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Transactions and Proceedingsof thePalaeontological Society of Japan
New SeriesNo. 141

Palaeo ntologica l Soc iety of Japan
Ap ril 30, 1986

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The fossil on the cover is Unuma (Spinunuma) echinatus ICHIKAWA and YAO, a
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Trans. Proc. Palaeont. Soc. Japan, N.S., No. 141, pp. 275-288, pis. 45-50, April 30,1986

807. EARLY INTERNAL SHELL MICROSTRUCTURE OF SOMEMESOZOIC AMMONOIDEA: IMPLICATIONS FOR HIGHER TAXONOMY*Y ASUO OHTSUKA
Department of Geology, Kyushu University, Fukuoka 812, Japan

Abstract. Characteristics of early .internal shell structure in four early Jurassic
and twenty-three late Cretaceous ammonoid species are described and their taxonomic implications are also discussed. Early whorls of all species examined are
distinctly divided into the ammonitella and post-ammonitella stages, which arebounded by a primary constriction; and only two stages of irregular subprismatic orprismatic structure are distinguished in the protoconch and the whorl of the ammonitella. Although the early shells of the species examined consist of common
structural elements, the form and growth of several early structural elements appear
to be stable within a given suborder of the Mesozoic Ammonoidea.

Introduction

whorls of four Jurassic and twenty-three Cretaceous ammonoid species, to evaluate the taxonomic significance of early internal structure.
Morphological variation and growth of earlyinternal shell characters of the species examined
and their bearing on early life history are summarized in another paper (Tanabe and Ohtsuka,1985).
This pl,lper is a part of Master's thesis submitted to Ehime University in 1983. The author
is grateful to Dr. K. Tanabe of Ehime University
for his guidance throughout this study and for
critical reading of the manuscript, Dr. W. J.
Kennedy of the University of Oxford for reviewing an early draft of the manuscript, and Profs.
Emeritus T. Matsumoto and T. Shuto of Kyushu
University for fruitful suggestions. Thanks areextended to Prof. H. Matsuo and Dr. M. Matsukawa of Ehime University for helpful discussions,
Prof. U. Lehmann of Hamburg Universitiit forproviding him with specimens of Eleganticeras,
and Dr. Y. Fukuda of Chiba Prefectural Instituteof Public Health for his kind advice on SEM
preparation.

Submicroscopic studies of ammonoid shellstructure have hitherto been made by many
authors (e.g., Branco, 1879-80; Grandjean,
1910; Shimizu, 1929; Spath, 1933; Bohmers,
1936; Erben et al., 1969). Recent microstructural observations on various Mesozoic taxa by
Drushchits and Khiami (1969,1970), Drushchits
and Doguzhayeva (1974), Zakharov (1974,1977), Drushchits et al. (1976) and Tanabe
et al. (1979) have further demonstrated thesignificance of early internal shell structure athigher taxonomic levels. Most previous taxonomic studies of ammonoid early ontogeny
are, however, based on optical microscopic
observations, and detailed microstructural relations of early morphologic features have little
examined.
In the present study scanning electron microscope (SEM) observations were on the early*Received December 10, 1984: Read October
17, 1982 at the Meeting of the Society at Mie
University.
275

Yasuo OHTSUKA

276

Table 1. List of ammonite species studied.
Registered numbers of the specimens examined are shown in parentheses.
Major taxonomic positions of the species follow Arkell et al. (1957),
Donovan et al. (1981), and Wright (1981).
Cretaceous Ammonoidea
Suborder Lytoceratina
Superfamily Tetragonitaceae
Family Tetragonitidae
Tetragonites glabrus (Jimbo)
Family Gaudryceratidae
Gaudryceras denseplicatum (Jimbo)
G. tenuiliratum Yabe
G. striatum (Jimbo)
Anagaudryceras yokoyamai (Yabe)
Suborder Phylloceratina
Superfamily Phyllocerataceae
Family Phylloceratidae
Hypophylloceras subramosum (Spath)
Phyllopachyceras ezoense Yokoyama
Suborder Ammonitina
Superfamily Desmocerataceae
Family Desmoceratidae
Mesopuzosia yubarense (Jimbo)
Kitchinites japonicus Spath
Desmoceras japonicum (Yabe)
Tragodesmoceroides subcostatus Matsumoto
Damesites damesi (Jimbo)
D. semicostatus Matsumoto
D. sugata (Forbes)
Desmophyllites diphylloides (Forbes)
Desmophyllites sp.
Family Pachydiscidae
Pachydiscus sp.
Pachydiscinae gen. et sp. indet.
Menuites p0sillus MatsumotoM. sp.
Superfamily Acanthocerataceae
Family Acanthoceratidae
Obiraceras ornatum Matsumoto
Family Col1ignoniceratidae
Collignoniceras woollgari (Mantell)Reesidites minimus (Hayasaka et Fukada)

7 specimens(EE.S 01-07)

2
1
4
1

specimens
specimen
specimens
specimen(EE.S 08,12)(EE.S 13)
(EE.S 09-11,17)(EE.S 14)5 specimens
2 specimens(EE.S 16,18-21)(EE.S 15,22)

4 specimens
5 specimens
3 specimens
3 specimens
2 specimens
2 specimens
5 specimens
3 specimens
2 specimens(EE.S 52,57-59)(EE.S 33-35,45,46)(EE. S 39-41)(EE.S 53-55)(EE.S 25,26)(EE.S 23,24)(EE.S 27-31)(EE.S 42-44)(EE.S 37,38)

1
1
1
1

specimen
specimen
specimen
specimen(EE.S 32)
(EE.S 47)
(EE.S 56)
(EE.S 36)

1 specimen(EE.S 51)

3 specimens
3 specimens(EE.S 48-50)(EE.S 90-92)

4 specimens
2 specimens(EE.S 61-64)(EE.S 65,66)

2 specimens
1 specimen(EE.S 80,81)(EE.S 60)

Jurassic Ammonoidea
Suborder Ammonitina
Superfamily Eoderocerataceae
Family Dactylioceratidae
Dactylioceras sp.
Peronoceras fibulatum (J. C. Sowerby)
Superfamily Hi1docerataceae
Family Hildoceratidae
Eleganticeras elegantulum (Young et Bird)
Grammoceras sp.

807. Early Internal Shell Structure of Ammonoidea

Material and methods
Material. -Table 1 lists the ammonoid species
examined in this paper. The author follows
Arkell et al. (1957), Donovan et al. (1981) and
Wright (1981) for their major taxonomic positions. The Cretaceous material utilized wascollected from the Upper Cenomanian to Upper
Campanian deposits in the central axial zone of
Hokkaido (Abeshinai, Obira, Manji and Urakawa
areas; see Text-fig. 1 for index map) by Tanabe
and the author. Their locations are shown in
Text-fig. 2. The author further examined ninespecimens of four early Jurassic species in thisstudy; they were collected from the shales of
the northern Holzmaden area, South Germany(for EE.S 60) and the Whitby area on the Yorkshire Coast, England (for EE.S 61-66) byTanabe, and from a derived nodule in a late
Quarternary glacial deposit near Hamburg, North
Germany (for EE.S 80, 81) by Lehmann. All of
the specimens examined were preserved incalcareous nodules. They are stored at Ehime
University with registered numbers beginning
EE.S.
Methods.-Every specimen examined was
prepared in the following manner for SEM obser142°

1400 E

144°

Q

o

44°N

AbeshinaiI
area)
Obira··".
areal\' t. \420 (Jo

100km

Text-fig.1. Index map of Hokkaido showing the distribution of Upper Cretaceous deposits(shaded) and areas of ammonite samples studied.

277

vation. Firstly, early whorls of less than 15 mm
in diameter were removed from each specimen.
Subsequently, they were cut and polished
precisely along or perpendicular to the medianplane. These sections were etched with 4%hydrochloric acid for several minutes and washedin distilletI water. The etched surface was coatedwith gold or platinum using an ion coater (EikoEngineering Co., IB-3 or IB-5). Observations on
early internal shell structure were made on a
JEOL, JXA-733 SEM. Measurements of several
characters were performed by means of a profile
projector (NIKON, V-12) attached to a digital
micrometer (accuracy, 1 J..!m).
General characteristics of early shell structure
The description given below summarizes thecharacteristics of early internal shell structure
which were commonly observed in the specie~
examined. Basic morphology and terminologyof the ammonoid early internal shell structure
in median and cross sections in the Lytoceratina,
Phylloceratina and Ammonitina are diagrammatically shown in Text-fig. 3. Descriptive
terminology used in this paper mostly follows
Branco (1879-80), Granjean (1910), andDrushchits and Khiami (1969). Measurementsof several early internal structural elements inmedian section are diagrammatically shown in
Text-fig. 4. All species examined possess a clear
constriction (primary constriction; Drushchits
et al., 1977; = nepionic constriction' Birkelund1981) near the end of the first w~orl (Text:
fig. 3; PI. 45; PI. 46, Fig. 2; PI. 48, Figs. 1-4).
Drushchits and Khiami (1969) named the conch
terminating at the primary constriction theammonitella. The early shell growth of ammonoids, thus, can be divided into the ammonitella
and post-ammonitella stages. Early whorls consistof such common structural elements as protoconch and outer shell walls, prosiphon and its
accessory ones, caecum, prosepta, septa andsiphuncular tube (Text-fig. 3).
Protoconch. -The protoconch is elliptical orsemi-circular in median section (Pis. 45-47).
It is distinctly separated from the succeedingYasuo OHTSUKA

278

A

Tsukisappu

c

River

Ikm

Hidakahorobelsu

OCEAN
Ikm

('-4140)

Text-fig. 2. A: Campanian fossil localities in the Abeshinai area, northern central Hokkaido. B:
The Middle Turonian to Lower Santonian fossil localities in the Obira area, north-western Hokkaido.
Detailed horizons are shown in Tanabe et al. (1977, figs. 6 and 9). C: The Upper Turonian fossil
locality in the Manji area, central Hokkaido. Detailed horizon is shown in Tanabe et al. (1978, fig. 1).
D: The Upper Turonian fossil locality in the Urakawa area, southern central Hokkaido. ( ): calcareous
nodule in the river gravels.

Abbreviations: The following abbreviations are used for internal shell structuralfeatures in SEM photographs. c: ,caecum, dp: dorsal prismatic layer, f: flange,
ip: inner prismatic layer, n: nacreous layer, op: outer prismatic layer, p: prismatic layer, pc: primary constriction, ps: proseptum, psh: prosiphon, s:
septum, sn: septal neck, sp: secondary prosiphon, sph: siphuncIe.

Explanation of Plate 45
Figs. 1-6.
Scanning electron micrographs showing the early internal shell structure of selected
Cretaceous Lytoceratina (1, 2), Phylloceratina (3) and Ammonitina (4-6).
Fig. 1. Gaudryceras striatum (Jimbo). EE.S 11.
Fig. 2. Anagaudryceras yokoyamai (Yabe). EE.S 14.
Fig. 3. Hypophyl/oceras subramosum (Spath). EE.S 19.
Fig. 4. Menuites sp. EE.S 36.
Fig. 5. Damesites damesi (Jimbo). EE.S 25.
Fig. 6. Reesidites minimus (Hayasaka et Fukada). EE.S 90.
Scale bar: 500 {.lm.

OHTSUKA: Early Internal Shell Structure of Ammonoidea

Plate 45

807. Early Internal Shell Structure of Ammonoidea-dorsal prismatic layer (dpl __ wAi"" ..,n""'AnW---outer prismatic layer(opl-- ~~~---nacreous 'ayer(n)-----II~i--inner prismatic layer(jp)--'</Q1j~~

A~~~~~siPhuncle(sPh)proseptum(ps)secondary"'-prosiphon~

_

(sp)

prima-;Y-r-constriction(pC)

primar~/varix (pv)\\,ammonltella(a~ ~~~_~'7/oText-fig. 3. Diagram of ammonoid early internal shell structures in median(A, C and D) and cross (B) sections. A and B: Lytoceratina, C: Phylloceratina, D:
Ammonitina. Terminologies from Branco (1879-80), Grandjean (1910), Shimizu(1929), Drushchits & Khiami (1969), Tanabe et al. (1979) and Lominadze (1981).

279

280

Yasuo OHTSUKA

Text-fig. 4. Measurements of the ammonoid early internal structural elements in mediansection. 1, 2: maximum and minimum diametersof protoconch, 3, 4: ammonitella size and length,
5,6: dimensions of caecum (D1, D2).

septate whorls by a caecum wall. The wall of
protoconch is made up of a single sub prismatic
layer about 5 pm thick. Enlarged SEM photographs (PI. 46, Figs. 3, 5) show that the subprismatic layer is further divided into the inner
sub layer of longer and wider crystallites andthe outer sub layer of shorter and narrower

crystallites, although the boundary between
the two sub layers is partly unclear. This observation is almost identical with those of Birkelund(1967) and Birkelund and Hansen (1974) on thewell-preserved specimens of Cretaceous Saghalinites from West Greenland. The primary protoconch wall disappears in the initial part of thefirst whorl (e.g., PI. 46, Fig. 3).
Outer shell wall of ammonitella.-Near theventral side of caecum a new prismatic layer
begins to appear beneath the preceding subprismatic layer of protoconch wall. It gradually
thickens with growth to form the main shellwall of the ammonitella (e.g., PI. 46, Fig. 3; PI.
47, Fig. 1a). Like the protoconch wall, theprismatic layer is divided into the inner andouter sublayers on the basis of crystallite size
(PI. 46, Fig. 4).
Prosiphon. -The prosiphon is a narrow circular or tabular horny tube, which extends
from the adapical part of the caecum to theinner side of protoconch (PI. 46, Fig. 3; PI. 47).
In the species referred to the Lytoceratina andthe Phylloceratina, one or two fine tubes arepresent in the ventral side of caecum. They werepreviously named the partial septa by Shimizu(1929). Based on optical microscope observations on many late Cretaceous ammonoid specimens, Tanabe et al. (1979) have pointed outthat the "partial septa" are easily distinguishedfrom the prosepta because of their restriction
to the ventral side of caecum. This fact has
also been confirmed by the present author in

Explanation of Plate 46
Figs. 1, 2.
Scanning electron micrographs showing the early internal shell structure of selected
Jurassic Ammonitina.
Fig. 1. Peronoceras fibulatum (J. C. Sowerby). EE.S 66.
Fig. 2. Eleganticeras elegantulum (Young et Bird). EE.S 80.
Figs. 3a-b. Scanning electron micrographs showing the early internal shell structure near caecumin Gaudryceras striatum (Jimbo). EE.S 11.
Fig. 4. Scanning electron micrograph of prismatic ammonitella wall in Anagaudryceras yohoyamai (Yabe). EE.S 02.
Fig. 5. Scanning electron micrograph of sUbprismatic protoconch wall in Tetragonites glabrus(Jimbo). EE.S 14.
Scale bar: 500 !Lm (1, 2), 100!Lm (3a) and 10!Lm (3b, 4,5). Arrow indicates the adoral direction.

OHTSUKA: Early Internal Shell Structure of Ammonoidea

Plate 46

807. Early Internal Shell Structure of Ammonoidea
the specimen examined. Under the optical
microscope, the "partial septa" are dark-colored,
like the prosiphon, without any trace of mineralized structure. Thus, they are more similar
to the prosiphon than septa. For these reasons,the author proposes the new term secondary
prosiphons for them. The secondary pro siphon
is absent in the species of Ammonitina examinedin the present study.
Caecum. -This corresponds to the initial partof siphuncle which is in part linked with theprosiphon, and in the case of the Lytoceratina
and the Phylloceratina, with both prosiphon andsecondary prosiphons. It is projected adapicallyshowing a gentle bowl-shaped curvature. The
wall of the caecum is much thicker than thesiphuncular wall, but both consist of multilayered conchiolinic membranes (PI. 50, Fig. 2).
A thin outer calcareous caecum wall describedin three Cretaceous ammonite specimens by
Tanabe et al. (1980) appears to be based on amisinterpretation of several exfoliated conchiolinic membranes.
Prosepta. -One or two septum-like structures,named proseptum or prosepta by Branco (187980) are recognized in the adoral end of caecumof every specimen examined. The prosepta are
adapically convex, and are made of a single prismatic layer (typically observed in Gaudryceras
striatum: EE.S 11; PI. 46, Fig. 3a)_ Thus, they
are easily distinguished from the succeedingnacreous septa in the different microstructure
and convexity.
Flange.-The protoconch wall is connectedwith prosepta near the dorsal side of the caecum.
In such species as Gaudryceras striatum; EE.S 11,
a flange, a short adapical extension of the protoconch wall, can be seen at the connected portion
with prosepta (PI. 46, Fig_ 3a; PI. 47, Fig. 2a),but is absent in other species examined.
Primary constriction.-As stated before, theprimary constriction is marked by abruptchanges in shell structure and whorl growth,and is present at the end of the first whorl.
Near the end of the first whorl a thin nacreous
layer first appears on the dorsal side of thepreceding subprismatic layer. Just before the281

constriction the nacreous layer abruptly thickens
forming a primary varix (PI. 48, Figs. 1-4). At
the end of the constriction, the nacreous layer
as well as the prismatic layer of the ammonitellasuddenly disappears and is replaced by a newouter shell wall in the post-ammoniteila stage.
The ventral shell wall in the post-ammonitellastage is composed of three layers: inner prismatic, middle nacreous and outer prismatic
layers (PI. 49, Figs. 4-6; PI. 50, Fig. 4).
Siphuncle. -The siphuncle is initially locatedin the central or sub central part of the chamber,but gradually or rapidly shifts its position toward
the ventral side during the growth of the first
whorl (PI. 45; PI. 46, Figs_ 1, 2). It is a long
horny tube which runs through each chamber.
The ratios of siphuncle diameter to whorl size
are relatively large in the first two or threewhorls (typically in the Ammonitina), but they
gradually decrease with growth. The siphuncularwall is constructed of multi-layered concentric
membranes of conchiolin (PI. 50, Fig. 3). The
outermost conchiolin membrane (pellicle) covers
not only the main siphuncular membranes but
also the inner surface of the chamber. Tanabe
et al. (1982, pI. 67, figs. 2, 3) showed clear
SEM photomicrographs of an exceptionallywell-preserved specimen of Reesidites minimus,
in which unorientated conchiolinic microfibrilsof the pellicle cover the main siphuncular wall
which consists of orientated, coarse conchiolinic
fibrils. Such fine structure of the pellicle was notobserved in any specimen examined during thepresent study. The horny siphuncular wall is notcontinuous between two contiguous chambers.
A thin calcareous layer is intercalated within the
septal neck region, where the horny layer ispartly absent (PI. 48, Figs. 1, 5; PI. 49, Fig. 3).
The specimen of Gaudryceras striatum (EE.S 9;
PI. 50, Fig. 1) retains the fine structure of thecalcareous layer, which is characterized byloosely packed, unorientated aragonitic needles.
Such a porous calcareous layer within the septal
neck region has already been found in wellpreserved specimens of Jurassic Quenstedtoceras(Bandel, 1982) and Eleganticeras (Tanabe et aZ.,
1982). As Bandel and Boletzky (1979) andYasuo OHTSUKA

282

Tanabe et al. (1982) have already emphasized,
the porous calcareous layer is apparently homologous with the pillar zone (chalky layer) within
the septal neck region of other modern and fossilchambered cephalopods.
Septa and septal necks. -The septa are com,posed of a nacreous layer, and their adapical andadoral sides are covered by a pellicle. The septal
neck is a tube-shaped projection of the septal
layer, which is extended adorally (prochoanitic),
adapically (retrochoanitic) and/or both adorally
and adapically (amphichoanitic) (PI. 49, Figs. 13).
Shell wall of the post-ammonitella stage. -As
already mentioned, the ventral shell wall in the
post-ammonitella stage consists of inner prismatic, middle nacreous and outer prismatic
layers (PI. 49, Figs. 4-6). The relative thicknessof these three layers, however, varies at different
growth-stages even in a single species. The dorsal
wall is made of a single prismatic layer (dorsal
prismatic layer) only, which is continuous with
the inner prismatic layer of the ventral wall(see Text-fig. 3). Thus, the outer prismatic andmiddle nacreous layers disappear at the umbilicalshoulder (PI. 50, Fig. 4).

Systematic descriptions
Suborder Lytoceratina Hyatt, 1889
Superfamily Tetragonitaceae Hyatt, 1900
Diagnosis. -Protoconch large in size, nearly
spherical; prosiphon short, narrow and circularin cross section; slightly convex ventrally (e.g.,
PI. 46, Fig. 3a), with qne or two more shortsecondary prosiphonal tubes near the ventral
side of caecum; caecum large, semi-circular inmedian section with a distinct constricted baseat the connection with siphuncle (PI. 45, Figs. 1,
2; PI. 46, Fig. 3a); flange well developed; ammonitella extremely large in size with a whorl longer
than 320 0 ; siphuncle initially located in a subcentral position, but immediately shifts toward
the venter in second or third chamber, thereafter maintaining a ventral position (PI. 45, Figs.
1, 2) throughout almost all stages of ontogeny;
siphuncle diameter generally narrower than the
Ammonitina and the Phylloceratina at the same
growth stage; near the primary constriction it
tends to decreased; septal necks short and retrochoanitic in the first whorl and prochoanitic
after the second whorl. As the shell grows, theseptal necks are conspicuously projected ado rally
to occupy about a half of a chamber (PI. 45, Fig.
1; PI. 49, Fig. 1).
Family Gaudryceratidae Spath, 1927
Observations. -Both protoconch and ammonitella sizes are the largest among the species examined at family level. The number of secondary
prosiphons is one in Anagaudryceras yokoyamai(EE.S 14; PI. 45, Fig. 2) and two in Gaudryceras
striatum (EE.S 11; PI. 46, Fig. 3a). Flange welldeveloped, especially in Gaudryceras species(e.g., G. striatum, EE.S 11; PI. 46, Fig. 3a). Spirallength of the ammonitella (ammonitella angle)
is rather long ranging from 3400 to 3600 in thespecimens examined. Primary constriction iswell marked by an abrupt thickening of the
primary varix. The gap of whorl growth followed

Explanation of Plate 47
Figs. 1-4. Scanning electron micrographs showing the early internal shell structure near the
caecum of selected Cretaceous Phylloceratina (1), Ammonitina (2) and Jurassic Ammonitina(3,4).
Figs. la-b. Hypophylloceras subramosum (Spath). EE.S 19.
Figs. 2a-b. Damesites damesi (Jimbo). EE.S 25.
Fig. 3. Peronoceras fibulatum (J. C. Sowerby). EE.S 66.
Fig. 4. Eleganticeras elegantulum (Young et Bird). EE.S 80.
Scale bar: 100 /lm (la, 2a, 3, 4) and 10 /lm (lb, 2b).

OHTSUKA : Early Internal Shell Structure of Ammonoidea

Plate 47

807. Early Internal Shell Structure of Ammonoidea
by the constriction is especially conspicuous in
G. striatum (EE.S 11; PI. 48, Fig. 5). Siphunclar
tube narrow in diameter, running through theventral side of the whorls in parallel with thegrowth of spiral.

283

Remarks.-According to Shimizu (1929, pI. 2,
fig. 2) and Tanabe et al. (1979, fig. 4-1) two or
three secondary prosiphons are present in theventral side of the caecum of Hypophylloceras
subramosum, but they are absent in Phyllopachyceras ezoense.

Family Tetragonitidae Hyatt, 1900

Observations.-The early internal shell structural features of Tetragonites glabrus belonging
to the Tetragonitidae are essentially similar to
those of the species of the Gaudryceratidae.
Although the author examined only sevenspecimens of T. glabrus, this species has a smaller
protoconch, caecum and ammonitella, andshorter ammonitella length than those of the
Gaudryceras species.
Suborder Phylloceratina Arkell, 1950
Superfamily Phyllocerataceae Zittel, 1884
Family Phylloceratidae Zittel, 1884

Diagnosis. -Protoconch medium-sized, nearly
spherical; prosiphon short, narrow and circularin cross section as in the Lytoceratina, butslightly convex ventrally; caecum elliptical inmedian section without a conspicuously constricted base (PI. 47, Fig. 1a): ammonitellamedium-sized, spiral length (ca. 270°-290°)
shorter than those of the species referable to the
Lytoceratina and the Ammonitina; siphunclar
tube almost straight within each of the first
three chambers, and thereafter convex ventrally
in parallel with the curvature of the outer shell
wall; thus in the earliest growth stage siphunculartube bends sharply at the septal neck region
forming an obtuse angle; siphuncle position
central or slightly approximated to the dorsalside within the first several chambers, thereafter
shifted toward the venter, but the marginal
approximation is prolonged at some stages of
the third whorl (PI. 45, Fig. 3); septal neck ofshort amphichoanitic type (projected both
adapically and adorally) within the first whorl,
but after the second whorl its adapical extension
is strongly projected than the adoral one (PI.
49, Fig. 2).

Suborder Ammonitina Hyatt, 1889

Diagnosis. -Protoconch small in size, nearly
spherical (PI. 45, Figs. 4-6; PI. 46, Figs. 1, 2);
pro siphon long, almost straight and spatulashaped, being quite different from those of the
Lytoceratina and the Phylloceratina; caecum
elliptical in median section without any conspicuous constriction at its base (PI. 47, Fig.
2a); ammonitella small in size as compared withthose of the Lytoceratina and the Phylloceratina;
siphuncle initially located in a sub central position within a chamber, gradually shifts its position toward the venter during the growth of thesecond to third whorls; nearly straight in eachchamber within the first whorl, but thereafter
gently curved ventrally; septal neck of retrochoanitic type in the first whorl and of longprochoanitic type after the second whorl (PI.
49, Fig. 3a).
Superfamily Desmocerataceae Zittel, 1895

Observations. -Protoconch small in size ranging from 0.4 mm to 0.5 mm in median section.
Ammonitella rather small (0.8-0.9 mm diameter). Of the species examined, protoconch,
caecum and ammonitella are largest among theAmmonitina at superfamily level. At familylevel, there is no great difference in the earlyinternal structural features between the Desmoceratidae and the Pachydiscidae. However, thespecimen of Damesites damesi (EE.S 25; PI. 47,
Fig. 2a) of the former family possesses a remarkable flange, while it is apparently absent in thespecimen of Menuites sp. (EE.S 36; PI. 45, Fig.
4) of the latter family. Owing to insufficientdata, it is unclear whether or not the two families
can be distinguished from each other on thebasis of the presence or absence of this flange.

Yasuo OHTSUKA

284

Superfamily Acanthocerataceae Grossouvre,
1894
Family Collignoniceratidae Wright and Wright,
1955
Observations. -Although the author examined
only two species belonging to the Collignoniceratidae, it can be pointed out that the protoconch, ammonitella and caecum are the smallest
in size among the species examined at superfamily level. The most characteristic feature in
the early stage of the Collignoniceratidae is aregular approximation of two contiguous septa
within the second to third whorls (PI. 45, Fig. 6).

Superfamily Eoderocerataceae Spath, 1929
Family Dactylioceratidae Hyatt, 1867
Observations. -Although the author examined
only an oblique section ofPeronoceras fibulatum,
it shows characteristic features such as, small
protoconch, elliptical caecum, long spatulashaped prosiphon and centrally located siphunciein the early stage, as in Cretaceous Ammonitina(PI. 46, Fig. 1). The prosiphon of the former isslightly convex ventrally as compared with thenearly straight one of the latter (PI. 47, Fig. 3).

Superfamily Hildocerataceae Hyatt, 1867
Family Hildoceratidae Hyatt, 1867
Observations.-One specimen of Eleganticeras
elegantulum examined has an extremely longprosiphon (PI. 46, Fig. 2). As the prosiphon
approximates to the protoconch, it is gel).tly

curved externally to cover the inner surface ofthe protoconch wall (PI. 47, Fig. 4). The otherearly internal structural features are essentiallysimilar to those of the Cretaceous Ammonitina.
Concluding remarks
As a result of this study, it was realized thatthe early internal shell structure is essentiallysimilar among the various taxonomic groups of
the Mesozoic Ammonoidea, and that each of the
Lytoceratina, Phylloceratina and Ammonitina
have their own characteristic features of prosiphon shape, caecum and septal necks, and position of siphuncie. This result has already confirmed in many ammonoid species by Drushchits
and Khiami (1969), Drushchits and Doguzhayeva(1974, 1982), Zakharov (1974) and Tanabe et al.
(1979). The resemblance of early internal structure between the Jurassic and Cretaceous Ammonitina also strongly suggests that these features
were stable through time within a given suborder.
Although the relative thickness of the ventral
and dorsal shell layers in the post-ammonitellastage changes with growth even in a single
species, it can be shown that in the Lytoceratina
the middle nacreous layer is the thickest developed. In the Phylloceratina the three ventral
layers have nearly the same thickness, being
thinner than the dorsal prismatic layer. In the
Ammonitina the ventral and dorsal layers arealmost equal in thickness. Below suborder level,
there is no significant difference among thespecies examined in terms of shape and growthof early qualitative characters. The variation of

Explanation of Plate 48
Figs. 1-4. Scanning electron micrographs of the primary constriction in selected Cretaceous
Lytoceratina (1,4), Phylloceratina (2) and Ammonitina (3).
Fig. 1. Gaudryceras striatum (Jimbo). EE.S 11.
Fig. 2. Hypophylloceras subramosum (Spath). EE.S 20.
Fig. 3. Damesites sugata (Forbes). EE.S 27.
Figs. 4a-b. Tetragonites glabrus (Jimbo). EE.S 2.
Fig. 5. Scanning electron micrographs of constriction showing the gap of whorl growth inGaudryceras striatum (Jimbo). EE.S 11.
Scale bar: 100 j.lm (1-3, 4a, 5) and 10 j.lm (4b). Arrow indicates th'e adoral direction.

OHTSUKA: Early Internal Shell Structure of Ammonoidea

Plate 48

285

807. Early Internal Shell Structure of Ammonoidea

Table 2. Measurements of selected early internal shell structural elements in the specimens examined.
OJ

~

I
: I

I

I
:

~:
I~ ~I

Species" :Ji~:

I

(J1:

I' I

I

Protoconch size:

Ammonitella

I

Caecum size-----~------------------------------------------------------:[:l: Max,(mm) : Min,(mm) :Size(mm) : Length(1T): Dl(mm):D2(mm)- - - __ ~ ___ I _________________ ~ __ ~ __________ ~ _________ ~ _________ ~ _________ ~ _________ ~ ________ _

co

,~
~

ci
g

~

T.
T.
T.
T.
G.

G.
G,
G.

glabrusglabrusglabrusglabrusdenseplicatum
denseplicatum
tenuiliratum
striatum~ i~: :~~~:=~;i

1:
3:

4:
7:

8:
12:
13:
9:

~~l

.55
.59
.58
.53
.56
.67
.63
.67

:~~

.51
.53
.52
.48
.53
.63
.59
.62

:~~

1.09
1.10
1.13
1.01
1.12
1. 37
1.26
1.39

~:~~

1.84
1.83
1. 91
1. 78
1. 93
1.94
1. 93
1.96

;:~~

.07
.08
.12
.08

.13
.12
.14

.13

:~~

.07
.10
.10
.07
.12
.14
.15
.13

:~~

--~-~N:-s~bramos;~----~i81---~55-------~46--------~95- -----i~56------:i3-------:i2---I
til

,.;

: N.

subramosum
subramosumI
IP. ezoense: >', : N.
I...:::

~

: 19:
: 20:
[
I
1221

.57
.50
.47

.47
.43
.38

1.03
.98
.85

1.62
1.59
1.58

.11
.12
.11

.10
.08
.10

:l

I

<lJ

----:K~-]apo;icu~------35:---:45-------~44--------:87------1:91------:12-------:13----oU....cojaponicum
39:
.47
.43
.95
1.87
.11
.12
japonicum
40:
.48
.43
.95
1.87
.11
.12
damesi
251
.41
.38
.78
1.74
.09
.09
sugata
27)
.42
.39
.85
1.89
.12
.08
sugata
301
.39
.37
.79
1. 78
.11
.10
sugata
31:
.39
.37
.82
1. 77
,.11
.10
diphylloides
42:
.44
.41
.83
1. 78
.09
.08
diphylloides
44:
.47
.42
.89
1. 79
.09
.10
'j : D. sp.
37:
.43
.41
.84
1. 76
.12
.11
'2 : pachydiscinae
47:
.48
.53
.88
1.95
.10
.10
~
pusillus
56:
.50
.46
.87
1.82
.11
.10
~ : M. sp.
36:
.49
.48
.91
1.89
.12
.11
1 C. woollgari
491
.36
.31
.65
1.63
.08
.07
: C. woollgari
50:
.36
.30
.65
1.56
.08
.07
: R. minimus
90:
.35
.30
.66
1.61
.09
.08
1-------------------------------------------------------------------------------------1•
1: E. elegantulum
: 80:
.42
.37
.88
1. 62
.12
.12
:l
1
1 E. elegantulum
1811
.40
.34
.80
1.54
.10
.08
"
1
OJ
H
U

: D.
: D.
1 D.
) D.
1 D.
: D.
: D.
~ : D.

1M.

quantitative characters in the early stage may bestable within a given superfamily or family, but
the range partly overlaps with that of the othertaxa.
The results of this work are concisely sum·
marized in Tables 2-3.
References
Arkell, W. J., Kummel, B. and Wright, C. W.
(1957): Mesozoic Ammonoidea. In R. C.
Moore (ed:): Treatise on Invertebrate Paleontology, Part L: L80-L456. Geol. Soc.
Amer. & Univ. Kansas Press.
Bandel, K. (1982): Morphologie und Bildung derfriihontogenetischen Gehause bei conchiferen
Mollusken. Facies, 7: 1-198.
--and Boletzky, S. V. (1979): A comparative

study of the structure, development andmorphological relationships of chamberedcephalopod shells. The Veliger, 21: 313354.
Birkelund, T. (1967): Submicroscopic structuresin early growth·stages of Maastrichtianammonites (Saghalinites and Scaphites).
Medd. fra Dansk Geol. Forening Ki5ben·haven, 17: 95-101.
- - (1981): Ammonoid shell structure. In
House, M. R. & Senior, J. R. (eds.): The
Ammonoidea, 177-214. Academic Press.
London & New York.
- - and Hansen, H. J. (1974): Shell ultrastruc·tures of some Maastrichtian Ammonoidea
and Coleoidea and their taxonomic implica·
tions. Kong. Dansk. Vidensk. Sel. BioI.
Skrift, 20: 1-34.

Yasuo OHTSUKA

286

Table 3. List showing the major internal shell structural features in the early growth stage of
the Ammonoidea at superfamily level.
Suborder

i

I
I

.

SuperfamIlyi

I
I

Caecumi .

:I

Proslphon

I:
I

Secondary.
proslphonI.

I Protoconch SizeI

I Position ofI .
I siphuncle:
I

Septal neck___________ 1____________ ..l _________1________ - - - f - - ________ + ____________ 1-- __ ____ l. ___ - - - - - - -Lytoceratina:.
I Tetragomtaceae_________ I ____.
PhylloceratmaI. .
I Short curved
I
I Lar eI SemI-cIrcular :I' : Present (1-2)
I
gII: Prochoanitic

I Ventral

I hornyI
I Phyllocerataceae
I:..
EllipticalI

I Short curved
I
I Medium
1 Subcentral II'' I Present (2-3) I
I
Amphichoanitic
I hornyI
I (0.47-0.57 mm) I - ventral I

I
I
I Desmocerataceae
I

I: Extremely long I
I.
' I
I straight,
I Absent
I
tIt

T

I

I

I

(0.53-0.69 mm) I

I-------L-------~----------r--------I-----------~-------r---------_________ -+- __________ 1... _________________ , _____ - - _1___ - - - . .
I EllipticalI

spa u a er----r---- __ L - - - - - - - - -III
I Small
I Sub central I..
I
I
I ProchoanItlc
I (0.39-0.50 mm) I - ventral I
1i~------------~-------~-----~---~--------t----------I------1---------I Acanthocerataceae 1 Ellipticali Long, stralght,: Absent
I Very small~ Sub central : Prochoanitic
I

Ammonitina:-------------t-------

Ii Eoderocerataceae
I

I

I

..

I spatulate-l-~:; ;e~t~; --r -------i-- ---- -- - --;- -- -- --:- - - - - - --I

I(0.35-0.36 mm)

II

I Absenti

I spatulate

I

:

:

: Extremely long, :IS

I straight,

I Absent: rna! u centra

I

I

I :

I curved,: Hildocerataceae
I!

I Elliptical

I

!

I

tit

I spa u a e

B6hmers, J. C. A. (1936): Bau und Struktur von
Schale und Sipho bei Permischen Ammonoidea. 125 p. Drukkerij Univ. Apeldoorn.
Branco, W. (1879-80): Beitdige zur Entwickelungsgeschichte der fossilen Cephalopoden.
Palaeontographica (Stuttgart), 26(1879):
15-50,27(1880): 17-81.
Donovan, D. T., Ca\lomon, J. H. and Howarth,
M. K. (1981): Classification of the Jurassic
Ammonitina. In House, M. R. & Senior, J.
R. (eds.): The Ammonoidea, 101-155.
Academic Press, London & New York.
Drushchits, V. V., Bogoslovskaya, M. F. andDoguzhayeva, L. A. (1976): Evolution of
septal necks in the Ammonoidea. Paleont.
Jour., 1976(1): 37-50.

I

I Sub central Il(0.49 mm ?)1_ _ _ _ _ _ _ _ _ _ _ _ ...1 _____ ---1---- ______ 1-- _______ .,. - _ - - - -Iventral I-:

EllIptlcal

I SmallI

II..

l Procho3mbc: - ventral I__ - - ..,-- - - - - -.1 __ - - - - -

IS b

- -

I :

(0.40-0.42 mm) I - ventral

1 Prochoanitic--and Doguzhayeva, L. A. (1974): Some morphogeneric characteristics of phylloceratids
and lytoceratids (Ammonoidea). Ibid.,
1974(1): 37-48.
--and - - (1982): Ammonites under theElectron Microscope. 240 p. (in Russian).
Moscow Univ. Press, Moscow.
- , - - and Mikhaylova, I. A. (1977): The
structure of the ammonitella and the direct
development of ammonites. Paleont. Jour.,1977(2): 188-199.
--and Khiami, N. (1969): Characteristics ofearly stages of ontogeny in some early Cretaceous ammonites. Moskov Obschch. Ispytateley Prirody Byull., Otdel. Geol., 44: 156157 (in Russian).

Explanation of Plate 49
Figs. 1-3.
Scanning electron micrographs of median-sections of septum and septal neck inselected Cretaceous Lytoceratina, Phylloceratina and Ammonitina. In Fig. 3 septum andseptal neck show thin intercalated prismatic layer.
Fig. 1. Tetragonites glabrus (Jimbo). EE.S 03. 51T stage.
Fig. 2. Hypophyl/oceras subramosum (Spath). EE.S 20. 5.51T stage.
Figs.3a-b. Desmocerasjaponicum (Yabe). EE.S 40. 61T stage.
Scanning electron micrographs of the shell wall in selected Cretaceous Lytoceratina,
Figs. 4-6.
Phylloceratina and Ammonitina.
Fig. 4. Tetragonites glabrus (Jimbo). EE.S 02. 41T stage.
Fig. 5. Hypophylloceras subramosum (Spath). EE.S 20. 51T stage.
Fig. 6. Kitchinites japonicus Spath. EE.S 45. 4.51T stage.
Scale bar: 100!.lm (1,2, 3a) and 10!.lm (3b, 4-6). Arrow indicates the adoral direction.

OHTSUKA : Early Internal Shell Struc ture of Ammonoidea

Plate 49

807. Early Internal Shell Structure of Ammonoidea-

and - - (1970): Structure of the septa,
protoconch walls and initial whorls in early
Cretaceousammonites. Paleont. Jour.,1970(1): 26-38.

Erben, H. K., Flajs, G. and Siehl, A. (1969):
Die friihontogenetische Entwicklung der
Schalenstruktur ectocochleater Cephalopoden. Palaeontographica, 132A: 1-54.
Grandjean, F. (1910): Le siphon des ammonites
et des belemnites. Soc. geol. France, Bull.,
Ser. 4, 10: 496-519.
Lominadze, T. A. (1981): The taxonomic significance of various features of the internal
structure of Callovian ammonitids. Plaeont.
Jour., 1981(4): 119-123.
Shimizu, S. (1929): On siphuncle in some Upper
Cretaceous ammonites. Saito Ho-on Kai Publ.
1929(4): 91-116 (in Japanese).
Spath, L. F. (1933): The evolution of the Cephalopoda. Bioi. Rev. 8: 418-462.
Tanabe, K., Fukuda, Y. and Obata, 1. (1980):
Ontogenetic development and functional
morphology in the early growth-stages ofthree Cretaceous ammonites. Bull. Natn.
Sci. Mus., Tokyo, C6: 9-26.
- , - and (1982): Formation and function of the siphuncle-septal neck structuresin two Mesozoic ammonites. Trans. Froc.,
Palaeont. Soc. Japan, N.S., no. 128: 433443.

- - , Hirano, H., Matsumoto, T. and Miyata, Y.
(1977): Stratigraphy of the Upper Cretaceous deposits in the Obira area, northwestern Hokkaido. Sci. Rep ts. , Dept. Ceol.,
Kyushu Univ., D, 12(3): 181-202 (in Japanese with English abstract).
- - , Obata, 1., Fukuda, Y. and Futakami, M.
(1979): Early shell growth in some Upper
Cretaceous ammonites and its implications
to major taxonomy. Bull. Natn. Sci. Mus.,
Tokyo, C5: 153-176.
- - , - - and Futakami, M. (1978): Analysisof ammonoid assemblages in the Upper
Turonian of the Manji area, central Hokkaido. Ibid., C4: 37-62.
-and Ohtsuka, Y. (1985): Ammonoid earlyinternal shell structure: its bearing on earlylife history. Paleobiology, 11 (3): 310-322.
Wright, C. W. (1981): Cretaceous Ammonoidea.
In M. R. House & J. R. Senior (eds.): The
Ammonoidea, 157-174. Academic Press:
London and New York.
Zakharov, Y. D. (1974): New data on internal
shell structure in Carboniferous, Triassic
and Cretaceous ammonoids. Paleont. Jour.,1974(1): 25-36.
- - (1977): Ontogeny of Ceratites of the genus
Pinacoceras and developmental features ofthe suborder Pinacoceratina. Ibid., 1977(4):445-452.

Abeshinai 7'"''/:1"1, Manji Jj'f:. Obira 'j"I". Urakawa liIi(uJr 'ijiO)fJ]M)\)i:ttq*] MhI'i)j]-~(j.:5H~U: O)~ If: ~tilii'@: J- fflIl'3ilE~iii'tO)f!il:ff:
r 23 ftc .!€@I&'UJI!j H ·;lO)T.m:; "- :7*ilf'7 /-i::I"1 r 4 ft>a:-lE:jtj'~i[
fllJi~~>a:- #jl. ,-r 1m~ L, .:to)fJ]J(Jhi-'J:WI)'J ,'ffII,l'i.illiO)}.ti'&>a:- <~L~x:-t Q C C b f=-i:':iiJ.:5tnl C O)~ If"P~ ~ 7 / -i::I"10)~1.'7 /-i::I"1>a:-~NLt.:o<Un (primary constriction) >a:- ~f=- L -r. fii(ammonitella) C:::: "':lO)f&:ftf\'i'll1~ JiJ)I"~>a:-jHJ"-:JiHM'~ J: I)
t.r. Q .:tntJfltf-O)f~iJ*O) 2 ''':If=-5j,,ft i?nQ o ;;HflJ!ljt.r.·f&:tt~ ('IEIHU~) J: I) t.r. Q I!f~ (protoconch) 11, i? 7 / -i: ~ T:7 f=-1J'ft-r O)j~'lI:hYi):Ji >b. f'i'1ll' (caecum) Hti>a:-~f=- 2 "':lO)l&mf=-5tft
i?nQ omJlJl~:Q:O)IIYifN:~Kif:l: ~H Lt.:-t~-r 0) fjlil{4>,,('jf<Jlli-t Q11;, .:to) IF~!L~&L!"J)li:fH=- C >b t.r. ? ~{~f:l:. '+I!U~7 /-i::I"1 r 0)ifli:i3 l/,",/v,,("i(:;EL-rI.'Qo)\J~!lIHt~H L t.:-t~-r O){IDIf*O)fJ]M!~'{\~f:l:1N:-mO)

H~-f\'i'I J: I) t.r. Q 7 / -i: ~ T:7

287

288

Yasuo OHTSUKA

Explanation of Plate 50
Figs. la-c. Scanning electron micrographs of the highly porous calcareous layer within the septal
neck region of Gaudryceras striatum (Jimbo), EE.S 09, consisting of unorientated aragonitic
prisms.
Fig. 2. Scanning electron micrograph of cross-section of caecum in Damesites semicostatus(Yabe), EE.S 24, consisting of multi-layered conchiolin membranes.
Fig. 3. Scanning electron micrograph of cross-section of siphuncle and shell wall in Kitchinites
japonicus Spath. EE.S 34.
Fig. 4. Scanning electron micrograph of umbilical shoulder in Gaudryceras striatum (Jimbo).
EE.S 17.
Scale bar: 100 J.Lm (la, 2-4) and 10 J.Lm (lb, c). Arrow indicates the adoral direction.

OHTSUKA: Early Internal Shell Structure of Ammonoidea

Plate 50

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 141, pp. 289-295, pis. 51-52, April 30, 1986

808. MICROSTRUCTURE OF GROWTH INCREMENTS IN THE SHELL OF
MERCENARIA MERCENARIA (LINNE)*
HIROKO KOIKE
Department of Biology, College of Liberal Arts,
Saitama University, Urawa, Saitama 338, Japan

Abstract.
Periodical growth increments in molluscan shells have been interpreted by anaerobiosis hypothesis which states that growth lines in growth increments are formed by organic deposits left after decalcification of the shell during
valve closure. Growth lines detected as transparent zones in thin section, however,are not stained with bromphenol-blue solution, suggesting that they are not organicrich deposits. A complete decalcification of the Mercenaria mercenaria shell with
the EDTA, CPC and formaldehyde solution showed the presence of two types oforganic membranes: "the interprismatic membrane" surrounding the calcified
prisms, and "organic membrane of the growth increment" intersecting the interprismatic membrane at a right angle. Comparisons between images of completelydecalcified sections and that of etched surfaces in the same individuals indicatedthat these organic membranes did not correspond to the etch-resistant zone produced by the organic-free etching, and the depressions seen in the organic-freeetching, and stained striations in the thin sections. The etch-resistant zone itself
was evidenced by lace-like row of the interprismatic membranes. The highly calcified zones frequently appeared immediately following after the organic membranes of the growth increment.

Introduction

Growth lines have been described as organicrich zones in the growth increments (Pannella,
1975; Carter, 1980) whose origin has been explained by the anaerobiosis hypothesis (Lutzand Rhoads, 1977, 1980). According to thishypothesis, growth lines are produced fromorganic deposits left after the decalcificationof the shell which took place in an acidic circumstance during anaerobiosis (Crenshaw and Neff,
1969; deZwaan and Wijsman, 1976). The anaerobiosis is induced by valve closure, especiallyduring tidal exposure (Gordon and Carriker,
1978). Growth lines, however, can be observedin many bivalves even among molluscs living
below the tidal zone. Moreover, anaerobic decalcification evidently takes place only inside the

Periodic growth increments are a striking
feature of molluscan shell. Clark (1974) andPannella (1975) in their reviews noted thatthese increments could reflect solar days maintaining internal circadian oscillations (Barker,
1964; Pannella and MacClintock, 1968; House
and Farrow, 1968), or lunar-day periodicity
created in direct response to environmental
fructuations, including the tides (Evans, 1972;
Richardson et aZ., 1979; Ohno and Takenouchi,1984).
*Received December 21, 1984; revised manuscript received June 18,1985.
289

290

Hiroko KOIKE

pallial line (Dugal, 1939; Wilkes and Crenshaw,
1979).
The purpose of the present paper is to de·scribe the microstructure of the organic andmineral components of growth increments inthe clam, Mercenaria mercenaria (Linne), and to
discuss their periodic formation.
Materials and methods
The clam, Mercenaria mercenaria was collected at middle Marsh near Beaufort, North
Carolina during May to September in 1979.
The calcified prisms of the clam was observedon fractured and growing surfaces of the shelledges. Shells used for the observation of thegrowing surface were fixed for 24 hours infiltered sea water containing 3% paraformaldehyde and 0.5% CPC (cetylpyridinium chloride). To observe the growth increment in crosssection, growth margin of the shells were embedded in SPURR embedding media and polished with carborundum sheets (#240 and #400)
and diamond paste. Simple etching: Polishedsurfaces were then etched with 0.1 M Na-EDTA
for 3 minutes, or 0.1 N HCl for 2 minutes. Organic etching: The samples of the adjacent portion were polished and immerced in Clorox(5.25% sodium hypoclorite) for 2 hours to remove the organic matrix before the etching, andthen etched by the same technique as the simple
etching.
The distribution of the organic membrane in
the shell was examined using thin sections (4060 J.1.m thickness) stained with bromphenol-blue
solution (1% alcoholic bromphenol blue-saturated with HgCI 2 ) for about 30 minutes. To observe organic membranes in the shell, thin sections of the shell (about 500 J.1.m in the thickness)were decalcified in a solution containing 0.1 M
Na-EDTA, 0.5% CPC and 4% formaldehyde forabout 2 weeks. After dehydration with an ethanol series and substitution in Freon 13, the decalcified sections were dried in a critical point
apparatus (SAMDRI PVT-3) with Freon 13. The
sections for SEM observations were examined
mainly with a JEOL TSMT20 scanning electron

microscope under 20 KV current.
Calcified prisms and growth increments
The shell of Mercenaria mercenaria has acomposite prismatic structure in the outer layer,
and outer part of the middle layer is composedof crossed lamellar structure which becomeshomogeneous structure inwards the inner layer(Taylor et al., 1973). The prism of the outerlayer
appears as an elongate cylindrical shape aligned
normal to the growth direction when viewed on
fractured sections (PI. 51, Fig. 1). When viewed
at growing surface of the outer layer (PI. 51, Fig.
2), the prisms exhibit a polygonal pattern andare about 10-15 J.1.m in diameter. The surface ofthe prism seems to be coated by thin organic
materials. The calcified part of the prism is composed of fine rods aligned normal to the growth
direction (PI. 51, Fig. 3).
As seen in radial thin sections through an
optical microscope, growth increments intersect
the prisms at a right angle. A growth increment
is made up of a transparent zone and an opaquearea. Pannella and 1\'lacClintock (1968) recognized the transparent zone as a growth line.
Marking experiments using tetracycline indicatedthat rhythmically-formed growth increments ofthe present species indicated a daily periodicity,with an variation in daily growth induced bylunar cycle.
Etching of the polished surface of the shellwith EDTA solution and Clorox treatment afteretching (PI. 51, Fig. 4) produced clear images ofa growth increment composed of a set of a narrow etch-resistant zone and an etch-sensitive
part. At higher magnification (PI. 51, Fig. 5), theprism is seen to be composed of fine rods, or"the second order of prisms" (Taylor et al...
1973; Nakahara et al., 1980) of under 0.2 J.1.m in
breadth. Etch-resistant zones have a greater
density of fine rods and are composed of slightly
larger rods than those in etch-sensitive parts ofgrowth increments. Comparing the growth-increment patterns on SEM photographs of EDT Aetched surfaces with those of the thin sections,the etch-resistant zones correspond to the trans-

808. Microstructure of Growth Increments in Shellparent zones in the thin sections.
Organic membranes
Bromphenol-blue staining is useful to detect
the organic membrane in the shell by the optical
microscope. Growth line has been interpreted as
an organic-rich portion. However, the transparent
zones in the thin section, or so-called growthlines, were not stained (PI. 51, Fig. 6), indicatingthat they are not organic-rich deposits. On theother hand, well-stained, fine striations appeared
frequently in the dark opaque parts, especially
immediately adjacent to the transparent zones.
Outer surfaces of the prisms also seem to becovered with organic membrane, as indicated bystained striations between prisms.
A complete decalcification of the shell with
the EDT A, CPC and formaldehyde solution
showed the presence of two types of organic
membranes (PI. 51, Figs. 7 and 8). One was"the interprismatic membrane" surrounding thecalcified prisms, which appeared as fibrous sheets
oriented in the growth direction. The interprismatic membrane corresponds to the blue-stainedouter surface of the prisms.
The other organic membrane is very thin andintersects the interprismatic membrane at a rightangle (PI. 51, Fig. 8). This membrane is called"organic membrane of growth increment" inthis paper. This membrane is about 0.2 11m inthickness and seems to correspond to the finestriation in the bromphenol-blue-stained section.
Interprismatic membrane was not homogeneous in thickness, becoming thin and lace-like inthe zones immediately following the organic
membrane of the growth increment. The widthof the lace-like zone is about 1-3 11m.
Complete decalcification of thin-sectioned
shells showed two types of organic membrane:
the interprismatic membrane and the organic
membrane of the growth increment. Organic
membranes similar to the interprismatic membrane of the present species are reported in theouter layer of shell composed of the prismatic
structure (Bevelander and Nakahara, 1980;
Nakahara et al., 1980) and of the crossed la-

291

mellar structure (Uozumi and Suzuki, 1979;
Nakahara et al., 1981) and the nacreous layer(Erben, 1974; Mutvei, 1980) of molluscan shells.
Organic-free etching
Although the transparent zones in growthincrements was not stained by the bromphenolblue solution, indicating that the so-called
growth line itself is not an organic-rich deposition, the organic membrane of growth increments was detected by the complete decalcification. Otherwise, the stained fine striations
detected in the dark opaque zone, frequently
located adjacent to the tr~nsparent zone. Theremight be a possibility that the organic membraneof the growth increment would obstruct the etching efficiency. Then, organic-free etching of thepolished surface by immersion in Clorox was
carried out to remove the organic matrix before
the etching. If the organic membrane of growthincrements would affect on the etching, organicfree etching could not produce clear etch-resistant zone. However, etch-resistant zones werestill observed after the organic-free etching,indicating that the etch-resistancy were notproduced by the influence of the organic membrane.
Fine depressions in the growth increments
close to the etch-resistant zones were produced
after removal of the organic matrix by Clorox.
In addition, depressions which correspond to theinterprismatic membrane were seen between theprisms.
Relationship between growth line andorganic membrane of growth increments
In order to clarify the relationship between
the etch-resistant zone and the organic membrane of growth increment, SEM micrographsof the organic-free-etched surfaces were compared with the simple EDT A-etched surfaces
and the completely decalcified sections of thesame individual (sample No. Mm 2003). A
growth increment observed after simple etchingappeared to consist of an etch-resistant zone

Hiroko KOIKE

292

and an etch-sensitive part (PI. 52, Fig. 1). Organic-free etching showed that an etch-resistantzone is accompanied by a fine depression (D in
PI. 52, Fig. 2) adjacent to, i.e., the place where
was precipitated just before the zone. A decalcified section at the same position (PI. 52,
Fig. 3) suggests that the depression corresponds
to the organic membrane of growth increment.
The etch-resistant zone itself cannot be observed in the decalcified section, but its pastpresence is evidenced by the remnant thin andlace-like zone seen in the row of the interprismatic membranes, since the race-like zone
appears immediately after the organic membrane
and thus corresponds to the etch-resistant zone.
Discussion
Growth lines, detected as transparent zones
in thin section and as etch-resistant zones formedby acid etching, have been interpreted as organicrich portions. Surfaces etched with EDTA or
HCI solution is frequently covered with organic
matrix which remained after decalcification, andsuch a mistreatment make the etch-resistantzone to look like a "convex stripe of organicline" (Pannella, 1975). The etch-resistant zone,
or transparent zone, however, is organic-poor
as shown in the organic-free etching and bromphenol-blue staining experiments. Its etch-resistance may be not due to organic membrane or
matrix, but rather to a difference in density ofcalcified rods. Their highly calcified features
are also suggested by the lace-like pattern in thecompletely-decalcified sections.
Periodic formation of growth increments inmolluscan shells has been explained by theanaerobiosis hypothesis which states that growthlines are formed by organic matrix left after
the decalcification of the shell during valve
closure (Gordon and Carriker, 1978; Lutz andRhoads, 1980). However, SEM observationsof growth increments on several etchings showedthat the growth line itself is an organic-poor
deposit. Growth lines seen in an EDT A etchingappeared as rows of especially dense rods (Koike,1980). This indicates that the formation of
growth increments cannot be explained by theanaerobiosis theory. According to Wilkes andCrenshaw (1979), the dissolution layer causedby anaerobic decalcification was observed only
inside the palliailine of bivalve shells.

Explanation of Plate 51
Shell structure and growth increments of Mercenaria mercenaria. Scale bars indicate length in Ilm
and arrows indicate the growth direction.
Fig. 1. Fractured section showing an elongate cylindrical prism (P).
Fig. 2. Growing surface in shell edge fixed with 4% formaldehyde, showing polygonal pattern ofprisms (P) of complex prismatic structure.
Fig. 3. Growing surface rinsed with Clorox to dissolve organic matrix covering the surface ofprisms (P).
Fig. 4. Growth increments in radial section showing etch-resistant zone (ERZ) and etch-sensitivezone (ESZ) produced by EDTA etching.
Fig. 5. Higher magnification of an etch-resistant zone (ERZ) consisting of slightly larger rods (R)than in the etch-sensitive zone.
Fig. 6. Fine striations stained by bromphenol-blue staining (SS) detected through the optical
microscope.
Fig. 7. Organic membrane retained after 2 weeks of decalcification with EDTA, CPC and formaldehyde solution. Interprismqtic membrane (IPM) appeared to be fibrous sheets oriented in
the growth direction. The organic membrane of the growth increment (MGI) intersecting theinterprismatic membrane.
Fig. 8. Higher magnification of the organic membrane of the growth increment (MGI) intersecting the interprismatic membrane (IPM).

KOIKE: Microstructure of Growth Increments in Shell

Plate 51

808. Microstructure of Growth Increments in Shell

In Plate 52, the etch-resistant zone is locatedimmediately following the organic membraneof the growth increment in the growth direction.
This pattern is most typical, more than 60% of
the growth increments which formed during 2
weeks of marking experiment. It is difficult,however, to determine the sequence of appearance of the etch-resistant zone and the organic
membrane, and to infer their function in shellformation. As shown in PI. 52, Fig. 4, the growthincrements had variable patterns: the etch-resistant zone sometimes was not accompanied byan organic membrane, or some organic membranes appeared even after the etch-reistant zone.
According to Nakahara et ai. (1980), the prismatic structure contained two types of organic
components: the interprismatic wall separating
the calcified prisms and the intraprismatic portions surrounding each crystallite. The latter wasrecognized as the "envelope" at the growing
surface of the prism. The "envelope" surrounding growing mineral crystals was commonly
found among molluscan shells (Bevelander andNakahara, 1980) and considered to be involvedin the initiation and acceleration of crystal
growth. The "envelope" is very thin (3-5 nm
thick) and. cannot be the same organic membrane in the growth increment described in thispaper.
In a study of shell regeneration using mussel,
Uozumi and Suzuki (1979) described an initial
mineralization of "organic membrane-shell"
which is composed of three layers: laminated,brown (homologous to the periostracum) and"conchiolin" membranous layers. The first deposition of the particles (nucleus of mineralization) takes place within the conchiolin membranous layer, and the conchiolin sheet wasrecognized to be closely associated with theinitiation of the shell regeneration. The organic
membrane in the growth increment may have afunction similar to that of the conchiolin sheet
in shell regeneration.
It is interesting that the organic membranesof the growth increment were frequently formed
just before highly-calcified zones. Further
investigation on microstructural differences of293

growing surfaces are needed to elucidate thefunction of this membrane in shell growth.
Acknowledgments
The author wishes to express her deepest
gratitude to Professor Miles A. Crenshaw of the
University of North Carolina in Chapel Hill for
his valuable instructions in the present research.
The author is indebted to Professor Karl M.
Wilbur of Duke University for his kind arrangements for field experiments and for the use ofscanning electron microscope in the Department
of Zoology, Duke University.

References
J3arker, R. M. (1964): Microstructural variationin pelecypod shells. Malacologia, 2(1): 6986.
Bevelander, G. and Nakahara, H. (1980): Compartment and envelop formation in theprocess of biological mineralization. In,
Omori, M. and Watabe, N. (eds.) The mechanisms of biomineralization in animals andplants, 19-27. Tokai University Press,
Tokyo.
Carter, J. G. (1980): Guide to bivalve shell
microstructures. In, Rhoads, D. C. andLutz, R. A. (eds.) Skeletal growth of aquaticorganisums, 645-673. Plenum Publishing
Corporation.
Clark II, G. R. (1974): Growth lines in invertebrate skeletons. Annu. Rev. Earth and
Palanet. Sci., 2: 77-99.
Crenshaw, M. A. and Neff, J. M. (1969): Decalcification at the mantle-shell interface
in molluscs. Am. Zoologist, 9: 881-885.
Dugal, L. P. (1939): The use of calcareous shellto buffer the product of anaerobic glycolysis
in Venus mercenaria. Jour. Cell. Compo
Physiol., 13: 235-251.
Erben, H. K. (1974): On the structure andgrowth of the nacreous tablets in gastropods.
Biomineralization, 7: 14-27.
Evans, J. W. (1972): Tidal growth increments inthe cockle, Clinocardium nuttalli. Science,
176:416-417.
Gordon, J. and Carriker, M. C. (1978): Growth294

Hiroko KOIKE

lines in a bivalve mollusk: Subdaily patterns
and dissolution of the shell. Ibid., 202:519-521.
House, M. R. and Farrow, C. E. (1968): Daily
growth banding in the shell of the cockle,
Cardium edule. Nature, 219: 1384-1386.
Koike, H. (1980): Microstructure of the growthincrement in the shell of Meretrix lusoria.
In, Omori, M. and Watanabe, N. (eds.)
The mechanisms of biomineralization in
animals and plants, 93-98. Tokai University Press, Tokyo.
Lutz, R. A. and Rhoads, D. C. (1977): Anaerobiosis and a theory of growth line formation. Science, 198: 1222-1227.
and (1980): Growth patterns within themolluscan shell: An overview. In, Rhoads,
D. C. and Lutz, R. A. (eds.) Skeletal growthof aquatic organisms, 203-254. Plenum
Publishing Corporation.
Mutvei, H. (1980): The nacreous layer in molluscan shells. In, Omori, M. and Watabe, N.
(eds.) The mechanisms of biomineralizationin animals and plants, 49-56. Tokai University Press, Tokyo.
Nakahara, H., Kakei, M. and Bevelander, G.
(1980): Fine structure and amino acid composition of the organic "envelop" in theprismatic layer of some bivalve shells.
Venus (The Japan. Jour. Malac.), 39(3):167-177.
- - , - - and - - (1981): Studies on the for-mation of the crossed lamellar structure in
the shell of Strom bus gigas. The Veliger,
23: 207-211.
Ohno, T. and Takenouchi, K. (1984): Tidal
growth patterns in recent Monodonta labio(Linnaeus, 1758) (Gastropoda, Trochidae).
NOM, no. 12, 51-55.
Pannella, G. (1975): Paleontological clocks andthe history of the Earth's rotation. In,
Rosenberg, G. D. and Runcorn, S. K. (eds.)
Growth rhythms and the history of the
Earth's rotation, 253-284. John Wiley& Sons.
- - and MacClintock, C. (1968): Biological andenvironmental rhythms reflected in molluscan shell growth. Jour. Paleont., 42: 6480.
Richardson, C. A., Crisp, D. J. and Runham,
N. W. (1979): Tidally deposited growthbands in the shell of the common cockle,
Cerastoderma edule (L.). Malacologia, 18:277-290.
Taylor, J. D., Kennedy, W. J. and Hall, A. (1973):
The shell structure and mineralogy of thebivalvia. Bull. British Mus. (Nat. Hist.)
Zool., 22(9): 255-294.
Uozumi, S. and Suzuki, S. (1979): "Organic
membrane-shell" and initial calcificationin shell regeneration. Jour. Fac. Sci., Hokkaido Univ., Ser. 4, 19(1/2): 37-74.
Wilkes, D. A. and Crenshaw, M. A. (1979): Formation of a dissolution layer in molluscan

Explanation of Plate 52
Fig.1. Feature of a growth line appeared as an etch-resistant" zone (ERZ) when produced bynormal etching with EDTA at the shell edge of specimen Mm 2003.
Fig. 2. Feature of the growth increment with organic-free etching at the adjacent portion in Fig.
1. The etch-resistant zone (ERZ) was accompanied by a depression (D) after dissolution of
the organic matrix.
Fig. 3. Organic membranes in completely-decalcified section of the adjacent portion in Figs. 1
and 2. Interprismatic membrane (IPM) becomes thin and lace-like (L) immediately following after the organic membrane of the growth increment (MGI) in the growth direction.
Figs. 4A-C. Schematic representation of the growth increment (GI) seen in a thin section
stained by bromphenol-blue solution (A), on an organic-free etched surface (B), and in acompletely-decalcified section (C). Based on comparisons of these images, the transparent
zones (TRZ), or so-called growth lines correspond to the etch-resistant zones (ERZ) in Fig. B
and to the lace-like portions (L) in the interprismatic membrane in Fig. C. On the other
hand, stained, fine striations (SS) in Fig. A correspond to the fine depressions (D) in Fig. B
and the organic membrane of the growth increment (MGI) and interprismatic membrane(IPM) in Fig. C.

KOIKE: Microstructure of Growth Increments in Shell

4

Plate 52

c

B

A

GI

MGI

ss

ss

808. Microstructure of Growth Increments in Shellshells. SEM 1979, 2: 457-465.
deZwaan, A. and Wijsman, T. C. M. (1976):
Anaerobic metabolism in bivalvia (Mol-lusca): Characteristics of anaerobic metabolism. Camp. Biochem. Physiol., 54B: 313324.

Mercenaria mercenaria O)~O)Jll1::L~JJl!O)j,!jld'illm~: ~~i¥JIl>y.®.ml::' J: ;;, c, .l't~IlX::L~dill!O)
JIilJil]rJ''lIf%l/:ft, rfl~IF.fO)~A(r'1il'Y.®.r-C=·ftJ't~!MiIDO)JlilEJU);:toc. IJ, tV c 1::'7~ ~.ttt'=1ljilMmiJ;
f&:~M! c L -C Jil.x.;;, c;\ll1Jfl ~.tt n,;;,
LiJ' UJ:iJ; G.l't~0) 7~~O)f;lj}H:' 7' / - Iv 7 '" / - Iv
-ctiH!:.i";;' c, llX::RtJl!flfl7.ht~ i Gf, ~ 'h~;;' f&:MJl!ft&:fj'~4o/JJ\l'l-C='fHJ:~' c ~, 5 ~r.~:a- ~'? t.=oMercenaria mercenaria (Linne) :a- m ~', .l't~4'O) liR~ 7J Iv '/? J,. z.1C~I::'~/"f;~ L,
1'f~4o/JJ\l'l0)ill&,ffijm~z..7,..;;' c, 7' ~ ;( J,. :a-"0"0t.J "interprismatic membrane" c, -t.tt c [i[~i";;' "organic membrane of the growth increment" 0)=iiT!mO)1l~4o/JJ!iJ;~f?ilO G.ttkojii]-ff/,lf,$:O)f,\'{*z. J'fh '-CjG~JlilEJ(f,\'{*0)1!HUi~ c = .y 7-:/ .?'(~z. !Uj,:i";;' c, c. O)=fiM:O)1l~4o/JJ\l'lft. ~ 'h~;;' 1lX::RM!ffil5t CftfiHt.-ltf, 7' / - Iv 7 '" / - IV)IH:~.t.tO)~~J!:to J: Lf~'~
4o/J~%;~1IlI.EJ<:t.t0) [1:Ij.7,..I::' J: < :M.ri:. U'=o -1JIlX::R~Jl!tm5tft,'ft~JlilEJ<:f,\'{*-C=H interprismatic
membrane O)ri < :¥1H::.tJ: -? t.= tm5tl::' :i<"Ht. L. organic membrane of the growth increment ft-tO)Jll1::Rj\jj[tm5tO)[i[MI::'~< l±:lmi";;,M"'Jz.~Lt.=o'HtM1:iT
0295

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 141, pp. 296-321, pis. 53-62, April 30, 1986

809. DUSISIREN DEWANA, N. SP. (MAMMALIA: SIRENIA),A NEW ANCESTOR OF STELLER'S SEA COW FROM THE UPPER
MIOCENE OF YAMAGATA PREFECTURE, NORTHEASTERN JAPAN*
SHIZUO TAKAHASHI
Yamagata Prefectural Museum, 1-8, Kajo-machi, Yamagata 990, JapanDARYL P. DaMNING
Laboratory of Paleobiology, Department of Anatomy, Howard University,
Washington, D.C. 20059
and
TSUNEMASA SAITO
Department of Earth Sciences, Yamagata University, Yamagata 990, Japan

Abstract. Dusisiren dewana, n. sp. (Sirenia: Hydrodamalinae) is described on
the basis of a skull and partial skeleton from the Hashigami Sandstone Member ofthe Hongo Formation (Upper Miocene, 9.0-10.4 Ma) in Yamagata Prefecture,
Honshu, Japan. It is morphologically, chronologically, and phyletically intermediate between Dusisiren jordani (Kellogg) and Hydrodamalis cuestae Domning,
and therefore directly ancestral to the recently exterminated Steller's sea cow,
Hydrodamalis gigas (Zimmermann). The new species exhibits reduced but still functional teeth in the adult, together with extremely reduced metacarpals and phalanges and a clawlike flipper structure. This combination of characters corresponds tothat predicted by Domning (1977,1978) for "Dusisiren Species D", which the new
species represents. The structure of the flipper provides the first unquestionablecorroboration of Steller's 18th-century description of the peculiar forelimbs ofHydrodamalis. Other recent reports of fossil sirenians from Japan are also reviewed;
in addition to Dusisiren dewana, Hydrodamalis gigas and possibly H. cuestae now
appear to have lived in Japan contemporaneously with their occurrences in North
America.

Introduction

severe drought that affected a large part of northeastern Japan in that year, the normally watercovered river bed became emergent, revealing
partially exposed vertebrae and ribs on the rocksurface. The specimen was brought to the Yamagata Prefectural Museum under the direction of
S. Takahashi, who undertook initial preparation

In the summer of 1978, a large fossil mammal
was discovered by two elementary school children in the bed of the Mogami River. Owing to a
*Received January 10, 1985; revised manuscript
received June 24, 1985.
296

809. Late Miocene Sea Cow, Northeastern Japanof the skeleton. During the course of preparation, three teeth were discovered, one still
attached to the lower jaw. One of the teeth
and photographs of the entire skeleton werethen sent to D. Domning in Washington, D.C.,
who identified the specimen as a fossil sea cow.
He subsequently visited Japan at the invitationof the Yamagata Prefectural Museum and studied
the skeleton while preparation was still in progress.
The Yamagata sea cow specimen is unusuallycomplete and comprises the entire front half ofthe skeleton, including the head and limb bones.
It is very significant in that it forms a "missinglink" between two previously known evolutionary stages and fills a gap in our knowledge of theevolution of this particular lineage of sirenians(the hydrodamaline dugongids).
In its age and stage of evolution, the Yamagata sea cow is intermediate between two fossil
forms known from California. The earlier ofthese, Dusisiren jordani (Kellogg, 1925), is about
10 to 12 million years old and is directly ancestral to the Yamagata sea cow, which is a new
species of Dusisiren. The latter in tum is older
than and directly ancestral to another species
described from California, Hydrodamalis cuestae
Domning, 1978. This in tum is the direct ancestor of Steller's sea cow, Hydrodamalis gigas(Zimmermann, 1780), which lived in the North
Pacific until the 18th century.
In the course of evolution leading to Steller's
sea cow, two notable anatomical changes occurred: the teeth were completely lost and thebones of the fingers were almost or completely
lost. Domning (1977, 1978) predicted the existence of an intermediate stage in which functional teeth were still present but the flipper had
already taken on a Hydrodamalis-like form.
Documentation of this intermediate stage waspreviously lacking, but the Yamagata skeleton
now fulfills this prediction precisely. The Yamagata sea cow possesses a fully developed set ofteeth which are, however, somewhat smallerand simpler than those of its immediate ancestor,
Dusisiren jordani. Of course, its dentition is far
better developed than anything in its descendants

297

H. cuestae and H. gigas, where the teeth arecompletely absent, at least in the adult. On theother hand, the Yamagata specimen has already
reduced the flipper to a form resembling thatof Steller's sea cow, which is to say that it isclawlike and almost entirely lacks finger bones.
This is in contrast to the earlier, more primitive
sea cows where the flipper still had a well-developed paddle-like form similar to that of themodem manatee and dugong. The phalanges andmetacarpals are greatly reduced in the Yamagata
specimen and, as we know from the description
made by Steller himself on Bering Island almost
250 years ago, the phalanges were even more
reduced, and possibly even completely lost, in
Steller's sea cow. The flipper's clawlike form was
useful for pulling the animal along the bottom
in shallow water and scaping algae off the rocks.
However, no complete flipper skeleton of Hydrodamalis has ever been found, so the Yamagata
specimen is additionally important in that itprovides our first adequate look at the type offlipper structure Steller described.
Abbreviation: UCMP = University of California Museum of Paleontology, Berkeley.

Geologic setting
The new sea cow specimen comes from the
bed of the Mogami River in the hamlet of Yoh,
Ohe Town, Nishimurayama County, Yamagata
Prefecture (Text-fig. 1). Several authors havedescribed the geology of this area (Ichimura,
1958; Funayama, 1961; Itoh et al., 1979). According to them, the fossil site lies in the Hashigami Sandstone Member of the Hongo Formation. Sediments of the Hongo Formation consist
largely of pyroclastic materials, and differencesin lithologic characters enable further subdivisionof the formation into four members. These are,in upward sequence, the Jyuhassai Pyroclastic
Debris Flow, Hashigami Sandstone, Kuzusawa
Siltstone, and Ohya Tuffaceous Sandstone
Members. The Hongo Formation rests conformably upon the Mizusawa Formation, which consists largely of dark gray siltstone, and is in tum
unconformably overlain by the nonmarine Ate-

298

Shizuo TAKAHASHI et at.

oI

Text-fig. 1. Maps showing fossil
sirenian localities in Japan and type
locality of Dusisiren dewana, n. sp. Key
to fossil sirenian localities shown on themap of Japan as follows: 1. Late Pliocene, Sarumaru Formation, Nagano Prefecture, Hydrodamalis sp.; 2. Late Miocene, Shiotsubo Formation, Fukushima
Prefecture, possibly Dusisiren dewana(reported as Dusisiren sp. cf. D. jordani);
3. Late Miocene, Hongo Formation,
Yamagata Prefecture, type locality ofDusisiren dewana; 4. Early or Middle
Pleistocene, Shimonopporo Formation,
Hokkaido, Hydrodamalis gigas; 5. Early
Pliocene, Takikawa Formation, Hokkaido, possibly Hydrodamalis cuestae (reported as Hydrodamalis n. sp.).
razawa Formation (Text-fig. 2).
The Hashigami Sandstone Member consists
predominantly of tuffaceous, cross-bedded, medium- to very-coarse-grained sandstone containing small pebbles of older rocks such as rhyolite,
andesite, propylite, and green tuff. The mostcharacteristic feature of this sandstone member
is the prevalence of large-scale cross-bedding
assignable to trough cross-stratification (Harms
et at., 1975). The fossil sea cow was found in
this cross-stratified facies. Trough sets of thetrough cross-stratification have a width of up

SEA

to three meters and a maximum length of morethan 15 m. From their size and appearance,these cross-strata are interpreted to have been
formed by migrating sand dunes. Local flow
directions ranging from northward to northnorthwestward were deduced from the orientation of scoop-shaped laminae present in thetrough-shaped sets. Ichimura (1958) showedthat the Hashigami Sandstone bearing the largescale trough cross-stratification occurs in a somewhat elliptical geographical area about 7.5 km
wide meridionally and about 13 km long latitudinally. Geological data on the surroundingarea indicate that the Hashigami Sandstone wasdeposited in a marine embayment which was
open to the northwest (Suzuki, 1979). The

809. Late Miocene Sea Cow, Northeastern Japan

Soft pumiceous tuff
Tuffllceous 5"ndy conglomerate
Alternating beds of tuffaceouss i 1ts tone. fi ne-gra lned sands tone and tuff
Trace fossils (sandpipes)
Pum; (eOUS tuff

Altern.HiIJ9 lied, of tuff, siltS tone and sands ton.,
Altern;ning beds of ~Hlve dnd
weakly strdtifie<l siltstone
wi th bedded tuff lilyen

Weakly strdtified fine-grdint:dtuff

Hed; um- to-very-coane_gra i ned
sandHone exhibitinQ large scale

trough cross stratification

Hasslve to 1ightly Hratificd
tuffaceous medium-grinned sand-stone
Tuffaceous sandstone

Alternating beds of tuff ilnd
S i 1tstonelapi 11 i tuff
Slumped beds

Thinly bedded dark gray silt-stone

Text-fig. 2. Geologic section in area oftype locality of Dusisiren dewana, n. sp. Arrow
indicates horizon of the fossil sirenian.

trough cross-stratification is therefore attributed
to strong tidal currents, which are known toform dune and sand-wave bed forms in many
partially enclosed seas and blind gulfs (Reading,1978).
With the exception of displaced freshwater
diatoms, only marine fossils occur in the Hashigami Sandstone. A shell bed about 70 cm thick,composed only of one pectinid mollusk (Mizuhopecten parapiebejus murataensis Masuda andTakegawa), crops out in a roadside cliff near
the hamlet of Taira, about 6.2 km southeast of
the sea cow site (Ogasawara, 1983). Chlamys
cosibensis (Yokoyama), another pectinid, also
occurs at a few localities. In addition, this sandstone member yields several forms of calcareous
microplankton: calcareous nannoplankton, Coc-

299

colithus pelagicus (Wallich) Schiller, C. neohelis
McIntyre and Be, Reticulofenestra pseudoumbilica (Gartner) Gartner, and Sphenolithus neoabies Bukry and Bramlette; and planktonic
foraminifera, Globigerina bulloides d 'Orbigny,
Globigerinoides immaturus LeRoy, G. ruber(d'Orbigny), G. trilobus (Reuss), and Sphaeroidinellopsis seminulina grimsdalei (Keijzer). Diatoms, which will be discussed later in moredetail, also occur in the basal part of this member. The sea cow fossil was found in direct
association with teeth of the large extinct white
shark, Carcharodon megalodon Agassiz (Ueno,
1983), and part of the skeleton of an unidentified whale has been found in the bed of theMogami River near the sea cow locality. Remainsof these large vertebrates show that whales andsharks frequented the embayment together withthe sea cow; the sharks no doubt preyed on themarine mammals and scavenged their carcasses.
Ogasawara (1983) considers the two pectinids
occurring in the Hashigami Sandstone Member tobe characteristic elements of a late Miocene
molluscan assemblage of northeastern Japan
called the Shiobara Fauna, and he estimates
the depth of deposition of the sandstone to beshallower than 30-40 m. Chinzei (1978) discussed in detail the distribution and species composition of the Shiobara Fauna and interpreted
it to be a coastal assemblage living in cold watersof the temperate region. However, Globigerino ides (all species), Sphaeroidinellopsis seminulina grimsdalei, and Sphenolithus neoabies
are all plankton inhabiting warm surface currents. Thus these species suggest that some warm
currents were washing the Sea of Japan side ofnorthern Japan during Late Miocene time, inmuch the same way as the warm Tsushima
Current flows up the present Sea of Japan coast.

Geologic age of the sea cow
Geologic age of the fossil sea cow is determined on the basis of diatom floras occurring in
the Hashigami Sandstone. Only diatoms occur
in sufficient numbers to include age-diagnostic
species. According to Akiba (1983a), three age-Shizuo TAKAHASHI et al.

300

diagnostic species are present in the Hashigami
diatom flora. These are common occurrencesof Denticulopsis katayamae Maruyama andActinocyclus ingens Rattray, and somewhat
less abundant Thalassionema nitzschioides
Grunow. This floral association suggests a correlation with the Denticulopsis katayamae
Zone of Maruyama (1984). Since the formal
description of the species D. katayamae Maruyama did not appear until the spring of 1984,
the zonal interval corresponding to the D.
katayamae Zone was previously called theDenticulopsis hustedtii a Zone by Barron (1981)
or alternatively Subzone A of the D. hustedtii
Zone by Akiba et al. (1982). Barron and Keller(1983) calibrated the North Pacific diatom zonation with the geomagnetic reversal sequence andgave a date of from 804 to 10.2 Ma to the D.
hustedtii a Zone. By reexamining stratigraphic
ranges of diatoms in DSDP holes 438A and 584,
Akiba (1983b) established the age of the D.
katayamae Zone as from 9.0 to lOA Ma. On
this basis, a middle Late Miocene age of the sea
cow is indicated. Two calcareous nannoplankton
species also provide broadly supportive evidence
for a minimum date for the sea cow, as Reticulofenestra pseudoumbilica and Sphenolithus neoabies are known to have become extinct nearly
simultaneously at about 3.5 Ma (Haq, 1984).
Systematics
Class MAMMALIA Linnaeus, 1758
Order SIRENIA llliger, 1811
Family DUGONGIDAE Gray, 1821
Subfamily HYDRODAMALINAE(Palmer, 1895 [1833]) Simpson, 1932
Genus Dusisiren Domning, 1978
Dusisiren dewana, new species

It was abolished in 1868 during the Meiji Resto-

ration, and survives only in the name of the
Dewa Hills, within which the type locality lies.
Holotype:-Anterior half of skeleton of ayoung adult individual, housed at the Yamagata
Prefectural Museum, Yamagata, Japan. Collectedby Yamagata Prefectural Museum party, August
1978. (Casts of upper teeth and bones of manus
deposited in Department of Paleobiology, UnitedStates National Museum of Natural History,
Washington, D.C.).
Type locality:-Bed of Mogami River near its
east bank, about 100 m upstream of the YohIron Bridge over the river, in hamlet of Yoh,
Ohe Town, Nishimurayama County, Yamagata
Prefecture, Honshu, Japan.
Formation:-Hashigami Sandstone Member of
Hongo Formation.
Age:-Late Miocene (Denticulopsis katayamae
Diatom Zone), 9.0 to lOA Ma.
Diagnosis:-Hydrodamaline dugongids morederived than Dusisiren jordani in reduction ofsize and complexity of molars, reduction of
rostral deflection to about 40°, development of
narrower and more rectangular mandibular
masticating surface, extension of a vertical ridge
onto anteromedial side of coronoid process,broadening of anterior process of manubrium,incipient development of median keel on xiphisternum, narrowing of supraspinous fossaof scapula, increased circularity of humeral
head, reduction of deltoid crest, medial bowingof radius-ulna, extensive modifications of carpals
and of distal antebrachial joint surfaces, reduction in size of metacarpals and phalanges, and(possibly) increased size of trunk relative tohead; less derived than Hydrodamalis in smaller
body size, dorsoventrally thinner zygomaticorbital bridge of maxilla, visibility of infraorbital foramen in ventral view, and retentionof functional teeth in the adult.

Dusisiren Species D, Domning, 1978, Univ. Calif.
Publ. Geol. Sci., 118: 72.

Morphology

Etymology:-From Dewa, the ancient name ofthe present-day Yamagata Prefecture. The namefirst appears in Japanese history in A.D. 712.

Body size:
Lengths of the skull and limb bones are
somewhat less than those of Dusisiren jordani809. Late Miocene Sea Cow, Northeastern Japan
specimens from California (Domning, 1978),though the ribs are larger than those of thelatter. Taking into account the dimensions of
the incomplete, partly articulated rib cage
(Text-fig. 3), the Yamagata specimen probably
had an overall length at least equal to that of
D. jordani (up to 4.3 m or more). It probably
weighed between 1 and 2 metric tons.
Skull (Tables 1-3; Text-figs. 4-7; PIs. 53-55.
For other photographs of the skull, mandible,
teeth, and limb elements, see Takahashi et ai.,
1983: figs_ III-I to III-13);

301

Premaxilla:-Dorsal keel thin forward, widens
aft as in Dusisiren jordani; sides of forward end
concave. Palatal surface not preserved_ Nasopalatine canal somewhat flattened dorsoventrally. Masticating surface of rostrum trapezoidal.
Incisors absent. Portion of nasal process incontact with jugal and frontal extends about
one-half length of mesorostral fossa (i.e., about
9.5 cm). Deflection of rostrum uncertain, 30° or
more; judging from the mandibular deflection,
it should have been in the neighborhood of 40°.
Nasai:-Sutures not discernible; evidently
fused with frontal_

Text-fig. 3. Diagram of holotype skeleton of Dusisiren dewana as found in the rock. Paired
dashed lines show lines along which block containing skeleton was fragmented. Scale = 1 m. Abbreviations: SK, MA, RM, LM, elements of cranium-skull, mandible, right and left molars; RSC, LSC,
RHu, LME, LHu, RRA -UL, LRA -UL, RME, elements of limb-right and left scapulae, humerus, rightand left radius-ulna, right and left metacarpals; Cer, AX, AT, TV, elements of vertebral columncervical, axis, atlas, thoracic vertebrae; Mu, Xi, elements of sternum-manubrium and xiphisternum;
RR, LR, right and left ribs.

302
Table 1.

Shizuo TAKAHASHI et al.
Skull measurements of holotype of Dusisiren dewana, in mm. Letters in parentheses
denote measurements used by Domning (1978: tab. 2). e = estimated.

Condylobasallength (AB)Height of jugal below orbit (ab)Length of premaxillary symphysis (AH)
Rear of occipital condyles to anterior end of interfrontal suture (BI)
Zygomatic breadth (CC')
Breadth across exoccipitals (cc')
Top of supraoccipital to ventral sides of occipital condyles (de)Length of frontals, level of tips of supraorbital processes to frontoparietal suture (F)Breadth across supraorbital processes (FF')
Breadth across occipital condyles (ff')
Breadth of cranium at frontoparietal suture (GG')
Width of foramen magnum (gg')
Length of mesorostral fossa (HI)Height of foramen magnum (hi)Width of mesorostral fossa (JJ')
Maximum height of rostrum (KL)
Posterior breadth of rostral masticating surface (MM')
Anteroposterior length of zygomatic-orbital bridge of maxilla (n'o')Length of zygomatic process of squamosal (OP)Anterior tip of zygomatic process to rear edge of squamosal below mastoid foramen (aT)
Length of parietals, frontoparietal suture to rear of external occipital protuberance (P)Length of row of tooth alveoli (p'q')
Anteroposterior length of root of zygomatic process of squamosal (QR)
Length of cranial portion of squamosal (ST)Breadth across sigmoid ridges of squamosals (ss')
Dorsoventral thickness of zygomatic-orbital bridge (T')
Height of posterior part of cranial portion of squamosal (UV)
Dorsoventral breadth of zygomatic process (WX)
Maximum width between pterygoid processes (yy')
Length of jugal (Y'Z')

Ethmoidal region:-Perpendicular plate reaches about 23 mm below roof of narial passage(proportionately slightly farther than in D.
jordani, UCMP 3794; Domning, 1978: fig. 10f).
Second concha of ethmoturbinalia prominent,
about 6 mm thick; third concha bulbous, welldeveloped; others not preserved or still enclosed
in matrix. Distance between second conchae atlevel of rear of mesorostral fossa = 37 mm.
Vomer:-Not preserved.
Lacrimal:-None discernible.
Frontal:-Supraorbital process moderately developed, with distinct posterolateral corner;
anterior tip blunt; dorsolateral side slopes very
steeply. Internasal process prominent and upturned, similar to that of one Dusisiren jordani

511e
52e
124+
269
264
182
124
177e
158e
127
72e
62
190e
46
81
72
64e
54e
136
193
107e
65e
61
110
211
14e
96e
46
60e
200e

(UCMP 77037). Dorsal surface of frontal slightly
and evenly convex; temporal crests slightly overhang lateral sides; cranial vault square in crosssection.
Parietal:-Frontoparietal suture indistinct,
location uncertain. Temporal crests lyriform,
forming thick rounded ridges about 2.5 em apartwith shallow concavity between them on anterior
part of parietal roof. Roof flat fore-and-aft, its
posterolateral corners indented by squamosals.
Endocranial surface not prepared.
Supraoccipital:-Low and wide; height 60
mm, width about 123 mm. Forms angle of 1280
with posterior part of parietal roof, resembling
Hydrodamalis gigas more than it does the earlier
species. External occipital protuberance hardly

TAKAHASHI et at.: Late Miocene Sea Cow, Northeastern Japan

Plate 53

Figs. 1-3. Holotype of Dusisiren d ewa na , n. sp . Skull : Fig. 1, dorsal view; Fig. 2, latera l view; Fig.
3, ventral view. Scale = 10 em .

809. Late Miocene Sea Cow, Northeastern Japan

Text-fig. 4. Holotype of Dusisiren dewana,n. sp. Skull: a, dorsal view; b, lateral view; c,ventral view; d, posterior view. Scale = 10 cm.
rises above plane of parietals. Median ridge welldeveloped.
Exoccipital: - Supraoccipital- exoccipital sutures indistinct but seem to form angle of about
135°. Exoccipitals do not meet in dorsal midline.
Foramen magnum probably had fairly acutedorsal peak, now somewhat distorted. Dorsolateral border of exoccipital about 25 mm thick,rugose, overhangs posterior surface. Paroccipital
process does not reach as far ventrally as condyle; forms curved flange as in adult D. jordani.
Curvature of condYle as in D. jordani, forms arcof about 100°. Supracondylar fossa absent, exoccipital surface distinctly convex dorsal to condyle and indented only slightly dorsolateral tocondyle.
Basioccipital:-Bears prominent, convex occipitosphenoidal eminence, not divided in midline. Apparently fused with basisphenoid, but a

303

break extends through approximate position of
suture.
Basisphenoid, Presphenoid, Orbitosphenoid,
Alisphenoid:-Not seen to differ from those of
D. jordani.
Pterygoid:-Pterygoid processes broken. Lateral and medial edges of pterygoid fossa appear
to intersect dorsally.
Palatine:-Poorly preserved, palatal extent uncertain.
Maxilla:-Dental capsule apparently atrophied. Edges of palatal surface lyriform, palatalgutter narrow anteriorly. Palatal and rostral
surfaces probably met in smooth curve. Edgesof palatal surface forward of alveoli fairly abrupt
and rounded. Zygomatic-orbital bridge elevatedhigh above palatal surface (about 15 mm on left,
about 25 mm on right; evidently distorted),about as in H. cuestae (UCMP 86433; Domning,
1978: fig. 8f). Bridge long fore-and-aft, edges
fairly sharp; bridge thin dorsoventrally. Anterior
opening of infraorbital foramen visible in ventral
view; about 21 mm high, about 18 mm wide.
Palate about 9 mm thick anterior to molar
region.
Squamosal:-Dorsally in contact with squared
posterior part of parietal roof. Posterior edge has
shallow indentation for mastoid foramen. Sigmoid ridge weak or absent near dorsal end of
mastoid foramen, well developed but roundedventrally (below level of zygomatic root). Cranial
portion of squamosal shows distinct bulge dorsal
to zygomatic root. Postglenoid process rather
low; postarticular fossa fairly deep. Processus
retroversus short, not inflected; posterior edge ofzygomatic root distinctly notched. Zygomatic
process perhaps slightly more sigmoidal in outline than lozenge-shaped, but posterodorsal edge
still long, relatively straight, and not noticeably
convex laterad. Anterior tip of zygomatic process
does not reach level of supraorbital process;anterior part triangular in cross section, lateraledge sharper than medial.
Jugal:-Ventralmost point lies below orbit.
Zygomatic process extends back to level offront edge of temporal condyle. Prominent
rounded protuberance present on anterodorsal

304
Table 2.

Shizuo TAKAHASHI et al.
Measurements of mandible, in mm. Letters in parentheses denote measurements used by
Domning (1978: tab. 7). e = estimated.

Anterior tip to front of ascending ramus (AG)
Anterior tip to rear of mental foramen (AP)Anterior tip to front of mandibular foramen (AQ)
Length of symphysis (AS)Height at deflection point of horizontal ramus (EF)Deflection point to rear of alveolar row (EU)
Front of ascending ramus to rear of mental foramen (GP)Minimum dorsoventral breadth of horizontal ramus (MO)Maximum breadth of masticating surface (RR')
Length of alveolar row (TU)
Maximum width between labial edges of left and right alveoli (VV')

margin of orbit.
Periotic, Tympanic, Auditory Ossicles:-Not
prepared.
Mandible (Table 2; Text-fig. 5; Pi. 54): Ascending rami only partly preserved. Coronoid
process very well developed, with backwardpointing dorsal tip. Sharp, prominent verticalridge on anteromedial side of ascending ramus
extends well up into coronoid process, as in
Hydro da ma lis. Region of mandibular foramen,
coronoid canal, and tooth alveoli poorly preserved. Bone surface lateral to rear of tooth row
slopes steeply, apparently as in young adult or
adult Dusisiren jordani. Horizontal ramus relatively long and slender as in other hydrodamalines. Dorsal edge forms thin plate between
tooth row and anterior masticating surface.
Single mental foramen of moderate size lies atabout level of anterior deflection, as in D.
jordani. Deflection of masticating surface = 43°;
deflection abrupt as in D. jordani. Masticating
surface deeply notched in posterior midline;
surface very narrow and rectangular in outline,with lateral edges only slightly overhanging,
like Hydrodamalis gigas rather than D. jordani.
Anteroventral edge of symphysis keel-like,thickened with concave sides, but slightly concave in outline, giving symphyseal region distinctly Hydrodamalis-like appearance in lateralview. Posteroventral surface of symphysis has
distinct bilateral "chin" protuberances separatedby shallow groove.
Dentition (Table 3; Text-figs. 6-7; Pi. 55):-

235e
123
181
107
117e
124e
143e
64e
44
58e
90e

Text-fig. 5. Mandible: a, ventral view; b,
lateral view; c, dorsal view. Scale = 10 cm.

TAKAHASHI et al.: Late Miocene Sea Cow, Northeastern Japan

Plate 54

Figs . 1-3. Mandible: Fig. 1, ventral view; Fig . 2, lateral view; Fig . 3, dorsal view. Fig. 4, hyoida pparatus. Scales = 10 em.

809. Late Miocene Sea Cow, Northeastern Japan

Table 3.

305

Dental measurements of holotype of Dusisiren dewana, in mm. L = crown length; AW =anterior width; PW = posterior width; w = dimension reduced by wear.

M':
M2:

M3:

M2:
M3:

L
AW
PW
L
AW
PW
L
AW
PW
L
AW
PW
L
AW
PW

No incisors or canines. Deciduous premolars
unknown; adult dentition apparently 0.0.0.3.
Anterior edge of Ml approximately level withposterior edge of zygomatic-orbital bridge;
empty DP alveoli reach less than halfway forward
along bridge. M? separated by at least 27 mmfrom presumed position of pterygoid process. All
teeth except the right Ml were loose in thematrix enclosing the skeleton; neither Ml was
located.
Ml: Loose on left but still in position onright, allowing its identification. Heavily worn;
all cusps except a tiny posterior cingular cuspule
coalesced into a single lake of dentine.
M2: Labial roots coalesced and closely adherent to lingual root. Maximum length oflabial root = 25 mm. Anterior interdental wear
facet present. Crown moderately worn. Protocone and paracone fonn continuous dentine lake;
no distinct protoconule. Protocone elongatedanteroposteriorly or coalesced with anterolingual
cingular cusp. Transverse valley constricted
lingually. Hypocone-metaconule forms single
lake, including posterolingual cingular cusp
(not distinct) and extending slightly labiad along
low posterior cingular ridge, which had at least
one distinct cuspule. Metacone distinct, isolated.
M3: Roots coalesced as on M2; maximum
length = 23 mm. Anterior interdental wear facet

LEFT
16.1
14.8
15.6
18.8
19.9
18.2
21.4
18.0
15.9
17.9w
17.0w
18.2
17.8w
18.0
17.2

RIGHT
16.7
14.5
19.0
19.2
18.2
20.1
18.1
15.4
18.6w
17.9
18.0
18.5w
17.7
17.1

present. Crown slightly worn anteriorly, almost
unworn posteriorly. Protocone elongate, nodistinct anterolingual cusp. Protoconule absent,
protoloph fonned only by protocone and paracone. Transverse valley deep, narrow. Hypoconemetaconule and posterolingual cingular cusp
approximately in line with paracone. Metacone
absent. Posterior basin enclosed only by tiny
posterolabial cuspule (absent on right).
These teeth differ from those of D. jordaniin their smaller size and (probably consequent)simplification: reduction of anterior and posterior cingula and loss of the protoconule and,on M3, the metacone.
M2: Has two straight coalesced roots, anteroposteriorly compressed; maximum length ofanterior root = 27 mm (posterior root slightly
shorter). Very large posterior interdental wear
facet present. Crown heavily worn, pattern obliterated.
M3: Roots coalesced as above; damaged. Verylarge anterior interdental wear facet present,
larger on left tooth. Crown moderately worn;large protoconid and smaller metaconid confluent anteriorly, forming single crescentic lakeof dentine. Metaconid with slight suggestion of aposterolabial basal projection. Transverse valley
constricted labially. Hypoconid and entoconid
also confluent, fonning crescentic lake concave

Shizuo TAKAHASHI et al.

306

Q
..

c

·c, ·
,

h

e

OJ

Text-fig. 7. Right (a-e) and left (f-j)
teeth, occlusal views: a, f, M3 j b, g, M'; c, h,
Ml ; d, i, M3 j e, j, M •. Scale = 2 cm.
anterolingual comer forms a right angle. Hypoconid elliptical, aligned anterolingual-posterolabially; reaches farther forward than entoconid.
Anterior bulge in midline of hypolophid suggests
a remnant of a central accessory cusp. No talonidbasin or posterior cingular cuspules present.
This tooth, like the upper molars, differs from
the M3 of D. jordani in its smaller size, coalescedroots, and simplified pattern, having completely
lost the hypoconulid lophule and posterior basin.
Text-fig. 6. Right teeth, labial views (ae), and left teeth, lingual views (f-j): a, f, M3 j b,g, M'; c, h, Ml j d, i, M3 j e, j, M•. Scale = 2 cm.
posteriorly; on left M3 protolophid and hypolophid lakes are confluent labially. Entoconid
has blunt rather than sharp posterior edge, but its

Hyoid apparatus (PI. 54):
Five elements are preserved, which do notdiffer significantly in size or proportions fromthose of Dusisiren jordani (Domning, 1978: pI.
2d). The tympanohyoids ilre missing.
Stylohyoid, epihyoid, keratohyoid:-Apparently fused into a single bone on each side. Bothleft and right elements lack the proximal ends

TAKAHASHI et al.: Late Miocene Sea Cow, Northeastern Japan

Plate 55

Figs. 1-20 . Teeth: Figs. 1-5, Left M' -J and M 2 _ J , lingual views; Figs. 6-10 , same occlusal views;
Figs. 11-15, left M3- ' and M J _ 2 , occlusal views; Figs . 16-20, same, lingual views. Scale = 2 cm.

809. Late Miocene Sea Cow, Northeastern Japan

307

Table 4. Measurements of sternum, in mm. e = estimated.
Manubrium
LengthMaximum breadth (at rib articulations)
Breadth of anterior process
Posterior thickness

225+
164
11ge
35

Xiphisternum
LengthAnterior thickness
Maximum breadth posteriorly
Posterior rib articulation to attachment of xiphoid cartilage

and are about 7.5 cm long. They are narrowest(10 mm) and show a distinct angle at their midsections; the distal ends are flattened and expanded (up to 22 mm wide).
Basihyoid:-Roughly triangular, 2.5 cm longand 3 cm wide, with anterior apex and blunt
posterior corners.
Thyrohyoid:-4 cm long on one side, 3.5 cm
on the other; 1.5 cm wide proximally, tapering
distally to some degree.
Postcranial skeleton:
Sternum (Table 4; Text-fig. 8; Pi. 60):-Manubrium and xiphisternum not fused. Anterior
process of manubrium broad as in Hydrodamalis;
about 12 mm thick where anterior edge broken.
Ventral surface of anterior process convex downward both fore-and-aft and transversely; ventral
keel lacking. Large blunt protuberances for rib
articulations project laterad and somewhat
ventrad near posterolateral corners of manubrium. Abaft these, bone narrows to width ofabout 6.5 cm and terminates within about 2 cm
in straight transverse suture. Ventral surface
transversely concave downward at level of rib
articulations. Xiphisternum shorter and narrower
than manubrium, somewhat spatUlate in shape.
Anterior part of ventral side convex, with low,smooth median keel that flattens out posteriorly.
Anterior part of each lateral edge bears rugose
surface about 7 cm long for rib articulation; behind this, lateral edge much thinner. Posterioredge thick and rugose for cartilage attachment.
Overall form of sternum intermediate between
those of Dusisiren jordani and Hydrodamalis,

153+
37

87
62e

b

e

Text-fig. 8. Sternum: a-c, manubrium; df, xiphisternum; a, d, dorsal views; b, e, lateralviews; c, f, ventral views. Scale = 10 cm.

but more similar to latter in having keel developed on xiphisternum rather than on manubrium.
Scapula (Table 5; Text-fig. 9; PIs. 56-57):Supraspinous fossa about 9 cm wide, much narrower than in Dusisiren jordani; anterior edge
convex in outline, but fairly thick and inflected
laterad as in Hydrodamalis cuestae. Spine welldeveloped, overhanging posteriorly, with robust
acromion extending close to distal end, likewise
resembling H. cuestae. End of acromion flattenedsomewhat in plane parallel to blade of scapula.
Coracoid process blunt, rounded, inflectedslightly mediad. Glenoid cavity oval, deeply

308

Shizuo TAKAHASHI et al.

Table 5.

Measurements of scapulae, in mm. Letters in parentheses denote measurements used by
Domning (1978: tab. 17). e = estimated.
Left

Maximum length, vertebral border to border of glenoid fossa (AB)Mediolateral width of glenoid fossa (BI)Lateral border of glenoid fossa to inside of concave distal end ofspine (BJ)
Maximum breadth of blade dorsally (CD)Minimum anteroposterior breadth of neck (EF)Maximum anteroposterior breadth of distal end (GH)Summit of spine to medial side of blade, measured parallel toplane tangent to posterior edges of spine and neck (KL)
Anteroposterior length of glenoid fossa (MN)
Length of teres major origin from teres protuberance to posterior
corner of blade (TMO)

a

b

c

c::::==- ----a

Text-fig. 9. Right scapula: a, anterior view;b, lateral view; c, distal view. Scale = 10 cm.

concave.
Humerus (Table 6; Text-fig. 10; PIs. 57-58):Tubercles large and massive, bicipital groove deepand narrowed by anteromedial flange of greatertubercle. Tubercles diverge at angle of about
75 0 • Greater tubercle has clear supraspinatus
and infraspinatus insertion scars as in Dusisiren
jordani. Deltoid crest less developed than in D.

66
63e
283e

Right
452e
65e

112e

55e
288
73
116

86e

75e
86

115e

102e

jordani, more resembling Hydrodamalis. Protuberance present on lateral side of neck, possibly for lateral triceps origin. Head nearly circular.
Humerus tapers distal to deltoid crest, having
dumbbell shape as in D. jordani. Pectoralis major
insertion not discernible, but depressed area forteres major insertion is well marked distal tolesser tubercle. Axis of trochlea canted about 80 0
to 85 0 to shaft. Posterior side of ectepicondyleabout even with posterior side of trochlea, but
entepicondyle extends about 1 cm farther aft.
Anteromedial edge of trochlea prominent;
trochlea trapezoidal in outline in distal view,as in Hydrodamalis and some D. jordani (UCMP
77037). Entepicondyle extends posteromediada distance less than half width of trochlea. Notch
in articular surface for humero-ulnar ligament
not visible. Olecranon and coronoid fossae
shallow.
Radius-ulna (Table 7; Text-figs. 10-12; PIs.
57-58):-Fused proximally; distal epiphyses
fused to each other but sutures with diaphyses
visible. Interosseous space continuous. Muchtorsion present between radius and ulna, as in
Dusisiren jordani, but both visibly bowed medially as in Hydrodamalis. Proximal end of radius
as in D. jordani. Distal articular surface much
more resembles that of H. cuestae; has subequal
convex facets on anterior and medial parts of
distal surface, medial facet facing posterodistad
and mediad. A separate protuberance, as in

TAKAHASHI et al.: Late Miocene Sea Cow, No rth eas tern Japan

F igs. 1, 2.

Scapu lae: Fig . 1 , left; Fi g. 2, right; latera l views. Scale = 10 cm.

Plate 56

809. Late Miocene Sea Cow, Northeastern Japan
Table 6.

309

Measurements of humeri, in mm. Letters in parentheses denote measurements used by
Domning (1978: tab. 18). e = estimated.

Maximum length, greater tubercle to distal end (AB)Maximum breadth, greater to lesser tubercle (CD)Maximum breadth, ectepicondyle to entepicondyle (EF)Maximum thickness, posterior side of head to anterior side ofgreater tubercle (GH)Maximum thickness, posterior to anterior ends of medial rimof trochlea (IJ)
Mediolateral breadth of head (KL)Proximo distal breadth of head (MN)
Breadth of anterior side of trochlea (OP)
Length, saddle between head and greater tubercle to saddle oftrochlea (QR)

Left
296
133
125

Right
296
129
119

129

136

49
78
79
86

74
79
90

270

ment of olecranon process resemble those of

H. cuestae. Semilunar articular surface notchedlaterally as in D. jordani and H. cuestae. Top

Text-fig. 10. Left humerus (a-c) and radiusulna (d-f): a, d, anterior views; b, e, medial
views; c, f, posterior views. Scale = 10 cm.

Hydrodamalis, lies lateral to this facet, which
however lacks the clearly developed posterolateral extension that forms the L-shape seen in
D. jordani and H. cuestae. Shape and develop-

edge of semilunar notch slopes laterad. Medial
side of olecranon process smooth, convex.
Coronoid process has slight concavity continuous with concavity on radius. Sharp ridge on
lateral side of distal ulnar shaft lacking. Distal
articular facet narrow as in H. cuestae andfaces mediodistad, but does not overlap withposteromedial end of radial facet. Groove on
lateral side of ulna for extensor digiti quinti
tendon distinct but shallow; grooves for otherextensor tendons not discernible.
Manus (Text-figs. 13-15):-The almost complete right manus is preserved in articulation
with the right radius-ulna; the left fifth metacarpal is also present. The manus consists of four
carpals, five metacarpals, and probably sevenphalanges (two each on digits II-IV, one on
digit V).
Fused scaphoid-lunar-centrale: Of all the
carpals, this is the least modified from its condition in Dusisiren jordani. Its outline in proximal
view is roughly that of a quarter-circle, but withthe convex side medial rather than lateral. The
concave proximal articular facet is kidney-shapedwith the notch in its outline on the posterolateral side, corresponding to the articular surfaceof the radius. The posterior side of the carpal's
outline has a deep indentation; the bone in this

Shizuo TAKAHASHI et al.

310
Table 7.

Measurements of radius-ulnae, in mm. Letters in parentheses denote measurements used by
Domning (1978: tab. 19). e = estimated.
Left

Total length of ulna (AB)Total length of radius, anterior lip of semilunar notch todistal end (CD)Height of semilunar notch, anterior tip of olecranon toanterior radial lip of notch (EC)Thickness of olecranon, anterior tip to posterior side (EF)Distal thickness, anterior side of radius to posterior side ofulna (GH)Maximum mediolateral breadth, radial portion of semilunar
notch (IJ)
Maximum mediolateral breadth, ulnar portion of semilunar
notch (KL)
Minimum mediolateral breadth of semilunar notch (at its
midsection) (MN)
Minimum thickness of olecranon, posterior side to semilunar
notch (OP)

Right
297
253

58
64e

55e

64e

94
76e

88

4ge

51

39

41e

43

45

a
Fig. 12. Right radius-ulna, distal view; lateralside at top. Scale = 2 cm.

Text-fig. 11. Right radius-ulna: a, anterior
view; b, medial view; c, posterior view. Scale =10 cm.

region is rather thin (11 mm) proximodistally,
and its articulation with the cuneiform-pisiform
is weaker than in D. jordani. The distal side
has two well-developed facets for the trapeziumtrapezoid-magnum, the anterior oval (18 mm
wide, 14 mm long) and slightly concave transversely, the posterior larger (22 mm wide, about

17 mm long) and deeply concave; the facets are
separated by a groove. The distal extremity ofthe bone lies medial, rather than lateral, to theposterior facet, and is formed by a distinct protuberance of the bone separated from the facet
by a groove. Anteroposterior length of bone =47 mm, breadth = 47 mm.
Fused cuneiform-pisiform: The anterior(cuneiform) portion is greatly reduced andflattened proximodistally, giving the bone awedgelike shape tapering anteriorly from therobust metacarpal articulation. This anterior
portion, only 11 mm thick, bears a slightly

TA KAHASHI et al.: Late Miocene Sea Cow, No rtheastern Japan

Plate 57

Figs. 1, 2. Scapulae, hum er i, a nd radi us-ulnae in art icu lation: Fig. 1 , r igh t; Fig . 2 , left; lateral views.
Scale = 20 cm.

809. Late Miocene Sea Cow, Northeastern Japan

311

r

"

A
III

---Text-fig. 13. Right manus, medial and lateral views. 13A, figure showing bones articulated aspreserved in the rock, together with part of distal end of radius-ulna (continuation of shafts indicatedby dashed lines). Scale = 5 cm. 13B, hypothetical restoration in approximate life position, together
with part of distal end of radius-ulna (continuation of shafts indicated by dashed lines). Phalanges
shown associated with digit II were found in contact with lateral surface of metacarpal III. cp, cuneiform-pisiform; r, radius; sic, scaphoid-lunar-centrale; ttm, trapezium-trapezoid-magnum; u, ulna; un,unciform; I-V, digits I-V. Scale = 5 cm.

saddle-shaped articular facet for the posteromediad-facing surface of t.he ulna. This facet,triangular but more elongate anteroposteriorly
than in D. jordani, is about 30 mm long. The
anterior end of the bone is 26 mm wide mediolaterally, and convex where it articulates withthe scaphoid-lunar-centrale. It is unclear whether
distinct facets were developed in the latter joint.
The distal facet for the unciform is broad, flat,and oval, 20 mm long and 15 mm wide, andoriented parasagittally (i.e., oblique to the longaxis of the cuneiform-pisiform, which is directed
posteromediad). Abaft this facet and separated
from it by a deep groove is a smaller oval facet,
15 x 9 mm, oriented perpendicular to the former
facet; this apparently articulated with the posterior side of the proximal end of metacarpal
IV. The pisiform portion of the bone is a robust
posteromediad projection with a convex posterodistal articular surface for metacarpal V. Thissurface is 19 mm wide and trapezoidal in pos-teromedial view, with its smallest proximodistal
dimension (about 14 mm) lateral and its largest(23 mm) medial. Maximum overall length ofbone = 44 mm.
Fused trapezium-trapezoid-magnum: Much
more complex in shape than in D. jordani. The
quarter-ellipse proximal outline of the latterform is still recognizable, but its posterolateralcorner is greatly elongated by a pointed spurlike
process directed posterodistad. The two proximal
facets correspond in size and shape to the distal
facets of the scaphoid-lunar-centrale; the posterior facet is elevated about 7 mm above the planeof the anterior. The after side of this elevation
bears a broad, flat facet for the unciform, andlateral and distal to it lies the proximomediad·facing surface of the spurlike process mentioned
above. This surface may also have articulatedwith the unciform. Anteriorly, the trapeziumtrapezoid-magnum is only 7 mm thick. Its distal
surface bears a flat, triangular anterior facet,Shizuo TAKAHASHI et aZ.

312

0'·
r:"

A

r<A

~

Q
B

F

tb
J f . ··.'
,

.

.

~

,
;

K'

A
V
·,:,,~···v.,·;" · ,
/

o
c

~,

~
L

l ' .'>

,'

..\.

~'

K

Text-fig. 14. Right carpals; A-C, scaphoidlunar-centrale; D-F, cuneiform-pisiform; G-I,
trapezium-trapezoid-magnum; J-L, unciform; A,
D, G, J, proximal views; B, E, H, K, distal views(anterior at top in both); C, I, posterior views;
F, L, anterior views. Scale = 5 cm.
widest (12 mm) anteriorly and about 14 mm
long, for metacarpal I, and an irregularly oval
or triangular posterior facet, 18 mm long and
12 mm wide, for metacarpal II. The posterior
facet is flat forward and slightly concave aft,and forms an angle of about 30° with the anterior facet. Lateral to the posterior facet andseparated from it by a groove is a massive flange
7 mm thick, projecting distally about 7 mm
below the plane of the facet. From its distalmost
extremity, the rounded border of this flange
ascends both anteriorly and posteriorly, and at
the rear becomes continuous with the posterodistad-projecting spurlike process. This flange
articulates with the lateral facet of metacarpal
II. A pit lies proximal to the flange's anterior
end, and its lateral surface bears an irregular

Text-fig. 15. Right metacarpals; A-C, metacarpal I; D-F, metacarpal II; G-I, metacarpal
III; J-L, metacarpal IV; M-O, metacarpal V;
A, D, G, J, M, proximal views; B, E, H, K, N,
posterior views; C, F, I, L, 0, medial views. Scale= 5 cm.
bulge posteriorly, separated by a small verticalgroove or fissure from a similar bulge on the
spurlike process. Overall length of bone = 48mm, breadth = 28 mm, maximum proximodistal
thickness = 28 mm.
Unciform:-Curiously wedge-shaped, 34 mm
long anteroposteriorly, 28 mm wide mediolaterally, and 17 mm thick proximo distally ,resembling (and apparently homologous to)the carpal of r-Iydrodamalis cuestae illustrated
by Domning (1978: fig. 25). The pointed end,
strangely, seems to have been directed anteriorly
and proximolaterally, contacting the lateral partof the joint between scaphoid-lunar-centrale andtrapezium-trapezoid-magnum. The opposite (posterior), flat end has a trapezoidal surface measuring 24 mm mediolaterally, 16 mm proximodistally at the lateral side, and 12 mm at the

TAKAHASHI e l al.: Late Miocen e Sea Cow, North eastern Japan

Plate 58

Figs. 1-10 . Humeri and radiu s-uln ae: Right (Figs. 1-3) a nd left (Figs . 4- 6) humeri : F igs. I , 4,a n ter ior views ; Figs. 2 , 5, m edia l views; Figs. 3,6, posterior views. Right (Figs . 7, 8 ) and left
(Figs. 9, 10) radius-ulnae: Fig . 7, lateral view ; Figs. 8, 10 , a n ter io r views; Fig . 9 , m edial view.
Sea le = 10 em.

809. Late Miocene Sea Cow, Northeastern Japan

medial side; this surface articulates with metacarpal IV. The proximal surface bears a large
flat oval facet laterally for the cuneiform. The
distal surface has a semicircular or rectangularposterior area for metacarpal III; each bone's
articular surface is divided by a groove in to anarrow medial facet and a much broader lateralone. Anterior to this surface and forming anangle of about 50° with it, a smaller, somewhat
lozenge·shaped facet articulates with the trapezium-trapezoid-magnum. Lateral to this facet andfacing distad rather than anterodistad is a surface
related to the spurlike process of the latter bone.
Anteromedially and proximally the unciform isrelated to the distal side of the posteromedial
corner of the scaphoid-lunar-centrale; a facet is
indistinctly developed here also.
Metacarpal I:-Vestigial; about 14 x 14 mm
proximally, 13 mm long; wedge-shaped, withflat proximal end and chisel-like distal end.
Apparently no phalanx articulated with it.
Metacarpal II:-Irregular, squarish bone 36
mm long, diminishing in mediolateral thickness
distally. Proximal end trapezoidal, 21 x 21 mm,with broad, flat medial facet and narrow lateralfacet facing proximolaterad, separated by sharp
ridge. Anterior surface flattened proximallywhere it is in contact with metacarpal I. A bulge
on medial side of posterior surface near proximal
end contacts metacarpal III. A flat oval facetlike area on lateral side of posterior surface does
not appear to articulate with anything. Lateralside of shaft concave, medial side more or lessflat. Distal end oblique, 21 mm long anteroposteriorly, posterior part extending farther
distad and much thicker (about 14 mm), with
distinct protuberance on palmar surface. Phalangeal articular surface not well marked.
Metacarpal III:-Anterior side of proximalend has facet for contact with metacarpal II;
area on posterior side in contact with metacarpal
IV less distinct. Large flat rectangular surface for
unciform faces posterad and proximad, sloping
steeply and divided as described above. Proximal extremity of bone formed by a styloid
process which reaches toward distal extremityof scaphoid-lunar-centrale and may contact it.

313

Indeed, it seems to form a hook lying anterior
to the distal process of the scaphoid-Iunarcentrale in such a way that contact between
the two would resist straightening of the metacarpal from its posteriorly inclined position;
this, however, is not certain. Lateral surface ofmetacarpal related to spurlike process of trapezium-trapezoid-magnum, but no articular facet
is developed. Posterior side of metacarpal broad,slightly concave. Bone tapers distally, end blunt,
somewhat compressed mediolaterally, and slightly curved backward, without distinct phalangeal
surface. Total length of bone = 48 mm; proximal
end 22 mm long anteroposteriorly, 20 mm wide
mediolaterally; distal end 17 mm long, 10 mmthick.
Metacarpal IV:-Stubby, 40 mm long, withrectangular proximal end 18 mm long and 20
mm wide; main articular surface irregularly
convex. Indistinct surfaces along anterior andposterior edges contact metacarpal III andcuneiform-pisiform, respectively. Lateral sideof shaft concave, medial side slightly convex.
Bone diminishes in thickness distally to only
12 mm, but broadens to anteroposterior lengthof 23 mm, with convex outline; lacks distinct
distal articular surface.
Metacarpal V:-By far the largest metacarpal,
64 mm long on right side. Proximal end oval
(posteromedial comer missing), concave, 26 mm
wide, more than 21 mm long. Shaft tapers distally to thickness of about 11 mm, but beyond
its narrow midsection it widens to an anteroposterior length of 22 mm. Its midsection isnarrower than in Hydrodamalis cuestae (UCMP
86433: Domning, 1978: fig. 26), but the bone
is otherwise very similar to the metacarpal of thelatter, which on this basis is almost certainly
metacarpal V rather than II as Domning (1978:
p. 90) suggested. Distal end convex in outline,with indistinct articular surface like the othermetacarpals. Left metacarpal V similar but
damaged proximally. None of the metacarpals
shows signs of incomplete epiphyseal fusion.
Phalanges:- Very small compared to metacarpals. Those apparently belonging to digit II
were found against the lateral surface of meta-

314

Shizuo TAKAHASHI etal.

carpal III; the proximal one measures 15 mm
proximodistally, 11 mm anteroposteriorly, 6 mmmediolaterally; the distal one, 8 x 11 x 5 mm.
Both are flattened kernels of bone without any
distinctive shape. The proximal phalanx of digit
III appears to be missing; the distal measuresabout 11 x 13 x 6 mm. The proximal phalanxof digit IV is the best developed of all, 29 mm
in length with expanded proximal and distal
ends, measuring 16 x 11 and 15 x 10 mm, respectively. The distal phalanx measures 14 x 16 x
8 mm and has a saddle-shaped medial surface,convex proximodistally and concave anteroposteriorly. Lying next to it in the matrix was aspheroidal lump of bone about 10 mm in diameter, apparently the sole phalanx of digit V.
Innominate:-Not preserved.
Vertebrae (Tables 8-11; PI. 59):-All sevencervical vertebrae are present, together with the
13 most anterior thoracics. An articulated seriesof nine more posterior vertebral centra (posterior
thoracics through anterior caudals?) was collected separately in the year before the rest of theskeleton was discovered. The vertebrae resemble

Table 8. Measurements of atlas, in mm.
External height
Inter~al height
Total breadth
Width between processes for transverse ligament
Breadth across anterior cotyles
Breadth across posterior cotyles
Length in dorsal midline
Length in ventral midline

108
65
173
55
143
119
40
39

Table 9. Measurements of axis, in mm. e = estimated.
Total height
Length, tip of odontoid process to rear of centrum
Breadth across cotyles
Breadth of cotyle
Posterior breadth of centrum
Posterior height of centrum
Width of neural canalHeight of neural canal
Length of neural arch in midline

119
68
114
40e
73e
43
45
42
47

Table 10. Measurements of cervical vertebrae, in mm. e = estimated.

Total height
Breadth across transverse processes
Anterior breadth of centrum
Posterior breadth of centrum
Height of centrum in midline
Thickness of centrum in midline
Width of neural canalHeight of neural canal
Breadth across prezygapophyses
Breadth across postzygapophyses

C3
96
72
88
41
12
52
45
108e

C4
100e
153e
71
92
42
17
57
46
108e

C5

C6

C7
120

86
92
43
18
51e

76
83
39
17
68e

84
101
41
21
73
59

TAKAHASHI et al.: Late Miocene Sea Cow, Northeastern Japan

Plate 59

Figs. 1-17 . Vertebrae , a nt erior views: Figs. 1- 7, cerv ica ls; Figs . 8-17, thoracics. Scales = 10 cm.

315

809. Late Miocene Sea Cow, Northeastern Japan

Table 11. Measurements of thoracic vertebrae of holotype of Dusisiren dewana, in mm. e = estimated.
Tl
Total height
Breadth across transverse
processes
Anterior breadth of centrum
Height of centrum in midline
Thickness of centrum in midline
Width of neural canalHeight of neural canal

46
33
79

T2
174e

T3
200

T4
216

T5
216e

T6
216

T7
218

T8

206e

204
82e
46
44
60
54

198e
62
47
47
62
51

198e

191
91
58
48
54
50e

174
74
72e

175e
97
68
55
48
44

37e
38
70
59

those of other hydrodamalines, especially Hydrodamalis cuestae. Dorsal arch of atlas appears tolack articular surface for axis. On C3--6, basesof neural arches and bars forming dorsal sides
of vertebrarterial canals broader than in Dusisiren
jordani and more like Hydrodamalis. C7 lacks avertebrarterial canal, as in H. cuestae. Dorsal
sides of thoracic centra not indented. Arches all
solidly fused to centra. None of the first ten
thoracics appears to have a neural canal with aslitlike apex. Neural spines only slightly inclined;
anterior edges thin, sharp; posterior sides thick.
Transverse processes begin to incline dorsolateradat T5, as in D. jordani.
Ribs (Table 12; Pis. 60--62): 12 left and 16
right ribs or fragments thereof from the anterior
part of the thorax are preserved. R1 has mod·

53
47
62
53

44
47

T9

105

erately developed process for m. longus capitis
origin on ventral side of neck; distal end flattened anteroposteriorly (60 x 19 mm on rightside). Other ribs have robust, ovoid cross-sections
throughout most of their lengths. Neck of R2
nearly lacks a ventral process. Ribs 2-5 haveslightly swollen distal ends. At least the first fourribs have truncated, rugose distal ends for cartilage attachment. After about R1G-n, tubercula
draw closer to capitula and become less prominent, and shafts become more mediolaterallycompressed. Angles indistinct. Ribs in generalintermediate in form between Dusisiren jordaniand Hydrodamalis cuestae, but posterior ribs
relatively much larger than in D. jordani, indicating a larger body in relation to the head.

Table 12. Measurements of right ribs, in mm. e = estimated.

Rl

R2
R3
R4

R5
R6
R7

Capitulum to
distal end
in straight line

Tip of capitulum
to lateral edgeof tuberculum

Maximum
midshaftdiameter

Minimum
midshaftdiameter

300
388e
469
500
580e
583
655e

61
73
93
92

43e
57
57
54
60
57
68
63
70
68
69
70
63
65
68

30e
52
43
53
51
48
52
45
41
35
41
37
35
33
29

R8
R9
RIO

Rll
R12
R13
R14

R15

760e
754e
743
756

103
l11e
82e
96
82
76
51
49
47

54
42
45

Shizuo TAKAHASHI et al.

316

Discussion
The skull and dentition of Dusisiren dewana,n. sp. show such close affinities with those of
D. jordani that its generic assignment is unquestionable. Almost the only major differencein the cranial region is the reduced size andcomplexity of the molars, which nonethelessare still fully functional. In sharp contrast withthe conservatism of the cranial morphology,
however, are the profound and obviously Hydrodamalis-like modifications of the postcranialskeleton, particularly the manus.
The anatomy of the manus of Dusisiren
dewana (the first known complete manus of anadvanced hydrodamaline) in general bears out
the suppositions of Domning (1978: p. 128129): the phalanges are vestigial (and may wellhave been lost entirely in Hydrodamalis); theafter edge of the flipper is the more robust andthe anterior digits are the most reduced; themetacarpals were held in a posteriorly inclined
and somewhat flexed position; and the carpals
are greatly altered in shape. However, there
seems to be little if any "built-in pronation"or posterad orientation of the palm; the posterior part of the flipper clearly transmitted
most of the force to the substrate.
Compared with Dusisiren jordani, the scaphoid-lunar-centrale is little changed, exceptthat (as is clear also from the distal antebrachialjoint surfaces) the articular facets and hence
the axis of force transmission have shifted
medially. The cuneiform is greatly compressed
proximodistally, tilting the manus posteriorly
around a transverse axis, and apparently bririging digit V into a more strongly "flexed" and"abducted" position. The pronounced lateralflange on the distal surface of the trapeziumtrapezoid-magnum is a strong brace resisting
extension of metacarpal II and forcing it likewise into a partly flexed position. In the same
fashion, the spurlike process of the trapeziumtrapezoid-magnum resists extension of metacarpal III. The styloid process of metacarpal III,apparently catching in front of the distal processof the scaphoid-lunar-centrale, seems to lockthese bones, together with metacarpal II andthe trapezium-trapezoid-magnum, into a rigid
unit when force is applied anteriorly or anterolaterally to the distal end of metacarpal III.
The carpal of Hydrodamalis cuestae previously illustrated (Domning, 1978: fig. 25) is now
seen to be the unciform, probably the left; but
its orientation and relations certainly could nothave been guessed prior to the discovery ofDusisiren dewana. It appears that fig. 25A represents the medial surface, B the lateral, C thesurface in contact with metacarpal IV, D theanterior aspect, E the proximal surface articulating with the cuneiform, and F the facets for the
trapezium-trapezoid-magnum (left) and metacarpal III (right). Still the match with the Yamagata specimen is not a perfect one, suggestingthat still further changes took place in the
carpus before the stage of Hydrodamalis cuestae
was reached. In particular, the anterior margin
seems to have become lengthened proximodistally, and the surface for metacarpal IV
reduced to the point of unrecognizability (ornon functionality) as an articular surface. Only
the discovery of a complete carpus of Hydrodamalis will finally show whether this interpretation is correct.
On the whole, the manus of Dusisiren dewana,in comparison with those of typical sirenians orother mammals, can only be termed extraordinary. Although reminiscent at first of asevere deformity, or of such highly modified
appendages as those of ground sloths or sauropods, it is on closer examination seen to beremarkably adapted for transmitting brute force
posteriorly or posteromedially to the sea bottom.
It dramatically corroborates Steller's well-known
description of HYdrodamalis gigas, which somelater authors have had difficulty believing: "Theulna and radius terminate bluntly with tarsus
and metatarsus [sic]. There are no traces offingers, nor are there any of nails or hoofs ... "(Steller, 1899, p. 188). It likewise corroborates
the other eyewitness descriptions of thesepeculiar forelimbs and the manner of their use,
as well as Domning's biomechanical interpretations of the forelimb (see Domning, 1978, p.
96-97, 124-129). The structure of the sternum,
scapula, humerus, and radius-ulna observed in

TAKAHASHI et al.: Late Miocene Sea Cow, No rth eastern Japan

Plate 60

Figs. 1-14. Left ribs , manubrium and xiphisternum : Figs . 1-12, left ribs, posterior views; Fig. 13,
manubrium ; Fig. 14, xiphisternum , ventral views with anterior at the top. Scal es = 10 em.

809. Late Miocene Sea Cow, Northeastern Japan
Dusisiren dewana also bear out these interpretations in that they are modified in the directionof Hydrodamalis, and therefore appropriately
designed for the exertion of force on the substrate as indicated by the structure of the manus.
They confirm that the Hydrodamalis type of
locomotor apparatus had fully evolved wellbefore the loss of teeth in this lineage. Consequently the loss of teeth and associated modifications of the feeding apparatus must be seen asa (possibly belated) response to the conditions
prevailing in a newly entered adaptive zone, thenature of which is suggested by the locomotor
adaptations and discussed in detail by Domning(1978).

Occurrences of fossil sirenians in JapanFor a number of years, one rib bone of
Hydrodamalis sp., described by Shikama andDomning (1970) from the Late Pliocene Sarumaru Formation of Nagano Prefecture, central
Japan, gave the only evidence of extinct sea
cows having inhabited coastal waters of theJapanese Islands. During the last few years,
however, several reports have announced additional discoveries of sirenian fossils in northern
Japan (Text-fig. 1).
Our specimen of a Late Miocene sea cow was
discovered in 1978 and its identification as a
species of Dusisiren was confirmed by one of us(Domning) in April of 1979. This discovery wasreported at the 86th annual meeting of the Geological Society of Japan (Takahashi, Domning,
and Saito, 1979) and in later publications (Takahashi, 1981; Takahashi et al., 1983).
Inuzuka et al. (1980) reported an upper molarof "Dugong" from the Middle Miocene Bambagawa Formation of southern Hokkaido. Since
this formation is correlative with the Kunnui
Formation of southern Hokkaido which yields
planktonic foraminifera indicative of Zones N.S
and N.9, it would be the oldest sirenian-bearing
bed in Japan. However, examination of the specimen by one of us (Domning) indicates that the
specimen is probably not a siren ian and may
instead represent a worn premolar of a des-317

mostylian like Paleoparadoxia; the latter genus
is known to occur at the same locality (Inuzuka,
personal communication).
In August 1980, a large skeleton of a sea cow
was discovered in the Takikawa Formation,
which is exposed in the bed of the Sorachi River,
Takikawa City, central Hokkaido. The specimen
was later described by Furusawa and Kimura(1982) as possibly representing a new species ofHydrodamalis. This specimen was found in direct
association with a large pectinid mollusk, Fortipecten takahashii. The Fortipecten-bearing bed
has been correlated with the lower Middle
Gilbert Chron (Early Pliocene, ca. 3.7-5.1 Ma)of the geomagnetic reversal sequence (Ujiie etai., 1977; Manabe, 1980). A very comprehensive
osteological description of the Takikawa specimen and descriptions of associated fossil floraand fauna appeared in a volume published by the
Takikawa City Board of Education (1984). Fromthe illustrations and measurements given there,
the specimen appears to be an adult Hydrodamalis cuestae, with a skull very similar to but
smaller than one recently found in the San Diego
Formation of California (Domning and Demere
1984). However, Furusawa (personal communication) feels that it is more derived than H.
cuestae, so its specific assignment is still in
doubt.
In November of 1980, another fossil sirenian
was discovered in the Shiotsubo Formation at
Takasato Village, Yama County, Fukushima
Prefecture. The find consists of a left scapulaand an incomplete skull. A short description of
the specimen was given by the Aizu Fossil Research Group (1982) and the specimen was
assigned to Dusisiren sp. cf. D. jordani. This
locality is situated 83 km south-southwest of the
Yamagata sea cow locality, and molluscan fossils
associated with the Shiotsubo sea cow appear toindicate that the Yamagata and Shiotsubo sea
cows are coeval. The assemblage of fossil mollusks present in the Shiotsubo Formation has
long been recognized by Japanese paleontologists
as the Yama Fauna (Nomura, 1935). This fauna
is considered to characterize offshore environments of the Late Miocene sea, whereas the318

Shizuo T AKAHASHl et al.

contemporary Shiobara Fauna, such as occurs
with the Yamagata sea cow, inhabited nearshore environments (Chinzei, 1978). The skullof the Shiotsubo sea cow has not been illustrated
or described. The scapula does resemble that of
D. jordani more closely than D. dewana in having
a broad supraspinous fossa, but this feature may
have been variable in the latter species. In viewof the probably equivalent ages of the Shiotsubo
and Yamagata fossils, the possibility must beseriously considered that the Shiotsubo sea cow
also represents D. dewana.
The latest discovery of a fossil sea cow innorthern Japan comes from Early or Middle
Pleistocene gravel beds exposed in a quarry
along the Otoebetsu River, Hiroshima Town,
Ishikari District, southwestern Hokkaido. The
find consists of broken fragments of skull, left
scapula, right humerus, left radius-ulna, andnumerous ribs (Kimura et al., 1983). Shinohara(1983) identified these bones as belonging toHydrodamalis gigas.
These publications now provide concrete
evidence that sea cows were important elementsof coastal marine faunas of the Japanese Islands
at least from the Late Miocene onward. At least
three species now appear to have occurred inJapan, representing the last three evolutionary
stages of the hydrodamaline lineage recorded
in western North America: Dusisiren dewana,Hydrodamalis cuestae (?), and H. gigas. Taken atits face value, the Japanese record now indicatesthat hydro dam aline sirenians first dispersed
northward and westward from California in the
Late Miocene, after they had evolved the degreeof cold-adaptation represented by Dusisiren
dewana (="Dusisiren Species D"). This is consistent with the suggestion of Domning (1978,
p. 110) that this species could tolerate somewhat
colder water than D. jordani, which so far has
not been definitely recorded from the western
Pacific.
The Yamagata sea cow's age of 9.0-1004 Ma
is in excellent agreement with the 8-9 Ma date
anticipated by Domning (1977) for Dusisiren
Species D. It is definitely earlier than any welldated occurrence of Hydrodamalis, corroborat-

ing Domning's hypothesis of an unbranchingphyletic sequence of hydrodamaline chronospecies. The earliest records of Hydrodamalis
are from the 3.7 to 5.1 million-year-old Takikawa site mentioned above and the lower San
Mateo Formation at oceanside, California,
correlated with the 4.5 to 8 million-year-old
Hemphillian Land Mammal Age (Domning and
Demerl\ 1984). Thus the known stratigraphic
ranges of Dusisiren and Hydrodamalis are mutually exclusive.
Whether the stratigraphic ranges of Dusisiren
jordani (estimated at about 10-l2 Ma) and D.
dewana are likewise mutually exclusive cannot
be conclusively determined at this time becauseof the lack of precise radiometric or biostratigraphic control on the localities of D. jordaniin California. However, no available evidence
necessitates a temporal overlap between these
species, and for the present the hypothesis of asingle hydrodamaline lineage stands unfalsified.
Acknowledgments
Our deepest gratitude is expressed to Masanori Watanabe and Masahiro Saito who, in thesummer of 1978 when they were elementary
school students, discovered the sea cow specimen in the bed of the Mogami River. Theiralertness led to the collection and eventual deposition of the fossil sea cow in the Yamagata
Prefectural Museum. A series of posterior vertebrae, which was detached and found lying on
the river bed, was collected sometime prior to
the discovery of the major portion of the skeleton by Sakae Saito, who kindly donated it to theMuseum.
Many people assisted in the excavation of theskeleton from the river bed. It is not possible toacknowledge separately each contribution, but
the following organizations and individuals wereparticularly helpful: the Board of Education of
Yamagata Prefecture; the Board of Education of
the Township of Ohe; Hogen Takayama of the
Cultural Properties Protection Committee (Township of Ohe); Yuei Watanabe, Hiroshi Saito,
Matsuji Saito, Takeshi Ohya, Reiichiro Watanabe,

TAKAHASHI et al.: Late Miocene Sea Cow, Northeastern Japan

Figs. 1-16.

Right ribs, posterior views. Scale = 10 em.

Plate 61

809. Late Miocene Sea Cow, Northeastern Japan

all of the hamlet of Yoh of Ohe Town; Mamoru
Okuyama, Aterazawa Primary School; Shintaro
Yoshimi, Murayama Agricultural High School;
Masahiro Matsuda, Sagae High School; andSaburo Shirata and Naoji Ohizumi. During thecourse of preparation of the specimen, assistancewas given by: Masaaki Funayama, Tohru Omiya,
Yoshiki Kohda (Iwaki City Board of Education),
Seiichi Itagaki, Katsunori Kamagami and Shoji
Ikeno.
During the course of research on the speci·men, the following individuals provided valuableassistance and helpful advice: Richard H.
Tedford (American Museum of Natural History,
New York), Yoshikazu Hasegawa (Yokohama
National University), Teruya Uyeno and Yukimitsu Tomida (National Science Museum,
Tokyo), Hiroshi Ozaki (Saito Ho-on Kai Museum, Sendai), Toshiro Kamiya (University ofTsukuba), Norihisa Inuzuka (University ofTokyo), Hitoshi Furusawa (Takikawa City Museum, Takikawa, Hokkaido), Masahiro Suzuki(Yamagata Technical High School), Hohei Uematsu (Yamazoe High School), and Ryoichi
Tamiya (Nature Protection Department, Yamagata Prefectural Government).
Grateful thanks are due also to Kyo-on
Honda, Raiji Endo and Mikio Suzuki (all ExDirectors), Gisuke Ohtomo (Current Director),
Tomoo Yoshino, Takeo Okuyama, and Kozo
Kaneyama, all of the Yamagata Prefectural Museum, for various forms of assistance and constant encouragement.
This research was greatly aided by Fumio
Akiba (Japan Petroleum Exploration Company)
who established the age of the sea cow throughhis analysis of associated diatom floras; byKenshiro Ogasawara (Institute of Geology andPaleontology, Tohoku University) who identified
fossil mollusks; and by Hisatake Okada who
identified calcareous nannoplankton. Yaeko
Ohta, Yoshiko Kurogane and Jennifer Emrydrew the figures and Tomonori Ogata aided inphotography.
Domning particularly thanks his Yamagata
colleagues for their many kindnesses, above all
the opportunity to visit Japan and study this319

uniquely interesting and important specimen.
He was additionally supported by National
Science Foundation grant DEB-8020265.

References
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Akiba, F. (1983a): Fossil diatoms. In: Research
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- - , (1983b): Revision of Neogene diatom
zonations in the middle-high-latitude North
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15, no. 2, p. 717-724.
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--and Demere, T. A. (1984): New material of320

Shizuo TAKAHASHI et al.
Hydrodamalis cuestae (Mammalia: Dugong-idae) from the Miocene and Pliocene of San
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(Mineral. Petrol. & Econ. Geol.), vol. 7, no.
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Haq, B. U. (1984): Jurassic to Recent nannofossil biochronology: An update. In: Haq,
B. U., ed., Nannofossil biostratigraphy.
p. 358-386. Hutchinson Ross Pub!. Co.,
Stroudsburg, Pa.
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and Walker, R. G. (1975): Depositional
environments as interpreted from primary
sedimentary structures and stratification
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Inuzuka, N. and Iwamizawa Research Group(1980): First discovery of Dugong (Dugonginae) from the Middle Miocene in Kogawa,
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!toh, 0., Suzuki, M., Shibahashi, K., Takahashi,
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1 map (in Japanese).
Kellogg, R. (1925): A new fossil siren ian fromSanta Barbara County, California. Carnegie
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Occurrences of early-middle Pleistocene
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Manabe, K. (1980): Magnetostratigraphy of the
Yamato Group and the Sendai Group,
Northeast Honshu, Japan (II). Sci. Rep., Fac.
Educ. Fukushima Univ., no. 30, p. 49-71.
Maruyama, T. (1984): Miocene diatom biostratigraphy of onshore sequences on the Pacificside of Northeast Japan, with reference to
DSDP Hole 438A (Part 1). Tohoku Univ.,
Sci. Rep., 2nd Ser. (Geol.), vol. 54, no. 2, p,
141-164.
Nomura, S. (1935): On some Tertiary mollusca
from Northeast Honshu, Japan: Pt. 2, Fossil
mollusca from the vicinity of Ogino, Yamagun, Fukushima-ken. Saito Ho-on Kai Mus.,
Res. Bull., no. 5, p. 101-125.
Ogasawara, K. (1983): Molluscan fossils. In:

Research report on the excavation of the
Yamagata sea cow. p. 61-64. Yamagata
Pref. Museum, Spec. PUbl., Yamagata,Japan (in Japanese).
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Publ., Oxford.
Shikama, T. and Domning, D. P. (1970): Pliocene Sirenia in Japan. Trans. Proc. Palaeont.
Soc. Japan, NoS., no. 80, p. 390-396.
Shinohara, A. (1983): On the fossil sea cow
recovered from the Nohoro Hills, Hokkaido.

Geol. Soc. Japan, Abstracts with Programs,
90th Ann. Meet., p. 292 (in Japanese).
Steller, G. W. (1899): The beasts of the sea.

Explanation of Plate 62
Restoration of the skeleton of Dusisiren dewana, n. sp. based on the holotype. Posterior halfof the skeleton, caudal vertebrae and ribs forming posterior part of thorax, restored with reference
to the skeleton of Dusisiren jordani (University of California Museum of Paleontology, Berkeley,Specimen no. 77037). Restored specimen, as displayed at the Yamagata Prefectural Museum,measures 3.8 m in overall body length and 3.5 m in thorax circumference.

TAKAHASHI et al: Late Miocene Sea Cow, Northeastern Japan

Plate 62

o
o

o

LO

o

E
0

809. Late Miocene Sea Cow, Northeastern Japan321

In: Jordan, D. S., The fur seals and fur·seal
islands of the North Pacific Ocean. Part 3,

Takikawa City

Art. 8, p. 179-218. Washington, Govt.
Printing Off.

206 p. Takikawa City Museum, Hokkaido,
Japan (in Japanese with English summary).
Uyeno, T. (1983): Sharks' teeth. In: Research

Suzuki, U. (1979): Petroleum geology of the
Sea of Japan, northern Honshu. Jour.
Japan. Assoc. Petrol. Tech., vo!. 44, no. 5,
p. 291-307 (in Japanese with English
abstract ).
Takahashi, S. (1981): Excavation of fossil sea
cow. Yamagata Applied Geol. Assoc. Publ.,
no. 1, p. 1-5 (in Japanese).
- , Domning, D. P. and Saito, T. (1979): On
the discovery of a fossil sea cow from Ohe
Town, Yamagata Prefecture. Geol. Soc.

Japan, Abstracts with Programs, 86th Ann.
Meet., p. 228 (in Japanese).
- e t al. (1983): Research report on the excavation of the Yamagata sea cow. 76 p. Yamagata Pref. Museum, Spec. Pub!', Yamagata,Japan (in Japanese).

Board of Education (1984):

Research Report of the Takikawa Sea Cow.

report on the excavation of the Yamagata
sea cow. p. 61-64. Yamagata Pref. Museum,Spec. Pub!., Yamagata, Japan (in Japanese).
Ujiie, H., Saito, T., Kent, D. V., Thompson,
P. R., Okada, H., Klein, G. de V., Koizumi,
1., Harper, H., E., Jr. and Sato, T. (1977);
Biostratigraphy, paleomagnetism and sedimentology of Late Cenozoic sediments innorthwestern Hokkaido, Japan. Bull. Nat.
Sci. Mus. (Tokyo), Ser. C (Geol. Pal.), vo!.
3, no. 2, p. 49-102.
Zimmermann, E. A. W. (1780): Geographische

Geschichte des Menschen und der vierfiissigen Thiere. Zweiter Band. 432 p.
Weygandschen Buchhandlung, Leipzig.

Aterazawa :tr.iR, Hashigamilit_l::. Hongo i:ll'.Il, ]yuhassai -t /\?, Kuzusawa EEiR, Mizusawa
7./I:iR, Mogamigawa AZLJII, Ohe :;kilo Ohya )~fr, Tsukinuno )1;{f1, Yoh ffl.

~~~-*~~~~*~~mK&.~~Gh~W~~J::M~~R~~nM~~§~~.
Dusisiren dewana: 19781f.8)1, IUif3!!j'dljHIUIl1)*iIIBT~iifE.h~~I-JII-c', ~1f;i!)7./I:~t,:co~tl::l Lt,: ;'-lltRf:::.:;J\:1~I!~mnm~'llftatJ'; ~ i h -Ct ,~~~ 2 i:l ~ 'J4!:J::.tJ;¥E f;iI. Lt,:o iiIJtR~EJl!lIli,
71;.:4!F>~~mJ:rrJi¥i,gj)Jl!lI-c', mmJI:ltJtlJ oJ"$,Iiill: o) Denticulopsis katayamae Zone (9-10.4 Ma)~H'i~J~-t ~ fL~1t.:G~ }J1-t ~o -i'm~.ft: ~ 6 ~ 8 -l: '/ '1-,

'1-~~ ~ 1:::..cl!tJ: t),

Il!l~14~15-l: '/ '1- ~tt'i!l,tJ; 140 -l: '/ft ~ 20~90-l: '/ '1-~);:, ~ <(.~fll! Lt,:ijtj'jlJ'!J;26;;!,::t'i\IJUi£x. Ght..:o itt~ ii1Ifff~':::"ift~5l-t ,/'1-~jjJ{ittJ;,~ lI'i fP 11' >h ~'2,co G.h t,: 0~l~~J~,I:::.~.i'im~TI:::' Lt..:1:JUL~-c'f~f{-~.h, ft~41-l: ,/'1-~-,(;t1I'm~ (rJi ¥i,tJ , G c t) tf:l-tl:::' -:>h -C, .:: ~f,\'(*li (;$:M-¥$~itmtJ;I:tll'7'C~f:::.1llfj.., t,:, ~co-Cft <flf:ff~ht,:*iiiJ4~1t."fi-cilS~.:: u;rjJj GtJ'l:::.tJ: -:,f":o jl1i' ~,lt~~tr:t=lliii~fi, ~iJC.t Lt,:*iiIjll'-;tJj~ ii1I~~rp\::@~ iG-t • .5l.ff-t ~ ~.t:WI1ft:-0)~*-C'ilS~0 itf~~t'fi'!!lO:::' J: t) I-UJr~~1r.
:qU, 11 V 7::t)L·"=-7tJ'Giic~~ht,: Dilsisiren jordani f=-j!IfJ;J.-t~tJ;, ilii~*~~tJ; jordani ~ >b ~~ 3/4 C 'j' ~ <, LtJ, >b rl!.(f'iYi~~mtJ;E!iMl-c', Mir7'J;~ 7.> Ll '~1t.~~-t_#,-c'*
f! <JP:.tJ:7.>o Mir~~1t.li, *ilii~~.im1t.*71J~ >h.., c >b~::t[..,t,:if;J1i:3r1t.-c·. *~~Mir~(Jffj;:{.
t,: JcUl.!!iJ, ~ Dusisiren ~tJ, G. MirtJ;~ it. L -C ~h.ht,: Hydrodamalis ~"'~ j!1t.*JIJtJ;;jU(
iJZi4"Jllljpx-c'nli:lL~.h -C l ' ~ ilii~4'fJ!!&:to HYlfFfl1l', ~it, -'Fmit~11J1i:tJ, G, *itmfi D.
jordani c Hydrodamalis cuestae ~M,~, c: h;l: -C' *ii~lI!X:~ ~r,,'~ ~ .-c'ilS ~ c: c tJ;~IJIj}j
L, '::'::1:::' Dusisirendewalla (fni:l: -\,"7:fl;$1;$1'1111¥~I/) cl'5%frN\~t!llil~Lt,:o H.
cuestae Ii, "'- V '/ .?'iIii-c'1768~f.::.~ir!X Lt':7- ~:7 -*ilii!f- (H. gigas) ~'idtltJ:~-c', 71,;
ffrNi~ii'iJEf:::' J: t). 'I'WJ11'~W:~ D. jordani f:::' ~tJ'O)li ~ 1'4f\:~ Aihi!f-~jffiiUUIJ7'J;1Jfl GtJ,
0

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 141, pp. 322-335, pis. 63-64, April 30, 1986

810. FOLLICUCULLUS (RADIOLARIA) FROM THE UPPER PERMIANKUMA FORMATION, KYUSHU, SOUTHWEST JAPAN*
HIROAKI ISHIGA
Department of Geosciences, Faculty of Science, Osaka City University,
Sumiyoshi-ku, Osaka 558
and
T AKAMI MIYAMOTO
Institute of Geology and Mineralogy, Faculty of Science, Hiroshima University,
Nal:a-ku, Hiroshima 730

Abstract: The Permian radiolarian assemblage characterized by Follicucullus
bipartitus Caridroit and De Wever and F. charveti Caridroit and De Wever occurs
from the Lepidolina kumaensis Zone of the Kuma Formation, Kyushu, Southwest
Japan. This assemblage is different from that of the bedded chert in the MinoTamba Belt, concerning the dominant components. However, it is considered to becoeval with the radiolarian assemblage from the upper part of the Follicucullus
scholasticus Assemblage-zone and/or the Neoalbaillella optima A-zone of the chert
facies.

Introduction

lella. However, the exact age of these zones has
not been detennined, because they have been
identified mainly in the bedded chert sequencesin which biochronologically useful fossils, suchas fusulinids and conodonts, are usually absent.
It is important to correlate the radiolarian zones
with other biozones based on fusulinids andother index fossils.
Recently, Ishiga (1984) reported the occurrence of Follicucullus from mudstone of thePennian Maizuru Group and a tentative correlation was made between radiolarian zones andfusulinid zones in the Maizuru Group. Caridroit
and De Wever (1984) reported some new speciesof Follicucullus from mudstone in Hyogo Prefecture, Southwest Japan which was supposed to
be Late Penni an in age. Miyamoto et al. (1984)
discovered some species of Follicucullus from

Since Onniston and Babcock (1979) described
Follicucullus (radiolaria) from the Guadalupian
Lamar Limestone in West Texas, the occurrenceof Follicucullus has been reported from various
localities in Japan. Follicucullus is now one of
the important index fossils of Pennian time.
Among 10 radiolarian assemblage-zones whichhave been distinguished in the Japanese Permian(Ishiga et al., 1982b; 1984), the seventh andeighth zones from the base are characterized by
Follicucullus monacanthus and F. scholasticus,
respectively. Furthennore, F. scholasticus occurs
from the ninth and tenth radiolarian assemblagezones together with some species of Neoalbail*Received January 10, 1985; revised manuscript
received October 11, 1985.
322

810. Follicucullus from Kuma Formation
mudstone of the Upper Permian Kuma Formation, Kyushu, which closely resemble the speciesof Follicucullus reported by Caridroit and De
Wever (1984). This paper presents the results ofthe biostratigraphical and paleontological studiesof radiolarians from the Kuma Formation andthe correlation between radiolarian zones andfusulinid zones in the Upper Permian of Japan.
Ishiga is responsible for the chapter on systematic paleontology.
Acknowiedgments:-The authors would liketo express their appreciation to Professor K.
Ichikawa of Osaka City University for his kindcomments and critical reading of the manuscript.
Special thanks are due to Dr. A. Yao of thesame university, for his reading and kind comments on the early version of the manuscript.
The authors appreciate the collaboration in thefield and laboratory works to Mr. J. Kuwazuru
of the Sumiko Consultant Co. Ltd., Mr. T.
Nomoto of the INA Shin-Doboku Co. Ltd.,Mr. H. Yamada of the Central Systems Co. Ltd.
and Dr. R. Tominaga of the Hiroshima University. For instructive advices and suggestions in
the various aspects, the authors are much indebted to Professor A. Hase, Assoc. Professor
Y. Okimura and Assoc. Professor 1. Hara of theHiroshima University.
Geologic setting
The study area is located at the upper drainages of the Hikawa River, in the vicinity of
Kayaba, Izumi-mura, Yatsushiro-gun, Kumamoto
Prefecture, Japan (Text-fig. 1). Geotectonicallyit belongs to the Chichibu Belt of the Outer
Zone, Southwest Japan. In the study area, theKakisako, Kuma and Hashirimizu Formations
are distributed from north to south and thesethree formations are in fault contact with eachother (Kanmera, 1952, etc.). Along the fault
between the Kuma and Hashirimizu Formations,plutonic and metamorphic rocks in addition to
Silurian and Carboniferous rocks are distributed.
The "Kakisako Formation" has been recently
divided into two formations, namely the Miyama
and Kakisako Formations from north to south

323

135·
Honshu:+-35·dStudy Area
(Text-fig.2)

a

100
200km
,'--_---J'

L'_ _ _

Text-fig.1.

Index map of the study area.

(Miyamoto et ai., 1984, 1985). According tothem, the Miyama Formation is mainly composed of Late Permian pebbly mudstone including exotic blocks of Permian chert, greenstone
and others of various size and shape, while the
Kakisako Formation consists of late Early
Carboniferous (VisE!an) limestone and silty shale.
The Hashirimizu Formation which is distributed along the south of the Kuma Formation
mainly consists of black phyllite, slate and sandstone with small lenticular bodies of chert andsandstone. Rarely, greenstones and limestones
are included. The age of this formation was
regarded as Middle Permian on the basis ofoccurrence of fusulinids from limestones (Matsumoto and Kanmera, 1964). However, Early
Jurassic radiolarians have been recently reported
from this formation (Miyamoto et al., 1984).
The Kuma Formation (Kanmera, 1953),
about 900 m thick, mainly consists of sandstone, black mudstone and conglomerate andsubordinately contains small lenses of limestone.
Generally, mudstone is predominant in the lower
and upper parts, and sandstone and conglomerate
are common in the middle part. Kanmera (1953,
1954) distinguished four horizons of the limestone lenses in the Kuma Formation. The limestone of the lowermost horizon contains Lepi-

324

Hiroaki [SHIGA and Takami MIYAMOTO

o

500m

====~I

Text-fig. 2. Geologic map of the study area after Miyamoto et al. (1985).
1: Hashirimizu Formation, 2-4: Kuma Formation (2: conglomerate, 3: mudstone, 4: sandstone), 5: Miyama Formation (newly defined by Miyamoto et al., 1984, 1985), 6, 7: Kakisako Formation (6: shale with conglomerate, 7: limestone), 8: mylonitic granite. e: radiolarian fossil localities.
x: fusulinid fossil localities after Kanmera (1953).

810. Follicucullus from Kuma Formation
dolina multiseptata shiraiwensis, but it does notyield L. kumaensis (Kanmera and Nakazawa,1983). The second and third horizons are characterized by the occurrence of Leipidolina
kumaensis and have the same specific composition with each other (Kanmera, 1954). From thelimestone of the fourth horizon, Leipidolina sp.,
Pseudodoliolina sp. and Schwagerina sp. havebeen reported (Kanmera, 1953, 1954). Codonofusiella and several smaller foraminifers havebeen found in limestone about 290 m above theLeipidolina limestone in the area 6 km west of
the present study area, and this horizon is theuppermost horizon of the limestone lenses in
the Kuma Formation (Kanmera and Nakazawa,1973).
In the study area, sandstone is predominant in
the lower part, while mudstone occurs frequently
in the upper part of the Kuma Formation. Concerning the fundamental geologic structure of
the Kuma Formation, it forms a syncline thattrends ENE-WSW with its axis running near thecentral part of the study area. The strata of thenorthern wing are folded (Text-fig. 2). The localities of fusulinids reported by Kanmera (1953,
1954) are shown in Text-fig. 2. The generalized
columnar section of the Kuma Formation in the-----178

70(80,370)

m
100
0J

-"·-+-138,351 ~~~r-t--104-

2,5,6,7!

1
4
3

Text-fig. 3. Generalized columnar sectionof the Kuma Formation for the northern wingof the syncline in the study area. The fusulinid
horizons (Kanmera, 1953, 1954) and the radiolarian horizons (this paper) are shown. 1: lime·stone. 2: mudstone. 3: sandstone.

325

northern wing and the horizons of the occurrences of both fusulinids (in Kanmera, 1953,
1954) and radiolarians are shown in Text-fig. 3.
Ku 138, 351 and 104 represent the second
horizon, while Ku 70, 80 and 370 belong to thethird horizon. Ku 78 represents the fourth horizon. The limestone of the first or the lowermost
horizon is distributed outside of the present
study area.
Material
Radiolarian fossil localities (1-7) are shownin Text-fig. 2 and their stratigraphic levels areshown in Text-fig. 3.
Loc. 1: Bedded black mudstone was collected
by J. Kuwazuru from the small outcrop about
750 m east of Futae. The outcrop (380 m above
sea level) is in the small valley which is situatednorth of the road from Futae to Kayaba.
Loc. 2: Massive black mudstone was collectedfrom the outcrop (380 m above sea level), in thesmall valley which is situated southwest of
Kayaba.
Loc. 3: Silty laminated mudstone was collected about 2 m below the limestone, which is
identical with Ku 138 in Kanmera (1953, 1954),
at the confluence of two rivers, east of Futae.
Black silty laminated mudstone graduallychanges upward into calcareous sandstone which
in turn changes into limestone and conglomeratic
limestone (see Text-fig. 4).
Loc 4: Black laminated silty mudstone fromthe road-side cutting about 340 m south of Futae.
Loc. 5: Black silty mudstone from the road·side cutting about 630 m south of Futae.
Locs. 6, 7: Black silty mudstone from theroad·side cutting about 800 m south of Futae.
Samples from the Locs. 2-7 were collectedby one of the present authors, T. Miyamoto. The
Loc. 3 is situated 2 m below the Ku 138, andstratigraphically Loc. 3 is situated between Ku
138 and Ku 104 both of which correspond tolimestone of the second horizon by Kanmera(1953, 1954). The Locs. 1 and 4 are situatedbetween the second and third horizons offusulinid limestone. Mudstone of these localities

326

Hiroaki [SHIGA and Takami MIYAMOTO(Ku 138)

brush under stereoscopic microscope.
Type and figured specimens are registeredand deposited in the Institute of Geology andMineralogy, Faculty of Science, Hiroshima University (IGSH R).
Systematic paleontology
Subclass RADIOLARIA MUller, 1858
Superorder POLYCYSTINA Ehrenberg, 1838,
emend. Riedel, 1967---

Suborder ALBAILLELLARIA Deflandere, 1953,
emend. Holdsworth, 1969
Loc.3

[I~

18
2~
3

r::?

Ei.J

4

Text-fig. 4. Detailed columnar section of the Kuma Formation at Loc. 3.
Loc. 3 shows the horizon where radiolarian samples were collected, while Ku
138 is the second horizon of the limestone lens by Kanmera (1953, 1954).
1 : Limestone and conglomeratic
limestone characterized by the occurrence of Leipidolina k umaensis. 2: Thinseams of mudstone. 3: Calcareous sandstone. 4: Silty laminated shale.
is from the Lepidolina kumaensis Zone. The
Locs. 6 and 7 are situated near the axis of the
syncline and are regarded as the same horizon
as Locs. 2 and 5, considering the folding in thenorthern wing of the syncline. Mudstone of the
Locs. 2, 5, 6 and 7 is situated between the third
and uppermost horizons of the limestones. Thoseare referred to as the upper part of the L. kumaensis Zone, since Lepidolina has been reported
from the limestone of the fourth horizon, Ku 78.
These samples were broken into small fragment pieces and put into a bowl with 5-10%
HF solution for 5-10 hours. Subsequently, theresidue was gathered by using #200 sieve andradiolarian skeletons were picked up with a fine

Family Follicucullidae Ormiston and Babcock,1979 emend. Kozur, 1981
Genus Follicucullus Ormiston and Babcock,1979

Type species:-Follicucullus ventricosus Ormiston and Babcock, 1979, p. 331, pI. 1, figs.
6-14.
Follicucullus bipartitus Caridroit and De Wever,
emend. herein
PI. 63, Figs. 1-18.
1984
1985

1984

Follicucullus bipartitus Caridroit and De
Wever, Geobios, no.17, pI. 1, figs. 1-3.
Follicucullus bipartitus Caridroit and De
Wever; Ishiga, "Earth Sci." (Chikyu
Kagaku), vol. 39, no. 3, pI. 1, figs. 1-14.
Follicucullus hamatus Caridroit and De
Wever, Geobios, no. 17, pI. 1, figs. 7-14.

Materia/:-Eight specimens figured in thispaper and more than 50 specimens from Loc. 2;
500 m southwest of Kayaba, Izumi-mura, Yatsushiro-gun, Kumamoto Prefecture.
Emended diagnosis:-A species of FollicuculIus with strongly curving apical cone.
Measurements:-Length of shell excluding
flaps: 500--592 11m (av. 536), based on three
specimens (PI. 63, Figs. 1-3).
Length of apical cone: 211-279 11m (av.
232), based on 14 specimens including those
illustrated in PI. 63, Figs. 1-13.
Width of the boundary between apical cone

810. Follicucullus from Kuma Formationand pseudothorax: 68-84 ,urn (av. 75), basedon 13 specimens (PI. 63, Figs. 1-13).
Diameter of curvature of apical cone: 18106 ,urn (av. 26), based on 13 specimens (PI. 63,
Figs. 1-13).
Maximum width of pseudoabdomen: 95126 ,urn (av. 111), based on 8 specimens (PI. 63,
Figs. 1-3,14-18).
Description:-Shell tube-shaped graduallytapering distally and curving to ventral side.
Circumferential stricture at middle part of shell
dividing shell into upper and lower parts. Upper
part corresponding to apical cone and lower
part to pseudothorax and pseudoabdomen. Shell
becoming thin around the stricture and easily
broken into two parts. In some specimens (PI.
63, Figs. 5, 11; IGSH R 15-74,15-72), middle
part of apical cone weakly constricted. Distal
part of apical cone curving, radius of curvature
variable among individuals as shown in PI. 63,
Figs. 8-13 (IGSH R 15-65,75,73,72,64,69).
Lower part of apical cone tube-shaped withweakly undulated shell surface, and nearly
elliptical in cross section. Pseudo thorax long,
about half length of shell and pseudoabdomen
short. Distinction between pseudothorax andpseudoabdomen obsqure. Pseudoabdomen weakly constricted nearby aperture. Aperture elliptical in outline with asymmetrical flaps. Dorsal
flap blade-like extending obliquely downward.
Ventral flap triangular in outline extending
horizontally. Apertural margin nearly horizontal.
In some specimens, ventral flap small and spinelike in shape extending obliquely downward(PI. 63, Figs. 17; IGSH R 15-59).
Remarks:-As indicated by Caridroit and De
Wever (1984), shell of this species becomes thinaround the stricture at the middle part and iseasily broken into two parts from there. Concerning the detached apical cone, the lower margin ischaracterized by a sharp truncation which occasionally looks like an apertural margin of thepseudoabdomen without complete flaps. Moreover, concerning the dimensions of the specimensfrom the "Tatsuno Formation", the length ofshell of Follicucullus hamatus Caridroit and De
Wever is nearly same as that of apical cone of F.

327

bipartitus Caridroit and De Wever. Judging fromthese observations, F. hamatus is regarded to besynonymous with F. bipartitus. As describedabove, specimens of this species from the Kuma
Formation show morphological variation, concerning the shape of the apical cone and flaps ofapertural margin.
Follicucullus bipartitus resembles F. scholasticus morphotype I of Ishiga (1984) in having
tube-shaped elongated shell, but it differs fromF. scholasticus m. I and other species of Follicucullus in its strongly curving apical cone.
Concerning the characteristic curving ofapical cone, Neoalbaillella grypus Ishiga, Kito
and Imoto reveals the same lines of morphologic
trend (Ishiga et al., 1982a).
Occurrence:-This species occurs at Locs. 2,
3, 4 and 7 of the Lepidolina kumaensis Zone of
the Kuma Formation.
This species was originally described from theblack mudstone of the "Tatsuno Formation"
in Hyogo Prefecture (Caridroit and De Wever,1984). Recently, this species has been reported
from bedded chert in the Mino Belt, the upper
part of the Neoalbaillella ornithoformis Assemblage-zone, and from red bedded siliceous shaleand bedded chert of the Katsumi Formation in
the northern margin of the Tamba Belt (Ishiga,1985).
Follicucullus charveti Caridroit and De Wever,
1984, emend. herein
PI. 63, Figs. 19-22; PI. 64, Figs. 1-8.
1984

Follicucullus charveti Caridroit and De
Wever, Geobios, no. 17, pI. 1, figs.

1985

Follicucullus charveti Caridroit and De
Wever; Ishiga, "Earth Sci." (Chikyu
Kagaku), vol. 39, no. 3, pI. 1, figs. 19-

1984

Follicucullus falx Caridroit and De
Wever, Geobios. no. 17, pI. 1, figs. 46.
Follicucullus orthogonus Caridroit and
De Wever, Geobios, no. 17, pI. 1, figs.

15-22.

22.

1984

23-29.
cf. 1980

Follicucullus sp. cf. Fo. ventricosus

Hiroaki [SHIGA and Talwmi MIYAMOTO

328

Ormiston and Babcock; Ishiga andImoto, "Earth Sci." (Chikyu Kagaku),
vol. 34, no. 6, pI. 4, figs. 16-19, non20.

cf. 1981

Follicucullus sp. cf. Fo. ventricosus
Ormiston and Babcock; Takemura andNakaseko, Trans. Proc. Palaeont. Soc.
Japan, N.S., no. 124, pI. 34, fig. 8.
cf. 1982 Follicucullus ventricosus Ormiston andBabcock; Nishizono et al., News ofOsaka Micropaleont., Spec. Vol., no. 5,
pI. 2, fig. 4.
Material:-Eight specimens figured in thispaper and more than 150 specimens from Loc. 2;
500 m southwest of Kayaba, Izumi-mura, Yatsushiro-gun, Kumamoto Prefecture.
Emended specific diagnosis:-A species ofFollicucullus which consists of long apical cone,
inflated pseudothorax and short pseudoabdomenwith long, thick ventral flap and small dorsal
flap.
Remarks:-Caridroit and De Wever (1984)
described five species of Follicucullus. Amongthem, Follicucullus charveti, F. falx and F.
orthogonus are similar to each other concerning
the ess('ntial features given in the specific diagnosis (see above). They are regarded as varieties
within a single species, F. charveti. In this paper,
the three forms of F. charveti are treated asmorphotypes, namely, morphotype charveti, m.
falx and m. orthogonus.
Follicucullus charveti differs from F. ventricosus Ormiston and Babcock in having large
ventral flap extending horizontally or obliquely
upward. As far as the species which have been
described under the genus Follicucullus Ormistonand Babcock, Pseudoalbaillella Holdsworth andJones and Neoalbaillella Takemura and Nakaseko are concerned, the ventral flap is usuallysmaller and shorter than the dorsal flap. Therefore, this species is unusual among the species ofFollicucullus in the relative size of the two flaps.
Occurrence:-These three morphotypes ofFollicucullus charveti occur together in black
mudstone at Loc. 2 of the Lepidolina kumaensis
Zone of the Kuma Formation. In addition, m.
charveti occurs from black mudstone at Loc. 7

and m. orthogonus from black mudstone at Loc.

4.
This species was originally described fromblack mudstone of the "Tatsuno Formation" in
Hyogo Prefecture (Caridroit and De Wever,1984). Recently, this species has been reported
from red bedded siliceous shale of the Katsumi
Formation in the northern margin of the Tamba
Belt (Ishiga, 1985).
Follicucullus charveti Caridroit and De Wever,
1984, morphotype charveti Ishiga

PI. 63, Figs. 19-22; PI. 64, Figs. 1-3, 6, 7
1984

Follicucullus charveti Caridroit and De
Wever, Geobios, no. 17, pI. 1, figs. 1522.

Material:-Eight specimens figured in thispaper and more than 50 specimens from Loc. 2;
500 m southwest of Kayaba, Izumi-mura, Yatsushiro-gun, Kumamoto Prefecture. Standard specimen of this morphotype is the holotype of
Follicucullus charveti from the "Tatsuno Formation" in Hyogo Prefecture, Southwest Japan.
Measurements:-Based on 7 specimens (PI.
63, Figs. 19-22, PI. 64, Figs. 1-3).
Length of apical cone: 153-221 11m (av.
186).
Length of pseudothorax: 64-116 11m (av.
95).
Maximum width of pseudothorax: 116-137
11m (av. 132).
Length of pseudoabdomen: 22-40 11m (av.
35).
Length of ventral flaps: 105-180 11m (av.
150).
Description:-Shell consisting of apical cone,
pseudothorax and pseudoabdomen. Apical cone
long, about half length of shell, slightly curving
to ventral side. Middle part of apical cone weakly
constricted. Boundary between apical cone andpseudothorax slightly cOllstricted and shell wallof this part thinner than other part and fragile.
Pseudothorax globular in outline and slightly
inflated. In small specimens, pseudothorax shortand flattened. Pseudoabdomen short, somewhat

810. Follicucullus from Kuma Formation
curving to ventral side. Large ventral flap extend·
ing horizontally or obliquely upward. Ventral
flap usually recurving distally. Proximal part ofventral flap blade-like and distal part elliptical incross section. Basal part of ventral flap keelshaped as shown in PI. 64, Fig. 1 (IGSH R 1514). Boundary between pseudothorax andpseudo abdomen indistinct. Dorsal side of apertural margin slightly slit ted. Small and shortspine-like dorsal flap extending downward.
Aperture obliquely facing to ventral side.
Remarks:-Follicucullus charveti m. charveti
differs from F. charveti m. falx in having "byspine" extending vertically downward from theventral flap. Morphotype charveti differs from m.
orthogonus in strongly curved pseudoabdomen.
Among these three morphotypes, morphology
of apical cone and pseudothorax is, however,similar to each other.
Specimens of this morpho type from theKuma Formation show variation in the size ofshell as shown in PI. 63, Figs. 19-22 (IGSH R
15-27, 31, 29, 30) and PI. 64, Figs. 1-3 (1514, 28, 10). Shell becomes thin at the boundary
between apical cone and pseudo thorax, so thatthe apical cone is liable to be detached frompseudo thorax in this morpho type. This tendency
is the same as that of Follicucullus bipartitus.
There have not been observed any internal
structure inside of the pseudothorax as shown in
PI. 64, Figs. 6 and 7 (IGSH R 15-26, 12).

Follicucullus charveti Caridroit and De Wever,
1984, morphotype falx Ishiga
PI. 64, Fig. 8.
1984
1985

Follicucullus falx Caridroit and De Wever,Geobios, no. 17, pI. 1, figs. 4-6.
Follicucullus charveti Caridroit and De
Wever morphotype falx; Ishiga, "EarthSci." (Chikyu Kagaku), vol. 39, no. 3, pI.
2, fig. 5.

Material:-One specimen figured in this paper
and additional 10 specimens from Loc. 2; 500 m
southwest of Kayaba, Izumi-mura, Yatsushirogun, Kumamoto Prefecture. Standard specimen329

of this morphotype is the holotype of Follicucullus falx from the "Tatsuno Formation" in
Hyogo Prefecture.
Measurements:-Based on one specimen (PI.
64, Fig. 8) and other 5 specimens from Loc. 2.
The apical cone of the specimens are iii-preserved, so that its measurement is not given.
Length of pseudothorax: 150-230 J.1m (av.
190).
Maximum width of pseudothorax: 100-140
J.1m (av. 135).
Length of pseudoabdomen: 20-43 J.1m (av.
38).
Length of ventral flap: 100-179 J.1m (av.
138).
Remarks:-As mentioned already, the morphology of shell is the same as that of the morphotype charveti, except for the existence of"by-spine" which is extending vertically downward from the ventral flap. Specimens of thismorphotype from the Kuma Formation show
variation in the shape of "by-spine". "By-spine"
usually shows an inverted triangular outline, but
in some specimens it is projected downward likea spine.

Follicucullus charveti Caridroit and De Wever,
1984, morphotype orthogonus Ishiga
PI. 64, Figs. 4, 5.
1984

1985

Follicucullus orthogonus Caridroit and
De Wever, Geobios, no. 17, pI. I, figs.
23-29.
Follicucullus charveti Caridroit and De
Wever morphotype orthogonus; Ishiga,"Earth Sci." (Chikyu Kagaku), vol. 39,
no. 3, pI. 2, fig. 12.

Material:-Three specimens figured in thispaper and additional 20 specimens from Loc. 2;
500 m southwest of Kayaba, Izumi-mura, Yatsushiro-gun, Kumamoto Prefecture. Standard specimen of this morphotype is the holotype of
Follicucullus orthogonus from the "Tatsuno
Formation" in Hyogo Prefecture.
Measurements:-Based on one specimen (PI.
64, Fig. 4) and other 4 specimens from Loc. 2.

330

Hiroaki [SHIGA and Takami MIYAMOTO

Length of apical cone: 160-237 J.Lm (av.
180).
Length of pseudothorax: 60-130 J.Lm (av.
100).
Maximum width of pseudothorax: 100-120
J.Lm (av. 112).
Length of pseudoabdomen: 38-55 J.Lm (av.
48).
Length of ventral flap: 100-190 J.Lm (av.
120).
Remarks:-This morphotype differs from
Follicucullus charveti m. charveti and m. falx
in having strongly curving pseudoabdomen.
Apical cone and ventral flap are arranged nearlyparallel to each other as shown in PI. 64, Fig. 4(IGSH R 15-21). Dorsal flap of this morphotype is longer than that of the other two morphotypes owing to the slit of both sides of thedorsal flap. In accordance with the increase in
the curving of the pseudoabdomen, both sidesof the dorsal flap are slitted.
Follicucullus scholasticus Ormiston andBabcock, 1979
PI. 64, Figs. 9-11.
Follicucullus scholasticus Ormiston andBabcock, Jour. Paleont., vol. 53, no. 2, p.
331, figs. 1-5.
1980 Follicucullus scholasticus Ormiston andBabcock; Ishiga and Imoto, "Earth Sci."(Chikyu Kagaku), vol. 34, no. 6, pI. 4,
figs. 4-10.
1981 Follicucullus scholasticus Ormiston andBabcock; Takemura and Nakaseko, Trans.
Proc. Palaeont. Soc. Japan, N.S., no. 124,
pI. 34, fig. 6.
1982a Follicucullus scholastricus Ormiston andBabcock; Ishiga et al., "Earth Sci."(Chikyu Kagaku), vol. 36, no. 1, pI. 3, fig.
1979

9.

1982b Follicucullus scholasticus Ormiston andBabcock; Ishiga et al., News of Osaka
Micropaleont., Spec. Vol., no. 5, pI. 2,
figs. 8-10.
1982 Follicucullus scholasticus Ormiston andBabcock; Kojima, ibid., pI. 3, fig. 4.
1982 Follicucullus scholasticus Ormiston andBabcock; Sato et al., ibid., pI. 1, fig. 5.

1982c Follicucullus scholasticlls Ormiston andBabcock; Ishiga et al., "Earth Sci."(ChikYli Kagaku), vol. 36, no. 5, pI. 4,
figs. 13, 14.
1982 Follicllcullus scholasticus Ormiston andBabcock; Nishizono et al., News of Osaka
Micropaleont., Spec. Vol., no. 5, pI. 2, fig.
3.
1983 Follicucullus scholasticus Ormiston andBabcock; Wakita, Bull. Geol. Suru. Japan,
vol. 34, pI. 5, fig. 8.
1983 Follicucullus scholasticus Ormiston andBabcock; Suyari et al., Jour. Sci. Univ.
Tokushima, vol. 16, pI. 3, figs. 1-9.
1984 Follicucullus scholasticus Ormiston andBabcock; Ishiga, "Earth Sci." (Chikyu
Kagaku), vol. 38, no. 6, pI. 1, figs. 1-8.
1985 Follicucullus scholasticus Ormiston andBabcock morphotype I; Ishiga, ibid., vol.
39, no. 3, pI. 1, figs. 15-21.
1985 Follicucullus scholasticus Ormiston andBabcock morpho type II; Ishiga, ibid., vol.
39, no. 3, pI. 1, figs. 22-28, pI. 2, figs.
1-4.
1982 Follicucullus ventricosus Ormiston andBabcock; Sato et al., News of Osaka
Micropaleont., Spec. Vol., no. 5, pI. 1, fig.
5.
Specific diagnosis:-A species of Follicucullus
characterized by conical shell which is weakly
differentiated into apical cone, pseudothorax
without wing and pseudoabdomen with small
apertural flaps.
Measurements:-Based on three specimens (PI.
64, Figs. 9-11) and other 7 specimens from Loc.

2.
Length of shell excluding flaps (L): 271-301
J.Lm (av. 288).
Length of apical cone 120-143 pm (av. 130).
Width of pseudothorax (W): 75-90 J.Lm (av.
85).
Ratio W/L: 0.25-0.33.
Description:-Shell consisting of apical cone,
pseudothorax and pseudoabdomen. Boundary
between them obscure, only slightly constricted.
Apical cone long, about half length of shell. Shellsurface of apical cone weakly undulated. Pseudothorax slightly flattened without pores. Widthof pseudothorax (Wt) nearly equal to that of

331

810. Follicucullus from Kuma Formation

pseudoabdomen. Ratio Wt/Ls (Ls: length of shell
excluding flaps) usually 0.3. Pseudoabdomen
short about 1/5 length of shell and weakly curving to ventral side. Apertural margin between
dorsal and ventral sides lobated. Dorsal flap
tongue-like in proximally, becoming distallyblade-like within plane of bilateral symmetryof shell. Both sides of dorsal flap weakly slitted.
Remarks:-Two morphotypes, namely, morphotype I and m. II have been discriminatedwithin Follicucullus scholasticus (Ishiga, 1984).
Morphotype I is characterized by elongatedconical shell without undulation, while morphotype II is characterized by having undulated shellwith rather clear differentiation into apical cone,
pseudothorax and pseudoabdomen. Concerning
the hitherto illustrated specimens of FollicuculIus listed above, F. scholasticus described from
West Texas (Ormiston and Babcock, 1979) andfrom the Sasayama area in the Tamba Belt,
Southwest Japan (Ishiga and Imoto, 1980) canbe assigned to morphotype I. Moreover, Follicucullus scholasticus m. I and m. II have been
recently reported from the Katsumi Formationin the northern margin of the Tamba Belt (Ishiga,1985). Other specimens belong to morphotype
II. Specimens of F. scholasticus from the Kuma
Formation are assigned to morphotype II.
Occurrence:-This species occurs at Locs. 17 of the Lepidolina kumaensis Zone of the Kuma
Formation.

Follicucullus scholasticus was originally described from the Capitan ian (Guadalupian)
Lamar Limestone of Delaware Basin in West
Texas (Ormiston and Babcock, 1979) and has
been reported from many localities in the MinoTamba and Chichibu Belts, Southwest Japan.
Morphotype II of this species was reported fromthe black mudstone of the Upper formation of
the Maizuru Group which corresponds to the
Lepidolina kumaensis Zone (Ishiga, 1984).
Follicucullus scholasticus m. II has long range ofthe occurrence from the upper part of theFollicucullus monacanthus Assemblage-zone to
the Neoalbaillella ornithoformis A-zone (Ishiga
et al., 1982b), while the occurrence of F. scholasticus m. I is regarded to be restricted to theF. scholasticus A-zone.

Discussion
A.

Radiolarian assemblage from the Kuma Formation
Radiolarians obtained from the Kuma Formation are listed in Table 1. Radiolarians from theLocs. 2, 3, 4 and 7 are characterized by theoccurrence of Follicucullus bipartitus Caridroit
and De Wever, F. charveti Caridroit and De
Wever and F. scholasticus morphotype II. Albaillella triangularis Ishiga, Kito and Imoto also
occurs from the Loc. 2_ Radiolarian specimensfrom the Locs. 1, 5 and 6 are rather ill-preserved,

Table 1. Radiolarians from the Kuma Formation in the study area.

1

2

3

Localities
4
5

6

7

+

+

+

+

+

+

F. bipartitus Caridroit and De Wever

+

+

+

F. charveti m. charveti Ishiga+

F. charveti m. falx Ishiga+

F. charveti m. orthogonus Ishiga+

Follicucullus scholasticus m. II

Pseudoalbaillella sp.
+

Haplentactinia(?) ichikawai Caridroit and De Wever+

Nazarovella gracilis De Wever and Caridroit

+

+
+

+
+

Albaillella triangularis Ishiga, Kito and Imoto

+

332

Hiroaki ISHIGA and Takami MIYAMOTO

although F. scholasticus m. II has been identified
among them.
As mentioned in the preceding chapter,
Follicucullus bipartitus has been found in theupper part of the Neoalbaillella ornithoformis
Assemblage-zone which is the uppermost radiolarian assemblage-zone for the Japanese Permian.
Takemura and Nakaseko (1981) reported the cooccurrence of specimens, which resemble Follicucullus charveti (pI. 34, fig. 8), with Neoalbaillella ornithoformis Takemura and Nakaseko, N.
sp. B (=N. optima Ishiga, Kito and Imoto) andAlbaillellidae gen. et sp. indet. (=Albaillella levis
Ishiga, Kito and Imoto). The radiolarian assemblage reported by them is similar to the assemblage in the lower part of the Neoalbaillellaornithoformis Assemblage-zone (Ishiga et al.,1982b), considering the association of N. omithoformis and Albaillella levis. Albaillella triangularis Ishiga, Kito and Imoto occurs from theupper part of the Follicucullus scholasticus Azone to the Neoalbaillella optima A-zone, but
it has not been reported from the N. ornithoformis A-zone. Judging from these stratigraphic
distribution of radiolarians, especially the occurrence of Albaillella triangularis, it is consideredthat the mudstone of the Loc. 2 corresponds tothe upper part of the Follicucullus scholasticus
A-zone and/or the Neoalbaillella optima A-zone.
The radiolarian assemblage of the Locs. 3,4 and
7 are considered to be nearly the same as thatof the Loc. 2.
B.

On the radiolarian assemblage characterized
by the association of Follicucullus bipartitus
and F. charveti
Recently, the radiolarian assemblage characterized by the association of Follicucullus

bipartitus and F. charveti has been found inclastic rocks of several places in Southwest
Japan. The radiolarian assemblage from black
mudstone of the "Tatsuno Formation" in
Hyogo Prefecture is characterized by the association of F. bipartitus, F. charveti and Albaillella triangularis (Caridroit and De Wever, 1984),
and its specific composition is essentially thesame as those from the Locs. 2, 3, 4 and 7 of theKuma Formation. Moreover, Haplentactinia(?)
ichikawai Caridroit and De Wever and Nazarovella gracilis Caridroit and De Wever, originallydescribed from the "Tatsuno Formation", arefound also in Loc. 2 (PI. 64, Figs. 14, 15 and 16).
Recently, a radiolarian assemblage, identical withthat of the Kuma Formation has been foundalso from the bedded siliceous shale of the
Katsumi Formation in the northern part of
the Tamba Belt (Ishiga, 1985). According tohim, the radiolarian assemblage from this formation is composed of Follicucullus bipartitus, F.
charveti, F. scholasticus m. I, F. scholasticus
m. II and Albaillella triangularis and corresponds
to that from the upper part of the F. scholasticus
Assemblage-zone in the Mino-Tamba Belt. Excepting the occurrence of F. scholasticus m. I,
the assemblage in the Katsumi Formation is thesame as that from the Kuma Formation.
Summarizing the radiolarian assemblage from
Locs. 2, 3, 4 and 7 of the Kuma Formation,"Tatsuno Formation" and Katsumi Formation,
the assemblage is characterized by the occurrenceof Follicucullus bipartitus and F. charveti andabsence of species of Neoalbaillella. Noteworthy
is that the radiolarian assemblage is different
from that of the bedded chert of the FollicuculIus scholasticus A-zone and Neoalbaillella optima
A-zone in the Mino-Tamba Belt by Ishiga et al.

Explanation of Plate 63
Figs. 1-18.
Follicucullus bipartitus Caridroit and De Wever
Fig. 1; IGSH R 15-39, 2; 7-6, 3; 9-17, 4; 15-70,5; 15-74,6; 15-76, 7; 15-77,8; 1565,9; 15-75, 10; 15-73,11; 15-72, 12; 15-64,13; 15-69,14; 15-57,15; 15-56,
16;15-50,17;15-59,18;15-60.
Figs. 19-22. Follicucullus charveti Caridroit and De Wever morphotype charveti Ishiga
Fig. 19; IGSH R 15-27,20; 15-31,21; 15-29,22; 15-30.
All from Loc. 2. Scale: Figs. 1-3; x85. Figs. 4-22; x133.

ISHIGA and MIYAMOTO : Follicucullus trom Kuma Formation

Plate 63

810. Follicucullus from Kuma Formation(1982b), concerning the dominant components.
However, the radiolarian assemblage characterized by Follicucullus bipartitus and F. charveti
is younger than and/or partly contemporaneouswith the F. scholasticus Assemblage. FollicuculIus bipartitus and F. charveti are regarded to haverather long range of occurrence from the upper
part of the F. scholasticus A-zone to the Neoalbaillella omithoformis A-zone.

c.

Tentative correlation of some Late Permian
radiolarian zones with fusulinid zones
On the basis of the fusulinid fossil evidence
from the Kuma Formation, Kanmera and Nakazawa (1973), and Ishii et al. (1975) distinguishedthree fusulinid horizons as follows. The lower
horizon is characterized by the occurrence of
Lepidolina multiseptata shiraiwensis and the
middle one is by Lepidolina kumaensis and L.
multiseptata. The middle horizon corresponds
to the second and third horizons by Kanmera(1953, 1954), which were referred to in thechapter on geologic setting. The upper horizon
is characterized by Codonofusiella, and Lepidolina is no more represented. This horizon is
not identified in the study area.
As mentioned already, the mudstone of Loc.
3 corresponds to the limestone of the second
horizon by Kanmera (1953, 1954) and the mudstones of Locs. 2 and 4 are situated between thethird and the fourth horizons by Kanmera(1953). The mudstone of Loc. 7 is situatednearly the fourth horizon by Kanmera (1953,
1954). These four localities (2, 3, 4 and 7) correspond to the middle horizon by Kanmera andNakazawa (1973), and Ishii et al. (1975) andthey belong to the Lepidolina kumaensis Zone.
Recently, Follicucullus scholasticus morphotype II has been reported from the mudstone of
the Maizuru Group and the F. scholasticus
Assemblage-zone is considered to correspond to
the Lepidolina kumaensis Zone (Ishiga, 1984).
In conclusion, the Follicucullus scholasticus
Assemblage and the radiolarian assemblage characterized by F. bipartitus and F. charveti arefound in the Lepidolina kumaensis Zone ofJapan.

333
References

Caridroit, M. and De Wever, P. (1984): Description de quelques nouvelles especes deFollicucullidae et d 'Entactiniidae (radiolaines polycystines) du Permien du Japon.
Ceobios, no. 17, p. 639-644, pis. 1-2.
Ishiga, H. (1984): Follicucullus (Permian radio·
laria) from Maizuru Group in Maizuru Belt,
Southwest Japan. "Earth Sci." (Chikyu
Kagaku), vol. 38, no. 6, p. 427-434, pI. 1.
- - (1986): Discovery of Permian radiolarians
from Katsumi and Oi Formations along
south of Maizuru Belt, Southwest Japan andits significance. Ibid., vol. 39, no. 3, p. 176186, pis. 1-2.
--and Imoto, N. (1980): Some Permian radiolarians in the Tamba District, Southwest
Japan. Ibid., vol. 34, no. 6, p. 333-346, pis.
1-6.
, - - , Yoshida, M. and Tanabe, T. (1984):
Early Permian radiolarians from the Tamba
Belt, Southwest Japan. Ibid., vol. 38, no. 1,
p. 44-62, pis. 1, 2.
- - , Kito, T. and Imoto, N. (1982a): Late
Permian radiolarian assemblages in theTamba District and an adjacent area, Southwest Japan. Ibid., vol. 36, no. 1, p. 10-22,
pis. 1-4.
--, and - - (1982b): Permian radiolarianbiostratigraphy. News of Osaka Micropaleant., Spec. Vol., no. 6, p. 17-22, pis. 1, 2.
- , - - and - - (1982c): Middle Permian
radiolarian assemblages in the Tamba District and an adjacent area, Southwest Japan.
"Earth Sci." (Chikyu Kagaku), vol. 36, no.
6, p. 272-281, pis. 1-4.
Ishii, K., Okimura, Y. and Nakazawa, K. (1976):
On the genus Colaniella and its biostratigraphic significance. Jour. Geosci. Osaka City
Univ., vol. 19, p. 107-138, pis. 1-4.
Kanmera, K. (1962): The Upper Carboniferous
and the Lower Permian of the Hikawa
valley, Kumamoto Pref. Kyushu, Japan.
Jour. Ceol. Soc. Japan, vol. 68, no. 676, p.
17-32 (in Japanese with English abstract).
- - (1963): The Kuma Formation with specialreference to the Upper Permian in Japan.
Ibid., vol. 69, no. 697, p. 449-468 (inJapanese with English abstract).
- - (1964): Fusulinids from the Upper Permian

334

Hiroaki ISHIGA and Takami MIYAMOTO

Kuma Formation, Southern Kyushu, Japan- with special reference to the fusulinidzone in the Upper Permian of Japan -.
Mem. Fac. Sci., Kyushu Univ., Ser. D, vol. 4,
p. 1-38, pis. 1-6.
--and Nakazawa (1973): Permian-Triassic relationship and faunal changes in the Eastern
Tethys. In: Logan, A. and Hills, L. V. ed.,The Permian and Triassic Systems and theirmutual boundary. Canad. Petrol. Geologists,
Mem., 2, p. 100-119.
Kojima, S. (1982): Some Jurassic, Triassic andPermian radiolarians from the eastern partof Takayama City, Central Japan. News ofOsaka Micropaleont., Spec. Vol., no. 5, p.
81-91, pis. 1-4 (in Japanese with English
abstract ).
Matsumoto, T. and Kanmera, K. (1964): Geological map of Japan and its explanatory
text, Hinagu Sheet (1 :50,000). Geol. Surv.
Japan (in Japanese with Engish abstract).
147 pp.
Miyamoto, T., Kuwazuru, J., Nomoto, T., Yamada, H., Tominaga, R. and Hase, A. (1985):
Discovery of Late Permian radiolarians
from the Kakisako and Kuma Formationsin the Futae district, Izumi-mura, Yatsushiro County, Kumamoto Prefecture, Kyushu (Short Report). "Earth Sci." (Chikyu
Kagaku), vol. 39, no. 1, p. 78-84 (in Japanese ).

- - , - - , Tominaga, R. and Yamada, H.
(1984): Discovery of Late Permian radiolarians from mudstones of the Kakisako
and Kuma Formations, Kyushu. Abst. Prog.
Ann. Meet. Geol. Soc. Japan, p. 229 (inJapanese).
Nishizono, Y., Ohishi, A., Sato, T. and Murata,
M. (1982): Radiolarian fauna from the
Paleozoic and Mesozoic formations, distributed along the Mid-stream of Kuma
River, Kyushu, Japan. News of Osaka
Micropaleont., Spec. Vol., no. 5, p. 311326, pis. 1-3 (in Japanese with English
abstract ).
Ormiston, A. and Babcock, L. (1979): Follicucullus, new radiolarian genus from the
Guadalupian (Permian) Lamar Limestoneof the Delaware Basin. Jour. Paleont.,
vol. 53, no. 2, p. 328-334, pI. 1.
Sato, T., Nishizono, Y. and Murata, M. (1982):
Paleozoic and Mesozoic radiolarian faunas
from the Shakumasan Formation. Newsof Osaka Micropaleont., Spec. Vol., no. 5,
p. 301-310, pis. 1-4 (in Japanese withEnglish abstract).
Suyari, K., Kuwano, Y. and Ishida, K. (1983):
Biostratigraphic study of the North Sub beltof the Chichibu Belt in Central Shikoku.
Jour. Sci. Univ. Tokushima, vol. 16, p.
143-167, pis. 1-7 (in Japanese with English
abstract ).

Explanation of Plate 64
Figs. 1-3, 6, 7. Follicucullus charveti Caridroit and De Wever morphotype charveti Ishiga
Fig. 1; IGSH R 15-14,2; 15-28,3; 15-10, 6; 15-26,7; 15-12.
Figs. 4, 5. Follicucullus charveti Caridroit and De Wever morphotype orthogonus Ishiga
Fig. 4; IGSH R 15-21,5; 15-6.
Fig. 8. Follicucullus charveti Caridroit and De Wever morphotype falx Ishiga
Fig. 8; IGSH R 15-38.
Figs. 9-11. Follicucullus scholastic us Ormiston and Babcock morphotype II
Fig. 9; IGSH R 15-45, 10; 15-46, 11; 15-11.
Fig. 12. Follicucullus sp. IGSH R 15-33.
Fig. 13. Albaillella triangularis Ishiga, Kito and Imoto IGSH R 15-47.
Figs. 14, 15. Haplentactinia(?) ichikawai Caridroit and De Wever
Fig. 14; IGSH R 15-82, 15; 15-89.
Fig. 16. Nazarovella gracilis De Wever and Caridroit IGSH R 15-81.
Figs. 17,18. Unnamed spumellaria
Fig. 17; IGSH R 15-97,18; 15-95.
All from Loc. 2. Scales: Figs. 1-12,15; x133. Fig. 13; x225. Figs. 14, 16, 17; x100.
Fig. 18; x50.

ISHIGA and MIYAMOTO: Follicucullus from Kuma Formation

Plate 64

810. Follicucullus from Kuma Formation
Takemura, A. and Nakaseko, K. (1981): A new
Permian radiolarian genus from the Tamba
Belt, Southwest Japan. Trans. Proc., Palaeant. Soc. Japan, N.S., no. 124, p. 208214, pIs. 33-34.

335

Wakita, K. (1983): Allochthonous blocks andsubmarine slide deposits in the Jurassic
formation, southwest of Gujo-hachiman,
Gifu Prefecture, central Japan. Bull. Geol.
Surv. Japan, vol. 34, no. 7, p. 329-342,
pIs. 4-8 (in Japanese with English abstract).

Hashirimizu lUJ, , Hikawa )j,JII. Izumi-mura )nH. Kakisako tm.;fl, Kayaba i'" ;,j-~. Kuma flClf.',
Miyama (~~III.

1-$---<,(.- .l<%JOj(If¥,~I.i' GiIt'f1:l Lt-: Follieuculllls (Ji'dl1.!.tU : A~*ifA/\I\::mI7J,Jli i-.ijfEJi'J(,::.5t:{fj-r-G.i:i(jI---<,t.-A*J;}(Jt''}I\l'lO) Lepidolillo kUlIlaellsis {t.rimJ: ,), Follieuellus bipartitus Caridroit and De Wever ts J: If F. ellan1eti Caridroit and De Wever I::' J: I) tifi'&--:5(rf G;/1 G}i'.ct\'J:1!.r.r1,j~~~5JIJ Lt-:o ::. O)!:n~Lt_ Y-it'l-l'lil~':h:0)~1j~+ i" - I-IJ' G~1!f ~,h -n, G 1Ji~Hdlf*=!: (i. ::I::tJ: IIliJJx:fmlJ; 'J!JJ: G tJ;, '1- l' - '-/',''/11'--( ,tilE ~:h --C \" G F, sellalastieus lifilHii-!:
N eoal baill ella optima l:r~'II;:O) !/{I1'{!lUn U~O) "I,j;H::', i t-:IH 'ft17'J'--)j l::.k.Jlt ~:h G !:Y-;;tG:hG o:{it!H~'IJ!J' '!;,;*~~

337

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Molluscan fauna of the Cabatuan Formationin the Tambac area, north Luzon .. Shuto, T.
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~*ff':rRelationships of globorotaliid taxa in theUpper Miocene to Pliocene from northeast
Honshu, japan. .. ... Oda, M., Bishop, S. and Scott, G. H.
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Taxonomic relationship between
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Systematic and paleobiogeographic studies on
the japanese Miocene argonautid"Nautilus" izu11loensis.. Noda, H., Ogasawara, K. and Nomura, R.
*~I1Hllffr1=. tt Astartidae (=t:J(:}"J O)n\.m tkO).till~B'~~~ ....... " ....... 'H~M;@;jl1j~~

A new species of Dosinia from the Pliocene
and Pleistocene formations in Hokkaido,
Japan .......................... Takagi, T.
Glossaulax didyma (Roeding) O)1ll!P-l%t~t
G. vesicalis (Philippi) O);@im\ ...... rl3'~~it-·,t'ffr.ili":::. '/ /'H.~,m Eosardinella hishinaiellsisO)*.m~Mf,f, .................... ftr:il.ti~~tn1'1'I?~JlW~LHf.*J,(m"7 r/ 1 'T !J ~ O)r ~tJ:
cl.::.~Gh0MMtttl'::''0l'-C ........ IMlmtr~~j,*~~~J;1(~llff.::.1!;-i.h0i§~-lj- /' 3·ltf~ .... ':p~O).f$:t-o J: rr~~iffi!tf'::' '0l '-C -Etl!~-lj- /' dli!tO).fI- ........................ t1FBf$ill
Fl ~ilUlJt 'm.ljH'l¥o~ 0) t/{ ~,(~f.'i ~. . . . .. I LH);r,'f IYl
lyH~iff}O)iiiiIJtJjtjj\1~JlI'f.::..l;.. Gh 01/d\J{~ llf ~f=1 *O)MJlLl$c.H Sika ~~O)j'IJ~IT-.j- ... *~fii;z'~~m.K10~~~mMO)~*-r~~mO)~m....................... *Hiill)j • j.;:~fW: 'iX~tl'l*O)il~~~$i2

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fWfJr ........................ jung. Kyu-KuifilililJ ~!jl,/J \:{', i)~ l,pi<~ Jj[~m¥/.J '1' (7) It'\; 'to if JL!:U (7) (* J.It7};{ff .................. ifijl~tHI*· :R:ftJlII'4ft~• • ~&~~KJ:Qm~*~AA(7)4~~~(7)*::111t.-tUl((7)-Jilti¥JJJX::R:-1:TIt.- ........ 1iITJ'*~~~.~OO.~K~~Q~~-m~*(7)~.m~~,'il'lJ'!%lJIiJ ... 7riili'~1; iF • im.l!iH-lIj~ • U~'llrjj: if{(
YJ,'@(Jl!1I1:Jrt'l: 1'f1L!:U n{ (7) ~t.1L~.............. ~t.!l:l. it· ffiiR ~. ~~t:~19851f~ A *,li1:.fu~f><(',i'l()c1tliFr11!i':,~-rr(7) Intraspecific vanatlOn in three speciesof Glossaulax (Gastropoda: Naticidae) from the Late Cenozoic strata in Central andSouthwest japan. Trans. Proc. Palaeont. Soc. japan, N. S .. No. 138, pp. 111-137, pis.
17-19, 1983 1::.'t.:l'VCB't1j·~h;t Lt.:o t.cMftl!l$X:Lt. 11t1.iJ l::.t~iI\I(~h;t-to19851f~ FJ *lli1:.fuCf:~+It.j1tltllllll.fZ:n-(7) 11tE t.c I? LfI::.m1:. 7:; 'l ;f-m(7)liIf'feJ 10.:l'V(t~lf·~h;tLt.:o tlI~~)clilrfjC<

11t.:fiJ f::'ft;\il'J:~h;t-to

New members approved by the Council Meeting held on January 31, 1985
Ordinary Members
Fujiura, Tsuyoshi; Iwauchi, Akiko; Muramoto, Kouji; Takagi, Yoshiyuki; Yoshida, Hidekazu.
New members approved by the Council Meeting held on June 14, 1985
Ordinary Members
Furukubo, Masako; Goto, Yoshihiro; Hashimoto, Kazuo; Hori, Rie; Iwata, Keiji; Kamishima,
Junichi; Kondo, Toshifumi; Kurashige, Yoshimasa; Lee, Yeon Gyu;Mizunuma, Bunji;Nemoto,
Naoki; Sato, Hidetoshi; Sato, Touru; Takabatake, Kazuhiro; Tanimoto, Masahiro; Tsukagoshi,
Minoru; Uchida, Shigehiro; Ueda, Tetsuro.
Foreign Members
Pa'n, Chang Wu; Wang, Chia Ching.
Withdrawing Members
Hasegawa, Junichi; Shindou, Tetsuya; Watanabe, Akiho; Durham, J. W.; Pak, Soon Heong.
Samaniego, R. M.; Schmidt Effing, R.; Stach, Leopold, W.
Patron Members: Sekiyu Kodan; SG Giken Co.
New members approved on January 30,1986
Ordinary MembersAndo, Jun; Futagawa, Toshiaki; Hayashi, Shunichi; Ishigaki, Shinobu; Ito, Yoshio; Koseki,
Osamu; Kotake, Nobuhiro; Miyahashi, Hiroshi; Miyasaka, Yoshihiko; Shigeta, Yasunari;
Shirato, Yutaka; Takamura, Kazuko; Tsuru, Toshiyuki; Yamamuro, Masumi; Yoshida, Kouichi.
Withdrawing Members
Hayashi, Shingo; Ichikawa, Wataru; Iguchi, Yutaka; Momoi, Kyoko; Nakagawa, Hiroshi;
Oda, Hiroshi; Sogabe, Masatoshi; Suda, Akihiko; Taguchi, Eiji; Yokoyama, Tsuruo; Yoshida,
Fumio.
Deceased Members
Ling, Chao Chi; Sugita, Munemitu; Takehara, Heiichi.
Fellows
Inoue, Yoko; Iwao, Yushiro; Kase, Tomoki; Nagai, Kouichi; Nishimiya, Katsuhiko; Nishimura, Akiko; Nishimura, Akira; Shibata, Hiroshi.

340

Palaeontological Society of Japan, Special Papers
List of Available Back Numbers
A, B (Yen) C (U.S.$)
No.9 lI962): Bibliography of Japanese Palaeontology and
Related Sciences, 1951-1960. By F. Takai (ed)No. 13 (1968): The Echinoid Fauna from Japan and AdjacentRegions. Part 2. By S. Nisiyama
No. 15 (1971): Early Devonian Brachiopods from the Lesser
Khingan District of Northeast China. By T. Hamada
No. 16 (1971): Tertiary Molluscan Fauna from the Yakataga
District and Adjacent Areas of Southern Alaska. By S. Kanno
No. 17 (1973; reprinted 1980): Revision of Matajiro Yokoyama'sType Mollusca from the Tertiary and Quaternary of the Kanto
Area. By K. Oyama
No. 18 (1974): Silurian Trilobites of Japan in Comparison with
Asian, Pacific and other Faunas. By T. Kobayashi and T.
HamadaNo. 19 (1976): Bivalve Faunas of the Cretaceous Himenoura
Group in Kyushu. By M. Tashiro
No. 20 (1977): Devonian Trilobites of Japan in Comparison with
Asian, Pacific and other Faunas. By T. Kobayashi and T.
HamadaNo. 21 (1977): Mid-Cretaceous Events - Hokkaido Symposium,
1976. By T. Matsumoto (org.)
No. 22 (1978): Bibliography of Palaeontology in Japan, 19611975. By K. Kanmera and H. Ujiie (ed.)
No. 23 (1980): Carboniferous Trilobites of Japan in Comparison
with Asian, Pacific and other Faunas. By T. Kobayashi and
T. HamadaNo. 24 (1981): Permian Conodont Biostratigraphy of Japan.
By H. Igo
No. 25 (1982): Multidisciplinary Research in the Upper
Cretaceous of the Monobe Area, Shikoku. By T. Matsumotoand M. Tashiro
No. 26 (1984): Permian Trilobites of Japan in Comparison with
Asian, Pacific and other faunas. By T. Kobayashi and T.
HamadaNo. 27 (1984): Some Ammonites from the Campanian (Upper
Cretaceous) of Northern Hokkaido. By T. Matsumoto
No. 28 (1985): Bibliography of Palaeontology in Japan,
1976-1980. By T. Kase and K. Asama[This new price list is available from August 1, 1986]

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PALAEONTOLOGICAL SOCIETY Of JAPAN, SPECIAL PAPERSORDER fORM

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Transactions and Proceedings of the PalaeontologicalSociety of Japan
April 30,1986

New Series No. 141

CONTENTS'TRANSACTIONS
807. OHOTSUKA, Yasuo: Early internal shell microstructure of some Mesozoic Ammonoidea: Implication for higher taxonomy . . . . . . . . . . . . . . . . . . . . . . . 275
808. KOIKE, Hiroko: Microstructure of growth increments in the shell of Mercenaria
mercenaria (Linne) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
809. TAKAHASHI, Shizuo, DaMNING, Daryl P. and SAITO, Tsunemasa: A new ancestorof Steller's sea cow from the Upper Miocene of Yamagata Prefecture, Northeastern Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
810. ISHIGA, Hiroaki and MIYAMOTO, Takami: Follicucullus (Radiolaria) from theUpper Permian Kuma Formation, Kyushu, Southwest Japan . . . . . . . . . . . . . 322
PROCEEDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337