters 

' 

Transverse width of calcaneum ____ - __ -_·_- Antero-posterior diameter at distal end ___ _ Transverse width of astragalus (tibialface) __ Thickness at anterior face _______________ _ Transverse width of navicular ____________ _ Thickness at anterior face _______________ . 

Transverse width of external cuneiform __ ..:_ Thickness at anterior face _______________ _ 

Transverse width of metatarsal III (proxi- . mal end) ___________________ - __ - ____ -_ 

Length of metatarsal IlL _______________ _ Total length of digit IlL _______ :_ ________ _ 

Vertical thickness of tarsus at' digit IlL ___ _ Total width of tarsus ___________________ _ 

m~f%3~n Mastodon 

arizonae americanum (catalog (catalog 

No. 10917) No. 8204) 

165 

135 

130 

50 

150 

46 

71 

52 

74 

100 

145 

165 

315 

175 

130 

130 

40 

155 

29 

90 

35 

75 

110 

205 

143 

350 

a Part of this foot of the Indiana mastodon is restored by using casts of the bones 

of the ''Warren" mastodon now on exhibition in the American Museum of Nat ural 

History, New York City. 

Although the axial skeleton of the type is by no means 

complete, its general characters are rather clearly 

indicated by several typical vertebrae and ribs. Portions of the first four dorsal vertebrae, including the 

spines, the last two dorsals, the three lumbars, the 

sacrum, and the anterior two caudals, are preserved. 

Many of the ribs are represented by pieces of various 

completeness. These taken together are sufficient to · 

form a fairly accurate basis for restoration of the body 

portion of the skeleton, which seems to correspond in 

general with that of the Indiana mastodon, although 

certain differences of detail may be noted. In the 

Indiana specimen the spine of the first dorsal approaches in height ·those of the second and· third, 

which are equal and the highest of the series. In the 

Arizona specimen the fourth dorsal spine is the highest,· the second is riext, the third a little shorter, and 

the first still shorter, being relatively much shorter 

than the corresponding one of the Indiana mastodon. 
90 SHORTER b ONTRIBUTIONS TO GENERAL GEOLOGY, 1925 

Specimen No. 10556, provisionally referred to 

Stegomastodon arizonae (p. 86), in so far as the corresponding portions preserved will permit comparison, 

seems to present the principal characteristics distinctive of the species. It differs from the type, however, in certain important details. These inay be 

briefly stated as follows: (1) It represents a larger 

individual (see table of comparative measurements, 

p. 87); (2) the cheek teeth are reduced to a single 

one (m3

) in each jaw; (3) m5, both upper and lower, is 

relatively and actually narrower than that of the type, 

and, although much worn, indicates clearly that the 

homologous lophs are relatively less elevated and the 

valleys correspondingly less open; ( 4) the tusks are 

notably larger and less cylindrical, being subquadrate 

in cross section; (5) the symphysis of the lower jaw is 

deeper; and (6) the palate is deeply arched and about 

twice the width of that of the type skull. 

Such differences as these, if found at all constant . 

where abundant material is available, would unquestionably be considered as indicating two distinct 

species. In the present instance, however, only two 

specimens can be compared, and I am therefore inclined to consider most of these differences, at least, as 

due to individual variatio s and age changes, both of 

which are generally recognized as being considerable 

in most species of proboscideans. Although both 

specimens are adult, the paratype was evidently a 

much older individual, and to this fact may be attributed, for example, its generally larger proportions and 

· the more advanced stage of development of the cheek 

teeth. It does not, however, account for the smaller 

size and different proportions of the teeth, !)Or would 

it seem to explain entirely the great difference in width 

and form of the palate, although this modification 

would doubtless he very considerably affected by it. 

The type is a young adult, yet it had reached the stage 

in which the limb bones and most of the vertebrae 

had entirely closed the sutures of their epiphyses. Although the second molars are worn nearly to the roots 

and were about to be shed, the hinder molars hadnot 

yet fully emerged from the jaw bone, and only the an~ 

terior loph of each is worn to any degree. In the referred specimen the anterior molars have entirely disappeared and the last molars had emerged to their 

full height in t4e jaws, yet in these only the two anterior lophs are deeply worn, the third is moderately worn, 

and the fourth is just beginning to show signs of wear. 

As both specimens seem to be of the same sex (male), 

sex variation need not be considered in this comparison. 

General features of the skeleton as mounted.-In 

addition to the characteristics pointed out in the 

above detailed description, a few features worthy of 

note are presented in the general skelet~l structure 

of StegorniLstodon arizonae as restored and mounted. 

The general proportions of the skeleton are in part 

·, 

conjectural. However, the length of the back, computed from the few characteristic vertebrae preserved, 

and the definitely known features of -the skull indicate 

rather clearly that S. arizonae was relatively higher 

and shorter than Mastodon americanum; both the 

pelvis and the skull are more elephantlike in general 

form, but the tusks are much more divergent than 

is usual in any proboscidean. 

Two characteristic _features _ relative to the fore 

limbs in the Proboscidea were very clearly brought 

out in the mounting of both this specimen and the 

skeleton of the Indiana mastodon. One concerns 

the proper location of the shoulder joint; the other 

relates to the normal position of the elbow joint. 

In seeking to determine where to place the scapulohumeral joint, it was observed that the second rib 

to a greater degree and the third to a less degree were 

bowed inward just above mid-section, and that the 

first rib was also depressed on its posterior border in 

the same region. Thus there is formed a broad, 

shallow depression in the anterior-superior rib structure, which obviously can be for no other purpose 

than to accommodate or give room for the limited 

play of the heavy shoulder joint. The skeletons of 

living species of elephants examined show 'a like 

structure; hence it may be assumed to be characteristic of the Proboscidea in general. To follow up 

this idea, several skeletons of the larger, heavier 

ungulates were examined, and most of them were 

found to show a similar but usually less distinct 

depressed area. Its position, however, is not the 

same in the ungulates as in the Proboscidea, being 

lower and more anterior, so that its center comes 

between the first and second ribs and :qear their 

distal ends. This difierence in position seems to be 

correlated with the greater angulation of the shoulder 

an_d elbow joints in the ungulates. - -

In determining the normal position of the elbow 

joint, it was found in articulating the bones of the 

fore leg that by placing the fore foot in a normal 

position-that is, rather well under the body-the 

elbow joint was brought around to a position in which 

its transverse axis was directed at a very oblique angle 

to the transverse a~is of the body, and thus the anterior planes -of these joints face obliquely inward, 

instead of nearly directly forward, as in most ungulates. This also seems to be a distinctly proboscidean 

feature an~ is apparently a purely mechanical adaptation necessitated by the great weight and bulk of 

the creature. An observer watching an elephant 

walk will note that the fore foot, as it leaves the ground 

and is started forward for the next step, is well to the 

' outside of the perpendicular longitudinal plan~ of the 

body; hence, in order to take the weight of the body 

again on coming to the ground, it is carried forward 

and obliquely inward across this plane. The opposite 

fore leg, swinging inward and forward in its turn, gives 
FOSSIL PROBOSCIDEA AND EDENTATA OF SAN PEDRO VALLEY, ARIZ. 91 

the peculiar side to side swaying motion of the shoulders as the animal moves forward. Thus the fore legs 

of proboscideans do not move directly forward in a 

straight walk but swing in an inward-directed oblique 

plane; hence the obliquity of the elbow joint when 

placed in a normal position. 

Order EDENTATA 

Suborder GLYPTODONTJ:A 

The existence of glyptodonts in the United States 

was first made known by Cope, who in 1888 described 

one-half of a single scute of the carapace as /the type 

of a new species, Glyptodon petaliferus. 8 In the next 

several years other fragments of glyptodonts were discovered and described, but nothing of importance 

came to light until 1903, when an American Museum 

expedition discovered in the Blanco (Pliocene) formation of western Texas a partial skeleton consisting of a 

nearly complete carapace, a pelvis, a sacrum, a caudal 

series, and a complete ·tail ·armature. This material 

was described by Osborn, who made it the basis of a 

new genus and species, Glyptotherium texanum. 9 Next 

followed Brown's description of some good specimens 

from Mexico, discovered in part by himself and in 

part by other collectors at a much earlier date. On 

this combined material he founded the new genus 

Brachyostracon. 10 Brown states that the earlier collections mentioned, consisting of two nearly complete 

carapaces of glyptodonts} were discovered near Tequixquiac. One of these is preserved in the Mexican 

National Museum of Natural History, the other in the 

National School of Engineers in Mexico City. The 

former was described in 1874 by Senores J. N. Cuataparo and Santiago Ramirez, who gave it the name 

Glyptodon mexicanus. This material was mentioned 

by Dr. Marino Barcena in 1882, by Cope in 1884, and 

again by Dr. Manuel M. Villada in 1903 (see Brown's 

article for references). Villada gave a faulty drawing 

of the carapace in the Natural History Museum. 

The descriptions given by these authors were very 

inadequate; hence our first real knowledge of the 

Mexican glyptodonts came through Brown's contribution, just cited. The next important contribution 

is that of H~y,11 who in 1917 described a specimen 

(catabg No. 6071, U.S.N. M.) from supposed Pleistocene deposits in Wolf County, Tex. This specimen 

includes several characteristic parts of the carapace 

and skeleton. Hay referred it to Cope's species 

Glyptodon petaliferus, and compared it in detail with 

the South American species Glyptodon asper Burmeister, to which he considered it generically related. 

Thus up to the present time only four valid species, 

representing three genera of glyptodonts, have been 

sAm. Naturalist, vol. 22, p. 345, 1888. 

t Osborn, H. F., Am. Mus. Nat. Hist. Bull., vol. 19, pp. 491-494, 1903. 

to Brown, Barnum, Am. Mus. Nat. Hist. Bull., vol. 31, pp. 167-177, pis. 13-18, 

1912. 

u Hay, 0. P., U. S. Nat. Mus. Proc., vol. 51, pp. 107-116, pis. 3-5, 1917. 

reported from North American localities. Two of 

these species came from Mexico, the other two from 

the United States. Now, a fifth species, represented 

by good material, has been discovered in· the Curtis 

Flats locality of the San Pedro Valley and is here 

described. This species seems to belong to the genus 

Glyptotherium ·as defined by Osborn. 

Genus GLYPTOTHE~IUM Osborn 

Genotype.-Glyptotherium texanum Osborn, from the 

Blanco (Pliocene) formation of western Texas. 

This genus is characterized by · a relatively elongate 

carapace, simple tail structure, · and relatively primitive carapace plates, which are arranged in more or 

less regular lateral rows extending over the back and 

of which the central areas are distinctly ·larger than 

the peripheral ones in all parts of the carapace. 

Another characteristic of this genus, given by Brown 

for Glyptotherium texanum and verified . in a specimeli 

of G. arizonae from the Curtis Flats locality collected 

in 1924 for the American Museum of Natural History, 

is that the pubes are reduced to thin rods of bone. 

Glyptotherium arizonae Gidley, n. sp. 

Plates XL-XLIV 

Type.-Part ·of a skeleton, including the lower jaws; 

complete limbs and feet of the right side; a section of 

the back bone; portions of the carapace, including the 

nearly complete border of the right side; and various 

detached scutes of the carapace and tail rings (catalog 

No. 10536, U.S. National Museum). 

Paratypes.-Nearly complete tail piece, including 

vertebrae and bony rings, · and hinder lower border 

portions of the carapace of both sides (catalog No. 

10537, U. S. National Museum); the greater part of 

the carapace with a few teeth and foot bones associated 

(catalog No. 10336). 

Type local~ty.-About 3 miles east of the Curtis 

ranch, in sec. 25, T. 18 S., R. 21 E., Cochise County, 

Ariz., about 10 feet above and 100 feet distant from 

locality of the type of Stegomastodon arizonae. 

Horizon.-Upper Pliocene deposits. 

Diagnosis.-Size large, length of carapace ·about 

1,700 millimeters (5 feet 8 inches) measured over curve 

of back, total length of animal about 2,285 millimeters 

(7 feet 7 inches); carapace elongate, with a small area 

of imbricated and more or less movable scutes bordering its anterior lateral margins; plates in all parts 

of the carapace, with central areas definitely larger 

than those of the periphery; carapace plates with depressed centers except those of the first, second, and 

parts of the third and fourth marginal rows; tail com .. 

prising twelve vertebrae and ten chevrons; tail armature with eight movable rings and a terminal cone 

composed of three closely sutured rings; tail armature 

and postero-:-lateral carapace plates moderately ornate. 
92 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19~5 

Skull not known. Lower jaws deep, with massive, 

spoutlike symphysis, lower border nearly semicircular in outline, and ascending ramus relatively broad 

and directed well forwar.d; cheek teeth all three-lobed, 

but th~ anterior two are not completely molariform, 

and the third from the front is more elongate than 

those posterior to it. Hind feet short and wide, with 

five subequal digits; fore feet short, with digit I vestigial or wanting, digits II and III subequal, constituting a stout, conspicuous pair, and digits IV and V 

much reduced. 

Detailed description.-The dentition is represented 

by the complete low~r series of the type and a few 

upper teeth associated with paratype No. 10336. 

It presents certain modifications which seem to be 

characteristic of the species. These teeth resemble 

FIGURE 4.-Glyptotherium arizonae Gidley. Type. Lower cheek teeth of left 

side, one-half natural size. 

in general form and proportions those of the South 

American glyptodonts, but differ in that the lobes 

of the molariform teeth are more oblique, their extremities are more angular, and the posterior face 

of the lower molars and anterior face of the upper 

are slightly indented by a shallow longitudinal sulcus. 

· This gives a concave outline to the posterior lobes 

of the lower teeth and to the anterior lobes of the 

upper. . In all other species of glyptodonts, so far as 

known, the posterior face of the lower cheek teeth is 

more or less convex. In general proportions the 

teeth of G. arizonae are like those of the South American genus. Glyptodon, but they are more nearly like 

those of Hoplophorus ornatus ( = Lomaphorus ornatus, 

fide Lydekker) as figured by Burmeister 12 in that 

they are relatively narrow and loosely. spaced. In 

degree of specialization the anterior three teeth are 

rather intermediate betwe.en the more simple ones of 

Hoplophorus and the more completely molariform 

ones'of Glyptodon. · 

Other features to be noted in the lower dentition 

of the Arizona species are the conspicuous prolongation of the posterior external angle, especially of the 

first four teeth, and the relatively gr.eat width of the 

anterior lobe in the hinder molars. Thus in the last 

four teeth of the ~erie!? the anterior lobes exceed in 

width the middle lobes, and in all but the last one 

of the group the midlobe is exceeded in width by the 

posterior lobe also. 1 

Of the elements of the vertebral column of this 

species ant~rio:r:: to the caudal ~egion, only the dorsal 

tube is known. This is composed of ten fused vertebrae, as in f!anochthus. According to Burmeister 

. u Museo publico de Buenos Aites Anales, vol. 2! pl. 19, figs. 2, 3, 1874. r f 

-Glyptodon has eleven vertebrae included in this tube 

and Hoplophorus has twelve. 

The caudal vertebrae , are twelve in number and, 

like the tail armature, more nearly resemble those of 

G. texanus than they do any of the South American 

forms. . They differ from those of the Texas species 

in that the processes of the anterior ones are relatively 

longer in the same proportion that the anterior rings 

are larger. . 

Both scapulae are well preserved in the type speci~ 

men and show some distinctive characteristics. As 

this element is.not known in any other of the North 

American species, it can be compa!ed only with 

South American forms. In general it resembles more 

nearly that of Glyptodon than thb.t of Panochthus as 

figured by Burmeister, but it differs widely from both in 

its greater antero-posterior expansion and the relatively 

much greater extent of the rounded superior scapular 

border. The respective areas of the prescapular and ' 

postscapular fossae have about the same proportion to 

each other as in Glyptodon, but their form is quite different. In Glyptodon the presc.apular fossa is ovoid in 

general outline, with the portion included in the suprascapular border only about one-half the extent of the 

prescapular border. In Glyptotherium arizonae this, 

fossa is nearly triangular in outline, with the portion 

included in the suprascapular border nearly twice 

that of the prescapular border. The postscapular 

border is likewise proportionately much less extended 

than in Glyptodon. 

The humerus of G. arizonae lacks the en tepicondylar 

foramen, as in Glyptodon, but in proportion and other 

respects is more like that of Hoplophoru's, which has 

this foramen well developed. Apart from the lack of 

the entepicondylar foramen, the humerus is distinguished · from that of H oplophorus in that· bo.th the 

deltoid and ·supinator ridges, though, just as ·strongly 

developed, are less extended along . the sb.aft. Also 

the .bicipital groove seems to be 11arrower in the 

Arizona specimen, both supratrochlear fossae are relatively deep, and there is present in the type a welldefined· supra trochlear foramen. 

Like the humerus, the radius and ulna are relatively slender and more nearly resenible those of 

Hoplophorus than they do those of the other South 

American ·genera. The Ulna especially is like that· of 

Hoplophorus. In Glyptodon the shaft of the ulna is 

greatly shortened and deepened. The. bones of the 

fore foot are 'peculiar only in that they are relatively 

very much shortened as· compared · with . those . of 

Hoplophorus and are nearly as robust as those of 

Glyptodon. 

The pelvis of this species ·can not at present be described, although a ~omplete one is preserved with a 

specimen . recently collected from' the Curtis Flats 

locality for. the American Museum. of Natural History . . This is still in the matrix and will not be avhll.:. 
FOSSIL PROBOSCIDEA AND EDENTATA OF SAN PEiDRO VALLEY, ARIZ. 93 

able for description until it can be cleaned up. From 

my observations in the field, however, it may be 

stated that this pelvis has a much reduced pubis, as 

reported by Brown for Glyptotherium texanum. 13 

The femur of G. arizonae is very heavy and massive 

as compared with the humerus, but like the other 

limb bones, it is more slender in proportions than that 

of Glyptodon. It differs from the femora of all the 

South American forms, especially in the conformation 

of its distal end, which is definitely offset from the 

median line of the shaft toward the inner side, thus 

making a greater obliquity to · the exterior border of 

the supinator ridge; it differs also in a definitely 

greater elevation of the great trochanter, which extends above the head of the femur. The femur of G. 

petaliferus described by Hay more closely resembles 

that of the Arizona species than it does that of Glyptodon. This is especially true of the form and character of the distal half o£ the shaft, which is quite as 

obliquely directed. The 1 

great trochanter, however, 

is much less elevated. 

In the Arizona species the hind foot shows some 

important differences both in structure and in proportions from those of South American glyptodonts. It 

is much broader and more robust than those of Panochthus and Hoplophorus and is less robust than that of 

Glyptodon. In the less reduction of the lateral toes, 

the hind foot of Glyptotherium arizonae is like that of 

Glyptodori and differs from those of Panochthus and 

Hoplophorus. The form and arrangement of the tarsal elements, however, seem to differ widely from 

those of Glyptodon as compared with the figures given 

by Burmeister.14 Among the most conspicuous differences to be noted are that the metatarsals in the 

Arizona species are proportionately long, the three 

cuneiforms, the cuboid, and the navicular are less 

widely expanded, the navicular is much less depressed 

in its middle anterior aspect, and the external and 

middle cuneiforms are entirely separated in front, 

owing mainly to the relatively greater elevation of the 

second metatarsal. Their borders come into direct 

contact in Glyptodon. 

Although many of the modifications noted in the 

foregoing description of Glyptotherium arizonae may 

not be considered individually as distinctive, the combination of characters emphasizes the generic distinctness between the South American and North 

American glyptodonts. 

It is not within the scope of this paper to review 

Hay 's description of the glyptodont from northern 

Texas, which he referred to Glyptodon petalijerus 

Cope. 15 It may be stated, however, that although the 

teeth of this Texas form are more like those of 

Glyptodon than those of Glyptotherium in general 

13 Brown, Barnum, Am. Mus. Nat. Hist. Bull., vol. 31, p. 175, 1912. 

u Museo publico de Buenos Aires Anales, vol. 2, pl. 36, 1874. 

16 Hay, 0 . P ., U.S. Nat. Mus. Proc., vol. 51, pp. 107-116, pis. 3-5, 1916. 

character, such resemblances, with modifications as 

above designated in comparing the femora (seem to 

apply to all the skeletal elements so far as they are 

known. For this reason it seems probable that the 

species proposed by Cope and more .adequately described on more ·complete material by Hay may prove 

to belong to a new genus. The great difference in 

geographic situation of the Texas locality and the 

type locality of Glyptodon adds to this probability. 

It is perhaps best, however, to retain this species 

where Cope and Hay have left it until more is known 

of the carapace and tail armature and the pelvic, 

sacral, caudal, and dorsal structure. 

Measurements of Glyptotherium arizonae (type), in millimeters 

Length of animal measured in straight line, including head and taiL __________________________________ _ 

Length of carapace measured over curvature ___ ------··-

Greatest width o(carapace measured over top_---~--- Length of tail armature ___________ _________________ _ 

Length of caudal vertebrae series _________ --------- __ _ 

Length of proximal ring __________________ -----------

Length of fourth ring ____________________ -----------

Length of eighth ring ______________________________ _ 

Length of terminal cone _________________ -· ____ ______ _ 

Vertical diameter of proximal ring __________ ----------

Vertical diameter of fourth ring _____________________ _ 

Vertical diameter of eighth ring _____________ __ -------_ 

Vertical diameter of terminal cone _____ ______________ _ 

Transverse diameter of first caudaL __________________ _ 

Transverse diameter of fifth caudaL _________________ _ 

Trans verse diameter of ninth caudaL ________________ _ 

Transverse diameter of twelfth caudaL _______________ _ 

Length of dorsal tube ______________________________ _ 

Total length of lower jaw ________________ .:. __________ _ 

Length of symphysis ____ ___________ ----------------- Length of tooth row _______________________________ _ 

Depth at sixth cheek tooth _____ ~------ --------------

Depth at condyle _____ ___ ______________ -- ___ ----- --_ 

Antero-posterior diameter of ascending ramus at tooth row __________ _________________________________ _ 

Greatest vertical depth of scapula ____________ ________ _ 

Greatest antero-posterior width _______________ ______ _ 

Antero-posterior diameter of articular face ____________ _ 

Greatest transverse diameter of articular face __________ _ 

Length of acromion, measured on curve _______________ _ 

Length of humerus, head to internal condyle ___________ _ 

Greatest diameter of head _______ __________ ----------

Transverse diameter of distal articular surface _____ ~----

Greatest diameter of proximal end ___________ ---------

Greatest diameter at distal end ______ ----------------- Narrow est transverse diameter of shaft _______________ _ 

Length of radius between articular faces ______________ _ 

Transverse diameter of proximal end _________________ _ 

Transverse diameter of distal end ____________________ _ 

Greatest length of ulna __________________________ ----

Length of olecranon ___________ ___________ ----------_ 

Length of shaft sigmoid notch to distal end ____________ _ 

Transverse width of sigmoid surface _________________ _ 

Transverse width of distal articular surface ____________ _ 

Length of carp~s betweeen radius and digit III ________ _ 

Length of digit III, including metacarpaL ____________ _ 

Length of terminal phalanx ___ ------- ______ ----------

Length of metacarpal IlL _____ ______________ -------_ 

Greatest width of carpus _______________________ -----

2,285 

1, 700 

2, 120 

895 

920 

83 

95 

105 

320 

360 

235 

135 

113 

368 

1'85 

85 

28 

465 

323 

145 

202 

0 93 

245 

128 

325 

443 

83 

40 

120 

355 

83 

72 

105 

110 

40 

170 

55 

65 

270 

85 

150 

65 

60 

48 

115 

70 

22 

100 
94 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1925 . 

Length of femur head to internal condyle _____________ _ 456 Length of tibia ___________________________________ _ 

Length of third trochanter to external condyle _________ _ 496 Transverse diamater of tibia and fibula, proximal end ___ _ Greatest diameter of head _________________________ _ 92 Transverse diameter of tibia and fibula, distal end ______ _ 

Transverse diameter of distal articular face __________ _ 130 Length of tarsus between tibia and metatarsal IIL ___ _ Greatest width at proximal end ______________________ _ 270 Transverse width of same ________________ .,. _________ _ 

Length of supinator ridge __________________________ _ 221 Length of digit III, including metatarsaL ___________ _ 

Transverse diameter of shaft at narrowest point ______ _ 100 Length of metatarsal IIL _________________________ _ 

Diameter of shaft at upper end of supinator ridge _____ _ 165 Length of terminal phalanx __ -- ___ ---------- _______ _ 

220 

130 

130 

40 

105 

115 

33 

53 
PLATES XXXII-XLIV 

95 

• 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XXXII 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

\ 

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Portion of skull of Anancus bensonensis Gidley, n. sp., type (No. 10538, U. S. Nat. Mus.). a, Palate view; b, view from above; c, view from left side; d, anterior 

view. a, b, c, about one-sixth natural size; d, much reduced 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XXXIII 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Skeleton of type of Stegomastodon arizonae Gidley, n. sp. (No. 10707, U.S. Nat. Mus.). A little less than one-twentieth natural size 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XXXIV 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Skull of type of Steqomastodon arizonae Gidley, n. sp . (No. 10707, U.S. Nat. Mus.). About one-seventh natural size. a, Front view; 

b, palate view 
4r 

U. S. GEOLOGICAL SURVEY PIWFESSIONAL PAPER 140 PLATE XXXV 

.., FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Left lower jaw of type of Steg{Jmastodon arizonae Gidley, n. sp. (No. 10707, U. S. Nat. Mus.). About one-third natural size. a!J View from above; b, inner side view 

# 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XXXVI 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Portion of skull of Stegomastodon arizonae Gidley, n. sp. (No. 10556, U. S. Nat. Mus.). About two-sevenths natural size. a, Palate view; 

b, view from right side 
U. S. GEOLOGICAL SUHVEY PHOFESSIONAL PAPEH 140 PLAT}] XXXVII 

a 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Left lower jaw of Stegomastodon arizonae Gidley, n. sp. (No. 10556, U. S. Nat. Mus.). About two-sevenths natural size. a, Outer side view; b, view from above 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XXXVIII 

2 2a 

1 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Bones of Stegomastodon arizonae Gidley, n. sp. All about one-sixth natural size. 1-3, Type (No.10707, U.S. Nat. Mus.); 4, No.10556, U. 8. Nat. Mus. 1, Right humerus, anterior view; la, same, 

outer side view; 2, right ulna, outer side view; 2a, same, anterior view; 3, right radius, anterior view; 4, distal half of left humerus, anterior view 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XXXIX 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Bones oi Stegomastodon arizonae Gidley, n. sp. 1-3, Type tNo. 10707, U.S. Nat. Mus.); 4, No. 10556, U.S. Nat. Mus. All about one-eighth 

natural size. 1, Left tibia, anterior view; 2, right scapula, outer view; 2a, same, view from below; 3, right femur, anterior, slightly oblique 

view; 4, portion of left scapula, outer view 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XL 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Glyptotherium arizonae Gidley, n. sp. 1, Skeleton, composite of three individuals, Nos. 10536 (type), 10537, and 10336, U.S. Nat. Mus.; about 

one-sixteenth natural size. 2, Left lower jaw of type (No. 10536), outer side view; about one-half natural size 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XLI 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Left scapula of Glyptotherium arizonae Gidley, 11. sp., type (No. 10536, U.S. Nat. Mus.). About one-third natural size. a, Outer side view; 

b, view from below 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XLII. 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Bones of Glyptotherium arizonae Gidley, n. sp. 1, Distal four caudal vertebrae of No. 10537, dorsal view, about one-fourth natural size; 2, right fore foot of type (No. 10536), plantar view, 

about one-half natural size; 3, right humerus, anterior view, about one-third natural size; 4, right fore arm and fore foot of type, outer side view, about one-third natural size 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 140 PLATE XLIII 

FOSSIL MAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Bones of Glyptotherium arizonae Gidley, n. sp., type (No. 10536, U.S. Nat. Mus.). 1, Right hind foot, plantar view, a little less than one- half 

natural size; 2, right tibia, fibula, and hind foot, inner side view, a little less than one-third natural size; 3, right femur, anterior view, a little 

less than one-third natural size 
U. s. GEOLOGICAL SURVEY PROFESSIONAL . PAPER 140 PLATE XLIV 

3 2 

FOSSIL :'\fAMMALS FROM SAN PEDRO VALLEY, ARIZ. 

Elements of tail sheath of Glyptotherium arizonae Gidley, n. sp., para type (No. 10537, U. S. Nat. Mus.). All about one-third natural size. 1, Terminal 

tube of tail sheath, dorsal view; 2, seventh ring of tail sheath, dorsal view; 3, sixth ring of tail sheath, dorsal view; 4, fourth ring of tail sheath, dorsal 

view; 5, anterior view of fourth ring of tail sheath with its corresponding vertebra and chevron in place