[SSN 0031-0204

Transactions and Proceedingsof thePalaeontological Society of Japan
New Series

No .

154

Palaeontologica l Society of Japan
June 30,

1989

Co-Editors

Hisayoshi Igo, Hiroshi Noda and Kei Mori
Editorial Board

Yoshikazu Hasegawa (Yokohama National University), Itaru Hayami (University of Tokyo),
Hisayoshi Igo (University ofTsukuba), Makoto Kato (Hokkaido University), Itaru Koizumi (Osaka
University), Yasumochi Matoba (Akita University), Kei Mori (Tohoku University), Hiroshi Noda
(University of Tsukuba), Kazushige Tanabe (University of Tokyo), Tsunemasa Saito (Yamagata
University), Kazuhiko Uemura (National Science Museum), Akira Yao (Osaka City University)

Officers for 1989-1990
President: Itaru Hayami
Honorary President: Teiichi Kobayashi
Councillors: Kiyotaka Chinzei, Takashi Hamada, Yoshikazu Hasegawa, Itaru Hayami,
Hiromichi Hirano, Hisayoshi Igo, Noriyuki Ikeya, Junji Itoigawa, Tadao
Kamei, Makoto Kato, Tatsuaki Kimura, Itaru Koizumi, Kei Mori, Hiroshi
Noda, Ikuwo Obata, Kenshiro Ogasawara, Tsunemasa Saito, Yokichi Takayanagi, Kazushige Tanabe, Hiroshi Ujiie
Members of Standing Committee: Kazushige Tanabe (General Affairs), Hiromichi Hirano(Finance), Hisayoshi Igo (Editor in Chief, TPPSJ), Hiroshi N oda, Kei Mori (Co-Editors,
TPPSJ), Noriyuki Ikeya (Planning), Kiyotaka Chinzei (Membership), Ikuwo Obata(Foreign Affairs), Yokichi Takayanagi (Editor, "Fossils"), Juichi Yanagida, Sumio
Sakagami (Co-Editors, Special Paper), Tatsuaki Kimura (Friends of Fossils)
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Auditor: Sakae O'Hara
The fossil on the cover is Phillipsia ohmorensis Okubo, an Early Carboniferous trilobite
from the Hikoroichi Formation in the Higuchizawa valley, Ofuna to City, Iwate Prefecture, northeast Japan (Collected by A. Haga, PAt 5766, X 3.0; after Kobayashi and
Hamada, 1980, pI. 6, fig. 4).
All communication relating to this journal should be addressed to the

PALAEONTOLOGICAL SOCIETY OF JAPAN
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Trans. Proc. Palaeont. Soc. Japan, N.S., No. 154, pp. 59-67, 3 Figs., July 30, 1989

875.

SILURIAN ORTHOCERATACEAE (MOLLUSCA: CEPHALOPODA)
FROM THE YOKOKURAYAMA FORMATION,
KUROSEGAWA TERRANE*SHUJI NIKO, T AKASHI HAMADA
Department of Earth Science and Astronomy, College of Arts and Sciences,
The University of Tokyo, Komaba, Tokyo 153
andTOSHIO Y ASUI
1764-1, Koda, Kochi City, 780

Abstract. Three Silurian orthoconic cephalopods are described from the G3 Memberof the Yokokurayama Formation in the Kurosegawa Terrane. These are; Kopaninoceras
kobayashii, sp. nov., which marks the first record of this genus in Japan, Protokionoceras
fessicancellallim Kobayashi, and Geisonoceratid, gen. et sp. indet. Conodonts associatedwith the cephalopod fauna indicate a late Wenlockian to early Ludlovian age.
Key words.

Orthocerataceae, Silurian, Y okokurayama Formation, Kurosegawa Ter-

rane

Kopaninoceras, Protokionoceras and an indeterminate form assignable to the family
Geisonoceratidae were found by one of us (T.
Y.). This new collection described herein
provides a new insight into the Silurian faunaof the Kurosegawa Terrane ..
The presence of orthoconic cephalopods in
the Mt. Yokokura area has been known since
1965 when Hirata reported the occurrence ofOrthoceras sp. from the Gomi quarry. Subsequently, Koizumi (1975) reassigned Hirata's
specimen to Kailiceras (?) sp., but the structure of siphuncle and organic deposits havenot been investigated. Furthermore, thisspecimen is too poorly preserved to determine
both its generic and specific assignment. In
1984, Kobayashi published the first detailed
description of the Yokokurayama cephalopod fauna including Michelinoceras
alticameratum Kobayashi, M. mizobuchii
Kobayashi, Arionoceras densiseptum

Introduction
The Middle Silurian to possibly late
Devonian Yokokurayama Formation consists essentially of un metamorphosed strata of
tuffaceous, arenaceous and calcareousdeposits, which form a huge xenolithic body
together with granitic and metamorphic
rocks. The linear arrangement of thesebodies extending over a more than 500 km
distance in an E-W direction forms the basis
to be defined collectively as the Kurosegawa
Terrane. The Middle to Late Silurian
sequence of the Yokokurayama Formation
has produced one of the most diverse middle
Paleozoic molluscan faunas in Southwest
Japan. During our field investigation of the
Mt. Yokokura area, four specimens of Silurian cephalopods representi ng the genera'Received May 23,1988; revised manuscript accepted
April 25, 1989
59

60

Shuji Niko et al.

Figure 1. Map showing the fossil locality in the Mt. Yokokura area, Kochi Prefecture.
segawa Terrane.

Kobayashi, Leurocyc!oceras (?) sp. indet.,
Orthocyc!oceras gomiense Kobayashi, O. aIr.
gomiense Kobayashi, Pl'Otokionoceras (?)
Jessicancellatum Kobayashi and two indeterminable cephalopods with a curved conch.
Abbreviations used in the text are as follows: UMUT, University Museum, the University of Tokyo; KGS, Laboratory of Geology, Faculty of Science, Kochi University;
and TYC, Toshio Yasui personal collection,
Kochi City.

Stratigraphy and fossil occurrence
The cephalopod fauna described herein
was collected from two limestone boulders(sample nos. YG3-3, 5) in a calclithite
exposed in the upper streams of the Shiroishi-Osawa in the Mt. Yokokura area, Ochi
Town, Takaoka County, Kochi Prefecture(Figure 1). The fossil locality is probably
the same as that found by Kobayashi (1984).
These limestones including the present cephalopods are characterized by the presence offibrous spar crusts in cavities and Renalcis(botryoidal calcareous algae), suggesting dep-

Ku: Kuro-

OSitIOn in a high energy, reef environment,
and lithologically belong to the bioclastic
grainstone. As pointed out by Kobayashi
and Hamada (1974, 1985), the boulders areprobably a derived mass from the wave resistant reef front to the fore-reef tal us. The
Yokokurayama Formation is more than 1,000m thick and is divided into the lower andupper, mainly acidic pyroclastic andtuffaceous sedimentary rock members (G 1G2, G4), and the middle, cliff-forming, limestone member (G3) (Hamada, 1959, 1961).
According to Yasui (1984), the base of the
Yokokurayama Formation abuts on theunderlying Yokokurayama granite.
The middle limestone member, from which
the cephalopod fossils were collected, is correlated with a middle Wenlockian to early
middle Ludlovian interval based on
conodonts (Kuwano, 1976, 1980), whereas its
trilobite fauna indicates a slightly younger
age, viz., late Wenlockian to middle (?) Ludlovian (Kobayashi and Hamada, 1985). We
found well-preserved conodonts in sample
YG3-5 that is accompanied by Protokionoceras Jessicancellatum Kobayashi and875.

Silurian Cephalopods from Mt. Yokokura

61

Geisonocerid, gen. et sp. indet. The conodont fauna dissolved from a 0.5 kg limestone
sample consists of a single element of Spathognathodus aff. sagitta bohemicus Walliser
and two elements of the coniform type (Walliserodus sp. and an indeterminate form). S.
sagitta bohemicus has been recorded frommany localities of the world and it is a valuable late Wenlockian to early Ludlovian indicator (e.g., Walliser, 1971). On the other
hand, the occurrence of Kopaninoceras in theother limestone boulder (YG3-3) suggests thetime span ranging from the Middle to Late
Silurian age. Although some reworked Ordovician conodonts were reported from thesame locality by Kuwano (1983), there are noevidence of any chronological inconsistency
between the examined two derived boulders
and the surrounding strata.

giving the diagnosis that "relatively widesiphuncle with a little inflated connecting
rings, relatively short living chamber, andelongated embryonic shell". However,
Kopaninoceras is distinguishable from allother genera in the family Geisonoceratidae,
including Geisonoceras, on account of its
relatively small siphuncle size and long septal
necks.
The genus Kopaninoceras has previously
been reported from Sardinia, Italy (Serpagli
and Gnoli, 1977), Czechoslovakia, Northern
Urals and Central Asia (Barskov and Kisselev, 1970; Barskov 1972), Xizang Zizhiqu(Chen, 1975), and southwestern China (Chen,
Liu and Chen, 1981). The range of theseknown specimens is either confined to theMiddle to Late Silurian age or questionably
has been extended up to the Early Devonian.

Systematic paleontology

Kopaninoceras kobayashii Niko, Hamada
and Yasui, sp. nov.

Superfamily Orthocerataceae M'Coy, 1844
Family Orthoceratidae M'Coy, 1844
Subfamily Michelinoceratinae Flower, 1945
Genus Kopaninoceras Kisselev, 1969

K opaninoceras Kisselev, 1969, p. 14 (fideBarskov and Kisselev, 1970); Barskov andKisselev, 1970, p. 66-67; Barskov, 1972, p.
39.
Michelinoceras (Kopaninoceras); Chen,
1975, p. 281; Chen, Liu and Chen, 1981, p.
18; Kobayashi, 1984, p. 244-245.
Type species: - Orthoceras jucundum
Barrande, 1870, Upper Silurian, Pridol Horizon, Czechoslovakia.
Diagnosis: - Shell large, orthoconic toslightly cyrtoconic with circular to subcircular cross section. Sutures straight andtransverse; shell surface frequently marked
by transverse lirae. Siphuncle small andsubcentral, with long, suborthochoanitic toorthochoanitic septal necks and cylindricalconnecting rings.
Remarks: - Dzik (1984) synonymized
the genus Kopaninoceras with Geisonoceras,

Figures 2-A, B

Material: - Holotype, UMUT PM 18256;
another poorly preserved specimen assigned
questionably to this species, TYC 002. Bothspecimens were obtained from sample YG33.
Diagnosis: - Kopaninoceras with moderately expanded orthoconic shell, circularcross section, and relatively short camerae forthe genus. Siphuncle small and somewhat
eccentric.
Description: - The holotype of Kopaninoceras kobayashii is a moderately expanded, incomplete phragmocone which is 65 mm
in length. The shell is orthoconic with acircular cross section, expanding from 5.3 mm
to 11.0 mm with the length of 53 mm.
Sutures were not observed but are assumed to
be transversal on the basis of observations inserially polished sections. Camerae are relatively short for the genus. Apically, approximately one and one-third camerae occupy alength equal to the apical conch diameter;

62

Shuji Niko et at .

875.

Silurian Cephalopods from Mt. Yokokura

adorally, this ratio increases to two. The
curvature of septa is relatively deep. The
vertical section at the dorsoventral planeshows a somewhat eccentric siphuncular position. The siphuncle is small, approximately
0.7 mm across at the adoral part, and is slightly constricted at the septal foramen. Septal
necks are long (approximately 2 mm at theadoral part) and orthochoanitic (Figure 2-B),
joined by thin cylindrical connecting rings.
Carbonate within camerae and the siphuncle
is inorganic.
Discussion: - Although the surface ornamentation of the holotype is unknown
because of the polishing of the specimen
through its siphuncle, its generic assignment
was made from the shell shape and the presence of relatively long camerae for the subfamily Michelinoceratinae, small siphuncle,
and long, orthochoanitic septal necks. This
specimen marks the first occurrence of thegenus in Japan.
Superficially, the shell morphology of
Kopaninoceras kobayashii resembles that ofK. ferganense Barskov (Barskov and Kisselev, 1970, pI. 3, figs. 4a, b, 5; Barskov, 1972,
pI. 2, fig. 15, pI. 3, fig. 1) from the Upper
Silurian rocks in Kirgizskaya S.S.R. However, K. ferganense has a larger ratio of thesiphuncular diameter to the corresponding
shell diameter than that of the present specimen.
Kopaninoceras jucundum (Barrande) (Barskov and Kisselev, 1970, pI. 3, fig. 2; Chen,
1975, pI. 4, figs. 3, 4, 7; Serpag1i and Gnoli,
1977, pI. 1, figs. la, b, text-fig. 3) describedfrom the Upper Silurian of Czechoslovakia,
northern Urals, Xizang Zizhiqu of China,
and Sardinia of Italy has a siphuncu1ar structure similar to that of the present species, but
it can be distinguished from K. kobayashii byhaving the longer camerae, a larger ratio of63

the siphuncular diameter to the corresponding shell diameter, and a less eccentric siphuncular position.
Etymology: - The trivial name honors
Dr. T. Kobayashi of the Japan Academy, for
his outstanding work on Paleozoic cephalopods.
Family Geisonoceratidae Zhurav1eva, 1959
Genus Protokionoceras Grabau
and Shimer, 1910

Protokionoceras Grabau and Shimer, 1910,
p. 58; Shimer and Shrock, 1944, p. 541;
Sweet, 1964, p. K237.
Type species: - Orthoceras medullare
Hall, 1868, Middle Silurian, Racine
Dolomite, Wisconsin.
Diagnosis: - Shell large, moderately
expanding orthocones with circular to subcircular cross section. Sutures straight andtransverse; shell surface with cancellate
markings produced by intersecting longitudinal and less prominent transverse striae
or 1irae. Siphuncle subcentra1 with shortand suborthochoanitic septal necks.
Remarks: - The genus Protokionoceras
was proposed by Grabau and Shimer (1910)
with Orthoceras medullare Hall as the typespecies, and is distinguised mainly from thegenus "Orthoceras" by having cancellate surface ornamentation. The internal structureof the type species has not been figured.
In addition to the Mt. Yokokura area, thegenus has been known from North America(e.g., Grabau and Shimer, 1910; Foerste,
1928), Norway (Troedsson, 1932; Sweet,1958), and East Australia (Teichert andG1enister, 1952), and it ranges from theMiddle Ordovician to the Middle Devonian.

~Figure 2. A, B, Kopaninoceras kobayashii, sp. nov. A, holotype, UMUT PM 18256, vertically anddorsoventrally polished section, X 3. B, partial enlargement of the siphuncle of Figure 2-A, X 10. C,
Geisonoceratid, gen. et sp. indet., TYC 001, vertically polished section, X 3. D, E, ProlOkionoceras
Jessicancellatum Kobayashi. D, topotype, UMUT PM 18257, vertical and dorsoventral thin section, venteron left, X 5. E, partial enlargement at the adoral end of the siphuncle of Figure 2-D, X 10.

Shuji Niko et al.

64

Protokionoceras Jessicancellatum Kobayashi
Figures 2- D , E; 3- A - D

1983

Protokionoceras (?) sp. nov.: Ko bayashi, p.

293.

1984

Protokionoceras (?) jessicance//atul11 Kobayashi , p. 249, 250, pI. 4, figs.3a , b.
1988 Protocycloceras (?) jessicance//alUl11 Kobaya-

shi , p.l.

Material : - Holotype, KGS 3587: The
specimen from the Yokokurayama Formation was originally designated as the holotype
by Kobayashi (1984). A specimen UMUT
PM 18257 from sample YG3 - 5 is herein
designated as the topotype.

Figure 3. Protokionoceras jessicance//alUl11 Kobayash i, LOpotype, UMUT PM 18257. A, dorsal
view, X 3. B, latera l view, venter on left, X 3. C, parti a l enl a rgement of th e shell surface, X 10. D, partial
enlargement of the denuded part of th e shell show ing latticework , x 10.

875.

Silurian Cephalopods from Mt. Yokokura

Description: - The present topotype ofProtokionoceras fessicancellatum is a longiconic orthocone approximately 49 mm inlength, the oral 22 mm of which is represented
by the body chamber. The cross section of
the shell is circular, expanding from 8.5 mm
to 13.0 mm in diameter over the length of thefragment. The shell surface is marked bynumerous longitudinal lirae with flattened
crests; the lirae are separated by interspacesof similar width and beaded by closely spaced
nodes which are crossed by slightly obliquetransverse lirae. The width of longitudinallirae shows some variation, and they rarely
adhere to adjacent lirae (Figure 3-C). A
fine lattice of lirae is recognizable at thedenuded part of the shell (Figure 3-D). On
the exfoliated portion of the shell, there is awrinkled layer on the internal mold. Suturesare straight and directly transverse. Camerae
are relatively short. Apically, approximately
two and one-half camerae occupy the length
equal to the apical conch diameter; adorally,
this ratio increases to approximately threeand one-half. The siphuncle is mediumsized, circular in cross section and slightly
removed to the dorsal side at the oral part.
Septal necks are short and suborthochoanitic; the last septal neck, however has acyrtochoanitic appearance at the dorsal side
(Figure 2-E). Connecting rings are homogeneous and somewhat thickening in the vicinity of the septal foramen. Siphuncular segments are constricted at the septal foramen;
there is a dorsal expansion of the rings into
the camerae. The maximum diameter of thesegments, located near the tip of septal necksin each segment, increases from 1.3 mm in themost apical camera to 1.7 mm in the mostadorad camera. Cameral deposits are mural.
Calcite within the siphuncle is difficult tointerpret due to recrystallization and solution.
Discussion:
The present specimen isconspecific with the type specimen that wasonce described by Kobayashi (1984) as Protokionoceras (?) fessicancellatum. The origi-

65

nal description of this species was based on asingle ill-preserved specimen, which was characterized by "slightly curved and more or lessbreviconic in adapical part" and the surface
ornamentation of "fine lattice of lirae". No
internal structure of the holotype was figured.
Although the "breviconic" appearance located only in the adapical part would indicate
an inordinate shell shape in the Orthocerida,
the diagnosis is probably due to the secondary deformation of the shell. Its ornamentation is virtually identical to the latticepattern in the denuded part of the shell of thepresent specimen. It can be concluded, bothfrom the external and internal structure of the
topotype, that the systematic position of thepresent species lies in the genus Protokionoceras (Geisonoceratidae), and thespecific concept should be amended to represent those characteritics of the topotype.
Recently, Kobayashi (1988) tentatively referred this species to Protothycloceras. However, this Early Ordovician genus possesses
prominent annulations which are not visibleon the shell surface of Protokionoceras fessicancellatum.
Protokionoceras fessicancellatum resembles
P. medullare (Hall) (Grabau and Shimer,
1910, fig. 1262; Foerste, 1928, pI. 69, fig. I, pI.
70, fig. 2; Shimer and Shrock, 1944, pI. 221,
fig. I ; Sweet, 1964, fig. 169, 7) which occurs
in the Racine Dolomite (Middle Silurian) of
Illinois and Wisconsin. However, the present species is distinguishable from the latterin having a more slender shell, finer longitudinal lirae and slightly oblique transverse
lirae.
Kionoceras styliforme Chen and Liu(Chen, Liu and Chen, 1981, pI. 8, figs. 1,6-8,
12, 15) from the Xiushan Formation (middle
Wenlockian) in Sichuan Province possesses
an interal structure similar to the examined
specimen except for the siphunclar position
and the shape of its connecting rings. The
Chinese form lacks some diagnostic charactesistics of the genus Kionoceras, and thus
its taxonomic position is in need of re-Shuji Niko et al.

66

examinations.
Geisonoceratid, gen. et sp. indet.
Figure 2-C

Descriptive remarks: - This figured
specimen (TYC 001) from sample YG3-5 isan imperfect fragment (approximately 33 mm
in length) of the orthoconic phragmocone,
which has a circular cross section, approximately 12 mm in diameter near the apical end.
Sutures were not observed but are assumed to
be transversal on the basis of observations inserially polished sections. Camerae are relatively short; three camerae occupy the length
equal to the apical conch diameter. The
siphuncle is subcentral with short and suborthochoanitic septal necks which are joined bycylindrical connecting rings. These rings areslightly constricted at the septal foramen.
The fragmentary nature and lack of data on
its surface ornamentation preclude the genericand specific assignment of the present specimen.
Acknowledgments

The authors wish to thank Dr. T. Kobayashi of the Japan Academy for his valuablesuggestions, and also Dr. H. Igo of the University of Tsukuba for identification of
conodonts and critically reviewing the manuscript. The first author in greatly indebted toDr. T. Nishida of Saga University for his
encouraging discussions and to Dr. I. S.
Barskov of Moscow State University, U.S.S.R.
for providing the literature used in this study.
We acknowledge the Japan Academy forpartial financial support toward this research.
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Gomi 1i~, Kochi ['i 1j 9:0, Kurosegawa ~ Wi )11, Ochi ~ 9:0, Shiroishi-Osawa BE*- if\,
Sichuan* [Z9)II, Takaoka ['ii1j[lIT], Xiushan* *LlJ, Xizang Zizhiqu* ®~Elft1IR, Yokokurayama (=Mt,Yokokura) h\'l;g-LlJ.
(*Chinese name)~Wi)II*, h\'l;g-LlJJ!!'i 7'.1' G0):/ /v !l-'*cMJE~ Orthocerataceae: ['ii1j9:0Jl1l-['ii1j [lIT]m~9:0IllJ{Ii\';g-LlJ
it!l:fg1ZO)~Wi)II*, h\'l;g-LlJJ!!'i (03 {fllJ!!'i) 7'.1, G~:j!§- G0 ) - A't(*I'.1;:!*~ L. t.: 4 @O):/ /v /v*cM
JE~1r.E~~~d::', OOf1'l-c·fi?OI\:g[I±l~c~lJ;tJ:IJ''':Jt.:~, Kopaninoceras O)-~;fi, K.

kobayashii ~%tr, Protokionoceras Jessicancellatum Kobayashi, Geisonoceratid, gen. et sp.
indet. 0) 3 ;fi~~5Jljgcmt L. t.:o IlifH=!=-t ~ ::1 / F':/ r 1r.Eft, ?.:I:.:/ P "' !l t!t~MIJ' G ':7 F' P
?t!tMM~~-to~~.~·~rn~±·'t(*.~Trans. Proc. Palaeont. Soc. Japan, N.S., No. 154, pp. 68-76,2 Figs., July 30, 1989

876. NUMMULITES AND ASSILINA FROM TANSEN AREA,
PALPA DISTRICT, THE NEPAL LESSER HIMALAYAS*KUNITERU MATSUMARU
Department of Geology, Faculty of Education, Saitama University, Urawa 338
and

HARUTAKA SAKAI
Earthquake Research Institute, University of Tokyo,
Yayoi I-I-I, Tokyo 113

Abstract. Middle Eocene (Lutetian) Nummulites beaumanti d' Archiac and Haime
and Assilina papillata Nuttall are described from the Bhainskati Formation (Kirthar Series),
Tansen Group in the Tansen area, Palpa district, the Nepal Lesser Himalayas. This is thefirst description of both species from Nepal. The specimens include only the megalospheric
form and their internal morphology is discussed. Two species are useful in establishing a
local and interregional correlation of marine Eocene strata. The paleoecology of the Nepal
nummulitid bed is briefly described.
Key words.

Nummulites, Assilina, Eocene, Nepal, Himalaya

beaumonti d' Archiac and Haime and Assilina
papillata Nuttall with a general discussion on
species described from the middle Kirthar(Lutetian) of Kutch, northwestern India andthe Middle Kirthar (Lutetian) of the Karachi
district, Pakistan, respectively.
The hypotypes of Nummulites and Assilina
and slides described herein have been deposited in the collections of Department of Geology, Faculty of Education, Saitama University. The specimens collected from the same
locality are deposited in the GeologicalMuseum of Department of Geology, Trichandra Campus, Tribhuvan University.

Introduction
Much information concerning the geology
and paleontology of the Nepal Lesser
Himalayas has been accumulated in the lastnineteen years (Hagen, 1969; Frank andFuchs, 1970; Hashimoto et al., 1973; Sharma, 1977; Sakai, 1982, 1983, 1985; Kimura
et al., 1985). Recently, the junior author,
one of Japan Overseas Cooperation Volunteers has undertaken the geological survey
around the Tansen-Palpa region, the Nepal
Lesser Himalayas from 1980 to 1983. In thecourse of the survey, he could collect shaly
limestone materials from the Bhainskati Formation (Kirthar Series), Tansen Group, andsubmitted them to the senior author for a
paleontological study. The present paper
contains an account of Nummulites

Fossil locality and notes on the geology

Nummulites beaumonti d'Archiac andHaime and Assilina papillata Nuttall arefound from a new locality in the western partof Tansen, in a Nummulites-bearing shaly'Received June 23, 1988; revised manuscript accepted May 22, 1989
68

876.

Nummulites and Assilina from Nepal

69

'S~C>
~S~;J
Riri
s~
~
2
BOlar

Kali Gandaki

83°45'

localities of Bhainskoti Fm.--oAmile Fm.------

Figure 1. Map showing the fossil locality of Nepal Nummulites and Assilina, and sketch-map of thegeology of the studied area. I, Sisne, Taltung and Dumri Formations; 2, Amile Formation; 3, Bhainskati
Formation; 4, Kali Gandaki Supergroup; MBT, Main Boundary Thrust.

limestone bed whose exposure extends fromthe upper stream of the Badahare-Amile River
to Taltung in the Tansen area, located midway between Pokhara and Butwal. The estimated position of this locality lies at Lat. 27'
50'N, Long. 83'20'E. (Figure I).
The Tansen area is situated in the Nepal
Lesser Himalayas, which is bounded by theMain Boundary Thrust from the subHimalayan Siwalik belt comprising Neogene
post-orogenic sediments in the south, and it isphysiographically divided into the Mahabharat Range and the Midland Range. Those
structually complex, unfossiliferous and poor
outcrop conditions of the Lesser Himalayas
have hitherto impeded progress of geologicalstudies.
The Lesser Himalayan rocks in the Tansenarea are grouped into two major stratigraphic
units, the Tansen Group and the Kali Gandaki Supergroup, by the junior author (1982,
1983, 1985), The Tansen Group consists of
the Gondwana and post-Gondwana rocks ofclastic sediments ranging in age from late
Carboniferous to Tertiary. This group is
separated from the underlying Kali Gandaki
Supergroup ranging in age from late Precambrian to early Paleozoic by a distinct uncon-

formity. The Tansen Group is subdivided
into the Lower Gondwana Sisne Formation(1020 m thick), Upper Gondwana Taltung
Formation (250 m), Amile Formation (230 to
300 m), Bhainskati Formation (160 to 200 m)
and Dumri Formation (100 to 725 m) inascending order, based mainly on paleontological and lithostratigraphic evidence (Figure. 2). The Nummulites-bearing shaly limestone bed treated in the present study is included in the Bhainskati Formation, which isespecially unique and important formation in
the Lesser Himalaya because of the presenceof fossiliferous beds yielding Nummulites
beaumonti d' Archiac and Haime, Assilina
papillata Nuttall, Asteracantus sp., landmammals, Teleostei, Chelonia and Trionichidae (Sakai, 1983). Furthermore, theBhainskati Formation is sandwiched between
the Cretaceous to probable Palaeocene Amile
Formation consisting of thick massive quartzose sandstones and the Oligocene to possible
early Miocene Dumri Formation comprisinga series of fluvial sandstones intercalated withshale.

Kuniteru Matsumaru and Harutaka Sakai

70

Paleoecology of the nummulitic shaly limestone or limy shale bands of the Bhainskati
Formation of the studied area
As seen in the stratigraphic succession of
the studied area (Figure 2), the Bhainskati
Formation overlies the Amile conformably
and is composed of a black shale which intercalates both molluscan fossil beds and nummulitic shaly limestone or limy shale bands inthe lower part. In the upper part, the Bhainskati consists of a red-purplish and green

Dumri(Oli ocene)

Bhainskati(Eocene)Amite

1!lllt(Late
Cret.
- Palaeocene)~

100

Tattung(Early Cret.)

1[]2~3~4§5.6B

7rnm 81§19§1~
Figure 2. Map showing the stratigraphic
succession of the Amile, Bhainskati and Dumri
Formations, and nummulitic bed (N). I, quartzose
sandstone; 2, Sandstone with shale interbeds' 3
bioturbated mudstone; 4, siltstone; 5, black sh~le;6, limestone; 7, variegated shale with oolitic
hematite; 8, red shale; 9, green shale; 10, mollus·
can fossil beds.

mottled shale, molluscan fossil beds andoolitic hematite, and is disconformably overlain by the thick fluvial sandstones of the
Dumri Formation. In the lower part of the
Bhainskati, the interbedded limestone or limy
shale bands indicate shallow warm marine
conditions with the precipitation of carbonate rocks. This interpretation is conformable to a paleolatitude estimate of 10 ±6 S for the uppermost part of the Bhainskati
Formation, based on the paleomagnetic study(Y oshida and Sakai, 1984).
In the Surkhet valley of western Nepal, 200
km further west of the Tansen area treated inthis paper, Tewari and Gupta (1976) described a larger foraminiferal assemblage
from a limestone of the Subathu Formation,
including Assilina cf. granulosa (d'Archiac),
A. leymeriei (d'Archiac and Haime), A.
granulosa var. chhumbiensis Gill, A. subdaviesi Gill, Nummulites cf. mamilla (Fichtel
and Moll), N. atacicus Leymerie and N.
djokjokartae (Martin).
In this paper, the nummulitic limestone of
the Subathu Formation, which is correlatedwith the Laki Formation of Pakistan(N uttall, 1925), is interpreted to be indicativeof shallow marine conditions where abundantly available carbonates led to the formation of nummulitic and other larger foraminiferal limestones. Although the Bhainskati Formation cannot directly be correlatedwith the Subathu Formati.on on the basis of
the larger foraminiferal fauna. Nummulitic
beds of both formations are similar in lithologic character and the paleoecological condition is referred to be shallow marine forboth of them.
00

Description of species
Family Nummulitidae de Blainville, 1825
Genus Nummulites Lamarck, 1801
Nummulites beaumonti d'Archiac and Haime
Figures 5-1-14

876.

Nummulites and Assilina from Nepal

1853

Nummulites heaumanti d'Archiac and Haime,
p. 133, pI. 8, figs. la-e, 2-3.
1926 Numm.,ulites heaumanti, Nuttall, p.130-131,
pI. I, figs. 4-5.
1940 Nummulites heal/monti, Davies, p. 206-209, pI.
9, figs. 1-9.
1959 Nummulites heaumanti, Nagappa, p. 180, pI. 8,
figs. 15-17; pI. 9, figs. 1-2.
1965 Nummulites heaumanti, Sen Gupta, p.91-93,
pI. 15, figs. 1-2, 5; pI. 16, figs. 3, 7,9-10; pI.
17, figs. 1,5-7,12.
1972 Nummulites heal/monti, Blondeau, p. 149, pI.
24, figs. 11-14.
1981 Nummulites heaumanti, Schaub, p. 135-136,
pI. 53, figs. 17-19, 22-25, tab. 14-p.

Description: -The test is small, thickly
lenticular to biconvex, regularly sloping andsometimes depressive in the umbo. The
sutures are visible as faint lines of radiating
septal filaments near the surface. The spherical to subspherical protoconch is followed bya reniform deuteroconch of second chamberand both chambers are followed by closel;
coiled whorls. The septa are straight, orslightly curved, usually near the distal end.
The spiral wall is thick. The axial plugs arecomposed of radiating columns of shell materials. The measurements are given as follows:

71

Stratigraphic horizon: -A 5 to 10 cm
thick shaly limestone bed bearing Nummulites beaumonti and Assilina papillata
lying about 50 m above the base of the Bhain:skati Formation (Kirthar Series), TansenGroup.
Geological age: -Middle Kirthar, Middle
Eocene (Lutetian).
Remarks: -As seen in the equatorial andaxial sections of this form from the Tansenarea, its small protoconch, a tight coiling ofspiral wall, rhombic style of chamber form
and regularly straight and radial septa are th~same as those in Nummulites beaumonti d'Archiac and Haime from Egypt, Lybia, andthe type area of the Lower Tertiary rocks of
the Pakistan-I ndian region (d' Archiac andHaime, 1853; Nuttall, 1926; Davies, 1940;
Nagappa, 1959; Sen Gupta, 1965 andothers). Although isolating the Tansen specimens from the matrix for the examination of
their surface markings was difficult, oblique
and tangential sections of this form show
radiating and regularly curved septal
filaments, and nonpapilate surface. Thesefeatures have already been observed in figuresof Nummulites beaumonti d' Archiac andHaime by some of the authors stated above.

Diameter (mm), 2.3-3.3; thickness (mm), 1.6-2.2; form ratio, I: 1.4-1: 2.0
Protoconch (inner diameter, J1), 90-136; protoconch (outer diameter, J1), 126-167
Number of whorls, 7 1/2-8
Number of chambers in whorls (one specimen shown on Figure 5-13)
Whorls

I

2

3

4

5

6

7

Chambers

13

25

34

38

41

44

42

I 7 1/2
I 36

Rate of growth of whorls (4 specimens measures, J1)
Whorls

I

2

3

4

5

6

7

8

Height range

197286340391442525609656782
816

95296611501187

1360

mean

247.5

365.5

494.3

630.8

797.3

960

1149.3-Thickness of spiral lamellae (4 specimens measured, J1)
Whorls

I

2

3

4

5

6

7

8

range

26-J4

24-40

34-48

36-54

36-54

36-60

40-54

44

mean

29.5

33.5

41.5

43.5

46.7

45.3

48

-

Kuniteru Matsumaru and Harutaka Sakai

72

2600

Radiusin ~Radius
in ~

1800

j

i j
i ii 11i ; 1
i i 11i ; 11

I

j

2200

j

i
i

i

i

1400

i

1000

i

i

i

i

/

/

i

i

I ;

600

!

ib
K3)!

1800

; I

i

/

. . . . ,1
/

1
1(1)
1

ii

iI

14

I. .I
i
i. /i

I

I.

I. ./
. /

i
(5)

i

;
i
I
i ii
i

1000

i

/

i

,I

600

200

23456789
Number of Whorls
Figure 3. Spira-diagram of Nummulites
beaumonti d' Archiac and Haime from (I) slide 18,(2) slide 14, (3) slide 2 (including a specimen of
Figure 5-13), (4) slide 2 of the Nummulites bed of the
Bhainskati Formation, Nepal and (5) one based on
the average of 5 specimens from the Lutetian of
Kutch, India (Sen Gupta, 1965, fig. I), respectively.

2 3 4 5 6
Number of Whorls
Figure 4. Spira-diagram of Assilina papillata
Nuttall from ( I) slide 6 of the Nummulites bed of the
Bhainskati Formation, Nepal and (2) slide C31455/
3 and (3) slide C31455/2, both from the Middle
Kirthar (Lutetian) of Karachi District, Pakistan(Schaub, 1981, pI. 97, figs. 3-4), respectively.

~
Figures 5.1-14. Nummulites beaumonti d'Archiac and Haime, 1-3. Axial sections. The axial plug
is very conspicuous in a specimen of 2; 4-7. Oblique sectitons. The radial septal filaments are shown inthe central part near the surface of test of 7; 8-12, 14. Tangential sections. 13. Equatorial section. IS-16. Assilina papillata Nuttall, IS. Axial section. The whorls are not embracing to the umbonal regionof test.; 16. Equatorial section. All figures X 16, except X 30 of 13.

876.

Nummulites and Assilina from Nepal73

74

Kuniteru Matsumaru and Harutaka Sakai

As shown in Figure 3, the spira-diagram of
Nummulites beaumonti from the Nummulites
bed of the Tansen area shows that ontogenetic
growth curves of coiled whorls of specimens
are more tightly than those of Nummulites
beaumonti d' Archiac and Haime from theMiddle Eocene (Lutetian) of Kutch, western
India (Sen Gupta, 1965). Sen Gupta (op.
cit., p. 92) has once considered that Nummulites beaumonti d' Archiac and Haime may
be a species showing much variation not only
in external shape and size, but also in internal
structure. Thus, difference between ontogenetic growth curves from Tansen specimens
and Kutch ones shown in Figure 3 can beconsidered as a species variation of Num-

mulites beaumonti.
De la Harpe (1883, p. 166) once indicatedthat there is a shade of difference among thethree species, Nummulites beaumonti d' Archiac and Haime, N. discorbinus (Schlotheim) and N. striatus Bruguiere, on the view
point of a tight coiling of spiral wall, chamber form and septa. This problem will be
discussed near future.
Sen Gupta (1965) considered Nummulites
pengaronensis Verbeek, N. stamineus Nuttall
and N. kelatensis (Carter) to be a synonym of
N. beaumonti d'Archiac and Haime. Afterall, Sen Gupta identified Nummulites
stamineus Nuttall as a synonym of N.
beaumonti d' Archiac and Haime, because heconsidered that the figures- of N. beaumonti
published by Davies (1940, pI. 9) are closely
related to those of N. stamineus. Meanwhile, Smout (1954) considered Nummulites
stamineus from Qatar as a synonym of N.
discorbinus (Schlotheim), and he retained N.
beaumonti as a valid species. Sen Gupta(1965) considered that although there is some
confusion about the identity of Nummulites
kelatensis of Carter (1861), N. kelatensis is
closely connected with N. beaumonti. The
present authors consider that the forms from
Timor described as Nummulites kelatensis
Carter by Henrichi (1934, p. 30-32) aredefinitely N. beaumonti, based on the increas-

ing whorl, regular spacing of the septa andpolar plug.
Sen Gupta (1965, p.93) described that
another synonym of Nummulites beaumontid'Archiac and Haime is N. pengaronensis
Verbeek. He mentioned as the typical features of Nummulites beaumonti are a tightcoiling of spiral wall, which is almost uniformly thick, and small embryonic chambers.
He also noted that these features are clearlyrecognized in the figures of N. pengaronensis
by Cole (1957).
Doornink (1932) reported in detail theoriginal descriptions of Nummulites pengaronensis from Borneo by Verbeek (1871) andN. nanggoelani from Java by Verbeek (1891),
in addition to Vlerk's description and illustration of N. pengaronensis (1929, p.20-21,
figs. 12, 35a-b). He concluded that Nummulites pengaronensis is the megalospheric
form and N. nanggoelani is the microsphericof the former. Doornink has the same opinion as Douville (1912) on this matter. Cole
(1957) identified both megalospheric andmicrospheric specimens from the Eniwetok
Atoll under the name Camerina pengaronensis (Verbeek), and Hashimoto et al. (1979)
and Hashimoto and Matsumaru (1981) reported Nummulites cf. pengaronensis from
Philippines, respectively. However, nobody
except Sen Gupta identified Nummulites pengaronensis as a synonym of N. beaumonti.
Gen us Assilina d'Orbigny, 1839
Recently, Hottinger (1977) included thegenus Assilina in the Operculina d'Orbigny,
1826, based on the similarity of structures ofstolons and canal systems in the wall of test.
Schaub (1981) regarded the Assilina to be thesubgenus of Operculina, being accepted with
Hottinger's opinion. The authors do nothave any data about the wall structures ofAssilina specimens from Nepal, but regard as
the Assilina having the peculiar characters of
evolute form and straight septa, following aclassification of Blondeau (1972).

876.

Nummulites and Assilina from Nepal

Assilina papillata Nuttal

75

Nuttall.

Figures 5-15-16

Acknowledgments
1926

Assilina papillata Nuttall, p. 144, pI. 6, figs. 57b.
1926 Assilina subpapillata N ultall, p. 145, pI. 6, figs.
2-3a.
1940 Assilina papillata, Davies, p. 214, pI. II, figs. I,
3,6,8,10-12b.
1959 Assilina papillata, Nagappa, p. 178, pI. 5, fig. 2.
1981 Assilina papillata, Schaub, p.205-206, pI. 96,
figs. 26-39; pI. 97, figs. 1-6, 8-12.

Description: -The diameter of the specimens would be more than 5 mm from theincomplete portions of the available sections
in measurement. The thickness of the specimens through the centre of test is from 0.9 to
1.1 mm. The openi ng of the spire shows
evolute form. The test is composed ofapproximately 5 volutions, with 7 chambersin the first whorl and 22 chambers in the 4th
whorl. The chambers are higher than broad.
The chamber walls are evenly and regularly
straight, and are radial with a sharp curvature
at distal ends. Transverse sections show themarginal cord with well developed pillar
structures at the whorl junction. The chambers in transverse sections much higher thanbroad and typically tapering in shape.
Stratigraphic horizon: -The same bed as
Nummulites beaumonti d' Archiac andHaime.
Geological age: -Middle Kirthar, Middle
Eocene (Lutetian)Remarks: -Although uncertainty of
specific identification may exist in dealing
with material of this type, these specimens arereferred to Assilina papi/lata Nuttall on thebasis of descriptions and illustrations given
by other workers stated above. There areagreements in the peculiar curve of the spiradiagrams between only one investigated specimen from Nepal and those of Assilina papillata from the Middle Kirthar in Gandbo Hill,
northwest Karachi, Pakistan (Schaub, 1981),
as shown in Figure 3. Therefore, the present
form is identified with Assilina papillata

Thanks are due to Dr. A. Blondeau, 44 rue
d'Aumale, 60500 Chantilly, France, for reading and criticizing the typescript; to Dr. K.
Kanmera of Kyushyu University, for kindlytransfering the fossil materials from the junior
to the senior author; and to Mr. A. Hayashi
of Seiryo High School, for providing inval uable technical assistance. The authors are
grateful to Dr. M. P. Sharma, Chairman of
Department of Geology, Tribhuvan University, and Mr. J. M. Tater, Deupty Director
General of Department of Mines and Geology, Nepal for their kind help and valuablesuggestions.

References
Archiac, A. d' and Haime, J., 1853; D'une monograph des Nummulites. Description des animauxfossiles du groupe nummulitique de l'lnde.
Gide et Baudry (editeur), Paris, vol. I, p. 1-373,
pIs. I-II.
Blondeau, A., 1972: Les Nummulites. VlIibert,
Paris, p. 1-25, pIs. 1-38.
Carter, H.J., 1861 : Further observations on the structure of Foraminifera and on the larger fossilized
forms of Sind, etc., including a new genus andspecies. Ann. Mag. Nat. Hist., Ser. 3, vol. 8, p.
309-333,366-382,446-470, pIs. 15-17.
Cole, W.S., 1957: Larger Foraminifera from Eniwetok Atoll driil holes. U.S. Geol. Surl'.,
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vol. 96, p. 199-230, pIs. 9-12.
Doornink, H.W., 1932: Tertiary Nummulitidae from
Java. Verhandl. Geol. Mignb. Genootsch. Ned.
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Denksch Schweiz. Naff. Ges., vol. 86, no. I, p. 1-

76

Kuniteru Matsumaru and Harutaka Sakai

185.
Harpe, de 1a., 1883: Monographie der in Agypten
und der libyschen Wuste vorkommenden Nummuliten. Paleontographica (n. s.), vol. 30, p.
155-216, pis. 30-35.
Hashimoto, S., Ohta, Y. and Akiba, C. (eds), 1973:
Geology of the Nepal Himalayas. Saikon
Publ .• Sapporo, p. 1-292.
Hashimoto, W., Kitamura, N., Balce, G.R., Matsumaru, K., Kurihara, K. and Aliate, E.Z., 1979:
Larger Foraminifera from the Phillipines. Part
X. Stratigraphic and faunal breaks between the
Maybangain and Kinabuan Formations in the
Tanay Region, Rizal, Philippines. Geol.
Palaeont. Southeast Asia, vol. 20, p.143-157,
pis. 30-35.
- - and Matsumaru, K., 1981 : Larger Foraminiferafrom the Philippines. XII. Eocene Limestone
from Southern Luzon. Ibid., vol. 22, p.63-73,
pis. 14-15.
Henrichi, H., 1934: Foraminiferen aus dem Eozan
und Altmiozan von Timor. Palaeontographica.
Suppl.-Band 4, p. I-56, pis. 1-4.
Hottinger, L., 1977: Foraminiferes operculiniforms.
M~m. Mus. Natl. Hist. Nat. (Paris), C. Sci. dela Terre, vol. 40, p. 1-159, pis. 1-66.
Kimura, T., Bose, M.N. and Sakai, H., 1985: Fossil
plant remains from Taltung Formation, Palpa
District, Nepal Lesser Himalaya. Bull. Nat.
Sci. Mus., vol. 11, no. 4, p. 141-150, pis. 1-3.
Nagappa, Y., 1959: Foraminiferal biostratigraphy of
the Cretaceous-Eocene succession in the IndiaPakistan-Burma region. Micropaleontology, vol.
5, no. 2, p.145-192, pis. I-II.
Nuttall, W.L.F., 1925: The stratigraphy of the Laki
Series (Lower Eocene) of parts of Sind andBaluchistan, India with a description of Larger
Foraminifera contained in these beds. Quart.
Jour. Geol. Soc., vol. 81, p. 417 -453.
--,1926: The zonal distribution and description of

the Larger Foraminifera of the middle and lower
Kirthar Series (Middle Eocene) of parts of western India. Rec. India Geol. Survey, vol. 59, p.
115-164, pis. 1-8.
Sakai, H., 1982: Geology of Tansen Group in theLesser Himalaya, western Central Nepal. Tribhuvan Univ .• Technical Rep. Kathmandu, no. I,
p. 1-111.
- - , 1983: Geology of the Tansen Group of theLesser Himalaya in Nepal. Mem. Fac. Sci .•Kyushu Univ .• Ser. D, vol. 25, no. I, p.27-74.
- - , 1985: Geology of the Kali Gandaki Supergroup of the Lesser Himalayas in Nepal. Ibid.,
vol. 25, no. 3, p.337-397.
Sharma, C.K., 1977: Geology of Nepal. Educational Enterprises. Kathmandu, p. 1-164.
Sen Gupta, B.K., 1965: Morphology of some key
species of Nummulites from the Indian Eocene.
Jour. Paleont., vol. 39, no. I, p. 86-96, pis. 15-17.
Shaub, H., 1981: Nummulites et Assilines de 1aTethys Paleogene. Taxinomie, phylogenese etbiostratigraphie. M~m. Suisses de Paleontologie, vol. 104, p. 1-236, 18 tabs; vol. 105, AtlasI, pis. 1-48; vol. 106, Atlas II, pis. 49-97.
Smout, A.H., 1954: Lower Tertiary Foraminifera of
the Qatar Peninsula. British Museum (Nat.
Hist.), London, p. 1-96, pis. 1-15.
Tewari, B.S. and Gupta, V.J., 1976: Foraminiferafrom the Subathu Formation, Surkhet Valley,western Nepal. Himalayan Geology, vol. 6, p.
209-216, pI. I.
Vlerk, I.M., van der., 1929: "Groote" Foraminiferen
van N.O. Borneo. Wetensch. Med., no. 9, p. 143, figs. I-51.
Yoshida, M. and Sakai, H., 1984: Some observationon the paleomagnetism of Tansen Group, west
Central Nepal. Jour. Nepal Geol. Soc., vol. 4,
Special Issue, p.53-61.

* /~ -Iv 'j' I::: ~ '7 -V UJ~/~ Iv /~:l!!!:n!J :/ -l! :/ :l!!!~g[ Nummulites :to J: Lf Assilina: 1:: ~:l!!!~(J) =f-lv!J -Iv~/~ -1 :/ ;<.. 7J 7- ~JI '/:), i? iW1Hl Nummulites ,I;:to J: Lf Assilina ,I; a-:f*~1..., ~1Lfi.jjIij*t:::. "?~ '-C-'t n.:fn beaumonti fl, papillata fla-ll'iJJ:E 1..., --'t n i? a-iW;J:f:t:::.~'i!rvn't..: (mij:j:, 1982,1983)0 4-@], jjIij::lSfijjlijflt:::,"?~'-c~1ta-rr~', ft!!.flrI3H:(J)Il'iJ¥g

A::lS t:::. "?~ '-C ~ ~~ 1... t..:o .: nfi* /~ -Iv t:::.~.lb i?n 7.J jjlijflt:::. "?~ '-C (J)JilfJJ(J)~1t~rii::>t""("~7.Jo jjlijflg[lliJl(J)~~~~M.KMnko

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 154, pp. 77-95, 7 Figs., June 30, 1989

877.

ON THE GENUS PLICATOUNIO (CRETACEOUS
NON-MARINE BIVALVIA) FROM KOREA*SEONG- YOUNG YANG
Department of Earth Science, Kyungpook National University
Daegu 702-701, Korea

Abstract. Fossils of PlicalOunio were collected from ten localities including thetype-locality of the type-species, Plicatounio (Plicatounio) naktongensis, all of which lie inthe Hasandong Formation, Gyeongsang Group in Korea, and in addition, from two localities in the Wakino Subgroup and the Mifune Group in Japan.
This paper reviews the type species with special stress on the hinge structure. The
cren ulation on the postero-Iateral hinge teeth is an original character and the presence orabsence of it depends on the state of fossil preservation. Two new species, P. (P.) okjuni
and P. (P.) yooni, are proposed.
Key words.

Cretaceous, P/icatollnio, non-marine, bivalve, Gyeongsang Groupdeposited in the University of Tokyo. I haverecently found several localities of the genus
including the type-locality of the type-species
and made a fairly large collection. And I
have had opportunities to visit the fossil
locality at Rikimaru, Fukuoka Pref. northern
Kyushu, and the locality at Kosa Town,
Kumamoto Pref., central Kyushu, Japan andcollect fairly good specimens and observed
also the collections deposited at Fukuoka
University of Education and at Kumamoto
University during my stay in Japan (19731975).
In this paper, I report the resul t of my study
on Plicatollnio naktongensis with special
stress on the hinge structure and discuss theclassification of the genus by comparison withother relevant species, proposing two new
species from the lower Gyeongsang Group,
Korea.
This study was undertaken with the aid ofgrants from KOSEF (Korea Science & Engineering Foundation, 1984). I express mysincere gratitude to Emeritus Professor Tatsuro Matsumoto of Kyushu University andIntroduction
Since the genus Plicatollnio was erected by
Kobayashi and Suzuki (1936) based on P.
naktongensis from the lower Gyeongsang
Group, Korea, many species have been reported from the Cretaceous non-marine deposits
in the Asian Continent (Hoffet, 1937; Yabeand Hayashi, 1938; Ota, 1959; Hase, 1960;
Maeda, 1962; Kobayashi, 1963; Martinson,
1965; Kobayashi, 1968; Gu and Ma, 1976;
Guo, 1981 and 1986; Tamura, 1982;
Kobayashi, 1984) and even northern Africa(Mongin, 1963). The present genus, thus has
been considered to be one of the most important non-marine bivalve genera in the late
Mesozoic together with the genus Trigonioides.
However, the internal structure of the typespecies, Plicatollnio (P.) naktongensis, was
not sufficiently known, and the original specimens are now missing except for several paratypes and a gypsum mould of the holotype"Received September 6, 1988; revised manuscript
accepted May 1, 1989
77

78

Seong-Young Yang

Emeritus Curator Dr. Norman D. Newell of
the American Museum of Natural History for
their continuous encouragement and criticalreading of the first draft of this paper. My
sincere gratitude is extended to Professor
Minoru Tamura of Kumamoto University
and to Emeritus Professor Yoshihisa Ota of
Fukuoka University of Education who kindly showed me their collections and guided me
to fossil localities. I am also indebted to Mr.
Seung-Soo Lee, one of my graduate studentsof Kyungpook National University for his
invaluable help in field and laboratory.
Brief review of previous works on
Plicatounio1) Kobayashi and Suzuki (1936) reported
Plicatounio naktongensis as a new genus anda new species based on several specimensfrom Yangpori, southern Korea. Its diagnostic characters were considered to be asymmetrical elongate outline, 4 or 5 plicae on theposterior part, and a hinge plate withcrenulated pseudocardinal teeth and lamellar
postero-Iateral ones. They also reported P.
triangularis as another new species from
Rikimaru, northern Kyushu, Japan. After
that, however, Kobayashi (1956) excluded itfrom Plicatounio.
2) P. sllzukii and P. maximliS werereported by Hoffet (1937) from a middle
Cretaceous formation at Muong-Phalane,Laos.
3) Yabe and Hayashi (1938) reported P.
naktongensis manchuricliS from about 70 km
northeast of Hoten (= Shen-yang), northeastern China.
4) Suzuki (1943) reported P. naktongensis multiplicatus from near Jinju, southern
Korea, pointing out as its subspecific character the fine radial ribs on the anterior andmiddle parts besides 4 or 5 posterior plicae.
5) Ota (1959) first described the hinge
structure of the genus in detail and reported
P. kwanmonensis as a new species. He
pointed out the hinge structure of P. nakton-

gensis with three crenulated pseudocardinals
on the right valve, two on the left valve; andwith two lamellar postero-Iateral ones on theright valve and one or two on the left valve.
That of P. kwanmonensis is distinguished bycren ulated postero-Iateral 0 nes. S u bseq uen tIy, Ota (1963) proposed the subgenus Kwanmonia for P. kwanmonensis and redescribed
the hinge structure of Plicatounio to possess
five hinge teeth on both valves, showing thedifference between Plicatounio (P.) andKwanmonia. The former has lamellar while
the latter has crenulated postero-Iateral teeth.
6) Maeda (1962) reported P. kobayashii
and P. tetoriensis from the upper formation of
the Tetori Group, northwestern part of central Japan.
7) Ku (1962) reported Plicatounio ex. gr.
suzukii and Plicatounio sp. from the late
Cretaceous non-marine formation, Yunnan,
China.
8) Mongin (1963) described P. flattersensis from a Cretaceous formation, Sahara,
northern Africa.
9) Martinson (1965) reported P. naktongensis and P. klaudziensis from Cretaceous
non-marine deposits, Fergana, U.S.S.R.
10) Kobayashi (1968) proposed a new
family Plicatounionidae based on Plicatounio
and described P. namphungensis from Nam
Phung dam site, Thailand.
II) Gu and Ma (1976) .reported many
species from Cretaceous non-marine depositsof China as follows: P. naktongensis, P.
multiplicatus, P. tetoriensis, P. manchuricus,
P. sp. aff. P. suzukii, P. equiplicatus, P.
zhejiangensis, P. jujianensis, P. latiplicatlls,
P. subrhombicus, P. (Kwanmonia) heilongjiangensis.
12) Guo (1981) described P. (P.) rostratus from Cretaceous deposits, Yunnan,
southern China.
13) Tamura (1981) considered that Ota's
P. "naktongensis" from the Wakino Subgroup, Japan should be excluded from P.
naktongensis from southern Korea on
account of the difference in the postero-Iateral

877.

On the genus Plicatollnio

teeth, i.e., with or without crenulations.
14) Guo (1986) described Plicatounio(Enotrigonioides) alatlls from the upper member of the lower Cretaceous Jingxing Formation, west Yunnan, China.
As briefly reviewed above, the genus
Plicatounio has been reported from worldwide localities with many species and some of
the authors (Kobayashi, 1968, 1984; Guo,
1981, 1986) have eval uated as representing a
distinctive family, but the hinge structure of
the type-species of the genus Plicatollnio,
Plicatollnio (s.s.) naktongensis has not been
fully described yet.

Material and localities
The fossils at hand were collected from thefollowing ten localities, all of which fallunder the Hasandong Formation, the 2nd
formation in ascending order, of the Gyeongsang Group.
Loc. 1 : Yangpori, Jingyo-myeon, Hadonggun, Gyeongsangnam-do (type-locality of
Plicatollnio naktongensis) (Figure I-B).
This locality is in the upper part of the
Middle Hasandong Formation which is composed of an alternation of dark grey limy
siltstones and fine-grained sandstones intruded by andesitic dykes (Figure I-B). Here,
Brotiopsis spp. (Cretaceous non-marine gastropods) occur gregariously forming layers at
7 horizons, of which the 2nd and 4th containoccasionally Plicatounio naktongensis andTrigonioides (T.) kodairai.
Loc. 2: At an island about 200 m southeastof Loc. I (Yangpori) (Figure I-B). The
Brotiopsis beds are more than 12 in number
and lithology is similar to that of Loc. I.
Loc.2 also falls within the upper part of the
Middle Hasandong Formation. Among the
12 fossiliferous horizons, PlicatOllnio naktongensis has been collected from the 3rd and 5th
beds.
Locs. 3 and 4: At a beach near Impo,
Hwanggeumri, Golyak-myeon, Jeolanam-do(Figure I-O). The outcrop of these local-

79

ities consists of grey fine-grained sandstone orsiltstone alternated with medium-grainedsandstone, which lies within the middle partof the Middle Hasandong Formation (Figure2). The fossiliferous bed is about 10 cm inthickness. It contains Wakinoa sp., Pseudohyria sp. and Brotiopsis sp. as well as
Plicatollnio (P.) yooni, n. sp. (described
below).
Loc. 5: At a beach near Sumoondong,
Keumnam-myeon, Hadong-gun, Gyeongsangnam-do (Figure I-C) (type-locality of
Trigonioides kodairai). The rock exposed at
this locality consists of greenish grey finegrained sandstone and siltstone alternatedwith medium- to coarse-grained sandstones,
which fall under the upper part of the Middle
Hasandong Formation (Figure 2). From
here, Plicatounio yooni (described below) and
Trigonioides kodairai have been collected.
Loc. 6: At a beach about 200 m south toHanchi, Sumoondong, Keumnam-myeon,
Hadong-gun, Gyeongsangnam-do (Figure 1C} ... This locality is represented by an alternation of light greenish grey siltstone andfine- to medium-grained sandstone, within the
middle part of the Middle Hasandong Formation (Figure 2). Here also, Plicatollnio naktongensis is associated with the crowded
Brotiopsis sp. There are at least 8 Brotiopsis
beds among which the 4th and 7th beds
contai n P. naktongensis.
Loc. 7: A channel outcrop at Yusuri,
Nadong-myeon, Jinyang-gun, Gyeongsangnam-do (see Yang, 1983 text-fig. 5). The
rock exposed at this locality consists of lightgreenish grey siltstone and fine- to mediumgrained sandstone within the upper part of
the Upper Hasandong Formation (Figure 2).
Here Plicatollnio naktongensis has been collected together with Trigonioides (T.) jaehoi.
Loc. 8: On a mountain side about 700 m
south of Bulnodong, Hyoryeong-myeon,
Kunwi-gun, Gyeongsangbuk-do (Figure 1A). Lithology at this locality is composed ofsiltstone and fine-grained sandstone within
the upper part of the Middle Hasandong

80

Seong-Young Yang

~5l~-+--I-+-+

8

1

Figure 1. Geological maps around the fossil localities. 1. Metamorphic rocks (Precambrian), 2.
Yeonhwadong Fm., 3. Hasandong Fm., 4. Dongmyeong Fm., 5. Bulguksa granodiorite, 6. intermediate tobasic dykes, 7. Alluvium, 8. Fossil locality with locality number.

Formation. Here, Plicatounio (P.) okjuni(described below) and P. (P.) sp. cf. P. (P.)
yooni, n. sp. (described below) have beencollected together with Wakinoa sp. cf. W.
tamurai, Nagdongia soni and Viviparus sp.
Loc. 9: In the valley of Baetae, Naeidong,

877.

On the genus Plicatounio

81

P. naktongensis and Trigonioides
kodairai are assembled here in a layer about
10 cm thick, associated with Brotiopsis sp.
Loc. 10: At a drainage side, Naegokji,
Mukeodong, Jangcheon-myeon, Seonsan-gun,
Gyeongsangbuk-do (Figure I-A). Lithology is composed of light grey siltstone andlimy mudstone in the middle part of the
Middle Hasandong Formation. Here, P.
naktongensis, Nagdongia soni and Brotiopsis
sp. have been collected.
In addition to these, at the following two
localities of Japan the fossils were collected:
At Rikimaru, Miyata and Kurate of northern
Kyushu (lower Wakino Formation, Kwanmon Group) and at a point 500 m southeastof Tashiro, Kosa Town of central Kyushu(Mifune Group).
tion.

o
50

100
150m

"o

"o

Systematic description
C>"

Order Unionoida Stoliczka, 1871
Superfamily Unionacea Fleming, 1828
Family Unionidae Fleming, 1828
Subfamily Unioninae Fleming, 1828
Genus Plicatounio Kobayashi and
Suzuki, 1936

~ ~~~~~~~~~~~
ro
ro

<f)

:I:

Lac. 7

Locs. 5,6

Lacs. 1 2

Figure 2. Stratigraphic columns. a. reddish
bed, b. shale, calcareous nodule bearing, c. mud- or
siltstone, calcareous nodule bearing, d. shale, e. siltor mudstone, f. fine- to medium-grained sandstone, g.
coarse-grained sandstone, h. pebbly sandstone orconglomerate, i. metamorphic rock, j. fossil horizon.

Hyoryeong-myeon, Kunwi-gun, Gyeongsangbukdo (Figure I-A). Lithology here is siltstone
and fine- to medium-grained sandstone in theupper part of the Middle Hasandong Forma-

Generic diagnosis.-Unioninae with surface ornamented with four or five posterior
radial plicae and crenulated pseudocardinalhinge teeth.
Included subgenera.-Plicatounio Kobayashi and Suzuki, Kwanmonia Ota, andEnotrigonioides Guo.
Remarks.-Since Kobayashi (1968)
proposed the family Plicatounionidae basedon Plicatounio without any definition, Guo(1986) and Kobayashi (1984) have followed
Kobayashi's opinion. But the taxonomic
characters of Plicatounio do not seem todeserve familial distinction from theUnionidae.

Seong- Young Yang

82
Table I.

Subgenus Plicatounio Kobayashi and
Suzuki, 1936

Measurements of Plicatounio (P.)
naktongensis Kobayashi and
Suzuki (linear dimension in mm).

L
H
D
Specimens(Loc.6)22.3+
KPE 1093 (BV)' 58.7+ 26.7
28.6
21.4
KPE 1094 (LV)' 64.6
30.7+ 21.9
KPE 1095 (RV)' 64.0
7.7
11.8
KPE 1096 (LV)
23.9
KPE 1097 (LV)
77.6
34.3+ 20.5
25.4
39.6
KPE 2456 (BV)
77.6
30.1
46.6
KPE 2457 (BV)
90.8
38.8
42.3
98.5
KPE 2458 (BV)
24.6
35.4
75.9
KPE 2502 (BV)
34.0
KPE 2503 (BV) 102.2+ 44.2
20.5
32.4
KPE 2504 (RV)
75.5
21.8
31.8
67.7
KPE 3042 (RV)
15.0
19.6
KPE 3043 (LV)
42.6
19.3
23.7
KPE 3045 (RV)
50.3
(Loc.2)
21.3
KPE 3001 (RV)
56.1 + 33.6
17.1
27.0
KPE 3002 (LV)
47.9
20.7
KPE 3003 (LV)
56.4+ 29.4
20.8
KPE 3005 (RV)
60.8
32.1
18.8
27.7
52.4
KPE 3006 (BV)
31.7
60.9
20.0
KPE 3007 (LV)
8.9+
KPE 3008 (LV)
25.8+ 16.6
59.5
KPE 3009 (LV)
27.5+ 20.7
KPE 3012 (LV)
30.4
20.4+
59.7
33.6
22.7
67.9
KPE 3013 (LV)19.8
KPE 3016 (LV)
30.1
56.8
KPE 3017 (LV)
20.6+
64.2+ 32.7
18.3
KPE 3018 (LV)
65.8
33.4
KPE 3020 (RV)
20.8
55.7
32.6
KPE 3022 (LV)
30.5
19.0
56.9
KPE 2023 (LV)
32.7
21.8
60.3
KPE 3024 (RV)
65.1
35.2
20.8
18.3
KPE 3026 (RV)
63.4+ 34.2
69.6
23.8
KPE 3028 (LV)35.2
KPE 3033 (RV)
23.7
72.9
35.7
34.5
KPE 3034 (RV)
73.6
19.8+
(Loc.7)
KPE 2111 (RV)
29.5
42.5
86.8
KPE 2112 (BV) 102.8
47.2
33.5
25.8
KPE 2114 (BV)
74.6
35.0
30.2
92.2
KPE 2115 (RV)42.3
KPE 2116 (BV)
79.4
33.9+ 32.3
KPE 2117 (BV)
22.6
74.5+ 36.3
KPE 2146 (BV)
78.9+ 35.5+ 29.3
KPE 2147 (LV)
42.8
27.5
81.6
KPE 2148 (RV)
77.1 + 37.8
24.6
KPE 2149 (BV)
41.2
86.9
24.5
KPE 2150 (RV)
82.2
40.5+ 25.0
KPE 2501 (BV)
86.2
42.4
27.7
42.9
KPE 2359 (BV)
14.4
21.3
(Loc.9)KPE 2380 (RV)
64.7
22.8
30.1
KPE 2381 (RV)
59.9
29.8
20.2
KPE 2382 (LV)
18.5
55.8+ 24.9
KPE 2383 (RV)
21.3
70.6+ 31.9
KPE 2389 (BV)
28.8
64.6
18.7
KPE 2390 (RV)
18.1
29.6
62.0
KPE 2392 (LV)
59.7+ 28.9+ 17.9

HjL

DjL

.45
.44
.48
.49
.44
.51
.51
.43
.47
.43
.43
.47
.46
.47

.38
.33
.34
.32
.26
.33
.33
.39
.32
. 33
.27
.32
.35
.38

.60
.56
.52
.53
.53
.52
.64
.46
.51
.49
.53
.51
.51
.58
.54
.54
.54
.54
.51
.49
.47

.38.36
.37
.34
.36
.33
.34
.35
.34
.33
.35
.32
.28
.37
.33
.36
.32
.29
.34
.33

.49
.46
.47
.46
.43
.49
.45
.52
.49
.47
.49
.49
.50

.34
.33
.35
.33
.41
.30
.37
.34
.32
.28
.30
.32
.36

.47
.45
.45
.45
.48
.48

.35
.34
.33
.30
.29
.29
.30

.50

.27+

(Wakino)
KPE

1071

(LV)

68.9

37.0

16.5

.54

.24

1295 (RV)
1297 (LV)

42.1
23.5

24.7
13.7

12.6
7.5

.59
.58

.30
.32

(Mifunc)
KPE
KPE(BV)' : conjoined valve,(R V)': right valve(LV)': left

valve,

Type-species.- Plicatounio

naktongensis

Kobayashi and Suzuki, 1936 .

Subgeneric diagnosis.-Plicatounio withelongated elliptical shell and surface ornamented occasionally with fine radial ribson the whole disc besides the four or fiveposterior plicae .
Included species.- Plicatounio naktongensis Kobayashi and Suzuki, P. suzukii
Hoffet, P. maximus Hoffet, P. manchuricus
Yabe and Hayashi, P. kobayashii Maeda, P .
tetoriensis Maeda, P. fiattersensis Mongin, P .
klalldziensis Martinson, P. namphungensis
Kobayashi, P. equiplicatlls Gu and Yu, P .
zhejiangensis Gu and Ma, P. fujianensis Gu
and Ma, P. latiplicatlls Gu and Yu, P. subrhombiclls Gu and Yu, and the following two
new species described below .
Plicalounio (Plicatollnio) naklongensis
Kobayashi and Suzuki, 1936
Figures 3-IA-16; 4-IA-7

1936. Plicatounio naktongensis Kobayashi and Suzuki, p. 252, pI. 28, figs. 1-4, 6-8.
1943. Plicatounio naktongensis Kobayashi and Suzuki; Suzuki, p. 210-211, pI. 16, figs. 14-15.
1956. Plicatounio naktongensis Kobayashi and Suzuki; Kobayashi, p.80, pI. 5, fig. 3.
1959. Plicatounio naktongensis Kobayashi and Suzuki; Ota, p. 15, pI. 3, figs. 4-8.
1960. Plicalounio afT. naklongensis naktongensis
Kobayashi and Suzuki; Hase, p. 313, pI. 39,
fig. I.
1963. Plicatounio (s.s.) naktongensis Kobayashi and
Suzuki; Ota, p. 507, text-fig. I.

Material.- The specimens at hand werecollected from the following six localities;
Loc.1 (KPE 1191-4, 1726-7); Loc.2 (KPE
3001-37); Loc.6 (KPE 1093-1100,3041-6);
Loc.7 (KPE 2111-50, 2456-65, 2501-11,2527); Loc. 9 (KPE 2379-87, 2389-92, 2559) ;Loc. 10 (KPE 2446) (see the explanation of
localities in the above 'Material and Local-

877.
Table 2.
Loc.

On the genus Plicatounio

83

Arithmetic means of the simple ratios HjL and OjL.

ratio

N

x±tO.050"x

2

HjL

21

.530±.019

2

OjL

21

V

o"x

.041

7.736

.009

.921

.46-.64.336±.013

.029

8.631

.006

.835

.27-.38

O.R.

6

HjL

14

.463±.015

.028

6.048

.007

.973

.51-.43

6

OjL

14

.332±.022.037

11.145.010.904.26-.39

7

HjL

13

.478±.015

.024

5.026

.007

.951

.43-.52

7

OjL

13

.335±.020.034

10.149.009.857.28-.419HjL

7.469±.019

.020

4.264

.008

OjL

7

.314±.022

.025

7.962

.009

.839
.574

.45-.50

9.29-.35

N; number of measurements, x±tO.050"x; arithmetic mean with 95% confidence level, s;
standard deviation of the mean, V; Pearson's coefficient of variation, O"x; standard error of themean, r; correlation coefficient, O.R.; observed range.

ities"). The above six localities of Korea fallunder the Hasandong Formation, Gyeongsang Group. In Japan, the specimens referred to the present species were collected fromthe locality at Rikimaru, Fukuoka Prefecture(KPE 1069-74, 1080-9, 2569-2571) (lower
Wakino Formation, Kwanmon Group) andfrom the locality near Tashiro, Kumamoto
Prefecture (KPE 1295-9) (Mifune Group).
Measurements (in mm).-In regard to shelldimensions, length (L) is the greatest linear
dimension measured roughly parallel to ventral line, height (H) is the greatest dimension
measured normally to Land umbonal distance (D) the linear dimension between anterior end and umbo. From these data, thesimple ratios, HjL and D jL and their 95%
ranges are calculated and shown in Table 2.
Description.-Shell medium in size (about
50-90 mm in length), occasionally larger than
90 mm in length, equivalve and elongatedelliptical, about twice as long as high (HjL ;0.50), inequilateral; umbo blunt, slightly
prosogyrous, situated at about one third fromthe anterior end (DjL; 0.33); anterior margin well rounded; postero-dorsal margin
long, gently curved; posterior margin somewhat produced postero-ventrally; ventral
margin broadly arcuate. Escutcheon andlunule narrow and elongated; ligament exter-

nal and transversely and finely cren ulated(Figures 3-4-5, 7).
Surface ornamented with four or five strong
plicae running obliquely on the posterior partand on the main part of the disc in front ofthese plicae, with fine radial ribs counted
more than 20, which become gradually finer
and indistinct toward the anterior margin.
The whole surface covered also with finenumerous growth-lines of irregular interval
and prominence.
Hinge plate moderate in breadth, provided
with pseudocardinal and postero-lateral
teeth; the pseudocardinal two on each valve,the postero-lateral ones one or two on theright valve, two on the left valve, forming thefollowing dental formula:
(PI)

4

2

PIll
Pll

PIV

where 5: narrow and low, with very finetransverse crenulations on the ventral (lower)side only,
3: rather heavy and prominent, with veryfine transverse crenulations on both sides,
subparallel to antero-dorsal margin,
PI: low and elongated, appearing only on
posterior half under PIlI, occasionally indistinct,
PIlI: elongated and prominent, with very

84

Seong- Young Yang

877.

On the genus Plicatounio

fine striations on the crest, parallel to thepostero-dorsal margin,
4: prominent and rather heavy, with veryfine transverse crenulations on both sides,
parallel to the antero-dorsal margin,
2: low and narrow, with very fine transverse crenulations on the dorsal (upper) side
only, subparallel to the antero-dorsal margin,
PH and PlY: elongated and prominent,
rather lamellar but sometimes faintly
crenulated in the crest, parallel to thepostero-dorsal margin.
Two adductor scars subequal in size, anterior one semicircular and strongly impressed,
accompanied with a minute pedal scar, posterior one trigonally ovate and larger, but not
so distinct. Inner ventral crenulations denseon the anterior margin, but gradually broader
in proceeding backward. Umbonal cavity
moderate in depth; test moderate in thickness and inflation rather weak.
Observation.-Most of the specimens are sowell preserved that the internal structures areobserved on the internal mould madeartificially with dilute hydrochloric acid.
The internal structures are fairly stable, but
on one exceptional specimen (KPE 2382,
Figure 3-1), radial striations are discernible
immediately below the umbo. The othercharacters are identical with those of otherspecimens. Thus, it cannot be separated
from other specimens. It is, however, open
to question what this exceptional charactermeans.

85

Occurrence.- The present species is associated with Trigonioides (T.) kodairai at
the type-locality (Yangpori, Loc. I) where
Brotiopsis spp. occurs gregariously. But thepresent species and Trigonioides (T.) kodairai are relatively rare and mostly represented
by conjoined specimens. This mode ofoccurrence may suggest their nearly original
habitats. At an island near Yangpori (Loc.
2), it is also found in a few beds with Brotiopsis spp. At the locality near Hanchi (Loc. 6)
the present species is also rare in several
fossiliferous beds containing abundant
Brotiopsis spp. At the locality near Yusuri(Loc. 7), it is preserved in situ associated withT. (T.) jaehoi, but without Brotiopsis spp.
At the locality near Baetae (Loc.9), it isassociated also with T. (T.) kodairai andBrotiopsis spp. forming a fossiliferous bed,
but the present species is a main component
and T. (T.) kodairai also in common, but
Brotiopsis spp. are very rare. At the locality
10, it is associated also with Nagdongia soni
and Brotiopsis sp.
The beds containing the present species are
generally light grey siltstone or dark grey orgreenish grey shale. It is notable that thepresent species is found so far confined to the
Hasandong Formation, Gyeongsang Group
in Korea.
At Rikimaru, Kyushu, Japan, the present
species is associated with Wakinoa wakinoensis Ohta, and at the locality near Tashiro,
Kumamoto, Japan, it occurs with Trigon i-~
Figures 3-1A-16. Plicatounio (Plicatounio) naktongensis Kobayashi and Suzuki. l. left valve(KPE 2382), lA; rubber cast, showing the postero-Iateral hinge teeth striated finely, and radial striations
immediately below the umbo, IB; internal mould, showing the internal structure (Loc. 9). 2. internalmould of the right valve (KPE 1726), showing the weakly striated crest of the postero-Iateral hinge teeth (Loc.
I). 3. rubber cast of the left valve (KPE 2392), showing the lamellar postero-Iateral hinge teeth (Loc. 9). 4.
rubber cast of the right valve (KPE 2383), showing the crenulated hinge teeth and the other internal structure(Loc.9). 5. internal mould of the left valve (KPE 1297), showing the crenulated postero-lateral hinge teeth(Loc.; type-locality of Trigonioides (Kumamotoa) mifunensis, see Tamura 1970). 6. internal mould of theconjoined valve (KPE 1080), 6A; dorsal view, showing the crenulated postero-Iateral hinge teeth (Loc. ;Rikimaru, Miyataku, Kyushu, Japan, see Ota, 1959), 6B; side view. 7. internal mould of the left valve(KPE 1071), showing the crenulated postero-Iateral hinge teeth (Loc.; ditto). 8. left valve (KPE 3002)(Loc. 2). 9. left valve (KPE2285) (Loc. 9). 10. left valve (KPE 3043) (Loc. 6). 11. left valve (KPE 1094)(Loc.6). 12. right valve (KPE 2389) (Loc. 9). 13. right valve (KPE 3026) (Loc. 2). 14. right valve (KPE
3033) (Loc. 2). 15. right valve (KPE 2148) (Loc. 7). 16. right valve (KPE 2390) (Loc. 9). All figures areapproximately of natural size.

86

Seong- You ng Yang

877.

On the genus Plicatounio

oides (Kumamotoa) mlfunensis Tamura.
Discussion.-Suzuki (1943) proposed P.
naktongensis multiplicatus as a subspecies ofthe present species by the presence of theradial ribs in front of the strong posterior
plicae. To my regret, I sought in vain any
samples of this subspecies at the type-locality(Okbongdong, Jinjushi, Gyeongsangnam-do,
Korea). However, the specimens similar toP. n. multiplicatus have frequently beenfound in association with the present species(Locs. 2, 6 and 7). Such a sympatric occurrence of two "subspecies" is unlikely; thedifference is regarded as due to individual
variation.
The postero-Iateral hinge teeth have been
described as lamellar by previous authors(Kobayashi and Suzuki, 1936; Ota, 1959 and
1963; Martinson, 1965; Gu and Ma, 1976).
But Tamura (1982) observed crenulations on
the postero-Iatera1 teeth of a specimen collected at the type-locality (Yangpori) andinsisted that Ohta's P. (P.) naktongensis from
Rikimaru should be separated from the present species. However, in my collection from
Rikimaru, I can also observe crenulations on
the postero-Iateral teeth (KPE 1080, 1071,
Figures 3-6- 7). Therefore, in my opinion,
the different views are due to insufficient andpoorly preserved material.
Without observation, I cannot give any
comment on the specimens described under
the name of P. naktongensis from China and
U.S.S.R.

87

Plicatounio (Plicatounio) okjuni, sp. nov.
Figures 5-1 A-2B

Etymology.- This species is dedicated to
Emeritus Professer Okjun Kim of Yonsei
University who has contributed much to tectonics of the Korean Peninsula.
Material.-Holotype (KPE 2261) and tenparatypes (KPE 2252, 2254, 2260, 2264, 2266,
2270, 2274, 2304, 2305, 2361,) collected from
Loc.8.
Measurements.-Carried out in the same
way as in P. (P.) naktongensis.
Diagnosis.- Test thick for the genus andthe posterior plicae low and wide, not so
distinct.
Description.-Shell fairly large (about 8090 mm in length), equivalve, inequilateral,
generally elongated suboval or subquadrate
in outline; the ratio of H/L about 0.52;
anterior margin well rounded; posterodorsal one long and rather straight; andposterior margin somewhat obtusely angulated at the postero-ventral corner; ventral
margin broadly arcuate; umbo robust, fairly
prominent, slightly prosogyrous, situated atabout two fifths of shell length from theanterior extremity (OIL; 0.36). Test fairly
thick. Surface covered with fine concentric
growth-lines and ornamented with low but
wide radial plicae on the posterior half,
which become gradually indistinct towards
the anterior part. The internal characters are
unknown.
Observation.- The holotype (KPE 2261,
Figure 5-1) is a conjoined specimen, 88.0 m~
in length and 46.8 mm in height. The fossIl

Fi ures 4-lA-7. PlicalOunio (P.) naklOngensis Kobayashi and Suzuki 1. right valve. (K~E 2113):lA.
view, showing the crenulated hinge teeth, lB. side
showing the weakantero-central part besides the strong posterior plicae (Loc. 7). 2. Int~rnal mould of the ng t va ve2560) showing the crenulated postero-Iateral hinge teeth (Loc. 7). 3. Internal mould of the left valv~ (K~E
2508)' showing the crenulated postero-lateral hinge teeth (Loc. 7). 4. left valve (~~E t4~), ~~;~~~i \~weak 'wave-patterns of the growth lines on the antero-central part (Loc. 7). 5. conJolde va3~~ h . ~hside view showing the ligament on the postero-dorsal side (Loc. 7). 6. right valve (KPE 2.~ : s ow~ng. e
weak rad;~l ribs on the antero-central part (Loc. 7). 7. conjoined valve (KPE.2112), left Sl e View, SOWIng
the ligament on the postero-dorsal side and the weak ~ave-patterns of growth hnes on the antero-central part(Loc. 7). All figures are approximately of natural size.

+---inte~nalvie~,

r~d~al n~s ~~~~

Seong-Young Yang

88

specimens now at my disposal are varied inoutline, but this is evidently due to secondary
deformation. One of the paratypes (KPE
2266) is fairly elongated, but this is due tovertical compression, as can be read from theextraordinarily large inflation. And anotherone (KPE 2264, Figure 5-2) is somewhat
subquadrate in form, but this also is due todiagonal compression. The relatively wellpreserved specimens among the collection areconjoined and others are fragmentary, and so
the internal structures can not be observed.
Occurrence.- The fossils are not gregarious, but are scattered. Many specimens areconjoined as pointed above. The occurrence
seems to reflect preservation in situ. The
present species is associated with Wakinoa cf.
tamurai, P. (P.) sp. cf. P. (P.) yooni described below, very immature specimens of
Nagdongia soni and Viviparus? sp.
Comparison.- The present species is very
similar to P. (P.) naktongensis in surface
ornamentation. The former is ornamented
with constantly low but wide plicae on theposterior half, within which the plicae do notshow difference in strength and width, but thelatter is ornamented with strong and wideplicae on the posterior portion and numerous
finer radial ribs on the main part of the disc.
In addition, the ratio of HjL is relatively
larger in the present species that is larger than
Table 3.

0.55 in the present species, while less than 0.50
in P. naktongensis. The radial ribs of thepresent species are somewhat similar to thoseof P. (P.) subrhombicus Gu and Yu, but they
are distinguished from each other in the thickness of the test. The test of the present
species is distinctly thicker than that of any
other described species of Plicatounio.

Plicatounio (Plicatounio) yooni, sp. nov.
Figures 6-1-7

Etymology.- This species is dedicated to
Dr. Sun Yoon of Busan National University,
who, one of my colleagues, specializes in
Tertiary molluscs.
Material.-Holotype (KPE 2601) and fifty
two paratypes (KPE 1053-9, 1090-2, 2540,
2561-5, 2602-37), collected from the following three localities; Loc. 3 (type-locality)(KPE 2601-20, 2622-37) and Loc.4 (KPE2621) and Loc.5 (KPE 1053-9, 1090-2,2540,
2561-5).
Measurements (in mm).-Carried out inthe same way as above.
Diagnosis.-Surface ornamented with 4 or
5 strong posterior plicae and the distinct
radial ribs counted more than 20 in front of
the strong posterior plicae.
Description.-Shell fairly large in size

Measurements of Plicatounio (P.) okjuni, n. sp. (linear dimension in mm).
L

Specimes

H

D

H/L

L

Specimens

D/L

H

D

H/L

D/L

.53

.37

KPE

2261'

(BV)

88.0

46.8

32.7

KPE

2252

(BV)

70.3+

36.0

31.7

.51

.45-

KPE

2264

(BV)

88.9

52.6

25.3

.59

.28

KPE

2254

(BV)

68.1+

37.6

25.9

.55

.38-

KPE

2266

(BV)

84.1 +

37.2+

29.0

.44

.34

(Loc.8)*KPE

2261; Holotype

Table 4.

Arithmetic means of the simple ratios H/L and D/L.

Loc.

ratio

N

x± to.0511x

8

H/L
D/L

5

.524±.069.364±.078

8

5

r

O.R.

.025

.769

.028

.053

.44-.59.28-.45

V

I1X

.056

10.687.062

17.033See page 83 (Table 2) for explanation of statistical parameters.

877.

On the genus Plicatounio

89

Figures S- lA- 2B. PlicalOul1io (P.) okjul1i , n. sp. 1. conjoined valve (KPE 2261), lA; right sideview , 18; left side view (Loc. 8) . 2. conjoined valve (KPE 2264), 2A; left side view , showing the fairly
thick test , 2B j right side view (Loc. 8). All figures are approximately of natural size.

(about 70- 100 mm in length), equivalve, inequilateral, generally elongated suboval in
outline, about twice as long as high (H / L
0.47); anterior margin somewhat projected
and well rounded ; postero-dorsal one rather
straight; posterior margin obtusely angulate
with postero-dorsal margin , sloping gently

down to postero-ventral corner ; ventral margin broadly arcuate. Umbo blunt and fairly
prominent, slightly prosogyrous, situated atabout two-fifths of shell length from the anterior extremity (O I L; 0.37) . Test moderate
in thickness; umbonal cavity fairly deep.
Surface ornamented with four or five strong

90

Seong- Young Yang

877.

On the genus Plicatounio

plicae running from the umbo obliquely
down to the posterior periphery and, on themain part of the flank in front of these plicae,
with more or less narrow but distinct radialribs. The fine radial ribs somewhat variable
in width and the grooves between the ribs
fairly narrow and counted slightly more than91

20 in large specimens.
Hinge plate narrow in breadth, provided
with the pseudocardinal and the posterolateral teeth, the pseudocardinal ones two on
each valve, the postero-lateral ones one onright valve, two on left valve, forming thefollowing dental formula:
5

Measurements of Plicatounio (P.)
yooni, n. sp. (linear dimension in mm).

Table 5.

Specimens

L

H

D

HjL

DjL

.34

2601* (BV)

84.8

34.7

28.5

.41

KPE

2602 (LV)

112.3

49.8

43.2

.44

.38

KPE

2603 (LV)

80.0

32.1

23.4

.40

.29

KPE

2605 (LV)

95.9

39.0+

34.5

.41 +

.36

KPE

2609 (RV)

98.9

38.9+

35.5+

.39+

.36

KPE

2611

(LV)

96.3

42.3

34.0

.44

.35

KPE

2615 (RV)

83.9

34.4

29.2

.41

.35

KPE

2618 (RV)

92.4

34.4

33.6

.37

.36

KPE

2620 (RV)

98.3+

44.1 +

36.8

.45

.37

KPE

2625 (BV)

88.3+

41.9+

32.9

.47

.37

KPE

2628 (LV)

79.0

35.7

32.5

.45

.41

KPE

2629 (LV)

95.8

41.6

34.2

.43

.36

KPE

2631

80.7

36.6

28.9

.45

.36

(RV)

(Loc.5)
KPE\053 (BV)

89.1 +

46.6

38.5

.52

.43

KPE

1054 (RV)

83.7

38.6

32.9

.46

.39

KPE

1090 (LV)

59.4

30.4

25.2

.51

.42

KPE

1091

53.4+

34.2

20.3

.64

.38

(KPE

(RV)

2601)*; Holotype

Table 6.

2

PII

PIV

The hinge teeth, pseudocardinal andpostero-lateral ones, finely crenulated or striated obliquely on one or both sides.
Anterior adductor scar strongly impressed,
accompanied with a small but distinct pedal
scar and posterior one somewhat larger but
not so distinct. The ventral crenulation
along the inner margin, fairly distinct on themain part, but weakened and becomes finer
towards the anterior margin. Pallial line
simple but hardly perceptible on the posterior
portion.
Observation.- The holotype (KPE 2601,
Figure 6-5) has conjoined valves, 84.8 mm inlength, 34.7 mm In height. The internal
structures can be observed on the artificial
mould made with dilute hydrochloric acid.
The number of radial ribs is constant anddifferent from that of other species. The
outline seemingly varies in the specimens at(Loc.3)
KPE

PIli

4

Arithmetic means of the simple ratios H/L and D/L.

Loc.

ratio

N

x±tO.05erx

V

erx

O.R.

3

H/L

13

.425+.017

.029

.843

.37-.47

D/L

13.358+.015

.027

6.824
7.542

.008

3

.007

.895

.29-.41

5

H/L
D/L

4

.533+.121.076

14.259.038.867.46-.644.405+.038

.024

5.926

.012

.980

.38-.43

5

See page 83 (Table 2) for explanation of statistical parameters.
+- Figures 6-1-7. Plicatounio (P.) yooni, n. sp. 1. internal mould of the left valve (KPE 2605),
showing the crenulated pseudocardinal and the postero-Iateral hinge teeth (Loc. 3). 2. internal mould of theright valve (KPE 2604), showing the crenulated pseudocardinal and the postero-Iateral hinge teeth (Loc. 3).
3. internal mould of the left valve (KPE 2633). showing the crenulated hinge teeth (Loc. 3). 4. rubber castof the left valve (KPE 2603) (Loc. 3). 5. rubber cast of the left valve (KPE 2601) (Loc. 3). 6. rubber castof the left valve (KPE 2602) (Loc. 3). 7. right valve (KPE 2621) (Loc. 4). All figures are approximatelyof natural size.

92

Seong-Young Yang

877.

On the genus Plicatounio

hand, but this may be partly due to secondary
deformation.
Occurrence.- The specimens at hand werecollected at three localities. At the locality
near Impo (Loc. 3), the present species occurs
on the same bedding plane with Wakinoa sp.,
Pseudohyria sp., and Brotiopsis sp. At the
locality 4 only one specimen (KPE 2621) wascollected. The fossils of the present species
are frequently conjoined at. Loc. 3. At the
locality near Sumoondong (Loc. 5), it is associated with Trigonioides (T.) kodairai, andNagdongia soni. The fossils occur not
gregariously but scattered, and do not show
any severe damage. This suggests that thefossils have been preserved in situ or at leastnear the original habitat.
Comparison.- The radial ribs of thisspecies so closely resemble those of P. (P.)
naktongensis multiplicatus that I (Yang, 1974,1975) reported tentatively this species as P.
(P.) multiplicatus (?). The fine radial ribs infront of the several strong plicae, however, aremore distinct, the umbo is blunter and theanterior margin is more projected in thepresent species than in P. (P.) multiplicatus.
The present species is also closely allied toP. (P.) kobayashii and P. (P.) tetoriensis
from Japan, but according to Maeda's
description (1962), the latter two species havethe umbo placed more anteriorly, at about
one-fourth of the shell length from the anterior extremity, while the present species has
the umbo situated at about two-fifths.
The present species is similar to P. maximus Hoffet, 1937 and P. suzukii Hoffet, 1937
in the radial ribs and outline, but the former
differs from the latter two species in thenumber of ribs, that is, Hoffet's species areornamented with denser radial ribs in front of
the strong posterior plicae, more than 28 in
number, while in the present species there areabout 20 radial ribs.

93

Plicatounio (P.) sp. cf. P. (P.) yooni, n. sp.
Figures 7-IA-3B

Material.-Seventy one specimens collected from Loc. 8 (KPE 2253, 2255-8, 2260,
2262, 2265, 2267-9, 2271-3, 2275, 2277-2303,
2305-10, 2357-60, 2362-3, 2412-28).
Measurements (in mm).-Carried out inthe same way as above.
Descriptive remarks.- The shell is generally the same as P. (P.) naktongensis in shapeand size. The radial ribs in front of theposterior plicae are somewhat more distinct
than those of the type-species but less thanthose of P. (P.) yooni, frequently becoming
indistinct and effaced. If comapred with P.
(P.) okjuni from the same locality, thisspecies is characterized by the thinner test anddifferent surface ornamentation.
References
Gu, Z. and Ma, Q., 1976: in "Fossil Lamellibranchsof China" ed. by Nanking [nst. Geol.
Palaeont., Acad. Sinica, p. 1-552, pis. 1-150.
Guo, F., 1981 : Bivalves from the Jingxing Formation(Cretaceous) in western Yunnan with notes on
the origin of the Trigonioidids in Asia. 12th

Ann. Con!. Pal. Soc. China, Selected Papers,
Sci. Publ. House, Beijing, p. 61-78, pis. 1-3.
- - , 1986: On Trigonioidaceans (non-marine
Cretaceous bivalves) and Asian non-marine
Cretaceous System. Yunnan Sci. and Techn.
Publ. House, Kunming, China. 206 pp. pis. 1-8.
Hase, A., 1960: The late Mesozoic formations andtheir molluscan fossils in west Chugoku andnorth Kyushu, Japan. Jour. Sci., Hiroshima
Univ., Ser. C, v. 3, n. 2, p. 281-342, pis. 31-39.
Hoffet, J. H., 1937: Les Lamellibranchia saum1itresdu Senonien de Muong Phalane (Bas-laos).
Bull. Servo geol. I'Indochine, v. 24, n.2, p.4-25,
pis. 1-5.
Kobayashi, T., 1963: On the Cretaceous Ban Na Yo
Fauna of east Thailand with a note on the
distribution of Nippononaia, Trigonioides andPlicatounio. Japan. Jour. Geol. Geogr., v.34,~ Figures 7-IA-3B. Plicatounio (P.) sp. cf. P. (P.) yooni, n. sp. I. conjoined valve (KPE 2299),
IA; right side view, IB; left side view (Loc. 8). 2. right valve (KPE 2263), postero-ventral part broken out(Loc.8). 3. conjoined valve (KPE 2255), IA; left side view, 3B; right side wiew (Loc. 8). All figures areapproximately of natural size.

Seong-Young Yang

94

Meaurements of Plicatounio (P). sp. cf. P. (P.) yooni, n. sp. (linear dimension in mm).

Table 7.
Specimens

L

H

D

HjL

DjL

Specimens

L

H

D

HjL

DjL

(Loc.8)

KPE
KPE
KPE
KPE
KPE
KPE
KPE

2251

(BY)

69.7

42.5

22.1

.61

.32

2253

(RY)

71.6+

32.5+ 29.3

.45

.41

2260

(BY)

87.4+

39.0

25.9

.45

.30

2265

(BY)

80.3

42.9

27.7

.53

.34

2267

(RY)

76.1+

44.7

25.3

.59

.33

2281

(RY)

77.1 +

40.7

24.1

.53

.31

73.9+

39.7

24.0

.54

.32

2286

(RY)

Table 8.

KPE
KPE
KPE
KPE
KPE
KPE
KPE

2302

(BY)

85.5+

49.3

29.6

.58

.35

2310

(BY)

67.5

37.4

24.4

.55

.36

2357

(BY)

71.1

34.5

25.3

.49

.36

2360

(LY)

74.8

38.3

25.6

.51

.34

2412

(RY)

79.5+

44.3

30.5

.56

.38

2420

(LY)

35.3

20.1

10.0

.57

.28

2427

(LY)

40.6

19.7

13.0

.49

.32

Arithmetic means of the simple ratios HjL and DjL.

Loc.

ratio

N

x± to.05 (J"X

8
8

HjL
DjL

14

.532±.02814.337±.022

O.H.

V

(J"X

.049

9.211

.013

.905

.45-.61.036

10.682.010.922.28-.41

See page 83 (Table 2) for explanation of statistical parameters.
n. I, p. 35-43, pI. 3.
- - , 1968: The Cretaceous non-marine pelecypods
from the Nam Phung Dam site in the northernpart of the Khorat Plateau, Thailand with a noteon the Trigonioididae. Geol. Palaeont. S.E.
Asia, v. 4, p. 109-138, pIs. 20-23.
- - , 1984: Mesozoic Bivalvia of the Khorat Group
with a note on the Trigonioidacea. Ibid., v. 25,
p.239-251.
- - and Suzuki, K., 1936: Non-marine shells of the
Naktong-Wakino Series. Japan. Jour. Geol.
Geogr., v. 13, n. 3-4, p. 243-257, pIs. 27-29.
Ku, C.W., 1962: Note on the occurrence of some late
Cretaceous fresh-water Lamellibranches in the
Chusiung district of central Yunnan with a brief
review of the continental Cretaceous of Yunnan.
Acta Pal. Sinica, v. 10, n. 3, p. 287-307, pIs. 1-2.
Maeda, S., 1962: Some lower Cretaceous pelecypods
from the Akaiwa Subgroup, the upper division of
the Tetori Group in central Japan. Trans. Proc.
Palaeont. Soc. Japan, N.S., n.48, p. 343- 351,
pI. 53.
Martinson, G.G., 1965: Biostratigraphy and fauna ofcontinental Cretaceous of Fergana. Sci. Acad.
U.S.S.R., p. 101- 152, pIs. I-II (in Russian).
Mongin, D., 1977: Quelques precisions taxonomiques sur des Unionacea du Cretace inferieur du Sahara (Africque). Arch. Moll., Band
108, Ij3, p. 63-66.
Ota, Y., 1959a: 1977: Plicatounio of the Wakino
Formation (Studies on the molluscan fauna of
the Cretaceous Inkstone Sereis, pt. I). Trans.
Proc. Palaeont. Soc. Japan, N.S., n.33, p. 1518, pI. 3.

Ota, Y., 1959b: Trigonioides and its classification(Studies on the molluscan fauna of theCretaceous Inkstone Series, pt. 2). Ibid., n. 34,
p. 97-104, pI. 10.
- - , 1960: The zonal distribution of the non-marine
fauna in the upper Mesozoic Wakino Subgroup(Studies on the molluscan fauna of the nonmarine upper Mesozoic Kwanmon Group, pt. 5).
Mem. Fac. Sci., Kyushu Univ., Ser. D, Geol., v.
9, n. 3, p. 187-209.
- - , 1963: Notes on the relationship of Trigonioides
and Plicatounio, non-marine Mesozoic Bivalvia
from eastern Asia. Geol. Rept., Hiroshima
Univ., n. 12, p. 503-512.
Suzuki, K., 1943: Restudy on the non-marine molluscan fauna of the Rakuto Series in Keisyo-do,
Tyosen. Jour. Sigenkagaku Kenkyusyo, v. I, n.
2, p. 189-219, pIs. 14- 19.
Tamura, M., 1981: A summary of the Cretaceous
non-marine bivalve studies in Japan at present.
Jour. Geogr., v.90, n.6, p. 369-392. (inJapanese).
Yabe, H. and Hayashi, Z., 1938: A Mesozoic unionid
from Manchuria. Japan. Jour. Geol. Geogr.,
vol. 15, nos. 1-2, p. 31-33, pI. 4.
Yang, S. Y., 1974: Note on the genus Trigonioides(Bivalvia). Trans. Proc. Palaeont. Soc. Japan,
N.S., n.95, p. 395- 408, pIs. 54-55.
- - , 1975: On a new non-marine pelecypod genus
from the upper Mesozoic Gyeongsang Group of
Korea. Ibid., n. 100, p. 177-187, pIs. 16-17.
- - , 1983: On the subgenus Wakinoa (Cretaceous
non-marine Bivalvia) from Gyeongsang Group,
Korea. Ibid., n. 131, p. 177-190, pIs. 38-40.

877.

On the genus Plicatounio

95

Bulguksa ffll§!l~, Bulnodong l'~¥I"J, Dongmyeong ~Ij)j, Fukuoka :mi1lITJ, Golyakmyeon 1t;5'00, Gyeongsangbuk-do !fj'5j~t:@:, Gyeogsangnam-do ~j'5ji¥i;@, Hadonggun ro.r~m, Hasandong ~LlJ¥I"J, Hwanggeumri jill~jL Hyoryeong-myeon *=%00,
Impo ttrm, Jangcheon-myeon ~JIIoo, Jeolanam-do ~mi¥i;@, Jingyo-myeon J.OC;j{joo,Jinju (shi) lHI'/CiTI), Jinyang-gun ~~m, Keumnam-myeon ~i¥ioo, Kumamoto ~~/.$:, Kunwi-gun .&lGW, Kwangyang-gun :J't~m, Mifune mJ~, Mukeodong ~~¥I"J,
Nadong-myeon ~1I".I00, Naegokdong p;]:fr¥I"J, Naegokji p;]:frl'lli, Naeidong p;]~¥I"J,
Okbongdong .:K ~ ¥I"J, Seonsan-gun ~ LlJ m, Sumoondong11".1, Wakino Mb!l!f,
Yangpori ~rm!l!, Yeonhwadong ~n¥I"J, Yusuri :wn~!I!

* r,

*.i£

=

• §!I B lIE~ ifF #ij 1:. i3c J'l. Plicatounio .Ii ~~ -') ~'-C: Plicatounio ~ m ~ ft-e ;h G
Plicatounio (Plicatounio) naktongensis ~m;;;t:ttl!.~~tr 10 :ttl!.,~iJ' 1?:J3lE$ L. t.:o .:.:h I? fi-t""" -C.§!1 ~ Gyeongsang Group ~ Hasondong Formation ~~ ~ '1 :h G ~ I? ~~ B /.$: ~ mJ~ 11
MtJ: I? <1t~Mb!l!fIlM~ 2 :ttl!.,~iJ' l?/.$:ft~:J3lE$ L. t.:o /.$:~)(-C:·fHlHm-.~ (hinge structure)~~l± § L. -cm;;;tftH~W L. t.:o 1&{I!~tim- (postero-lateral hinge teeth) ~~~ I?:hG~tim-tI\~~U(crenuation) fifJJ1:.i¥JtJ:.~-e, -t~1f1!\lifi1t:o ~f*fttl\1i\1~~~{*-t" G ?b ~-C:';h Go /.$:Wf~-e 2 ~ft P. (P.) okujuni c P. (P.) yooni Hno~~ L. t.:o~ ~*0Trans. Proc. Palaeont. Soc. Japan, N.S., No.IS4, pp.96-116, 14 Figs., June 30,1989

878.

UPPER CRETACEOUS ELASMOSAURID (REPTILIA,
PLESIOSAURIA) FROM HOBETSU,HOKKAIDO, NORTHERN JAPAN*
HIDEO N AKA Y A
Department of Earth Sciences, Faculty of Education,
Kagawa University, Takamatsu 760

Abstract. An elasmosaurian fossil is described from the Upper Yezo Group exposed
along the Sanushube River, Hobetsu-cho, Hokkaido, northern Japan. Other fossils associated with the elasmosaurian specimen indicate an early Campanian age (Late Cretaceous).
The specimen is represented by a partial skeleton of the trunk and parts of limb bones. The
specimen exhibits a characteristic morphology of the family Elasmosauridae (Reptilia,
Plesiosauria, Plesiosauroidea), but its generic and specific positions are indeterminable.
The distribution pattern of the known Jurassic and Cretaceous plesiosaurians suggests that
the Cretaceous Plesiosauria of northeastern Asia is a migrant from North America throughthe North Pacific region.
Key words.
Japan

Reptilia, Plesiosauria, Elasmosauridae, Cretaceous, Hokkaido, Northern

ure I). The importance of the discovery waswell understood, because these bones arereferable to plesiosaurians. The Hobetsu
Research Group of Plesiosaurian Excavation

Introduction
The Plesiosauria represents one of the most
famous fossil reptiles in the Japanese Islands.
The first plesiosaurian material is the one
reported as Plesiosaurus sp. from the Futaba
Group (Upper Cretaceous), Fukushima Prefecture, Honshu, Japan (Tokunaga and Shimizu, 1926). Many plesiosaurian fossils
have been discovered from the JapaneseIslands during these sixty years (Obata et at.,1970, 1972; Suzuki, 1984), but nearly all ofthese specimens have not yet been described.
This paper presents a result of study of aplesiosaurian fossil from Hobetsu, Hokkaio,
Northern Japan.
In June 1975, Shintaro Araki of Hobetsu
Town found a block of mudstone containing
digit bones in the riverbed of a tributary of
the Sanushube River (42°55'N, 142°8'E; Fig-

Figure 1. Locality map. Arrow shows the
locality of the plesiosaurian fossil (HMG I). (Basemap after a IS-minute quadrangle topographic map"Momiziyama" of Geographical Survey Institute).

*Received September 16, 1988: revised manuscript
accepted May 22, 1989
96

878.

Upper Cretaceous elasmosaurid from Japan(HRGPE) was soon organized by the joint
participation of Hobetsu Town Board of
Education, Mountain Club of Hobetsu, Conservation Club of Hobetsu, HistoricalMuseum of Hokkaido, Geological Survey of
Hokkaido and Hokkaido University. Nearly all of the specimens recovered were excavated by HRGPE from 4th to 8th of July, 1977
and contained of about ninety calcareous
mudstone blocks (N akaya, 1982). The
plesiosaurian specimen, now being stored in
Hobetsu Museum with the registration number HMG I, was prepared by Tetsu Miyakoda
of Hobetsucho Kyodo-Shiryou-Kan (later
named Hobetsu Museum) from May 1978 to
December 1981.
This plesiosaurian fossil was reconstructed by the present author in December, 1982
(N akaya, 1984) (Figure 14-3). A part of thisstudy was presented at the 88th and 89th
Annual Meetings of Geological Society ofJapan.

Geologic setting and occurrence
The Upper Yezo Group is exposed in the
Hobetsu area (Otatsume, 1941; Matsumoto
et al., 1979, Takahashi and Wada, 1985). A
one meter thick layer of weathered mudstoneof the Upper Yezo Group has yielded many
calcareous nodules including various kinds offossils. The calcareous nodules are distributed sporadically for a distance of about 20
meters along the Sanushube River. The
plesiosaurian fossil was found both in mudstone and calcareous nodules.
The mode of occurrence of the plesiosaurian remains is briefly described as follows:
Some articulated digits lie on top of ribbones. Some bones of the pelvic girdle were
found lying on the top of the vertebral column and rib bones. Articulated cervicalvertebral column turn round on the sagittal
axis of rotation. Gastroliths are also foundin these nodules.
It is inferred that the plesiosaurian bodywas not buried as a whole at the time of97

death, because the skull, neck part and tailwere separated from the trunk and they are
missing. Various body parts had been
moved around from their original position, sothat some parts of this specimen became piled
up with each other. The specimen was later
buried in sediments (N akaya, 1985).
The following fossils occur in association
with the plesiosaurian remains.
Elasmobranchii (Kuga, 1984) Notorynchus? sp.; Cephalopoda (Takahashi and
Wada, 1985, Kito et al., 1986) Neophylloceras
subramosum Spath, Damesites sp., Gaudryceras tenuiliratum Yabe, Tetragonites sp.,
Eupachydiscus sp. and Polyptychoceras sp.;
Radiolaria (Kito et al., 1986) Acanthocircus
parvulus var. latelarispinosus (Campbell and
Clark), Patellula verteroensis (Pessagno),
K uppelella sp., Septinastrum ? sp. and so on ;Planktonic foraminifera (Kito et al., 1986)
Silicosigmoilina futabaensis Asano.
Inoceramus naumanni Yokoyama, whichindicates a late Coniasian to early Campanian age, has been reported from a site near
the plesiosaurian locality. Furthermore,radiolarians and planktonic foraminifersfrom the nodules which contained theplesiosaurian remains indicate a Campanian.
Planktonic foraminifers Globotruncana arca
(Cushman) and others which indicate an
early Campanian to early Maastrichtian age,have been reported from an outcrop near theplesiosaurian locality. Therefore, the age ofthe plesiosaurian fossil seems to be an early
Campanian from these macrofossil and microfossil evidence (Kito et al., 1986).

Preservation of materials
The vertebral column, consisting of posterior cervicals, pectorals, dorsals and sacra Is, isfound disjointedly. The dorsal ribs, ventral
ribs (gastralia), parts of pectoral and pelvic
girdles, forelimbs and hindlimbs are alsopresent.
The vertebral centrum is very well preserved, but spinous processes and transverse

Hideo Nakaya

98

processes are sometimes lacking due to a poor
state of preservation. Almost all the costal
fossa are evident, so the vertebrae can be
identified by their positions. Some posteriorcervical ribs and pectoral ribs are complete
but almost all the dorsal ribs are incomplete.
The gastralia (ventral ribs) are fragmented.
The scapula, coracoid, clavicle and interclavicle are incomplete or fragmentary. The
acetabular part of ischium and pubis ispreserved. The ilium is fragmented.
In the forelimb, both humeri are damaged;
radius, ulna and carpal bones are preserved,
but some carpal elements are lost. In thehindlimb, the shape of femur is similar to
humerus, the tibia, fibula and tarsal bones arecomplete, the metatarsal bones are complete
except for the first metatarsal. One fourth of
the whole phalanges is preserved. Ten gastroliths (stomach stones) are found.

Systematic description
Class Reptilia
Subclass Synaptosauria Baur, 1887
Order Sauropterygia Owen, 1859
Suborder Plesiosauria de Blainville, 1835
Superfamily Plesiosauroidea Welles, 1943
Family Elasmosauridae Cope, 1869
Elasmosauridae gen. et sp. indet.
Figures 2-4, 10-14
Elasmosauridae gen. et sp. indet., Nakaya, 1985, 4350, figs. 5-7, pI. I.

The material list and measurements of thematerials are shown in appendix.
Vertebra; (Figures 2, 10-1-9)
The vertebrae are large, long, and amphicoelous, their articular faces being only
slightly concave. The surface of the centrum
is smooth in well-preserved specimens. The
ventral surface has a pair of sagittal foramina: .........

z

3

n

"

, I
: I

:, :,
.' '

6
5

Figures 2. 1-5. Left lateral view of vertebrae (above) and anterior view of vertebrae (below); 1,
posterior cervical vertebra, HMG 1-3; 2, the last cervical vertebra, HMG 1-8; 3, pectoral vertebra, HMG
1-10; 4, dorsal vertebra, HMG 1-14; 5, sacral vertebra, HMG 1-45. scale=1O centimeters, (after
Nakaya, 1985)

878.

Upper Cretaceous elasmosaurid from Japan99

and a weak sagittal keel. These vertebrae
have a single costal fossa on each side. The
spinous processes of the vertebrae are arranged vertically, and do not incline posteriorly.

columnar. The cross section of the caput of
the rib is circular and becomes elliptic dorsoventrally in the posterior part. Some cervical ribs are fused with the vertebrae.

Cervical Vertebra
The cervical vertebrae are more elongatedantero-posteriorly than other vertebrae. The
anterior and posterior faces are elliptical
dorso-ventrally. The costal fossa is developed on the ventral edge of the centrum andgradually moves dorsally near the pectoralvertebra. The arch does not fuse with thecentrum, and is sometimes completely separated.

Pectoral Rib
The body of the pectoral rib is short andtakes the form of triangular column with acrest. The caput of the rib is circular in crosssection or becomes elliptic dorso-ventrally.

Pectoral Vertebra
The costal fossa of the pectoral vertebra isdeveloped partly on the centrum and partly
on the arch. The anterior and posterior faces
are higher than those of the cervicals.
Dorsal Vertebra
The centrum of the dorsal vertebra is higher
and larger than that of other vertebrae andtheir ends are circular in cross section. The
transverse processes are extended dorsolaterally and are cylindrical in outline. The
costal fossa is present near the turminus of thetransverse process.
Sacral Vertebra
The articular faces of the vertebra are elliptic in outline, flattened dorsally and swollen
ventrally. The transverse processes are short
but laterally high. The costal fossa is developed between the centrum and the arch of thevertebra. The fossa is a chevron-shaped
depression.
Ribs; (Figures 11-1-5)
The body of the rib is columnar. The rib
has a single caput on the end of the body inwell preserved material.

Cervical Rib
The body of the cervical rib is short andDorsal Rib
The body of the dorsal rib is long, straight,
thick and columnar. The cross section of thecaput of the rib is elliptical dorso-ventrally.
Almost all the dorsal ribs do not fuse with thevertebrae.
Sacral Rib
The body of the sacral rib is short, columnar and slightly bending ventrally. The
caput of the rib is chevron shaped and isrectangular in cross section.
Gastralia (Ventral rib); (Figures 11-6-8)
Apart from these general features, the gastralia (ventral ribs) are morphologicallydivided into two types.
One is the normal type (Figure 11-6) whichtakes a normal shape as gastralia. Almost
all the gastralia belong to this type. These
gastralia are long with a dorsal groove but
bear no caput (Figure 11.-6).
Another is the atypical type (Figures 11-7,8) which is characterized by a bifurcatedbody. Two gastralia belong to this type andthey are somewhat different from each other.
Namely, one is flattened (Figure 11-7) whereas the other is columnar (Figure 11-8).
Also, these gastralia have no caput.
Pectoral girdle; (Figures 12-1-3, 6)

Coracoid and Scapula
The medial part of the scapula and theantero-medial part of the coracoid form the"midline bar". The midline bar of the cor-100

Hideo Nakaya

acoid distinctively extends anteriorly. The
lateral part of the scapula extends posteriorly.
The scapula contacts with the coracoid, butthey do not fuse with each other. The
grenoid cavity is an elliptical opening
antero-posteriorly. The posterior part of thecoracoid is long, thin, and flat. The posterior edge of the coracoid seems to be curved
posteriorly. The lateral edge of the coracoid
is missing.

Clavicle and Interclavicle
The clavicle and interclavicle do not fusewith each other, and these bones are separated
from the scapula and coracoid. The body ofthe clavicle is thick, platy and triangular inshape. The mesial edge of the body has acrest. The interclavicle is made of one element. The body is crescent shaped withround ends and bends ventrally. The anterior end of the interclavicle is thick andconcave posteriorly.
Pelvic girdle; (Figures 12-4, 5)

Ischium and Pubis
In comparison with the grenoid cavity ofthe pectoral girdle, the acetabulum of theischium and pubis is turned caudo-Iaterally.
The external line of the obturator foramen
curves gently. The ischium and pubis are
more robust than the pectoral girdle.
Ilium
The ilium is separated from the ischiumand pubis. The body of ilium is platy andits platy end fans out dorsally. The dorsal
part of the ilium is preserved.
Forelimb; (Figures 3, 13-3-7, 14-1)

HumerusThe humerus is short and robust. The
process of the humerus curves anteriorly.
The shaft is thick and columnar. The distal
part of the humerus is not well preserved, andits surface is suffered some damage. How-ever, its tuberosity runs parallel to the head.
The length and breadth of the ulnal articularsurface of the humerus are slightly larger thanthose of the radial surface. The proximaland distal parts of the humerus are rugose.
The rugosities of these parts extend to the endof the humerus.

Ulna and Radius
The ulna and radius seem to have noappendicular bone. The internal faces of theulna and radius are concave. These bones
are short and thick. In the medial view,
these bones are flat pentagon in shape. The
rugosity is developed on the proximal anddistal parts of these bones.
Carpal and Metacarpal
The carpal bones are not complete, but theproximal and distal rows of the carpal possibly comprise three bones each in the row.
The radiale is parallelogram-shaped withrounded corners. The intermedium is flatand hexagonal in shape. The metacarpal isshaped very similarly to the phalanx. Sizealone distinguishes the metacarpal from thephalanx. The metacarpal is larger than thephalanx.
Phalanx
The number of phalanges in each digit
seems to exceed more than ten. The phalanxof the forelimb is difficult to discriminate
from that of the hindlimb. The body of thephalanx takes a spool-like shape. The proximal and distal articular surfaces of thephalanges are convex. Bodies of the first andfifth phalanx become thin laterally. The
sagittal section of the whole forelimb shows astream-lined shape.
Hindlimb; (Figures 4, 13-1-2, 14-2)

Femur
The femur is slightly thinner, shorter andslender than the humerus. Its trochanterruns parallel to the head. The tibial

878.

Upper Cretaceous elasmosaurid from Japan

D"' ",.

101o~<:)25~

E?c9'HiFYl

I~

tlml~

~~~H~
~D[JL]g
Lll:W
LIDO\JflllFigure 4. Reconstruction of hindlimb.
scale== IO centimeters. (after Nakaya, 1985)

DOl]
1Il71lo fl 0Figure 3. Reconstruction of forelimb.
IO centimeters. (after N akaya, 1985)

scale==

articular surface of the femur is similar in size
to its fibulal articular surface. Both theproximal and distal parts of the femur arecovered by rugosities likely manner as thoseof the humerus.

Tibia and Fibula
The shape and rugosity of the tibia andfibula are similar to those of the radius andulna, but these bones are slightly smaller than
the radius and ulna. The tibia and fibula
have no appendicular bones.
Tarsal and Metatarsal
The size of the tarsal bones is smaller thanthat of the carpal bones. The shape of thesebones is similar to that of the carpal. The

proximal and distal rows comprise threebones each in the row. The position of thefifth metatarsal moves proximally to that ofthe distal tarsal row. The metatarsal is very
similar to the phalanx in shape.

Phalanx
The phalanx of the hindlimb resembles thatof the forelimb. The hyperphalangy seems
over ten phalanges. The sagittal section of
the hindlimb is shaped in the same streamlined shape, as the forelimb.
Gastrolith
Subangular to round and pebble tocobble-sized stones with glossy surface arefound in the trunk part of the plesiosaurian
skeleton. These stones are mudstone, finegrained sandstone, black shale, chert andgreen rock. They differ from rocks that

Hideo Nakaya

102

Saint-Seine, 1955; Romer, 1956; Talro,
1960; Persson, 1963; Novozhilov, 1964;
M iiler, 1968; Brown, 1981). Many generaand species have been proposed, althoughsome new species were based on only one
vertebral body or one digit. According toBrown (1981), a large number of existing taxa
are considered being invalid. It is now generally accepted that the suborder Plesiosauria
can be divided into two superfamilies

include the fossil specimens. These stones
are regarded as gastroliths (stomach stones).

Discussion
Comparison
A great deal has been written about theclassification of Plesiosauria (e.g. Andrews,
1910, 1913; Williston, 1925; Nopcsa, 1928;
Kuhn, 1934, 1964; Welles, 1943, 1952, 1962;
Table l.

Comparison of characters of the limb bones of the Hobetsu specimen (HMG I) and theCretaceous Plesiosaurian superfamily, family and subfamily from Romer (1956) andWelles (1962). (characher present: I, character absent: 0, in cervical rib, double
headed: 2, single headed: I)

Romer(l95G).

Superfam i I y

PLESIOSAUROIDEAPLIOSAUROIDEA

HMG 1

short

I

0

1

I

0

1

PI i osa- Polyco- Leptour idae tyl idae cleidae

HMG 1

!

cerv I ca I icentrum I IIi th lateral keel

Plesio- Thaumato
sauridae sauridae

Fami Iy

head of cervical rib-Ishort
epi pod ial I
II i th accesso ry bones

I
I

Elasmosauri dae

1

2

1

1

1

0

1

0

1

0

1

0

0

1

1

2

2

0

IJelles(J962)
Superfam i I y

PLESIOSAUROIDEAPLIOSAUROIDEA

HMG 1cerv. centrum long

1

0

1

propodial long

0

I

0

f i bual faset>tibial

0

1

0

Fami Iy

PI es i osaur idae

EI asmosaur i dae

PI iosauridae

Do I i co I i ncop i dae

HMG 1head of cervical rib

2

1

2

1

1

epipodial short

0

1

0

1

1

Subfami Iy

mid line bar

1Elasmosau r i nae

Alzadasaur i nae

HMG 1

I

0

1

878.

Upper Cretaceous elasmosaurid from Japan

Plesiosauroidea and Pliosauroidea, but sometaxa are referred two differing superfamilies
by different authors. For example, Thaumatosaurus is classified as Pliosauroidea bySaint-Seine (1955), as Plesiosauroidea by
Romer (1956) and as Plesiosauria incertae
sedis by Novozhilov (1964). Therefore, theclassification scheme of Plesiosauria is not yet
settled.
In the Hobetsu specimen (HMG I), thecervical vertebra is not long, the humerus islarger than the femur, and the tibial articularsurface of the femur is similar in size to thefibulal articular surface. These characters
indicate that the Hobetsu specimen belongs to
the superfamily Plesiosauroidea (Romer,
1956; Welles, 1943, 1952, 1962). Furthermore, the ulna, radius, tibia and fibula are notslender and the caput of cervical rib is single
headed. Such characters suggest that the
specimen is assignable to the family Elasmosauridae (Romer, 1956; Welles, 1943,
1952, 1962; Novozhilov, 1964). Judging
from Welles' description, the midline bar(pectoral bar) of the pectoral girdle of thepresent specimen shows those characters of
the subfamily Elasmosaurinae (Elasmosaurus
and Brancasaurus; Table 1). However,
Brown (1981) claimed that this character is
exclusively observed only in an adult (Table
1). Such elasmosaurids as, Alzadasaurus,
Hydrotherosaurus and Elasmosaurus have noappendicular bone of the epipodial of both
limbs, but such a bone is present in the forelimb of Morenosaurus, Aphrosaurus andThalassonomosaurus.
The presence of appendicular bone of the
epipodial is the important character for theparticular group of the family Elasmosauridae. The Hobetsu specimen has no appendicular bone of the epipodial of the hindlimb.
However, it can not be determined, whether
or not the appendicular bone of the forelimb
is present or not because of the state of preservation. In this respect, the Hobetsu specimen is referable to the family Elasmosauridae, but its generic and specific positions are103

indeterminate.
Analyzing morphological characters of theUpper Jurassic Plesiosauria, Brown (1981)
divided them into four categories, i.e.
"ontogenetic growth," "specific and genericdiagnoses," "primitive and advanced grades"and "divergent evolutionary trends." He
used not only the characters of limbs andgirdles but also those of skull. Because skull
characters play the essential role in theclassification of Reptile, his classification ismost useful. However, he did not deal with
the Cretaceous Plesiosauria.
Nevertheless, the Hobetsu specimen (HMG
1) lacks the skull and a large part of girdles.
Therefore, the Hobetsu specimen cannot besatisfactorily analyzed to ascertain the existence in it of those characters representing thefour categories recognized by Brown (1981).
The Cretaceous strata of the JapaneseIslands have yielded some plesiosaurian
remains. Among them, only one small
centrum from the Futaba Group (Late
Cretaceous) was described by Tokunaga andShimizu (1926), but other materials were reported only preliminarily.
Tokunaga and Shimizu (1926) assigned
their specimen to the anterior cervical vertebrae of Plesiosaurus sp., but measurements ofthe specimen do not agree with the cervicalvertebrae of the Plesiosauroidea. Theseauthors measured its length, breadth andheight as 22, 49 and 21 mm, respectively.
Judging from their photograph (pI. 23, figs.
la, b, c), the specimen seems too short anteroposteriorly being assigned to the cervicalvertebrae of the Plesiosauria (original specimen was lost by air raid during the Second
World War). It has two articular surfaces
for cervical rib, being elongated laterally, andlacks lateral keel. Therefore, this material isidentifiable with the cervical vertebrae of the
Pliosauroidea.
The second plesiosaurian from the Futaba
Group is well preserved (Obata et al., 1970).
This specimen consists of a skull, vertebra,
ribs, pectoral and pelvic girdles and hind-Hideo Nakaya

104

ians range in age from the Cenomanian to
Maastrichtian. Most of them are fossils of
the superfamily Plesiosauroidea, but a few
belong to the superfamily Pliosauroidea.
The materials reported by Tokunaga andShimizu (1926) belong to the latter taxon, notto the Plesiosauroidea as originally given.
The migration route of the Plesiosauria is
an important problem. According to thefossil record of the Plesiosauria, they
distributed mainly in western Europe
throughout the Early Jurassic Period (Figure6). During Late Jurassic times, it invaded
the region of Urals and China through the
Tethys Sea and the mid-western region of
North America (Figure 7). Furthermore, it
spread to the Pacific coast of Central Americaand Australia during the Early Cretaceous

limbs. Obata et al. (1970) mentioned that it
resembles somewhat Alzadasaurus, Hydrotherosaurus or Morenosaurus, but it is distinct
from any known species of Plesiosauria.
Unfortunately, no systematic description ofthis material has been published, and the
Hobetsu specimen cannot be compared indetail with this material.
Distribution
Around the Japanese Islands, specimens of
the Plesiosauria have been recovered from theLate Cretaceous strata of the Iwaki region in
Hoshu, Urakawa, Hobetsu, Mikasa, Obira,and Nakagawa areas in Hokkaido, and Sakhalin Island (Riabinin, 1915; Tokunaga andShimizu, 1926; Obata et al., 1970, 1972;
Suzuki, 1984) (Figure 5). These plesiosaur-Il£U@
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65Ma~>liil;;J\l?1iS1liJlln>lliil

72

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l1::>lffiID[1Jillliil!OlIiil

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83

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,

,

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90

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rn!W@Iiil~OlIiil

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11::@Iiil@ffiID@!j\]~OlIiil

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if
"¢)<"

~x

Figure 5. Temporal and spacial distribution of the Late Cretaceous Plesiosauria in northeastern Asia.
(Revised from Riabinin, 1915; Obata et al., 1970, 1972). Plesiosauroidea:., Pliosauroidea: 0,
Plesiosauria indet.: X.

878.

Upper Cretaceous elasmosaurid from Japan

Figure 6. Distribution of the Plesiosauria in
the Early Jurassic. (Paleocontinental arrangement
is after Smith and Briden, 1977 with some revision;
Paleogeographic distribution of the Plesiosauria is
compiled from Persson, 1963; Obata el al., 1970,
1972; Welles and Gregg, 1971; Dong, 1980; Suzuki, 1984; Zhang, 1985)
Plesiosauroidea: . , Pliosauroidea: 0, Plesiosauria indet.: X. N; North pole, S; South pole, AF ;Africa, AN; Antarctica, AS; Asia, AU; Australia,
EU; Europe, GN; Greenland, NA; North America, PA; Pacific Ocean, SA; South America, SC;
Sichuan (South China), TE; Tethys Sea, UT;Urung-Tumus (North Siberia), WAF; West Africa,
WE; West Europe.

Period (Figure 8). In the Late Cretaceous,
the range of Plesiosauria expanded to the
Pacific coast of South America, New Zealandand the Japanese Islands and attained thewidest distribution (Figure 9).
According to the distribution of thePlesiosauria around the Japanese Islands, in
Middle to Late Jurassic times, Sinopliosaurus(Young, 1944), Bishanopliosaurus (Dong,
1980) and Yuzhoupliosaurus (Zhang, 1985)
seem to have migrated into the southern
region of China through the Tethys Sea.
However, the Late Cretaceous Plesiosauria
occurred around the Japanese Islands probably migrated from North America and or
North Europe into Japan through the North

105

Figure 7. Distribution of the Plesiosauria inthe Late Jurassic.

Figure 8. Distribution of the Plesiosauria in
the Early Cretaceous.

Pacific region. Especially, the present
author considers the Plesiosauroidea of Japan
is to be a possible boreal element, not of aTethyan element, because at present there isno evidence of migration from the Tethys.
This idea is also corroborated by the evidence
based on the upper Cretaceous bivalvesHideo Nakaya

106

Figure 9. Distribution of the Plesiosauria In
the Late Cretaceous.

(Tashiro, 1985).
Conclusions
The plesiosaurian specimen from Hobetsu,
Hokkaido, northern Japan comprises the
body part exception of skull, and such bodyparts as mandible, anterior cervical, and caudal vertebrae. The morphological charactersof this specimen exhibit those referable to thefamily Elasmosauridae, although its genericand specific positions cannot be determinedbecause of its poor state of preservation.
This specimen was obtained from early
Campanian rocks of the Upper Yezo Group
as its age indicated by associated invertebrate
fossils. The elasmosaurid of the JapaneseIslands is interpreted to have migrated during
the Late Cretaceous via North Pacific region
in the likely manner as the marine bivalve
faunas.
Acknowledgments
The present author is deeply grateful toProfessor T. Kamei of Kyoto University andProfessor S. Uozumi of Hokkaido University

for guidance during the course of this works.
He is much indebted to Drs. Y. Kawamura of
Aichi University of Education, N. Kuga and
H. Saegusa of Kyoto University, D.S. Brownof the University of Newcastle, R.T. Zanon of
the University of Chicago, S.P. Welles of the
University of California, P.O. Persson of
Harby, Sweden and Messrs. R. Hirayama of
Kyoto University, M. Watabe of HistoricalMuseum of Hokkaido, T. Suzuki of Iwaki
Museum of Coal and Fossil, for their helpfuladvice and various suggestions on this subject. Furthermore, the present author would
like to thank Mr. S. Suzuki of Hobetsu
Museum, Dr. K. Takahashi of Geological
Survey of Hokkaido, Dr. M. Akamatsu ofHistorical Museum of Hokkaido and Mr. N.
Kito of Hokkaido University for valuable
discussion on the geological setting andoccurrence of this specimen, and finally
wishes to thank Mr. K. Kon of the Director of
Hobetsu Museum for providing the sample
and permission to publish this works.
References cited
Andrews, C.W., 1910: A descriptive catalogue of themarine reptiles of the Oxford Clay. (Pt. 1).205
p., British Museum (Natural History), London.
- - , 1913: Ditto (Pt. 2). 206 p., British Museum(Natural, History), London.
Brown, D.S., 1981: The English Upper Jurassic
Plesiosauroidea (Reptilia) and a review of thephylogeny and classification of the Plesiosauria.
Bull. British Mus., Nat. Hist. (Geol.), 35(4), 253347.
Dong, Z.M., 1980: A new Plesiosauria from the Liasof Sichuan Basin. Vert. PalAsiatica, 18(3), 191197, pis. 1-2.'"
Kito, N., Kaiho, K., Takahashi, K. and Wada, N.,
1986: Geologic age of the plesiosaurian fossil
from Hobetsu-cho, Hokkaido, Japan. Bull.
Hobetsu Mus., 3,1-7, pis. 1-3.*
Kuga, N., 1984: Note on Cretaceous shark tooth
associated with plesiosauroid reptile from
Hobetsu-cho, Hokkaido. Ibid., 1,33-36.**
Kuhn, 0., 1934: Fossilium Catalogus, I: Animalia
Pt. 69, Sauropterygia. 127 p., W. Junk, Gravenhage.
- - , 1964: Fossilium Catalogus, 106: Sauropterygia (Supp. I). 72 p., W. Junk, Gravenhage.

878.

Upper Cretaceous elasmosaurid from Japan

Matsumoto, T., Kanie, Y. and Yoshida, S., 1979:
Notes on Pachydiscus from Hokkaido (Studies
on the Cretaceous ammonites from Hokkaido
and Saghalien-XXXIX). Mem. Fac. Sci., Kyushu Univ., Ser. D, Geol., 24(2), 47-73, pis. 8-13.
Miller, A.H. (ed.), 1968: Ordnung Sauro pterygia.
In Lehrbuch der Paliiozoologie. Bd. 3(2), 145188, Veb Gustav Fisher Verlag, Jena.
Nakaya, H., 1982: Excavation of the plesiosaurian
fossil in Hobetsu, Hokkaido. - A note of evolution and distribution of the Plesiosauria-.

The Nature and Animals (Doubutsu to Sizen),2( 6), 11-16.'- - , 1984: Restoration of the plesiosauroid reptile
from Hobetsu-cho. Bull. Hobetsu Mus., I, 3740.'- - , 1985: Preliminary report of plesiosaurian fossil(HMGI) from Hobetsu-cho, Hokkaido, Japan.
Ibid., 2, 43-50.'
Nopcsa, F.B., 1928: The genera of reptiles.
Palaeobiologica, I, 20-44.
Novozhilov, N., 1964: Order Sauro pterygia. In
Orlov, Yu. A., ed., Osnovy Paleontologii, Tom.
15, 299-332, Nauka, Moskva.#
Obata, I., Hasegawa, Y. and Suzuki, T., 1970: Discovery of elasmosaur from the Upper Cretaceous
Futaba Group. Jour. Geol. Soc. Japan, 76(3),161-164.'- - , - - , and Otsuka, H., 1972: Preliminary reporton the Cretaceous Reptile fossils from Hokkaido.
Mem. Natn. Sci. Mus., 5, 213-223."
Otatsume, K., 1941 : On the overthrust-sheets in thesouthern part of the Isikari Coal-Field, Hokkaido. Jubilee Publ. Commem. Prof. H. Yabe
60th. Birthday, vol. 2, 973-988."
Persson, P.O., 1963: A revision of the classification of
the Plesiosauria with a synopsis of the stratigraphical and geographical distribution of thegroup. Lunds Univ. Arsskrift, N.F. Avd. 2,
59(1),59 p.
Riabinin, A., 1915: Notes on Plesiosaur from Sakhalin Island. Geol. Vestn., I, 82-84. #Romer, A.S., 1956: Osteology of Reptiles. 772 p.,
Univ. Chicago Press, Chicago.
Saint-Seine, P., 1955: Sauropterygia. in Traite dePaleontologie, Tom. 5, 420-458, Masson, Paris.
Smith, A.G. and Briden, J.e., 1977: Mesozoic andCenozoic paleocontinental maps. 63 p., Cambridge Univ. Press, Cambridge.
Suzuki, S., 1984: On Cretaceous reptiles from Hobetsu-cho, Hokkaido (Preliminary report). Bull.
Hobetsu Mus., 1,47-52.'
Takahashi, K. and Wada, N., 1985: Geology ofHobetsu-cho. Ibid., 2, 1-15.'
Talro, L.B., 1960: A review of upper Jurassic
Pliosaurs. Bull. British Mus. Nat. Hist. (Geol.),4(5), 147-189, pis. 20-28.

107

Tashiro, M., 1985: The bivalve faunas and theirbiostratigraphy of the Cretaceous in Japan. Mem.
Geol. Soc. Japan, 26, 43-75."
Tokunaga, S. and Shimizu, S., 1926: The Cretaceous
formation of Futaba in Iwaki and its fossils.
Jour. Fac. Sci. Imp. Univ. Tokyo, Sec. 2, I, 181212, pis. 21-27.
Welles, S.P., 1943: Elasmosaurid Plesiosaurs withdescription of new material from California andColorado. Mem. Univ. Calif., 13, 125-217, pis.
12-29.
- - , 1952: A review of the North American
Cretaceous Elasmosaurs. Univ. Calif. Publ.
Geol. Sci., 29(3), 47-144.
- - , 1962: A new species of Elasmosaur from theAptian of Colombia and a review of theCretaceous Plesiosaurs. Ibid., 44(1), 1-96.
- - and Gregg, D.R., 1971 : Late Cretaceous marine
reptiles of New Zealand. Rec. Canterbury
Museum, 9(1), 1-111.
Williston, S.W., 1925: The osteology of the reptiles.
300 p., Harvard Univ. Press, Cambridge (reprinted by Society for the Study of Amphibians
and Reptiles in 1971).
Young, e.e., 1944: On the reptilian remains from
Weiyuan Szechuan, China. Bull. Geol. Soc.
China, 24(3-4), 187-210.
Zhang, Y., 1985: A new plesiosaur from Middle
Jurassic of Sichuan Basin. Vert. PalAsiatica,
23(3), 235-240, pis. 1-2. , ••• . in Japanese, ": in Japanese with English
abstract, • ": in Chinese with English abstract, #: inRussian.

Appendix
Material list of HMG 1
cervical vertebra (HMG 1-) 1-9, 12; pectoralvertebra 10, II ; dorsal vertebra 13-44; sacral vertebra 45, 46; cervical rib 9; pectoral rib 47-54; dorsal
rib 55-115; sacral rib 116-119; rib or chevron
120,251; gastralia (ventral rib) 121-136; bifurcatedgastralia 137, 138; scapula 139; coracoid 140, 141,
145, 149; clavicle 142; interclavicle 143 ilium 144;
pubis 150; ischium 151; humerus 153, 154; radius
158, 159; ulna 160; radiale 165, 172; carpal intermedium 166; distal carpal II 173: distal carpal III +IV 174; metapodial 195, 197-201; phalanx 179-194,196,202-217,220-239,241-246,248-250;
femur 155, 156, 157; tibia 161, 162; fibula 163, 164;
tibiale 167, 168; fibulare 170; tarsal intermedium
169, 171; distal tarsal I 177; distal tarsal II 175;
distal tarsal JII + IV 176; carpal or tarsal 178, 252-255,258,259; bone fragments 175-177,218,219,
240, 247, 256, 257, 260, 261 ; gastrolith 262-271.

Hideo Nakaya

108
Table 2.

1
(HMO 1-)
I

2
3
4
6
7
8
9
10
II

225

2

3

6

7

77
76
79

78
108 10575
111 115
83 148 112 106

III

4

5

124

Measurements of the vertebrae. (mm)

8

9

64

65
63
64

III

82
79 81 149 115
83 83 120 115
82 79
116
81 89
III
101 91
114
76 70
105
88 88
102
195 100 101 95 106

229

114
117
112
112
118
94
107
105

108
126
119
117
121
120

12
13
14
235+
15
88
115
16
88 94
78
190+
18
110
156+
19
110
20
100 107150+
21
106 10822
99 97
103 9523
194 102 104 94 82
80+
24
95
107
25
97 96
85+
26
82
27
145 84 82
99 78
28
85
132
29
110+
30
118
220+
34
99
37
90
41
43
45
163 85 83 79 93 94 115 III
Explanation for the measuring points.
1 greatest height
2 height of the cranial face of the body
3 height of the caudal face of the body
4 height of the spinous process
5 breadth of the cranial face of the body
6 breadth of the caudal face of the body
7 breadth of the costal fovea part of the body
8 breadth of the transverse process
9 cranio-caudal length of the body
10 cranio-caudal length of the spinous process
11 breadth of the cranial articular process10

11 12 13 14 15 16 17 18 19 19' 20 20'

75 42
53

38
38
38
61 94 45 43
59 95 45 37
61 94 42 33
57
37 28
64
62 53
65
45
75 47

33

39

28

29

27

35

37
38

36

39
32

30 26

25
29
35
35

35
27 28 26 31
30 34 25 33
34 43 30 27
34 34 44 22

20
25
34
30
33

32

21

30 33 45

64

35

51 37
32

46 45

29

46

34 29

71
73
71
71
57

77

72

57
65

32
87

52 39
52 41

32
34
26
22 49
49

36 21
35

25 46
44
26· 30

41

28
35

73
56 46
59

81

43

32

36

28

56

59

34

12 breadth of the caudal articular process
13 cranio-caudal length of the costal fovea (left)
14 ibid. (right)
15 height of the costal fovea (left)
16 ibid. (right)
17 height of the vertebral foramen
18 breadth of the vertebral foramen
19 longer diameter of the end of the transverse process
19' ibid. (opposite side)
20 shorter diameter of the end of the transverse process
20' ibid. (opposite side)Upper Cretaceous elasmosaurid from Japan

878.
Table 3.
I
(HMG 1)
52
45
55
42
24
57
44
59
48
60
61
35
64
21
66
26
24
67
20
68
69
27
70
71
35
72
43
22
73
74
26
75
22
76
39
27
77
23
79
25
80
82
83
38
22
84
29
85
28
86
87
44
51
88
43
89
21
90
22
92
24
93
25
94
26
95
26
96
41
97
24
98
100
33
36
101
24
102
26
103
22
104
24
105
32
106
37
107
23
108
24
109
19
110
23
111
25
112
27
113
29
114
115
30
116
55
49
117
118
50
119
59

Measurements of the ribs (dorsal ribs). (mm)
2

3

4

5

6

7

8

21
22
18
14
29
20
16
12
13
15
21
18
26
25
14
13
17
21
19
17
13

29
27
21
25
24
27
20
19
19
20
25
29
23
27
16
25
21
22
16
20
25

15
15
14
13
12
13
14
15
13
14
19
18
11
19
15
13
16
17
16
18
13

15
23
16
26
21
24
19
20
11
29
27
26
10
25
16
24
23

9
14
9
16
13
15
11
8
20
5
19
18
10
21
16
14
12

264
146
104
141
109
110
144
257
242
264
223
172
203
203
167
110
209

18
17

10
17
26

15
21
13

14
21
16
21
29
30
35
16
12
14
19
17
20
15
18
14
24
22
21
15
19
17
11
20
19
16
20
16
21
20
21
24
25
29
25

29
22
25
27
23
33
27
25
20
18
24
24
26
26
24
23
19
25
25
24
25
27
25
24
23
23
25
22
23
24
23
20
24

15
18
21
18
16
20
13

28
20
22
23
24
25
21
25
20
20
23

17
14
20
17
19
19
14
10
17
17
19

23
25
22
16
23
23
24
24
23
23
29
24
21
22
26
24
22
24
22
23
22

19
22
21
24
17
20
20
23
21
21
11
20
19
13
16
19
18
17
17
19
20

103
125
150
116
173
130
106
165
144
157
164
179
160
212
197
197
207
189
210
189
147
192
191
190
208
146
150
145
145
149
145
183
132
187
103
90

24

25

44

23

104

12
12
17
18
23
18
19
26
20
23
21
17
18
17
13
20
19
14
16
18
18
17
15
22
24

Explanation for the measuring points.
I longer diameter of the proximal end
2 shorter diameter of the proximal end
3 longer diameter of the middle of the body
4 shorter diameter of the middle of the body
5 longer diameter of the distal end
6 shorter diameter of the distal end
7 total length (remain part)
8 bending index

11
22
16
25
18
19
9
30
4
6

7
10
24
15
16
9
9

23
19

14

3

11

19
9
22

Table 4.
1
2
(HMG 1-)
179
34
180
33
181
182
29
183
29
184
27
186
38
187
188
43
189
44
190
37
191
25
192
43
194
26
195
38
196
43
197
42
198
41
44
199
200
45
201
35
202
41
203
39
205
38
206
28
208
10
209
210
11+
216
18
217
22
218
219
220
27
221
25
222
223
43
224
49
225
46
28
226
227
33
228
36
229
33
230
40
231
42
232
41
233
35
234
20
235
25
236
40
42
237
238
36
18
239
240
37
241
44
242
243
46
244
37
49
245
51
246
248
40
249
45
250
35

109

Measurements of the metapodials andthe phalanxs. (mm)
3

4

5

22
26

17
18

15
15

19
22
20
27

15
14
12
19
24
19
25
19
10
29
15
24
20
20

17
15
14
17
20
23
23
21
14
22
15
23
23

30
27
28
23
35
22
34
29

6

7

40
29
32

29
23
24

42
43
43
45
40
25
36
26
37
33
40

27
30
33
34
30
31
23
33
31
42

72
63
61
56
73
48
77
72
75

46

45
37
40
36

69
73
68
65

30
23
13
22
15+
18
25
37
16
22
21
32
40

29

57
53
27
40+
36
31
43

56
57
77

42
43
44
39
39
34
26
10
11+
11
17

17
16
38
40
46
25
29
29
32
31
35
37
33
20
33
40
24
15
32

34
41
24
23
33

30
24
26
23

32
22
27

22
19
8
12
9
10
14

22
15
7
9
7
8
13

7+
14
11
12
31
27

6+
11
10
12
18
22

16
17
21

19
20
21

37
41
32

26
30
27

66
71
77

20
20
24
23
15
17
17
31
23
11
17

22
24
28
16

42
41

35
36

69
76

30
18
26
40
40
37

21
29
37
36
31

31

27

58
43
49
64
70
56
46+
60

29
22
29
34
19
19
20

24

39+
43

41

30

46

45

13
18

29

29

12
25
22
20
10
17

47
44

11
19
14+
15
20
28
11
15
16
24
32

34+
41
43
74

82
65+
74
65
80
75

Measuring points are the same as for Table 5.

Hideo Nakaya

110
Table 5.

Measurements of the limb bones (propodials, epipodials, metapodials). (mm)
2

3

4

5

6

7

89
66
80
62

72

230+

69
132
65

110
172+
107
164

273

222+
133
213

115

65

123
98
120
104+
110
79+
107
64+
75
96

125
66
55
56+
50
54
57
58
54
56

86
125
116
99+
112
71+
101
70+
72
90

119

58

117
84+
102
87+
71
83
52

45
44
52
50
35
50
38

61

38
46
50
44
41
37
38
37

103

43
45

36

72
50
40
30+
42
42
49
49
44
41
32
42
41
42
46
34
24
28
30
38
31
41

part
(HMG 1-)
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178

humerushumerushumerus
femur
femur
femur
radiusradius
ulna
tibia
tibia
fibulafibularadialec-intermedium
tibialetibialet-intermedium
fibularetibialeradialecarpal II
carpal III + I V
tarsal III + IVtarsal II

64
73
70
57
78
48
50

Explanation for the measuring points.
1 breadth of the proximal end
2 thickness of the proximal end
3 breadth of the middle of the body
Table 6.

1

3

4

5

6

48
68
42

4

82+
84
91+
81
80
72
69

48
43
37
48
40
37

68
67
54
44
76
42
66
37

58
75
50
78
85
72

46
39
35

53
65

thickness of the middle of the body

5 breadth of the distal end
6 thickness of the distal end
7

Measurements of th gastralia (ventralribs). (mm)
2

70
95

110

7

8

(HMG 1-)
121
18
21
II
14
16
14
171 12
122
25
17
21
16
20
12
150
5
123
20
14
18
II
143
124
23
13
22
II
20
9
156 12
125
22
18
24
17
25
16
150
4
126
22
21
II
12
16
201
9
7
127
21
12
24
II
23
26
130
128
17
12
15
II
7
102
II
129
23
15
19
14
20
8
223
132
23
15
23
217
12
9
6
7
134
18
7
21
12
14
13
313 31
137
315
138
165
Measuring points are the same as for Table 3.

medio-distal length

Table 7.

Measurements
(mm)

of

rock nameroundness(HMG 1-)
262 mudstone
263 mudstone
264 fine sandstone
265 fine sandstone
266 black shale
267 black scale
268 chert
269 black shale
270 green rock271 chert

subroundsubround
round
round
round
round
round
round
subangularsubroundthegastroliths.

longer shorter
diameter diameter
29
30
40
42
41
102
83
50
67
27

17
21
23
21
25
60
51
39
26
21

Figures 10_ 1, posterior view of cervical vertebra, HMG 1-3, X 1/3; 2, left lateral view of cervical~vertebra, HMG 1-3, X 1/3; 3, anterior view of first pectoral vertebra HMG 1-10, X 1/3; 4, right lateral viewof first pectoral vertebra, HMG I-10, X 1/3; 5, posterior view of dorsal vertebra, HMG 1-14, X 1/3; 6,7,
anterior view of dorsal vertebra, HMG 1-17, X 1/3; 8, anterior view of sacral vertebra, HMG 1-45, X 1/3 ;9, left lateral view of sacral vertebra, HMG 1-45 X 1/3. Scale = 10 centimeters.

878.

Upper Cretaceous elasmosaurid from JapanIII

Hideo Nakaya

11 2

1
2

3

4
5
6

8
Figures 11. 1, anteri or cervical rib, HMG I - 48, X 1/ 3; 2, posterior cervical rib , HMG I - 52, X 1/ 3; 3.
medial part of dorsal ri b, HMG 1- 105, X 1/ 3 ; 4, latera l part of dorsa l rib, HMG 1-66, X 1/ 3 ; 5, medi a l partof sacra l rib, HMG 1- 11 6, X 1/ 3 ; 6, grooved ventral rib, HMG I - 134, X 1/ 3; 7, branched ventra l rib , HMG
1- 138, X 1/ 3; 8, branched ve ntral rib, HMG 1- 137, X 1/ 3. Scale = 10 centimeters.

878.

Upper Cretaceous elasmosaurid from Japan

113

2

3,4
Figures 12. 1, ventral view of interclavicle, HMG 1- 143, X 1/ 3; 2, ventral view of clavicle, HMG 1- 142,
x 1/ 3 ; 3, ventra l view of " Midline bar" part of scapula, HMG 1- 139, and coracoid, HMG 1- 140, X 1/ 4 ;4, dorsal view of acetabulum part of ischium, HMG 1- 151 , and pubis, HMG 1- 150, x 1/ 4 ; 5, dorsa l partof ilium, HMG 1- 144, x 1/ 3; 6, posterior part of coracoid, HMG 1- 149, X 1/ 3. Sca le = 10 centimeters.

Hideo Nakaya

114

-2

Figures 13. 1, medial view of left hindlimb X 1/ 3, 1- 1, femur, HMG 1- 155, 1-2, fibula , HMG 1-161,1 3, tibia, HMG 1- 163, 1-4, fibulare, HMG 1- 169, 1- 5, intermedium, HMG 1- 170 ; 2 shaft of femur, HMG 1157, X 1/ 3; 3, latera l view of right forelimb X 1/ 3, 3- 1, humerus, HMG 1- 157, 3- 2, radius, HMG 1- 158,
3- 3, ulna, HMG 1- 160, 3- 4, radiale, HMG 1- 165, 3- 5 intermedium, HMG 1- 166. Scale = 10 ce ntimeters.

878.

Upper Cretaceous efasmosaurid from Japan

3

Figures 14. I,carpa l bone X 1/ 3, I- I, radiale, HMG 1- 172, 1- 2, distal carpal II , HMG 1- 173, 1- 3, distal
carpal III + IV , HMG 1- 174 ; 2 tarsal bones, meta tarsa ls and phalanx X 1/ 3, 2- 1, distal tarsa l II , HM G 1176, 2- 2, distal tarsal III + IV , HMG 1- 175, 2- 3, fifth metatarsal , HMG 1- 195,2- 4, proximal phalanx, HMG 1- 196, 2- 5-7, metatarsals, H MG 1- 196-20 I ; Scale = 10 cen timeters. 3, restoration o f th e elasmosaurid
skeleto n from Hobetsu, Hokkaido, HMG I. (after Nakaya, 1984.)

11 5

116

Hideo Nakaya

Hobetsu 1m,8Ij, Hokkaido ~t$~, Futaba ~~, Fukushima mill;, Honshu *;'1'1. Sanushube-Ij-:;(y"--,, Yezo.:L'/(IiN~), Iwaki~'b~, Urakawa1i'liroJ, Mikasa=~, Obira,pF-,
Nakagawa <P)II.
~$~ 1m~~~~$eD*~9.WLk.:L~~~-Ij-~~~N(.~~, gC§,.~CD §) {r.::fi: ~t$~~:J1m1m,8Ij~~-Ij-:;( y "- -')II ~ 9 §EJ! ~ .ht..:.~C (.~~, gC§, .~CD §) {r.::fiz.~~Lt..:. *~*t~c ~ tJ:? fX1*fb¥iJ{r.::fi:to ~ m!\~Hr.::fiil'I?{r.::fi~1f.f\;;f;tf&JtIl eD*c,~ -Ij-:/ r =- 7 :/ ii, I? 7J :/ /~ =- 7 :/ C ~;:t I?.h Q. *~*f;t1*~ c 1ZY!IJi~$5til~f*1f ~.h -c:to 9, ~f&, §!Ji$~iji$~:9t!tffiiil~.IMr.i L kf&t~J!!'M ~ .ht..: c ~;:t I?.hQ. i k-t-~~~i¥J!f!fl!:a.~c~<p-r· ~ 7° v y;;t-lj- ~ II.- ~~N~.:L ~ ~ ~-Ij- ~ II.-~Nt~~-t Q': c z.~L -C~'Q. LiI' L~tJT~5t~lWt~"?~'-CfV"~-r'~ Q. B *7Ulll;p.iJ)ll~
f&JtIleD*c,~.~Cf;t,;/ "- ~~UIl1f:~.§!Ji.~5t;(Pz.~WL-C.lj,Q c,~ Y7~~t$i t..:f;t~t 7;1 ~ 7J ii, l?~t:;t3f~z.~E13 L -c3fb L -C ~ t..: c ~;:t I?.h Q. .: ~.: c f;tll'Jllif~;:1.-~$~=~A~~-~c~~~i¥J~~Q.

*~~~Trans. Proc. Palaeont. Soc. Japan, N.S., No. 154, pp. 117-139, 15 Figs., July 30, 1989

879. COMPARATIVE MORPHOLOGY OF NIPPONITESAND EUBOSTRYCHOCERAS (CRETACEOUS NOSTOCERATIDS)*T AKASHI OKAMOTO
Geological Institute, University of Tokyo,
Bunkyo-ku, Hongo 7-3-1, Tokyo 113

Abstract. Nipponites and Eubostrychoceras, Late Cretaceous nostoceratid ammonites,
seem to be closely related to each other as recognized from the similar shell surface sculptureand early shell morphology. As the result of detailed comparison of their shell morphology
and stratigraphic occurrence, six discrete morphotypes were recognized by the shell surface
ornamentation and mode of coiling as well as their ontogenetic change. Both of Nipponites
and Eubostrychoceras slightly and stepwise changed their form with the time. Morphotype
A, the most primitive form of Nipponites, shares many diagnostic characters with thecoexistent Morphotype F of Eubostrychoceras, although there is a clear difference in thecoiling pattern after their early growth stage. A saltatory evolution from Eubostrychoceras
to Nipponites (meandrous form) is strongly suggested not only by theoretical aspect but also
by empirical evidence.
Key words.

Nipponites, Eubostrychoceras, Cretaceous, Hokkaido

has quite similar ornamentation to N. mirabilis on the helicoid whorls. He alreadyrecognized the affinity of Nipponites to suchcontemporary helicoid heteromorphs, anddiscussed the possibility of pathology. Berry(1928) speculated the origin of the meandrous
whorls; it was produced by the extreme
development of the retroversal hook of someheteromorphs (e.g. Heteroceras and Nostoceras). He also expected a "trochoid
coiled" species as the ancestor of Nipponites.
Matsumoto (1977) noticed the similarity ofearly stage coiling and surface sculpture
between N. mirabilis and E. japonicum, andsuggested that the former was derived fromthe latter. However, nobody yet acquired
any transitional specimen between Nipponites
and helicoid species.
Recently, I discussed this problem from atheoretical viewpoint and concluded that,even if the same computer program is applied,
continuous change of hypothetical dateresults in a drastic change of three-dimen-

Introduction

Nipponites is one of the most curious andconspicuous heteromorph ammonite genera
from Japan. It was first described by Yabe
(1904) as Nipponites mirabilis together withmany Cretaceous ammonites from Hokkaido.
First, some foreign investigators regarded it asa pathologic individual of some "Bostrychoceras-like" species, because it revealed too
extraordinary meandrous shell unlike otherheteromorph ammonites and because it wasrepresented by only one specimen at thattime. Subsequently, however, Shimizu(1926) reported the second specimen withsimilarly coiled shell, and taxonomic distinctness of Nipponites was generally confirmed.
Yabe (1904), also in the same paper, described another heteromorph species as"Helicoceras (?) japonicum" (treated here as
Eubostrychoceras japonicum (Yabe) which·Received November· 14, 1988; revised manuscript
accepted May 22, 1989
117

Takashi Okamoto

118

sional shell architecture (Okamoto, 1988c).
In this paper actual morphologic and stratigraphic data of Nipponites and Eubostrychoceras are summarized, and the phylogenetic relation between the two genera isempirically examined.
Material and methods
More than one hundred heteromorph specimens including four valid holotypes were
examined. All of them (except one of theholotypes from Sakhalin) were collected from
the Middle and Upper Yezo Groups in Hokkaido, and accompanying fossils indicate a
Turonian or Coniacian age. They share simple transverse ribs which occur at regularintervals and lack any tubercles and spines.
The shell outline of the middle growth stage
can be classified into two discrete forms:
dextral or sinistral torticone type and meandering type, which correspond to Eubostrychoceras and Nipponites, respectively. I provisionally use these two generic names in thispaper to express the major features of shellcoiling.
Information of early shell morphology anddevelopmental process of suture line is generally important to reconstruct the phylogenetic
relationship of ammonites. However, theammonitella stage of heteromorph ammonite
is rarely preserved, and even if they are observable, it might be difficult to distinguishthe early shell morphology between such
phylogenetically close groups. Furthermore,
all the specimens of the two genera share thesame sutural elements and their developmental characteristics. Yet, several morphotypes can be discriminated by the difference in the rib pattern and its ontogenetic
change both in Eubostrychoceras andNipponites. Phylogenetic relationships
between these morphotypes can be estimatedby comparing the rib patterns and stratigraphic occurrences.
The depository of specimens is as follows:
UMUT, University Museum, University ofTokyo; GK, Department of Geology, Kyushu University; WEA, Institute of Earth
Science, Waseda University; and KPMG,
Kanagawa Prefectural Museum. Consecutive specimen numbers are also given for allof the specimens examined, and their collation with register numbers is shown inAppendix Table.
General morphology and remarks

Nipponites: 53 specimens of Nipponites
were analyzed. Three growth stages (early,
middle and late) are recognized in their
ontogeny. The shell form in the early stage
is usually open planispiral, but slight torsion
and rather irregular coiling occasionallyoccur. The early whorls are followed bymeandrous whorls in the middle stage. A"symmetric plane" and a "coiling axis" arerecognized in the meandrous shell; meandering occurs equally on both side of the "symmetric plane", and the centers of whorl sections along the "symmetric plane" are locatedwell on an equiangular spira\. The meandrous shell of Nipponites consists of threefundamental modes of coiling: crioceratoid,
dextral and sinistral helicoids, and is
produced as a result of regular switching ofcoiling mode (Okamoto, 1988c). The meandrous whorls become more or less loose andirregular in the late stage. A hook-likewhorl is observed near the ~nd of this stage insome specimens.
Six types of ribs are distinguishable in thesurface ornamentation of Nipponites shell andare itemized as follows (see also Figure I).
I. Normal ribs: these occur sequentially at
regular intervals, and each of them is symmetrical in the growth directional cross section.
2. Serrated ri bs: these also occur sequentially at regular intervals. The crosssection is asymmetrical and less steep toward
the growth direction. 3. Periodic ribs: solitary and strong (highly elevated) ribs which
occur sparsely and periodically between normal ribs. 4. Periodic double ribs: pairs of879.

Nipponites and Eubostrychoceras

119

(A)
Normal ribs

Serrated ribs

!IllII......

i-.

:c.
<!).

U..J ·10 ....

:c

.-

..l.

.-

0::

Periodicdouble rib

Periodic rib~~"-ABroad rib11:c . 5~.

.

Constriction

Nipponites'!>'\.
,~--"'--~~.~r
Minor rib:Ito·2~0 .. "100

WHORL LENGTH

It(B)
0'1-'1- ._--E. ~ ~~~ .. , ..

15 mil!.
i-adoralinternal

Figure 1. Index figure showing schematic crosssections of the transverse ribs and corresponding
symbols for the description of the ontogenetic rib
pattern. Dashed line indicates the exterior trace of
inner mould.

:c_.

..- -.-<!).

UJ·:c ·10
..l

0::

'!>,

o·

:c

~ ·5

,!='
t<-

Eubos trychocerss

100

strong (highly elevated) ribs which occur
periodically at the end of the crioceratoid
coiling. 5. Broad ribs: strong and broadribs which are approximately symmetrical in
the cross section. 6. Minor ribs: faint costa
or secondarily inserted weak ribs.
Relative growth pattern between the whorl
length and whorl height was analyzed in awell preserved specimen (Figure 2-A). The
whorl height means the diameter of tube crosssection along the ventral and dorsal margins,
and the whorl length is defined as the lengthof tube center line. Because this diagram isshown in normal scale, constant relative
growth is plotted on a straight line, and its
inclination is related to whorl enlarging rate.
Two constant growth phases are recognizedin Nipponites; the first phase has a highwhorl enlarging rate and the second has arelatively low enlarging rate. They correspond to early and middle-late stages of coiling, respectively.
The angle between a rib and a normal
plane to the growth direction was measured.-

200 ....

WHORL LENGTH

Figure 2. Relative growth pattern between
whorl height and whorl length plotted on the normal
scale_ A, Morphotype A, specimen No. 71, B, Morphotype F, specimen No. 12. Two isometric phases
are similarly recognized in Morphotypes A and F_
E indicates the whorl enlarging rate in each phase.

as the rib obliquity. When ribs are rectiradiate, the value is about zero. The plus
and min us signs of this value indicate rursiradiate and prorsiradiate ribs, respectively.
Rib obliquity remarkably and regularlychanges during the ontogeny of Nipponites.
An example of rib obliquity change is shownin Figure 3-A. In the early crioceratoidstage, the obliquity is constantly small (nearlyrectiradiate). Then the value gradually
increases toward the transitional interval
between early and middle stages. In the
middle stage, rib obliquity frequently oscillates between rectiradiate to prorsiradiate
corresponding to the switching of coilingmode; rib obliquity reaches maximum andTakashi Okamoto120. ... 0'" ... '. y:\.... •.
••O• • ~q;,....
J/:J... G.. <1.~;-.. ~
..".

....

Nipponites..: . ...,.

.•.
•-...",.0 . ,.... .
.
..
••. .. , .
,....••.
,•.
••...•.. .: . •..'....

..J
CQ

30·

o
CQ

RIB NUMBER

0::

100

(A)

.

..

.
••

·.0•

• 0

'It

• • 200c

Eubostrychoceras (B)
..J
CQ

o
CQ

0::

30·

RIB NUMBER

200

c
Figure 3. Ontogenetic change of the rib obliquity in Nipponites and Eubostrychoceras. A, Morphotype A, specimen No. 72, B, Morphotype F, specimen No. 12. Solid and open circles mean normal rib
and periodic rib, respectively. The modes of coiling are also expressed with the rib number (C; crioceratoid, Hd; dextral helicoid, Hs: sinistral helicoid). After the consistent rectiradiate ribs in the early stages,
the rib obliquity regularly oscillates in Nipponites corresponding to the switch of coiling mode, while inEubostrychoceras the value increases and then maintains an almost constant prorsiradiate value.

minimum at the ends of helicoid and crioceratoid coiling modes, respectively. In somespecimens the change of rib obliquity
becomes a little obscure in the late stage.
The distribution of Nipponites is probably
confined to the Middle Turonian to theConiacian of the northern Pacific region:
Hokkaido (Yabe, 1904; Shimizu, 1926,
1933; Matsumoto and Muramoto, 1967, andMatsumoto, 1977), Sakhalin and Kamchatka(Kawada, 1929; Druczic and Pergament,
1963; Verechagin et al. 1965; Mihajlova,
1983) and Oregon (Ward and Westermann,
1977).

Euhostrychoceras: Judging from the earlyshell morphology, the genus "Eubostrychoceras" contains two discrete groups; one ischaracterized by a straight shaft aroundwhich later helicoid whorls are formed (i.e.
E. muramotoi Matsumoto, 1967 and E.
matsumotoi Cobban, 1988), and the othershows open planispiral whorls in the earlystage (i.e. E. japonicum (Yabe, 1904). In
this paper, I use this generic name restrictedly
to the latter group, though the early morphology of the type species: E. indopacificum
Matsumoto, 1967, is unknown. About 70
specimens of Eubostrychoceras were examined.
The post-ammonitella stage (early stage) of
Eubostrychoceras in very similar to that of
Nipponites and represented by open planispiral whorls. Unlike Nipponites, however,dextral or sinistral helicoid coiling mode ismaintained throughout the middle stage.
Therefore, a highly torticone shell is formed.
The axis of helicoid coiling in the middle

879.

Nipponites and Eubostrychoceras

stage does not coincide with the axis of earlier
planispiral coiling. A hook is occasionallyobserved in the adult stage. Some rib types
are shared with Nipponites; normal, periodic
strong and broad ribs are also observed, but
serrated and periodic double ribs never occur
in Eubostrychoceras. Constriction is characteristic in one morphotype of this genus (Figure 1).
An example of relative growth pattern
between whorl length and whorl height isshown in Figure 2-B. The pattern is very
similar to that of Nipponites; the whorl enlarging rate in the first phase is larger thanthat in the second phase, and the two phases
correspond well to the early and middle
stages defined by coiling pattern.
The ontogenetic change of rib obliquity
was analyzed also in Eubostrychoceras (Figure 3-B). Nearly rectiradiate ribs occur inthe early stage. After gradually increased
during the transitional stage (about one
whorl), the rib obliquity becomes about 30
degrees. The value is almost invariablethroughout the middle stage.
The distribution of Eubostrychoceras isprobably restricted to the Lower to Middle
Turonian of the northwest Pacific region:
Hokkaido (Yabe, 1904; and Matsumoto,1977), Sakhalin and Kamchatka (Verechagin
et at., 1965; Mjhajlova, 1983), though adoubtful specimen was illustrated as "Bostrychoceras otsukai" from the Santonian ofCalifornia (Matsumoto, 1959).
Morphotypes of Nipponites

Three morphotypes (A, Band C) of
Nipponites are recognized by the difference ofrib pattern (Figure 4). Each morphotype isdefined also by the coiling pattern as follows.
Morphotype A is characterized by theappearance of periodical broad ribs during
the late growth stage. Periodic ribs alsofrequently occur in the early stage of thismorphotype at regular intervals of several
normal ribs, but they are less frequent in the121

middle-late stage. The coiling pattern in theearly stage is almost simple crioceratoid,
though the ammonitella is not yet known.
The shell of this stage is thus almost planispiral and represented by more than one and ahalf whorls. The whorl diameter of thisstage is about 2-2.5 cm at most. Because of
the regular switching of coiling pattern, atightly meandrous shell is produced in the
middle stage. The switching becomes blurred in the late stage, and the meandrous shell
becomes somewhat loose in comparison withthe middle stage.
Morphotype B can be distinguished by theserrated ribs developing in the middle-late
growth stage. In the early stage this morphotype shares the combination of normal
ribs and periodic ribs with Morphotype A.
The asymmetricity in the cross section ofserrated ribs is most distinct in the later partof the middle stage, and again becomes lesstypical in the late stage. The coiling patternof this morphotype is similar to Morphotype
A, though the coiling is looser in general.
The early planispiral shell is about 3 cm indiameter. Gently meandering shell is
produced in the middle stage, and is followedby an irregularly coiled whorl, which occasionally forms a retroversal hook in the latestage.
Morphotype C is characterized by thedevelopment of periodic double ribs whichcorrespond to the switching point fromcrioceratoid to dextral or sinistral helicoid.
Though the periodic double ribs do notalways appear at the turning point, this feature serves a diagnostic character to distinguish clearly from the other morphotypes.
Ribs occur at regular intervals relative to thewhorl height. The rib pattern in the earlystage is similar to Morphotypes A and B;
some periodic ribs are observed among normal ribs. Serrated ribs, which are graduallychanged from the normal ribs, are seen in the
middle stage as in Morphotype B. The coiling pattern is sometimes irregular in the earlystage. It becomes loose and slightly irregularTakashi Okamoto

122

morphotype...9J!'
ss.."sss

777217tt1t1t1tiH! 46

2222??17I¢I

morphotype.!liJ~::_·~Q:(i_m2I~:~:1a,

~J

Lsss

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SSS_Wt!mlfll!!fllII"_"m!Uut:~ 48

L220~:::.·.·,-,-_-djIjljl§::.-.·_·_·.·-.qqqql

SS_212 .... -:\ss

22w!IfI""!I!~ 66

ad 58 ~ssb~Lbr--------,!.~:(

I 49

tltIflfllllllllllfllllllllflllflflflIIII"1II1!

sssss~::~:j!!!!!ll!!\:i!!l1!!!!!!!!!! 70

u_ssssU-'ID!U_@I!lllDllIJI!UQQllllllgI22

morphotype!;;;u:;t;s-';;t;12;2-W:;;;;;Ij[qW[l!mllll""IIll""~'N~IJm!!l!Wm11lllllWltll!mqqlll!I!U!UI!!!IIllI!!!~!!!~22;;2_;;;;;;;';;S~II 51
1m;;;;;U;L......u:J68 r "m;;;J!,w..JLJ 54
c=122
II ssJIm;;Jssl 56
1lIIW~~ym"lU!Wqqq_::::::_ 61m....

~: ....-:::.-::~:~::-.-:::::~:..:-_.::::::......-...-..:.-:::::::::_....-_:~ 57~~~\J~:~~:~:\n-IL......tW2

II sl64 ~w2-U:s;Mllm;;;;oj 59
bl-n:ssss II 2m ::;;J::. . . . . :. . . :::::::::::::~:: . :. . . . . . . . . . .::::g 63~~:::J,;-J;Csss

I H!

c::::::::\ I

""ss

ls I

"q

121

I@U:Ssss)!f1!JJ_!mrrr!l!~I1I111111""~ 124

L2I2-u.M::::9WJIlJWIII!!I11t1I(. 128...9J!' 'C'm~52~sssss~:::::~ 67

0\

-==

=
Cssss

Issss

?222~SSS

2aa" ssss265

crloceratold coilingdextral helicoId
sInIstral helicoId
heteromorph coilIng

0i

50
i

RIB NUMBER"aLL,-aL,;;;oJ 73c;;;=J;..L~::: :::(~Va;;;,;;;;;s;;SSS~!;;;;J~12~??;;;;;~ss;;ss~d 120
40(WHORL HEIGHT)

Figure 4. The onotogenetically analyzed rib pattern and modes of coiling of Nipponites. See Figure
I for the rib form symbols. The rib number is taken in the abscissa and approximate scale of whorl heightis also shown to express the specimen size. Three morphotypes can be recognized.

879.

Nipponites and Eubostrychoceras

123u

CONIACIAN
L

TURONIAN

specimen No.

46 41 53 60 62 11 12 123 125

49 48 58 66 10 122

51 54 56 51 59 61 63 64 61 121 124 128

52 51 65 61 69 13 120

Figure 5. The stratigraphic occurrence of the specimens of Nipponites examined in Figure 4. An
asterisk indicates in situ occurrence from outcrop. White rectangle indicates the possible stratigraphic
horizon which is indirectly restricted from the locality and associated index fossils. Dotted area is the
expected range of each morphotype. Three morphotypes can be distinguished also by the stratigraphic
occurrence.

also in the late stage, but retroversal hook has
not yet been confirmed in this morphotype.

Occurrence: The stratigraphic occurrenceof each examined specimen is shown in Figure 5. Biostratigraphic age of the Middle
and Upper Yezo Groups have been determined by leading fossils (e.g. Inoceramus
and short-ranged ammonites, Matsumoto
1977, 1984). Morphotypes A, Band Caredistinguished also by the different stratigraphic distribution; they occur from the Middle Turonian, Upper Turonian, and Upper
Coniacian, respectively (indicated as asterisk
in Figure 5). On the other hand, specimens
found in the derived nodules are stratigraphically less reliable, but their possible timespan estimated by the biochronological dataof assosiated fossils is consistent with thestratigraphic distribution of the three morphotypes (see white rectangles in Figure 5).
Based on these direct and indirect stratigraphic data, the presumable shortest range ofeach morphotype is shown as a dotted area in
Figure 5.
The stratigraphic range of Morphotype B
may extend to the Lower Coniacian.
Because the three morpho types are distinguished by their stratigraphic occurrences,and because any two morpho types never coexist in the same nodule, the rib pattern andits ontogenetic change are regarded as a good

criterion for natural grouping of Nipponites.
There are several immature or fragmentary
specimens (shown as A' in Figures 4 and 5) inwhich all the characters aforementioned
could not be observed. These specimens
possess, however, some diagnostic charactersof Morphotype A.
Furtermore, Morphotypes A and A' sharethe same stratigraphic range, and they sometimes occur from the same nodule. Therefore, these specimens can be included inMorphotype A, though the ontogenetic
change of rib pattern is by no means observable.

Relation to previously descrihed species:
The following four species-group names
have been proposed for Nipponites :Nipponites mirabilis Y a be, 1904
N. mirabilis var. sachalinensis Kawada,
1929
N. bacchus Matsumoto and Muramoto,1967
N. occidentalis Ward and Westermann,
1977
The holotypes of N. mirabilis [No. 46 J,
N. mirabilis var. sachalinensis [No. 48J andN. bacchus [No.49J were also examined.
Morphotype A contains the holotype of N.
mirabilis (Figures 4 and 14), and evidently itcorresponds to this species. Morphotype B
contains holotypes of N. mirabilis var. sa-

Takashi Okamoto

124

chalinensis (Figures 4 and 15) and N. bacchus (Figures 4 and 15). Though the two
taxa cannot be distinguished by the surface
ornamentation as examined in this study, they
were defined by some other diagnostic characters; N. m. var. sachalinensis has small tube
diameter relative to the tube length (Kawada,
1929), and N. bacchus is characterized by thepresence of a retroversal hook at the end ofgrowth (Matsumoto and Muramoto, 1967).
The tube diameter is, however, quite variablein actual coexistent specimens of Nipponites,
and the holotype of N. m. var. sachalinensis
can be regarded as an end member of Morphotype B. The retroversal hook cannot be
observed in this holotype because of its incomplete preservation or its immaturity.
There is a slight difference in stratigraphic
position between the two type specimens:[No.49J was obtained from the uppermost
Turonian, while [No.48J is probably fromthe Coniacian. On the other hand, there isno described specimen corresponding to theMorphotype C. If the three morphotypes
can be regarded as constituting distinct
species, the Morphotype B should be called
N. sachalinensis. I have not yet examinedthe detailed rib pattern about N. occidentalis
from Oregon, U.S.A. So far as I examined
the illustration by Ward and Westermann(1977), N. occidentalis may be another morphotype of Nipponites; the Oregonian specimens have serrated ribs, as in the Morphotypes Band C, and also some strong ribs
occurring at the changing point of coilingmode, as double ribs in Morphotype C.

following equation:

Whorl enlarging rate: The whorl enlarging rate (E) was defined in my previous
article (Okamoto, 1988a) by the following
equation:

Meandering amplitude and frequency:
There are peculiar measurements for thedescription of meandrous shell like Nipponites. The meandering amplitude is a/A as
shown in Figure 9, where a and A means ahalf of wave height and a half of wave length
measured along the tube center line. The
meandering is generally strong in the Morphotype A and very weak in some specimensof Morphotype C. This measurement, how-

In E=d/ds (In r)
where sand r indicate the growth stage andtube radius, respectively. This value canalso be estimated from the relative growth
diagram shown in Figure 2 and from the

E= l+dl/2dh
where dl/ dh indicates the slope in the relative growth diagram.
The whorl enlarging rate in the later phaseis measured in each specimen (Figure 8).
The histogram mode of this value is about
1.020 in Morphotype A, and slightly higher
values are suggested in Morphotypes Band C,
though the differences are statisticallyinsignificant.

Rib density and obliquity: The rib density
is defined as the number of ribs in a unit
distance along the ventral margin. The unit
distance is equal to the tube radius at any
growth stage. The rib density, which isalmost invariable throughout growth, wasmeasured mainly in the middle growth stage(Figure 8). Morphotype A shows fairly variable rib density which ranges from 2.0 to 4.0.
Unlike Morphotype A, the values in Morphotypes Band C lie around 2.0 with smaller
deviations.
The rib obliquity in the middle stage of
Nipponites regularly oscillates between two
constant values (Figure 3-A). The oscillation range of rib obliquity is shown in Figure
9. The maximum value of rib obliquity isquite variable even within each morphotype,while the minimum value is almost constantin every specimen. Morphoiype A reveals
generally a wider obliquity range than Morphotypes Band C. Sometimes Morphotype
C shows a very narrow range.

879.

Nipponites and Eubostrychoceras

ever, does not serve a good criterion to distinguish these morphotypes because of the wide
range of variation in each morphotype.
The meandering frequency is defined as thenumber of meandering cycles within one revolution in the "symmetric plane". Because theactual values of this character were obtained
only from nine specimens in total, it isdifficult to discuss the difference between
these morphotypes. The meandering frequency in Nipponites is fairly constant, lying
morphotype_

crioceratoid cOilingI2'Zz.2jdextral helicoid=

slnlslral helicoid

within the range from 2.5 to 3.0 (Figure 10).
Morphotypes of Euhostrychoceras
Three morphotypes are recognized by thedifference of rib pattern in Eubostrychoceras(Figure 6). Each morphotype has two discrete forms: dextral and sinistral helicoids
after the initial planispiral coiling. The
ratio between dextral and sinistral individuals
is almost even in each morpho type. The!!l1

1ZL;;272222227j~n7ilZ2777777/2n22

I~·umtll07

ifbZZ77T7&777J 25
I ,1:::.<;t2b;JI;:;t;;] 28

II

~13

A 45

kssssssssssss~ssssssssssssssl21
1221121212~t, 2221212222222 zl 44!

morpholype

2222

11b:;;;;;22121I2JJ2I?11? I?

o RIB NUMBER 50!

125

17777777d·.~O

ksssssssssssssssstssssssssssssssssll0

1ZZZZZZ2712112211LLJ'2222ZZ>ZZZ777777777JI24~'s~O 26

OS;;;;:::222222221:lzzzzzz??zz??ZZ272722;7272272ZZ222ZZ????????22????b2??222??2??2J~??221??72272272ZZ2ZZZ);ZZ2?2?2?ZZ2?22?2?d 131

morpholype

Y

C=\SSSSSSSssssssss~sssmsssssssss[::::~::::.~ 1~~~A?2222222222);2222222?22222122222aa2?2aa2a22al 2
I I

I I. "1;;;=;s1;:t;ssssSSSSS'SSS\~~ssssssssssss!sssssssssssssssJ 12

III

III I,II 122~2?L2bLJ?2I,J17~126,. p. ,J H" "'L " I sssstsssissssJ;,ssJssss,ssssssss,ssssssssss<sssssssd 18~)

1(1 I I Issss!sssssssssssssssssLss,s"ssssJsss"ss"ssss~ 31

UJiJ;J2t7A7J7/)j;22LJmmJ2ImI2lJ;?22m2~?22W2ll)J 36
I I

iL!slJkss&sssssL""Lsssssd 37

l'sJsstL J"JsssJssJss sssd 39
b2l22 222222A'2 a t ;~;;;r''''(
0' I 'r I

172222222221 12 122122a22A2I I 212121 222,J

74

22222222222222;~ 22 2 222 22,J 43

rnO

I II II I JsslssLJsss LJ"Jsssll0l~:'Q~::::cr---t;;tn;;t175~I';;;;;;t;;tt;;;;;;;;;t;t;;;;lI;lI~1;;;ll;;tl~Is;"tls~sd114 b22L22 22 22 A,2111121 21 I i 21 L112 22122 J, 22112 22 2122 2121 22121 J12 a , J 102

b2a22222222JI?2I2I2222I2J22112111"211IA}tl?l222I~J 113

~ 127

40
(WHORL HEIGHT)

Figure 6. The ontogenetically analyzed rib pattern and mode of coiling of Eubostrychoceras. The rib
form symbols are the same as Figure 4. Morphotype D can be distinguished by the existence of constriction.
Morphotypes E and F, which show clear difference in rib density (Figure 8), cannot be distinguished onlyby this diagram.

I

Takashi Okamoto

126

Mo

u

specimen No.

13 21 44 45101

10 24 25 26 21131

1

2 12 11 11 31 36 31 39 43 14 15 101102113 114 126 121

Figure 7. The stratigraphic occurrence of Eubostrychoceras examined in Figure 6. The format andsymbols are the same as Figure 5. Three morphotypes are clearly distinguished in stratigraphic ranges.
Because almost all the specimens are obtained from the Tappu area in Hokkaido, the stratigraphic subdivision by Tanaka (1963) is also shown on the right.

three morphotypes are defined as follows.
Morphotype D is characterized by the presence of constrictions. The constrictions correspond to the periodic strong ribs which
occur two or three times per a whorl. Several fragmentary specimens are assigned tothis morphotype. The ammonitella andearly stage cannot be observed in these specimens. Transverse ribs appear at regularintervals during the middle stage. A hook,which is represented by an almost planispiralsemiwhorl, is developed in the adult stage.
The dextral and sinistral coilings can be
regarded as intra populational variation in the
middle stage of this morphotype.
Morphotype E has thick whorls with fineand dense ribs occurring at regular intervals.
The ammonitella and the shell of the latest
stage are unknown, and early planispiralstage is only partly observable in the specimen [No.28]. Strong ribs occur periodically in the early stage and becomes lessfrequent with growth. Dextral and sinistral
individuals often occur in the same nodule.
Morphotype F shows relatively loose andvariable shell morphology in comparison
with Morphotype E. The ammonitella ofthis morphotype, which was described as
Eubostrychoceras japonicum by Tanabe etal. (1981), is very large and about 2 mm indiameter. A few planispiral whorls areformed in the early stage, and are followed byseveral helicoid whorls of middle growthstage. A hook observed in the late stage isrepresented by a rather simple and crioceratoid semiwhorl without torsion. Ribs on
whorls occur at regular intervals. Periodic
strong ribs are frequent in the early stage, andbecome less frequent with growth. Periodic
broad ribs can be observed on the later
whorls of some mature specimens. Though
the surface ornamentation during the growthis very similar to that of Morphotype E, thetwo morphotypes can be clearly distinguishedby the density of ribs.

Occurrence: The stratigraphic occurrenceof each examined specimen is shown in Figure 7. Many specimens of Eubostrychoceras
were obtained from the Tappu area. BothMorphotypes E and F occur in the Middle
Turonian, and their ranges are slightly but
clearly different. So far as I am aware,
Morphotype D never occurs with Morphotypes E or F in the same nodule. Though
the stratigraphic data of Morphotype D is still
deficient, its occurrence may be restricted to
the Lower Turonian. The three morphotypes defined by shell ornamentation,
therefore, probably represent the naturalgroups of Eubostrychoceras.

879.
MEANDER

Nipponites and Eubostrychoceras

127"Nlpponltes"

I

TORTI CONE :

•

n=ll.

"Eub 0 s frye hoe era s"

n :33

1.01

1.02

1.03

ENLARGING RATE

2

3

4

5

6

RIB DENSITY

Figure 8. Histograms showing frequency distributions of whorl enlarging rate and rib density of six
morphotypes measured in their middle growth stage. Morphotypes E and F can be discretely distinguishedby the rib density. Morphotypes A and F show similar distributions both in the enlarging rate and rib
density.

Relation to previously descrihed species:
Only one species name Eubostrychoceras
japonicum (Yabe, 1904) has been used forthese three morphotypes. The type specimenof E. japonicum (Figures 6 and 14), which istreated here as [No. 74] belongs to Morphotype F.
Whorl enlarging rate: The whorl enlarging rate in the middle stage was measured alsoin Eubostrychoceras (Figure 8). Morphotypes D and E have a relatively low enlarging
rate which is usually smaller than 1.02.
Morphotype F shows wide variation in thischaracter ranging from 1.01 to more than 1.03.
Though the range of variation in Morphotype
F partly overlaps with those of Morphtotypes
D and E, its mean value is significantly
different.
Rih density: The rib density is variable inEubostrychoceras but shows different frequency distributions among the three morphotypes (Figure 8). This character is useful
to distinguish Morphotype E from F; Morphotype E has very high rib density, which isusually more than 4.0, and is distinct from theMorphotype F having smaller value ranging
from 1.8 to 4.0. Morphotype D has moderate
rib density ranging from 3.0 to 3.6, though thesample size is small.
Comparative morphology of
Nipponites and Euhostrychoceras
Six morphotypes are recognized in
Nipponites and Eubostrychoceras by several
distinct characteristics. The morpho types ineach genus are also distinguished by thedifference of their stratigraphic distribution.
Several characters examined in this study aresummarized in Table 1. The surface ornamentation of Nipponites and Eubostrychoceras seems to have changed slightly but discontinuously with time: (Morphotype A-+
B -+ C in Nipponites and Morphotype D -+ E-+ F in Eubostrychoceras). The geographic
distribution of both genera is almost identicaland restricted to the north Pacific region.
Therefore, these morphotypes of Nipponites
and Eubostrychoceras may represent monophyletic lineages.

Takashi Okamoto

128

Table I.

Itemized characteristics of six morphotypes. Shared characters with Morphotype A are shown by
striped area, and Morphotype F is most similar to Morphotype A. The abbreviations are as
follows: planispiral shell (plani.), meandrous shell (meand.), helicoid shell (helic.), heteromorphshell (hetero.), Turonian (Turon.) and Coniacian (Coniac.).

morpho types
normal rib
serrated rib
periodic rib
periodic double rib
broad rib
constriction
rib density
crioceratoid
helicoid (dextral)helicoid (sinistral)enlarging rateearly stage
middle stage
stratigraphic range

0'- - -

A

B

c

D

E

F

---1----------- -----------"~

54

MEANDERING AMPLITUDE
Figure 9. Relationship between the range of rib obliquity and meandering amplitude in Nipponites.
Black, striped and white rectangles indicate Morphotypes A, Band C, respectively. Linear relationship canbe generally recognized between the meandering amplitude and maximum value of rib obliquity. [Correction; The rectangle for the specimen 48 should be striped].

879.

Nipponites and EubostrychocerasMorphotype B can be distinguished from
Morphotype A by the development of serrated ribs in the middle stage and the absenceof broad ribs in the late stage. Morphotype
C is characterized by the addition of periodic
double ribs which corresponds to the switching points of coiling from crioceratoid tohelicoid. On the other hand, Morphotype D,
the oldest form of Eubostrychoceras, is distinguished from Morphotypes E and F by theexistence of constrictions accompanying periodic rib. Morphotype D is possibly theancestral form of Morphotypes E and F,
though its stratigraphic distribution is still
obscure. Morphotype E changes to Morphotypes F with having coarser densed ribs
and slightly loose helicoid whorls.
The most impressive similarity is recognized between Morphotype A of Nipponites
and Morphotype F of Eubostrychoceras.
Morphotype A is the oldest and mostprimitive form of Nipponites, and Morphotype F is contemporary form of Eubostrychoceras. They can hardly distinguished by
the surface ornamentation but for rib obliquity. They share not only similar early
planispiral (crioceratoid) whorls, but also thebasic modes of coiling throughout growth.
The crioceratoid coiling, which is intermittently appears in the middle stage of Morphotype A, is occasionally observed in thelate stage of Morphotype F. Both dextral
and sinistral helicoid coilings are alternately
appear in the middle stage of Morphotype A,
while in Morphotype F dextral and sinistral
helicoid coilings appear alternatively andconsistently as dimorphism. The standardized torsion (see Okamoto, 1988a) of helicoid
coiling in Eubostrychoceras is generally
ranges from 0.02 to 0.04. These val ues seemto be almost equal to those of the helicoid
parts of Nipponites, though it is very difficult
to measure this value accurately in
Nipponites. In spite of the similarity of thedevelopmental patterns of surface ornamentation and basic modes of coiling, there is,needless to say, clear difference of shell out-

129

line between the two morphotypes in theirthree-dimensional architecture.
Another difference between Morphotypes
A and F can be recognized in the rib obliquity of their middle stage (Figure 3).
The rib obliquity is, however, closely
related to the life orientation in the sea water(Okamoto, 1988b, 1988c). The life orientation is determined by the positions of centerof buoyancy and center of gravity, and canalso be estimated by computer calculationand simulation. The life orientations of
Nipponites and Eubostrychoceras in the middle stage, as theoretically inferred by computer simulation (Okamoto, 1988b for Eubostrychoceras japonicum and Okamoto, 1988cfor Nipponites mirabilis), are completely
different; the elevation angle of growth direction in the middle stage of Nipponites regularly oscillates between the almost constantmaximum and minimum values, while that of
Eubostrychoceras is nearly constant throughout the middle stage. The rib obliquity wellcorresponds to the estimated change of

0,\-Ov.
:V/ : .. .

0)--- -----:-.------UiIll.

8

:

0(0
meandering

fr~qUency = 2,,<3/8

MEANDERING

Figure 10. Histogram showing the variation ofmeandering frequency in Nipponites. Black, striped
and white rectangles show Morphotypes A, Band C,
respectively. Most specimens have the value
between 2.5 to 3.0.

Takashi Okamoto

130

>0'

.•....co....tU

..o
.-•
C

Qj

....

Qj

Age

TURONIANCONIACIAN

Figure 11. Concluding diagram showin g the relationship of six mo rphotypes. Th e ordinate is time,a nd the absc issa indicates the preferred life o rientatio n est im ated by comp uter simu latiton a nd r ib o bliquity.
Rib pattern c ha nged slightl y but stepw ise during the time. The abr upt change of co ilin g from Euboslrychoceras to Nipponiles strong ly influences th e preferred life or ientatio n.

growth d irectio n of Nipponites and Eubostrychoceras. Therefore, the difference of the rib
ob liqu ity between Morphotypes A a nd F iscaused by the difference of growt h direction
during the middle stage, and it is a lso clo sely
re lated to the different shell outline. The
reg ul atory mechani sm of rib o bliquity can be
regarded as identical between the two genera.
In sp ite of the impressive similarity between
Morphotypes A a nd F , no intermediate form
has been actually know n. If Nipponites was
phylogenetically derived from Eubostrychoceras , the morphologica l change musthave been accomp li shed in stantly.

Coiling regulatory hypothesis
for the meandering shellpreviou sly suggested the morphologicalsaltation between Eubostrychoceras japon-

icum a nd Nipponites mirabilis o n the b asis ofa theoretica l approach with computer simul ation s (Okamoto, J988c). The " coi lin g
regul a tory model " app lied in that study isbriefly introduced below .
The three-dimen sionally mea ndered shellin Nipponites is interpreted as a n effect ofho meostati c regulation of its life o rientat ion .
The mea ndered whorls are regul a rly di sposedaro und a certa in central point. This model
hypo thesized that the center of buoyancy is
identical with the center of coi ling, a nd thedi sta nce from the center of buoya ncy to theaperture is ass umed to increase iso metri ca ll yw ith whorl height. The three modes of coiling, i .e. crioceratoid, dextral a nd si ni stra lhelico ids, are introduced in th is model.
Crioceratoid is defined as a coiling mode in
the vertica l plane ; therefore, if the life o rientation does not ro ll right or left d uri ng the879.

Nipponites and Eubostrychoceras

growth of this coiling mode, planispiral
whorls are produced. Crioceratoid coilinglifts the growth direction of apertural part ormaintains a large elevation angle. On theother hand, helicoid (either dextral or sinistral) is defined as a spiral coiling mode withconstant torsion (which is standardized by the
tube radius and is assumed as 0.03 in thissimulation, see Okamoto, 1988a). Therefore,
helicoid coiling changes the growth direction
downward or keeps a small elevation angle.
The following three variables are also
introduced in the computer simulation; PI
T: ratio of phragmocone to total cone
length, Up: the upper limit of growth direction, Lo: the lower limit of growth direction.
These variables keep constant throughout one
simulation. The life orientation is hydrostatically determined in every growth stage byassuming the neutral buoyancy and homogeneous materials for phragmocone and living
chamber. If the elevation angle of growth
direction exceeds upper limit by crioceratoid
coiling, the mode of coiling switches to dextral or sinistral helicoid which is efficient todecrease the elevation angle. If the growth
direction falls under the lower limit, the modeof coiling again becomes crioceratoid so as toelevate the growth direction. The computer
simulation for the meandering growth of
Nipponites was most successful with inputting
the constant values of P/T=0.55, Up=40°
and Lo=O°.
Meandering variation is theoreticallydeduced with slight modification of initialconditions; the PIT ratio gives strong effectto the meandering frequency, and the range
between the upper and lower limits is
influential mainly to the meandering amplitude (Okamoto, 1988c). These expectations
can be verified by the quantitative analysis ofactual specimens.
According the computer simulation, themeandering frequency per one revolution(2n) increases approximately from 2 to 4 as
the PIT ratio decreases from 0.7 to 0.4(Okamoto, 1988c, figure lOA). On the con-131

trary, the variation in meandering frequencyof actual specimens is comparatively narrow.
The meandering frequency in the almost all
specimens is within the range of 2.5-3.0 (Figure 10). This meandering frequency is
produced by the computer simulation with
the PIT ratio of 0.6-0.5. Because considerable length of phragmocone is necessary tomaintain the neutral buoyancy, the actual
distribution of meandering frequency is quite
reasonable. I did not measure the PIT ratioof actual specimens, but Ward and Westermann (1977) measured the values in two
specimens of N. occidentalis as 0.55 and 0.57.
From the result of calculation of total averagedensity, they concluded that the species could
maintain the neutral buoyancy in the sea
water.
A strongly meandering shell was outputtedwhen a wide growth direction range (Up-Lo)
was inputted. A weakly meandrous shellwas, in contrast, produced with a narrow
direction range (Okamoto, 1988c, figure lOB).
I assume that Nipponites kept a constantaperture angle relative to the horizontal plane
during growth. Because the rib runs parallelto the aperture at every growth stage, if theabove assumption is appropriate, the rib
obliquity should be influenced by the meandering intensity. The linear relationshipbetween the range of rib obliquity and meandering amplitude is also obvious in actual
specimens (Figure 9). These lines of evidence indicate that the growth direction
regulatory model is appropriate for the interpretation of meandrous coiling of Nipponites.
When an extremely small lower limit is
inputted in the same computer program, apersistent torticone shell form is outputted,
because the coiling feedback does not occur
throughout the growth. This hypotheticalcoiling pattern is quite similar to that of
Eubostrychoceras japonicum. As recognizedby the simulation, the change from torticone
shell to meandrous shell occurs abruptly
without any intermediate form, even if theinitial condition of growth direction range is

Takashi Okamoto

132

2morphotype
morphotype

?if

!!!J

879.

Nipponites and Eubostrychoceras

continuously changed (Okamoto, 1988c, figure 11). The intermediate form between
Morphotypes A and F does not appear not
only empirically but also theoretically. A
morphological saltation from torticone tomeandrous shell is deduced also in the growthsimulation based on the coiling regulatorymodel.
Origin of Nipponites
Both the result of computer simulations(Okamoto, 1988c) and the fossil records in
Hokkaido strongly suggest that Nipponites
was abruptly derived from Eubostrychoceras
without any intermediate form. The stratigraphic ranges of the two genera partly overlap each other in the Middle Turonian(Inoceramus hobetsensis Zone); Morphotype A of N. mirabilis and Morphotype F of
E. japonicum constitute a concurrent zone
(Figure I I). Because gradual morphologicalchange is theoretically impossible in this case,the origin of Nipponites may offer an interesting problem in evolutionary paleontology.
Several different interpretations may bepossible about the biological relationshipbetween Morphotypes A and F. In this casesubspecific relation and ecophenotypic effectare rather unlikely, because the two morphotypes share the same stratigraphic range
and often coexist in the same calcareous
nodules. Nipponites is usually rarer in occurrence than Eubostrychoceras, but there is an
exceptional nodule in which three individualsof Morphotype A are contained without any
individual of Morphotype F. Pathologic
anomaly is also unlikely for Nipponites,
because Morphotypes Band C never coexist
with any similarly ornamented Eubostrychoceras (Figure II).
The origin of Nipponites should be sought

133

in a (or a few) mutant individual with meandrous coiling which suddenly appeared in a
popUlation of Eubostrychoceras. If complete reproductive isolation is assumed simultaneously with the drastic mutation, the first
appearance of Nipponites may represent
instant speciation or "hopeful monster" ofGoldschmidt's (1940) sense. The difficultyof such an instant speciation was discussed at
length by Mayr (1963). Probably the "hopeful monster" could hardly find its suitable
mate, unless an unusually high mutation rate
were assumed.
On the other hand, if the morphologicaldifference between the two morphotypes were
only due to polymorphism in a randomly
mating population, the evol ution from
Eubostrychoceras to Nipponites would be
explained by phenotypic substitution (ortransient polymorphism) like the famous
industrial melanism of Biston betularia.
Such a mode of evolution was well documented by Hayami (1973, 1984) in a PlioceneRecent pectinid, Cryptopecten vesiculosus,
and was also assumed by Hirano (1978) in therelation between two successive forms ofGaudryceras. The possibility of phenotypic
substitution cannot be denied in this case.
However, the morphological change fromtorticone shell to meandrous shell also yields
drastic changes of life orientation and behavior. Even if there was no genetic difference,the decisive morphological and ecological
gap may result in some difficulty of mating
between the two morphotypes.
Though the data are too insufficient tosolve the problem, I presume, as the third
possibility, that some homogamy (preferenceof an individual to mate with similar phenotype) may have contributed to establish the
new lineage of Nipponites. At least in theinitial stage of speciation, incomplete repro-~ Figure 12. Eubostrychoceras from the Lower-Middle Turonian. 1, UMUT MMI8548 [=No. 44J,
Morphotype 0, from Nakakinembetsu-gawa, Tappu, xl. 2, UMUT MMI8530 [=No.13J, Morphotype
0, from Hifumi-zawa, Tappu, xO.9. 3, WEAOl9Y [=No. 131J, Morphotype E from Isojiro-zawa,
Oyubari, xl. 4, UMUT MMI8527 [=No.IOJ, Morphotype E from Kamikinembetsu-gawa, Tappu, xl.

Takashi Okamoto

134

morphotype

Ymorphotype ~Figure 13. Eubostrychoceras and Nipponites from the Middle Turonian. 1, UMUT MM 18529 [= No.
12J , Morphotype F, from Hifumi-zawa, Tappu, X I. 2, GK .H5796 [= No.130J, Morphotype F , from
Shirakin-zawa, Oyubari , X I. 3, UMUT MMI8571a [= No.72 J, Morphotype F , from Higashi-uni,
Wakkan a i, X I.

~
Figure 14. Euboslrychoceras and Nipponties from the Middle Turonian . 1, UMUT MM 18524a [=No. I J, Morphotype F , from San-no-sawa, Tappu, X 1. 2, UMUT MM 18524b [ = No. 2J, Morphotype F,
from the same nodule as above, X I. 3, UMUT MMI8533 [= No.17 J, Morphotype F , from
Kamikinembetsu-gawa, Tappu, X I. 4, UMUT MM7559 [= No. 74J, holotype of Eubostrychoceras
japonicum (Yabe), Morphotype F, from Yubari-gawa, Yubari. 5, UMUT MM7560 [= No. 46J, holotype
of Nipponiles mirabilis Yabe, Morphotype A, from Obirashibe-gawa?, Tappu , X I. 6, UMUT MMI8254[= No. 71J , Morphotype A, from Kamikinembetsu-gawa, Tappu , X I 7, UMUT MMI8571a [= No. 72J ,Morphotype A, from Higashi-ura, Wakk anai , x l.

879.

morphotype

J

Nipponiles and Euboslrychoceras

morphotype ~

135

136

Takashi Okamoto

morphotype!!tlmorphotype

C{f

879.

Nipponites and Eubostrychoceras

ductive isolation may be required to increase
the mutant individuals.
The coexistence of N. mirabilis and E.
japonicum may be actually a result of allopatric speciation (and subsequent migration), but, if so, such a morphologic saltationmust have occurred in the peripheral isolate.
I emphasize here the possibility of sympatricspeciation by drastic morphological (notnecessarily genetic) saltation which preventsthe mutant from random mating with thewild-type individuals. The causes of punctuated evolution in fossil organisms are ofcourse multiple. The origin of Nipponites
seems to suggest that a certain architectural
factor (Seilacher, 1970) also is significantly
related to the disjunct pattern of macroevolution.
Conclusion

Nipponites was probably derived from
Eubostrychoceras in the Middle Turonian,judging from the similarities of surface ornamentation, basic mode of coiling and shellmorphology in the early stage. The morphological difference between them can berecognized only in their three-dimensionalshell architectures, though it is quite impressive. Unlike Eubostrychoceras, Nipponites
developed the coiling regulatory mechanism
so as to keep the slightly upward growth
direction, and the meandrous shell was formed probably as a consequence of hydrostatic
adjustment. Both fossil records and the computer simulation of coiling suggest that themorphological saltation occurred without
any intermediate form. Nipponites took
some minor stepwise changes during its lineage. The last morpho type of Nipponites

137

having serrated ribs and periodic double ribs
became considerably different from Eubostrychoceras. If the derived new form hadprospered and diversified, it would haveresulted in the origin of a new family. I
emphasize here that such abrupt morphological saltation may cause the establishment of a higher taxonomic group. Unfortunately, the lineage of Nipponites became
extinct probably at the end of Coniacian
without leaving any descendant.
Acknowledgments
This research was carried out as a part of
doctoral dissertation at University of Tokyo.
Scientific Research Fund (No. 63790264) for
Fellowships for Japanese Junior Scientists
was partly used during this work. I thankItaru Hayami and Kazushige Tanabe (University of Tokyo) for their critical reviews andconstructive suggestions. I am also gratefulto Haruyoshi Maeda (Kochi University),
Koji Hayakawa (Waseda University) andYasunari Shigeta (University of Tokyo) for
their help during my field and laboratory
works. I am indebted to Tatsuro Matsumoto(Kyushu University), Yoshiaki Matsushima(Kanagawa Prefectural Museum), Hiromichi
Hirano, Koji Hayakawa (Waseda University), Yoshiaki Mizuno, Masatoshi Yamaoka,
Isao Nonogaki and Masatoshi Nonogaki(Tokai Fossil Society) for the loan of specimens.
Thanks are especially due to Toshiya
Miyauchi and Toshio Saheki for offering ofvaluable specimens of Nipponites.

Figure 15. Nipponites from the Upper Turonian (1, 2) and Coniacian (3-5). 1, GK.H5444 [=No.
49], ho1otype of Nipponites bacchus Matsumoto and Muramoto, Morphotype B, from Pombetsu-gawa,Ikushumbetsu, X .6. 2, UMUT MM 18570 [= No. 70], Morphotype B, from Hidarimata-zawa, Ikushumbetsu, X I. 3, UMUT MM7666 [=No. 48], ho1otype of Nipponites mirabilis var. sachalinensis Kawada,
Morphotype B, from Miho-gawa, south Sakhalin. 4, WEA018T [= No. 128], Morphotype C, fromObirashibe-gawa, Tappu. 5, UMUT MM18255 [=No. 68], Morphotype C, from Okufutamata-zawa,
Tappu.

Takashi Okamoto

138

References cited
Berry, E., 1918: Cephalopod adaptations-The record
and its interpretations. Q. Rev. Bioi., Baltimore
3, 92-108.
Cobban, W.A., 1988: The Upper Cretaceous Ammonite Eubostrychoceras Matsumoto in the WesternInterior of the United States. U.S. Geological
Survey Bulletin 1960, Shorter Contributions to
Paleontology and Stratigraphy. AI-5, pI. I.
Druczic, V.V. and Pergament, M.A., 1963:
Nipponites from the Upper Cretaceous of Kamchatka and Sakhalin. Paleont. Jour., 2, 38-42.
Goldschmidt, R., 1940: The material basis of evolution. Yale Univ. Press. 436p.
Hayami, I., 1973: Discontinuous variation in an
evolutionary species, Cryptopecten vesiculosus,
from Japan. Jour. Paleont., 47, 401-420, pis. 12.

- - , 1984: Natural history and evolution of
Cryptopecten (a Cenozoic-Recent pectinid
genus). University Museum, University ofTokyo, Bulletin 24, 1-149. pis. 1-13.
Hirano, H., 1978: Phenotypic substitution of Gaudryceras (a Cretaceous ammonite). Trans.
Proc. Palaeont. Soc. Japan, N. S., 109,235-258.
pis. 33-35.
Kawada, M., 1929: On some new species of ammonites from the Naibuchi district, South Saghalien.
Jour. Geol. Soc. Tokyo (Japan), 36, 1-6, pI. 14.
Matsumoto, T., 1959: Upper Cretaceous ammonites
of California, part II. Mem. Fac. Sci., Kyushu
Univ., Ser. D, Special Vol., 1, 1-172, pis. 1-41.
- - , 1967: Evolution of the Nostoceratidae(Cretaceous heteromorph ammonoids). Ibid.,
18,331-347, pis. 18-19.
- - , 1976: Zonal correlation of the Upper
Cretaceous in Japan. Palaeont. Soc. Japan,
Special Papers, 21, 63-74.
- - , 1977: Some heteromorph ammonites from theCretaceous of Hokkaido. Mem. Fac. Sci.
Kyushu Univ. Ser. D, 23, 303-366, pis. 43-61. '- - , 1984: The so-called Turonian-Coniacianboundary in Japan. Bull. Geol. Soc. Denmark,33, 171-181.
- - and Muramoto, T., 1967: Two interestingheteromorph ammonoids from Hokkaido.
Mem. Fac. Sci., Kyushu Univ. Ser. D, 18,361-

366, pis. 22-24.
Mayr, E., 1963: Animal species and evolution.
Harvard Univ. Press. 797p.
Mihajlova, LA., 1983: Systematics and phylogenyof Cretaceous Ammonoidea. Nauka, Moscow,
280p.
Okamoto, T., 1988a: Analysis of heteromorph ammonoids by differential geometry. Palaeontology, 31, 35-52, pI. 7.
- - , 1988b: Changing in life orientation during the
ontogeny of some heteromorph ammonoids.
Ibid., 31, 281-294.
- - , 1988c: Developmental regulation and morphological saltation in the heteromorph ammonite Nipponites. Paleobiology, 14,271-285.
Seilacher, A., 1970: Arbeitskonzept zur Konstruktions Morphologie. Lethaia, 3, 393-396.
Shimizu, S., 1926: Three interesting Cretaceousammonites recently acquired from Hokkaido.
Proc. Imp. Acad. Tokyo, 2, 547-550.
- - , 1933: Note on two intersting Senonian ammonites from Hokkaido and Saghalien. Jour.
Shanghai Sci. Inst., Section II, 1, 11-15, pI. 2(I ).

Tanabe, K., Hirano, H., Matsumoto, T. and Miyata,Y., 1977: Stratigraphy of the Upper Cretaceous
deposits in the Obira area, northeastern Hokkaido. Sci. Rept., Kyushu Univ., Geol., 12,
181-202. (in Japanese)- - , Obata, I. and Futakami, M., 1981: Early shellmorphology in some Upper Cretaceous heteromorph ammonites. Trans. Proc. Palaeont. Soc.
Japan, N. S., 124,215-234. pis. 10-11.
Tanaka, K., 1963: A study of the Cretaceous sedimentation in Hokkaido, Japan. Rept. Geol.
Surv. Japan, 197, 122p, pis. 1-3.
Verechagin, V.N., Kinasov, V.D., Parakechov, K.V.
and Terexova, G.P., 1965: Field atlas of theCretaceous Fauna from Northeast USSR.,
Magadan, 215pp., 74pls.
Ward, P.D. and Westermann, G.E.G., 1977: First
occurrence, systematics, and functional morphology of Nipponites (Cretaceous Lytoceratina) fromthe Americas. Jour. Paleonl., 51, 367-372. pI. I.
Yabe, H., 1904: Cretaceous Cephalopoda from the
Hokkaido. Part 2. Jour. Coli. Sci., Imp. Univ.
Tokyo, 20, 1-45, pis. 1-16.

879.

Nipponites and Eubostrychoceras

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Jtlc;1t~lc J: -? -C!liitflilfftml~Et:JlcjfflM ~ :ht-:,"Nipponites ft, Eubostrychoceras ii,
I?~ <~~IC (cpra'mlt.c L IC) 1: C t-:" c ~'? {IiiIDl~, .Ittl:lfft1i.~~Et:J:to J: rf~Ff~Et:J{J!Urniil'(J ft,

1lITJ* Ili

1?3Z:M'-tG~Il)-c-tI!:>GoAppendix table.

Collation of the consecutive specimen numbers and register numbers.

Specimen No.

Register No.

Nos. 1-4
Nos. 5-8
No.9
No. 10No. II
No. 12
No. 13
No. 14
Nos. 15-16
No. 17
No. 18
Nos. 19-20
No.21
Nos. 22-23
Nos. 24-28
No.29
No. 30No.31
Nos. 32-34
Nos. 35-38
Nos. 39-40
No.41
No. 42
No. 43
No. 44
No.45
No. 46
No.47

UMUT MM18524a-d
UMUT MM18525a-d
UMUT MMI8526
UMUT MMI8527
UMUT MM 18528
UMUT MMI8529
UMUT MMI8530
UMUT MMI8531
UMUT MM18532a-b
UMUT MMI8533
UMUT MMI8534
UMUT MM18535a-b
UMUT MMI8536
UMUT MM18537a-b
UMUT MM18538a-e
UMUT MMI8539
UMUT MMI8540
UMUT MMI8541
UMUT MM18542a-c
UMUT MM18543a-d
UMUT MM18544a-b
UMUT MMI8545
UMUT MMI8546
UMUT MMI8547
UMUT MMI8548
UMUT MMI8549
UMUT MM7560
GK.H5846(replica: UMUT MM18550)
UMUT MM7666
GK.H5444(replica: UMUT MM18551)
GK.H5853(replica: UMUT MM18552)
replica: UMUT MMI8553
replica: UMUT MM 18554
replica: UMUT MMI8555
replica: UMUT MMI8556
replica: UMUT MMI8557
replica: UMUT MMI8558
replica: UMUT MMI8559
replica: UMUT MMI8560
replica: UMUT MMI8561
replica: UMUT MM I 8562
replica: UMUT MMI8563
replica: UMUT MMI8564

No. 48
No. 49No. 50No.51
No. 52
No. 53
No. 54
No. 55
No. 56
No. 57
No. 58
No. 59No. 60No.61
No. 62

Specimen No.
No. 63
No. 64
No. 65
No. 66
No.67
No. 68
No. 69No. 70No.71
Nos. 72-73
No. 74
No. 75
No. 76
No. 77
No. 78
No. 79
No. 80No.81
No. 82
No. 101
No. 102No. 103
Nos. 104- 106
No. 107
No. 108
No. 109
No.IIO
No.111
No.112
Nos. 113-115
No.116
No.117
No.118
No.119No. 120
No. 121
No. 122
No. 123
No. 124
No. 125
No. 126
No. 127
No. 128
No. 129
No. 130
No. 131

Register No.
replica: UMUT MMI8565
replica: UMUT MMI8566
replica: UMUT MMI8567
replica: UMUT MMI8568
replica: UMUT MM 18569
UMUT MMI8255
UMUT MMI7738
UMUT MM 18570
UMUT MMI8254
UMUT MM18571a-b
UMUT MM7559
UMUT MM18572
UMUT MMI8573
UMUT MM 18574
UMUT MMI8575
UMUT MM 18576
UMUT MM7667
UMUT MM 18577
UMUT MM7668
KPMG6373
KPMG3258
KPMG3215
KPMG6372a-c
WEA005T
WEA006T
WEA007T
WEA008T
WEA009T
WEAOIOTWEAOIIT-I-3
WEAOl2T
WEAOl3T
WEAOl4T
WEAOl5T
KPMG3215
GK.H5988
replica: UMUT MM 18578
WEAOl6T
WEAOl7T
replica: UMUT MM 18579
replica: UMUT MM 18580
replica: UMUT MMI8581
WEAOl8T
GK.H5850
GK.H5796
WEAOl9T

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Transactions and Proceedings of the PalaeontologicalSociety of Japan

June 30, 1989

New Series No. 154

CONTENTS
TRANSACTIONS
875. Shuji Niko, Takashi Hamada and Toshio Yasui: Silurian Orthocerataceae(Mollusca: Cephalopoda) from the Yokokurayama Formation, Kurosegawa
Terrane .......................................... , ..... " ............ 59876. Kuniteru Matsumaru and Harutaka Sakai: Nummulites and Assilina fromTansen area, Palpa district, the Nepal Lesser Himalayas .................. 68877. Seong-Young Yang: On the genus Plicatounio (Cretaceous non-marine
Bivalvia) from Korea ................................................ 77
878.
879.

Hideo Nakaya: Upper Cretaceous elasmosaurid (Reptilia, Plesiosauria) from
Hobetsu, Hokkaido, northern Japan .................................... 96
Takashi Okamoto: Comparative morphology of Nipponites and Eubostrychoceras (Cretaceous notoceratids) .................................... 117