ISSN 0031-0204

Transactions and Proceedingsof thePalaeontological Society of Japan
New Series

No .

156

Palaeontological Society of Japan
December 30,

1989

Co-Editors

Hisayoshi Igo, Hiroshi Noda and Kei Mori
Editorial Board

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

Officers for 1989-1990

President: Itaru Hayami
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The fossil on the cover is Phillipsia ohmorensis Okubo, an Early Carboniferous trilobite
from the Hikoroichi Formation in the Higuchizawa valley, Ofuna to City, Iwate Prefecture, northeast Japan (Collected by A. Haga, PAt 5766, x 3.0; after Kobayashi and
Hamada, 1980, pI. 6, fig. 4).
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Trans. Proc. Palaeont. Soc. Japan, N.S., No. 156, pp. 255-269, 6 Figs., December 30, 1989

887. LARGER FORAMINIFERA FROM THE EOCENE SHIMIZU
AND MIOCENE MISAKI FORMATIONS IN TOSA SHIMIZU CITY,
KOCHIPREFECTURE,SHIKOKU,JAPAN*
KUNITERU MATSUMARU
Department of Geology, Faculty of Education,
Saitama University, Urawa 338
and

KOSHI KIMURA
Idowr Engineering Co. Ltd., Heiwa Bldg.,
Kouenji-Kita 2-19-6, Suginami, Tokyo 166

Abstract. Larger foraminifers from two localities of the Eocene Shimizu and Miocene
Misaki Formations in Tosa Shimizu City, Kochi Prefecture, Shikoku, Japan are firstdescribed and discussed. Two species among five species described herein are new species,
and all these species are useful for age determination and correlation of these formations in
the Indo-Pacific region.
'
Key words. Asterocyclina, Orbitoclypeus. Discocyclina, Nephrolepidina. Shimizu andMisaki Formations, Shikoku.

described herein have been deposited in thecollections of Department of Geology, Faculty of Education, Saitama University.

Introduction
Recently, the junior author investigated thestratigraphy and sedimentary facies of the
Tertiary Shimizu and Misaki Formations inthe southwestern part of Shikoku (Kimura,1985). Both formations are distributed inand around Tosa Shimizu City, occupying apart of the Shimanto Terrain. Some samplesof tuffaceous mudstone and muddy sandstonecollected in Tosa Shimizu City by the juniorauthor were examined by means of random
thin sections. In two of these samples there
occur interesting larger foraminifers, one ofwhich represents Late Eocene, and the otheris regarded as Early Miocene.
The purpose of this paper is to make adescription of these species. All specimens·Received October 3, 1988: revised
accepted November 1, 1989

Fossil localities and geologic setting
Fossil localities treated in this paper are in
the hilly land, northwestern part of Tosa
Shimizu City, Kochi Prefecture, Shikoku andsamples from the following two localities
were studied in detail (Figure 1).
Locality 1. This locality is about 800 m
northeast of Takahata, Tosa Shimizu
City (32°49'55"N. Lat., 132°54'34"E.
Long.). Chaotic deposits of the Shimizu Formation exposed at Locality 1
are composed of irregular-shaped blocks
and clasts of andesite, conglomerate andsandstone dispersed in argillaceous
matrix. The samples are taken frommanuscript

255

256

Kuniteru Matsumaru and Koshi Kimura

Legend,~~~3m;a;tf~

5

't

6

/

/

J../

2

4

o

Figure 1. Map showing the fossil locality and geological sketch map of the studied area, Tosa Shimizu
City, Kochi Prefecture, Shikoku. 1-3, Misaki Formation (I, Upper Member; 2, Middle Member; 3,
Lower Member); 4, Shimizu Formation; 5, Kurusuno Formation; 6, Fossil locality.

gray colored tuffaceous mudstone in thematrix.
Locality 2. This locality is about 800 m
south of Yokomichi, Tosa Shimizu City
(32°48'20"N. Lat., 132°55'15"E. Long.).
Samples are tak~n from poorly sorted
muddy sandstone of the Lower Memberof the Misaki Formation (Figure 2).
Tertiary rocks in Tosa Shimizu City are
stratigraphically grouped into two forma-tions, the Shimizu and Misaki Formations by
the junior author (Kimura, 1985). The
Shimizu Formation co~tains mainly chaotically mixed deposits, and partly coherently
stratified sediments. As a whole, the Shimizu Formation is referable to submarine sliding deposits. Mudstone of the Shimizu Formation yields the following planktic foraminiferal species: Globigerina ampliapertura Bolli (from P17-21 of planktic for-

887.

Larger Foraminifera from Shikoku

Ss/mdsm10

muddy Ss
silt
mds

FAULT

o

Pebbly mds(ShImizu Fm)

Figure 2. Columnar section of the Lower
Member of the Misaki Formation, at the fossil locality (Loc. 2) of Figure 1. The symbol on left side of
the columnar section shows the fossil-bearing bed.
Ss/mds = Alternation of sandstone and mudstone; Ss = sandstone: mds = mudstone; Fm. = F ormation.

aminiferal Zone of Blow, 1969), and G.
anguliofficinalis Blow (from PI7-2I Zone)
from sample s-4, and Globorotalia opima
opima Bolli (from P20-2I Zone) from sample
s-5 (Kimura, op. cit., table I). Therefore, thegeological age of the Shimizu Formation at
samples s-4 and s-5 is considered to range
from Late Eocene to Late Oligocene (PI7 to
P21 of planktic foraminiferal Zone).
The thin sections of mudstone from Locality I show the presence of Asterocyclina stella(GUmbel), Orbitoclypeus kimurai Matsumaru, n. sp., O. sp., Discocyclina sella (d'Archiac), and other fossils as calcareous
algae, echinoids, bryozoas and corals.
Asterocyclina stella and Discocyclina sella
have a common range of Middle Eocene(Lutetian) to Late Eocene (Priabonian), in
the Aquitaine Basin, France (Neumann,

2571958) and the Priabonian stratotype, Italy(Sirotti, 1978).
As having some morphological similarities
with each other, the Takahata specimens ofOrbitoclypeus kimurai, n. sp. are comparedwith the French specimens of O. chudeaui(Schlumberger) by Weijden (1940) and
Neumann (1958), but both forms are not
identical each other. According to
Neumann (1977), Orbitoclypeus chudeaui
from the Mesogean Eocene sediments inwestern Europe has a range from Middle
Eocene (Hantkenina aragonensis Zone; PIO
Zone of planktic foraminiferal Zone) to early
Late Eocene ( Globogerapsis semiinvoluta
Zone; Pl5 Zone), and this species is in association with Discocyclina sella (d' Archiac).
Also, according to Bieda (1963), Orbitoclypeus chudeaui occurs mainly from theUpper Tatra Eocene in Poland and Czechoslovakia, and this is in association with
A sterocyclin a stella (GUmbel). Sirotti(1978) described ten species of the Discocyclinidae, including Asterocyclina stella andDiscocyclina sella, from the Priabonian typesection in Lessini Mountains, Vicenza, Italy.
It is recognized that the Shimizu Formation at Locality I represents the presence of
Late Eocene (Priabonian), based on theoccurrence of Asterocyclina stella, Discocyclina sella and Orbitoclypeus kimurai, n. sp.,which has similar morphology to O.
chudeaui. In the field observation, theShimizu Formation from the mudstones ofLocality I to those of samples s-4 and s-5(Kimura, 1985, fig. 8) is cut by the WNWESE trend fault, one branch of the Misaki
Fault. Then, the stratigraphic position
between both mudstones is unknown. On
the basis of the concurrent ranges of thediagnostic species of larger and planktic foraminifers, it is concluded that the mudstonesof Locality I may be situated in the lower
horizon than those of samples s-4 and s-5.
On the other hand, the Misaki Formation iscomposed of alternation of sandstone andmudstone in various sand-mud content ratio.

258

Kunitel'u Matsumal'u and Koshi Kimura

887.

Larger Foraminifera from Shikoku

This formation is regarded as a shallow
marine deposit, based on lithofacies, sedimentary structure and fossils. Following planktic foraminifers were discovered from mudstone samples of the Lower Member of the
Misaki Formation at Locality 2 (sample m-3,
Kimura, 1985, fig. 8, table I), and four otherlocalities (samples m-5, 7, 8 and 9 of Kimura,op. cit.): Catapsydrax stainforthi Bolli,
Loeblich and Tappan (from N5-lower N7Zone), Globigerinoides altiapertura Bolli(from N5-lower N7 Zone), G. immaturus
LeRoy, G. subquadratus Bronnimann,
Globorotalia zealandica Hornibrook (fromAwamoan to Altonian of New Zealand stage,
Hornibrook, 1968), Globorotaloides suteri
Bolli and Praeorbulina sicana (de Stefani)(from uppermost N7-9 Zone). Accordingly,
the geological age of the Lower Member ofthe Misaki Formation should be determinedas late Early Miocene (Burdigalian).
The thin sections of mudstone from Locality 2 show the occurrence of Nephrolepidina
praejaponica Matsumaru, n. sp., Amphistegina radiata (Fichtel and Moll), Sphaerogypsina globulus (Reuss), Rotalia sp.,
Globigerina sp., and other fossils as
bryozoans, molluscs, echinoids and calcareous algae. Nephrolepidina praejaponica, n.
sp. could be considered as an ancestor of
Nephrolepidina japonica (Yabe), because ofa
small size and a primitive form of embryonicchambers which show an early stage of theembryonic acceleration of Nephrolepidina(Matsumaru, 1971).

Description of species
Family Discocyclinidae Vaughan
and Cole, 1940
Subfamily Orbitoclypeinae
Bronnimann, 1945
Genus Asterocyclina Gumbel, 1868

259

Asterocyclina stella (Gumbel, 1861)
Figures 3-3,8, II; 4-1-5

1861
1868

Hymenoeye/us stella GUmbel, p. 653.
Orbitoides stella, GUmbel, p.716-717, pI. 2,
figs. 117a-c; pl.4, figs. 8-10, 19.
1940 Diseoeye/ina (Diseoeye/ina) stella GUmbel,
Weijden, p. 50-53, pI. 8, figs. 1-4.
1940 Asteroeye/ina stella GUmbel, Bronnimann, p.
28-29, pI. I, figs. 3, 7; pI. 2, fig. 2.
1958 Asterodiseus stella (GUmbel), Neumann, p.
112-114, pI. 28, figs. 1-6; text-fig. 36.
1978 Asteroeye/ina stella (GUmbel), Sirotti, p.62,
64, pI. 4, figs. 11-15.
1980 Asteroeye/ina cr. stella (GUmbel), Matsumaru,
p. 217-218, pI. 25, figs. 1-14.

Description: - The test is small, thicklenticular or inflated, 1.8 to 2.6 mm in diameter; 0.8 to 1.3 mm in thickness and 2.7 to 3.0
is the form ratio of the diameter to the thickness. There are 5 to 6 rays which are shortwith bluntly rounded ends and merge into thecentral part. Seven to 8 papillae occur on
the central inflated portion of test and are 68
to 160/Lm in diameter.
The embryonic chambers are bilocular andshow nephrolepidine type: protoconch being
subspherical is slightly embraced by a reniform deuteroconch. Internal diameters ofprotoconch 62 X 68,84 X 70,88 X 84, 126 X
170, 130xllO, 158xI25/Lm, and deuteroconch 1I2x85, 125x80, 160x98, 144x90, 154x
102, 182 X 88 /L m, are measured respectively
from six equatorial sectioned specimens.
The outer wall of the embryonic chambers is
11 to 15/Lm in thickness. Total diameter ofembryonic chambers is 170x 169, 196x 187,
207 x 197 and 240 x 270 /Lm in four specimens.
Distinct nepionic chambers over de uteroconchal wall are flat-arcuate with radial
diameters of 23 to 26/Lm and tangential
diameters of 33 to 35/Lm. There are about~ Figure 3. 1,2, 4-7, 9, 10, 12. Orbitoe/ypeus kimurai Matsumaru, n. sp. 1. Centered oblique section; 2, 4, 6, 9. Vertical sections; 5,7, 12. Transeverse sections; 10. Oblique section. 3,8, 11. Asteroeye/ina stella (GUmbel); 3. Centered oblique section; 8. Vertical section; 11. Nearly centered verticalsection. All figures X 40.

260

Kuniteru Matsumaru and Koshi Kimura

22 to 25 nepionic chambers in the peri embryonic ring. The equatorial chambers in
the rays are radially elongated square withradial diameters of 50 to 70 pm and tangential diameters of 28 to 36 pm. The interray chambers are tangentially elongate squareto square or hexagonal in shape with radial
diameters of 35 to 46 pm and tangential
diameters of 18 to 35 pm.
The lateral chambers are arranged in regular tires in vertical section. The lateralchambers over the embryonic chambers haveslit-like openings between thick floors androofs, with length of 42 to 56 pm and heightof 12 to 14 pm. The number of lateral chambers varies from 16 to 18 layers over theembryonic chambers. The pillars between
lateral chambers are well developed in thecentral part of test, with a diameter of 68 to
160 pm.
Stratigraphic horizon: - Shimizu Formation.
Geological age: - Late Eocene (Priabonian).
Remarks: - The present specimens werecritically compared with the specimens from
Biarritz (Weijden, 1940) and Landes(Neumann, 1958), both in France, northwest
Morocco (Bronnimann, 1940), and Priabona,
Italy (Sirotti, 1978), which have been referredto Asterocyclina stella (GUmbel). The peculiar nephrolepidine embryonic chambers anddistribution of pillars as seen in tangential
section (Figure 4-5) are very similar to
A sterocyclin a stella from France andMorocco. However, the Tosa Shimizu specimens have more or less small sized embryonicchambers. But the specimens are safely
identified with Asterocyclina stella (GUmbel)
from France, Morocco and Italy.
The senior author (Matsumaru, 1980)
figured specimens named as Asterocyclina cf.

stella (GUmbel) from the Kurusuno Formation at Zaimisaki Cape, Tosa Shimizu City,
Kochi Prefecture. Although these specimens
are more or less stressed into the distorted
forms, the specimens are the same as thosefrom the Shimizu Formation in this paper,and all the specimens from the Kurusuno andShimizu Formations are, therefore, identified
as Asterocyclina stella (GUmbel).
The present species from Takahata (Locality 1) resembles Asterocyclina stellatus (d'Archiac) by Weijden (1940), Neumann (1958)
and Sirotti (1978), but it is distinguished fromthe latter by its smaller shell size, smaller
embryonic chambers and many nepionicchambers. The Takahata specimens resembles Asterocyclina matanzensis Cole from
Eniwetok Atoll (Cole, 1957a) and Saipan(Cole, 1957b), but the former is discriminatedfrom the latter by its large embryonic chambers.
Genus Orbitoclypeus Silvestri, 1907
Orbitoclypeus kimurai Matsumaru, n. sp.
Figures 3-1,2,4-7,9, 10, 12; 5-1,2, 5

Type material: - Holotype, equatorial
section, Saitama University ColI. no. 8801
(Figure 5-5).
Description: - The test is with an umbonal central part surrounded by a thinflange. The umbo is either arched (Figures
3-2,4, 10, 12), gently arched (Figures 3-5, 7)
or flat-topped (Figures 3-6, 9) in the center.
As most of the specimens are much worn, theflange is usually only partly preserved. The
diameter of the specimens is more than 2.1
mm as the portion of available sections has
this measurement. The thickness throughthe centre of test is 0.8 to 1.1 mm. The
papillae, slightly raised, occur on the um-~ Figure 4. Asterocyclina stella (GUmbel). 1-4. Centered oblique sections. Ib, enlarged of la, and2, enlarged of Figure 3-3, showing the embryonic, nepionic and neanic chambers, and their chamberformations, respectively. 3-4. Tangential sections, showing the embryonic, nepionic and neanic chambers,
and their chamber formations, respectively. 5. Tangential section, showing the distribution and development of pillars. All figures X 118, except x45 of la and 5.

887.

Larger Foraminifera from Shikoku

261

262

Kuniteru Matsumaru and Koshi Kimura

bonal part and have a diameter of 70 to 100,urn.
The embryonic chambers of eulepidine areconsisting of a protoconch with diameters of
84 X 84, 104 X 91, 119 X 105 ,u m, and a deuteroconch with diameters of 189 X 182, 217 X 189,
210 X 228 ,urn, respectively from three equatorial sectioned specimens. The distanceacross both chambers is 190 to 230,um. The
outer wall of the embryonic chambers is 10,urn in thickness. The dividing partition
between a protoconch and a deuteroconch isnearly circumflex and is 7 ,urn thickness. In
vertical section, the large, elliptical- to pearshaped embryonic chambers have lengths of
167 to 177 ,urn and heights of 70 to 100,um.
The periembryonic chambers differ fromchambers of the nearby ring. There areabout 27 to 30 hexagonal chambers in theperiembryonic ring. Distinct two primary
auxilliary chambers are rectangular to shorthexagonal with raidal diameters of 20 to 42,urn and tangential diameters of 42 to 49,um.
Nepionic chambers on the outer edge of thedeuteroconch are hexagonal with radial diameters of 30 to 35 ,urn and tangential diametersof 25 to 35,um. The annular stolon is situated on the proximal side of the radial chamber walls of nepionic chambers.
The equatorial chambers are arranged inirregular rings and connected to each other byradial stolons. The annular walls are usually thicker than the radial ones, which alternate regularly in adjacent annuli. There is atendency for the rings to become stellate with
8 rays. The equatorial chambers are radiallyfrom square through spatulate to hexagonalwith maximum radial diameters of 35 to 40,urn and maximum tangential diameters of 25
to 30,um.
The lateral chambers are rectangular inshape and are arranged in regular tiers invertical section. The chambers over the central area of test are spaceous, with a length of

45 to 80 ,urn and with a height of 13 to 28 ,urn.
The thickness of floors and roofs is 6 to 18,urn. Number of lateral chambers per tierover the embryonic chambers is 16 to 18
layers. The pillars are well seen in the central part of test in vertical section.
Stratigraphic horizon: - Shimizu Formation.
Geological age: - Late Eocene (Priabonian).
Remarks: - The specimens from Locality
1 at Takahata closely resemble the specimensfrom France figured by Weijden (1940) and
Neumann (1958) under the name of Discocyclina chudeaui (Schlumberger). However,the small embryonic and ad auxiliary chambers, and many lateral chamber layers of the
Takahata specimens are distinguishable fromthese of the French species. Discocyclina
chudeaui, however, was treated as a species of
the genus Orbitoclypeus by Sirotti (1987).
The vertical section of Orbitoclypeus
kimurai, n. sp., is similar to that of Asterocyclina stella (Gumbel), but the present new
species is discriminated from the latter inhaving higher lateral chambers. Hanzawa(1959) described Fabiania cassis (Oppenheim) and "Discocyclina" sp. from conglomerate of the Eocene Nimyo Formation, on thevicinity of Kuma, Ehime Prefecture, Shikoku.
Though he found only two vertical sectionsof "Discocyclina" from more than twenty thinsections, he did not identify it in exact genus
and species level. However, Hanzawa's specimens (pI. 9, figs. 16-17) are Asterocyclina
stella (Figures 3-3, 8, 11) than Orbitoclypeus
kimurai, n. sp. (Figures 3-2, 4-7, 9, 12) fromthe Shimizu Formation, because of smallheight of lateral chambers and developmentof pillars. From the occurrence of Asterocyclina stella from the Nimyo Formation, theShimizu, Kurusuno and Nimyo Formations
could be correlated each other.
The new species, kimurai, is named in~ Figure 5. 1,2,5. Orbitoclypeus kimurai Matsumaru, n. sp. 1. Centered oblique section; 2, 5.
Equatorial sections. 5. Holotype, slide AZ 141-6, Saitama Univ. coli. no.8801. 3. Orbitoclypeus sp.
Tangential section. 4. Discocyclina sella (d'Archiac), Equatorial section. All figures X 120.

887.

Larger Foraminifera from Shikoku

263

264

Kuniteru Matsumaru and Koshi Kimura

honor of the junior author who collected thematerial used in his paper.

Subfamily Discocyclininae Bronnimann, 1945
Genus Discocyclina Gumbel, 1868
Discocyclina sella (d' Archiac, 1850)

Orbitoclypeus sp.

Figure 5-4

Figure 5-3

1850

Description: - A tangential section assigned to the genus Orbitoclypeus appears in
one of random thin sections. This section
which is nearly centered, has a diameter ofmore than 1.7 mm. The embryonic chambers are eulepidine. The internal diametersof protoconch are 152 X 164 jl.m andprotoconch is completely surrounded by adeuteroconch with diameters of252x255 jl.m.
The outer wall is thick lamellae, about 17 jl.min thickness. Two primary auxiliary chambers are rectangular with radial diameters of
20 to 22 jl.m and tangential diameters of 30 to
35 jl.m. The nepionic chambers are rectangular to spatulate with radial diameters of 20 to
35 jI. m and tangential diameters of 20 to 40
jl.m.
The equatorial chambers are arrangedin polygonal rings, and are from square to
hexagonal in shape, with maximum radial
diameter of 46 jl.m and maximum tangential
diameter of 36 jl.m.
Stratigraphic horizon: - Shimizu Formation.
Geological age: - Late Eocene (Priabonian).
Remarks : -This specimen is characterized by peculiar features of large irregular
protoconch, large deuteroconch and thickouter walls of embryonic chambers like Eulepidina (Lepidocyclinidae). Therefore, thepresent form may be assigned to Discocyclina(= Orbitoclypeus?) ramaraoi Samanta( 1967). The former is, however, distinguished from the latter by its eulepidine
embryonic chambers, and equatorial chambers.

1922
1940
1958
1965
1974
1978

Orbitolites sella d' Archiac, p. 405, pI. 8, figs. 16,
16a.
DiscocyC/ina sella (d' Archiac), Douville, p. 6970, 89-90, pI. 4, figs. 6-7.
Discocyclina (Trybliodiscodina) sella d'Archiac, Weijden, p. 48-50, pI. 7, figs. 3-5.
Discocyclina sella (d' Archiac), Neumann, p.
106-109, pI. 22, figs. 1-8; pI. 26, figs. 5-7; pI.
36, figs. 2,4; text-fig. 33.
Discocyclina sella (d'Archiac), Samanta, p.
426, pI. 2, figs. 1-7; pI. 4, fig. 11.
Discocyclina changi Hashimoto and Kurihara,
p.38-40, pI. 1, figs. 1-6; pI. 2, figs. 1-9; pI. 3,
figs. 1-4.
Discocyclina sella (d' Archiac), Sirotti, p. 59, pI.
2, figs. 3-7.

Description: - A centered oblique section
was examined in a sample from Locality I.
This specimen has a diameter of more than 2
mm. The broken embryonic chambers areeulepidine. The protoconch has internal
diameter of 91 X 91 jl.m and is nearly surrounded by deuteroconch having diameters of
231 x210 jl.m. The partition between a
protoconch and deuteroconch is 6 jl.m inthickness. The outer wall of embryonicchambers is about 13 jl.m in thickness. The
nepionic chambers over the protoconchal
chamber wall are shortly rectangular andhave radial diameter of 14 jl.m and tangential
diameter of 42 jl.m. The nepionic chamber
wall is 8 jl.m in thickness. There are morethan 30 nepionic chambers in the periembryonic ring.
The equatorial chambers are elongatedrectangular and have radial diameters of 29 to
43 jl.m and tangential diameters of 18 to 22
jl.m.
The annular stolon is situated on theproximal side of the radial chamber walls.
The radial chamber walls are well developedand straight, with II to 12 jl.m thick. Thoseof one annulus row alternate in position withthose of the next adjacent annuli. The radial887.

Larger Foraminifera from Shikoku

stolon is situated on the joining annular wall,with 15 to 16 Jim in thickness, between alternate radial chamber walls.
Stratigraphic horizon: - Shimizu Formation.
Geological age: - Late Eocene (Priabonian).
Remarks: - Although there is no verticalsections of the specimen, the present form iseasily identified as Discocyclina sella (d' Archiac) by small eulepidine embryonic, nepionic and equatorial chambers, and remarkable regular shape and arrangement. This
species is described from the Middle Eocene(Lutetian) to Late Eocene (Priabonian) inFrance, Spain and Italy, and the Late Eocene
of India (Assam).
According to Cotter (1938), the Late
Eocene Yaw Shales (Stage) in north Minbu
and Pakokku, Burma yielded Nummulites
yawensis Cotter, Discocyclina sella (d' Archiac) and Operculina cf. canalifera d'Archiac. The Late Eocene Kyet-u-bok Bed in
Burma also yielded Discocyclina omphalus
Fritsch, D. papyracea Boubee var. javana
Verbeek, Gypsina globulus Reuss, Nummulites beaumonti d' Archiac and Haime, N.
obesus d' Archiac and Operculina cf. canalifera d'Archiac. Although the continuous
tracing of the Kyet-u-bok Bed towards the
Yaw Shales has been rendered difficult in thefield, it is noted that the fauna of the former
bed must be correlated with that of the Yaw
Stage of Pakokku, because it may be notedthat Nummulites yawensis is possibly present
in the Kyet-u-bok Bed. Cotter (1938) described that the fauna of Discocyclina sella
and Nummulites yawensis points to Late
Eocene, and that the Yaw Stage is equivalent
to the Nanggulan Stage in Java, Indonesia.
In the Phillipines, Hashimoto and Matsumaru (1984) regarded that the both Data
Fauna from the Sagada Limestone of Bondoc,
Mountain Province, Luzon and the Caguray
Fauna from the Tertiary b-Formation of the
Caguray River in Southern Mindoro are to be
Late Eocene. Although Discocyclina sella265

has not been recorded in both fauna, it may
be expected to the near future. In Taiwan,
Hashimoto and Kurihara (1974) once described Discocyclina changi from the Late
Eocene Tsukeng Formation. However, thisspecies agrees in all respects with features ofDiscocyclina sella described by many authors.
Discocyclina sella is, therefore, one of themost widely distributed representatives andmay be restricted to the Late Eocene in the
Indo-Pacific region.
Family Lepidocyclinidae Scheffen, 1932
Genus Nephrolepidina H. Douville, 1911
Nephrolepidina praejaponica
Matsumaru, n. sp.
Figures 6-1-13.

Type material: - Holotype, central
oblique section, Saitama University coil. no.
8802 (Figure 6-1)
Description: - The megalospheric specimens (Figures 6-1-12) are small lenticular
test with diameter of 2.0 to 2.9 mm and thickness of 0.7 to 0.8 mm. Surface bears widely
scattered low papillae between polygonal
shallow pits bounded by low ridges of shellmaterials. The diameter of papillae is 60 to
100 Jim.
The embryonic chambers are of nephrolepidine type. The protoconch is subcircularwith diameter of 105 to 130 Jim. The second
large chamber, deuteroconch, which embraces
the protoconch has internal diameters of 214
to 252 Jim. The ratio (= 011/01) of theinner diameter of deuteroconch (II) to that ofprotoconch (I) is 1.7 from the holotype specimen. The distance across both the protoconch and deuteroconch is 230 Jim in one oriented vertical section. Two main periembryonic chambers (= adauxiliary chambers)
occur, one at either end of the partition
dividing the embryonic chambers.
The equatorial chambers are arcuate near
the periembryonic chambers through ogival
to short hexagonal near the periphery with

266

Kunileru Malsumaru and Koshi Kimura

9

13

887.

Larger Foraminifera from Shikoku

radial diameters of 50.um near the periembryonic to 136.um near the periphery. The
height of the equatorial layer near the center
is about 60.um and at the periphery about
120.um.
The lateral chambers are rectangular inshape and are arranged in regular tiers. The
lateral chambers over the central area of test
are spaceous, with a length of 170 to 180.um
and with a height of 25 to 30.um. The thickness of more or less wavy floors and roofs is
15 to 17.um.
The associated microspheric specimen (Figure 6-13) is thin lenticular test with a faintdepressive to a tier on one side of the equatorial layer at the centre of test; about 3.8 mm
in diameter; about 0.5 mm in thickness.
The rectangular shaped lateral chambers arearranged in regular tiers. Number of lateralchambers per tier over the embryonic chambers is more than 6 layers.
Stratigraphic horizon: - Lower Memberof Misaki Formation.
Geological age: - Late Early Miocene(Burdigalian).
Remarks: - The original description of
Orbitoides (Lepidocyclina) japonica (Yabe)
was incomplete and it is illustrated by drawings rather than photomicrographs (Yabe,
1906). Afterwards, Yabe and Hanzawa(1922) redescribed it from the Lepidocyclina
Limestone, which has been defined as the
Abuta Limestone Member of the Idozawa
Formation by the senior author (Matsumaru,1967). They were correct in the originalassignment of Lepidocyclina (Nephrolepidina)and described more detail. However, they
did not designate the holotype of this species
and did not describe the dimension of theembryonic chambers. Later, the seniorauthor (Matsumaru, op. cit.) described the
topotype specimens of Lepidocyclina (Nephrolepidina) japonica (Yabe), and afterward
he raised the subgenus Nephrolepidina to the267

genus rank (Matsumaru, 1971).
The specimen from the Misaki Formationshows a remarkable similarity to Nephrolepidina japonica, but differs from the latter inhaving small test and small embryonic chambers in size, primitive form of embryonicchambers, short hexagonal equatorial chambers, more spaceous in lateral chambers andwavy floors and roofs. Also, the microspheric form from the Misaki Formation looks likean aberrant form of Lepidocyclina omphalus
Tan Sin Hok (1935, pI. 1, figs. 4-8; pI. 2, figs.
1-10; pI. 3, figs. 1-9) and Eulepidina omphalus (Tan Sin Hok) described by Hashimoto and Matsumaru (1978, pI. 11, figs. 9,
11,13-14), respectively. As a whole, the features of the Misaki form show more primitive
than those of Nephrolepidina japonica. In
addition, the present form is occurred fromthe Burdigalian on the view point of theplanktic foraminiferal zone.
This new species resembles Nephrolepidina
sondaica (Yabe and Hanzawa) from Klias
Peninsula, Borneo, Indonesia (Yabe andHanzawa, 1925) and from Cebu and Mindoro, Philippines (Yabe and Hanzawa, 1929),
but the present species is discriminated fromthe latter in having lenticular test, considerably smaller embryonic chambers and hexagonal equatorial chambers. Nephrolepidina
praejaponica, n. sp. resembles Nephrolepidina
sumatrensis (Brady) from Saipan (Cole,
1957b), but is distinguished from the latter by
its short hexagonal equatorial chambers andlateral chambers with spaceous floors androofs arranged in regular tiers.
Acknowledgments

Thanks are due to Professor Achile Sirotti,
Institute of Paleontology, University of
Modena, Italy, for his kind criticisms during
the present study; and to Professor Yuji
Okimura, Institute of Geology and Mineral-+- Figure 6. Nephrolepidina praejaponica Matsumaru, n. sp. 1. Centered oblique section, holotype,slide 12, Saitama Univ. coil. no. 8802. 2, 4-6, 10. Oblique sections. 3,7-9,11-13. Vertical sections.
13, showing the microspheric form. All figures X 30, except X 60 of 6 and 8.

268

Kuniteru Matsumaru and Koshi Kimuraogy, Faculty of Science, Hiroshima University, for his kind suggestions to transfer thefossil materials from the junior author to thesenior.
References
Archiac, E.J.A.d., 1850: Description des fossiles dugroupe nummulitique recueillis par M.S.P. Prattet M.J. Delbos aux environs de Bayonne et deDax. Soc. Geol. France, Mlm., Ser. 2, vol 3,
pt. 2, p. 396-456, pis. 8-13.
Bieda, F., 1963: Duze otwosnice eocenu Tatrzanskiego (Larger foraminifers of the Tatra
Eocene). Inst. Geol. Prace, vol. 37, p. 1-215,
pis. 1-26.
Blow, W., 1969: Late Middle Eocene to Recent planktonic foraminiferal biostratigraphy. In Bronnimann, P. and Renz, H.H. eds., 1st. Conf. onplanktonic microfossils, Proc. (Geneva, 1967).
EJ. Brill, Leiden, p.200-421.
Bronnimann, P., 1940: Ober die tertiiiren Orb itoididen und die Miogypsiniden von NordwestMarokko. Schweiz. Pal. Gesel., Abhandl., vol.
63, p.I-113, pis. 1-11,2 tabs.
--,1945: Zur Frage der verwanstschaftlichen Beziehungen zwischen Discocyciina s.s. und Asterocyciina. Eciog. Geol. Helv., vol. 38, no. 2, .579615, pis. 21-22.
Cole, W.S., 1957a: Larger foraminifera from Eniwetok Atoll drill holes. U.S. Geol. Surv.
Prof. Paper, 280-1, p.321-360, pis. 94-118, 4
tables.
- - , 1957b: Larger foraminifera [of SaipanJ.
Ibid., 280-1, p. 321-360, pis. 94-118,4 tabs.
Cotter, C. de P., 1938: The geology of parts of the
Minbu, Myingyan, Pakokku and Lower Chindwein Districts, Burma. Indian Geol. Surv.
Mem., vol. 72, pt. I, p. 1-136, pis. I-II.
Douvillt:, H., 1911: Les foraminiferes dans Ie Tertiaire des Philippines. Philippines Jour. Sci.,
vol. 6, no. 2, p. 53-80, pis. A-D, 9 figs.
- - , 1922: Rt:vision des Orbitoides. Douxieme
partie: Orbitoides du Danies et de I'~ocene.
Soc. Geol. France, Bull., Ser. 4, vol. 22, p.55100, pis. 4-5, 28 figs.
GUmbel, C.W., 1861: Geognostische Beschreibung
des bayerischen Alpengebirges und seines
Vorlandes. Gotha b. Just. Perthes, Bd. I, p.
536-653.
- - " 1868: Beitriige zur foraminiferenfauna dernord-alpinen Eociingebilge oder der Kressenberger Nummulitenschichten. Abh. K. Bayer.
Akad. Wiss., Bd. 10, Abt. 2, p. 581-730, pis. 1-4.
Hanzawa, S., 1959: The foraminiferal species

Fabiania cassis (Oppenheim), in Japan. Cont.
Cushman Found., Foram. Res., vol. 10, pt. 4, p.
119-122, pI. 9.
Hashimoto, W. and Kurihara, K., 1974: Discocyciina
from Tsukeng Formation, Tsukeng, Nantou,
Central Taiwan, and its geological significance.
Bull. Geol. Surv. Taiman, no. 24, p.35-49, pis.
1-3.
- - and Matsumaru, K., 1978: Larger foraminiferafrom the Philippines, VIII. Larger foraminiferafrom Central Samar. Geol. Palaeont. Southeast
Asia, vol. 19, p. 81-88, pI. II.
- - and--, 1984: Mesozoic and Cenozoic larger
foraminifera of the Philippines and a references
to those found from Borneo by the APRSA's
paleontological reconnaissance. Ibid., vol. 25,
p. 147-166, I tab.
Hornibrook, N. de B., 1968: A handbook of New
Zealand Microfossils (Foraminifera andOstracoda). N.Z. Dep. Scient. Ind. Res. Inf.
Ser., no. 62, p. 1-136.
Kimura, K., 1985: Stratigraphy and sedimentary
facies of the Tertiary Shimizu and Misaki Formations in the southeastern part of Shikoku.
Jour. Geol. Soc. Japan, vol. 91, no. 12, p.815831 (in Japanese with English abstract).
Matsumaru, K., 1967: Geology of the Tomioka area,
Gunma Prefecture, with a note on "Lepidocyciina" from the Abuta Limestone Member. Sci.
Rep., Tohoku Univ., 2nd Ser. (Geol.), vol. 39,
no. 2, p. 113-147, pis. 7-8,31 figs.
- - , 1971: Studies on the genus Nephrolepidina inJapan. Ibid., vol. 42, no. 2, p. 97-185, pis. 9-26,
42 figs.
- - , 1980: On the genus Asterocyciina from theKurusuno Formation, Tosa Simizu City, Kochi
Prefecture, Shikoku, Japan. In Taira, A. andTashiro, M. eds., Geol. Paleont. Shimanto Belt,
Select Paps., Hon. Prof. J. Katto, p.217-220,
pI. 25.
Neumann, M., 1958: Rt:vision des Orbitoidides du
Crt:tact: et de I'~ocene en Aquitaine occidentale.
Soc. Geol. France, Mlm., N. S., vol. 37, no. 83,
p. 1-174, pis. 1-36, 54 figs.
- - , 1977: Le genre Discocyciina en Mesogee.
Valeus stratigraphique des differentes especes.
Bol. Geol. Pub. Espec., no. 7, p. 1427-1449, I fig.
Samanta, B.K., 1965: Discocyciina from the Upper
Eocene of Assam, India. Micropaleont., vol. II,
no. 4, p. 415-430, pis. 1-4,2 figs.
- - , 1967: Discocyciina from the early Tertiary sediments ofPondichery, south India. Ibid., vol. 13,
no. 2, p. 233-242, pI. I.
Scheffen, W., 1932: Zur morphologie und morphogenese der "Lepidocyciinen". Paliiont.
Zeitschr., vol. 14, p.233-256, pis. 9-10, 6 figs.
Silvestri, A., 1907: Fossil dordoniani dei dintorni di887.

Larger Foraminifera from Shikoku

Termini Imerese (Palermo). Atti Pont. Accad.
N. Lincei, vol. 60, no. 3, p. 105-110.
Sirotti, A., 1978: Discocyc1inidae from thePriabonian type section (Lessini Mountains,
Vicenza, Northern Italy). Boll. Soc. Paleont.
Italiana, vol. 17, no. I, p.49-67, 2 figs.
- - , 1987: Ontogeny in Tethyan Discocyc1inidae
and Orbitoc1ypeidae (Foraminifera). Idid., vol.
26, no. 3, p. 269-278, pis. 1-2, 5 figs.
Tan Sin Hok, 1935: Zwei neue mikrosphere Lepidocyc1inen von Java. Ingenieur Ned. -Indies,
Bandoeng, Java, Jaarg. 2, Afd. 4 (Mijnb. Geol.),
p. 9-18, pis. 4-7.
Vaughan, W. and Cole, W.S., 1940: Discocyclina, inCushman, J.A. Foraminifera, their classificationand economic use. 3rd ed. Harvard Univ.
Press (Cambridge Press), 353 p., 48 pis.
Weijden, W.J.M. van der, 1940: Het genus Discocy-269

clina in Europa. Thesis Univ. Leiden, p. 1-116,
pis. 1-12, N.V. de Leidsche Courant, Leiden.
Yabe, H., 1906: On the Orbitoid limestone from
Kuboi on the north of the Lake Kawaguchi andfrom Nakakosaka. Jour. Geol. Soc. Japan, vol.
13, no. 156, p. 313-320, 1 fig. (in Japanese)- - and Hanzawa, S., 1922: Lepidocyclina fromNaka-kosaka, Province of Kozuke. Japan.
Jour. Geol. Geogr., vol. 1, no. 1, p. 45-50, pis. 58.
- - and - - , 1925: A Lepidocyclina-limestone
from Klias Peninsula, B.N. Borneo. Gedenkbock Verbeek, Geol. Mijnb. Genoot. Nederl.
Kol. verh., vol. 8, p. 617-632, pis. 1-4, 4 figs.
- - and - - , 1929: Tertiary foraminiferous rocksof the Philippines. Sci. Rep. Tohoku Univ, 2ndSer. (Geol.), vol. II, no. 3, p. 137-190, pis. 15-27.

.~.±~.*m~MM~.*.~~~~$M~~_.~.W~*~~R~:.~.±~.*m~t7J~MM~.*.~iI'G~;MMM~ (Priabonian) ~*~~R~{~:O 3 S 4~

iI~96J! ~:h, ~c.tIr: ~:h 1.:0 -t-:h Gfi, Asterocyclina stella (GUmbel), Orbitoclypeus kimurai
Matsumaru, n. sp., O. sp., Discocyclina sella (d'Archiac) ~.~ Go .:. ~ ?~, Orbitoclypeus
S~96J!fi B :;fo;::.~\',-r:m/Ji'.)-r~tIr: ~:h Go $M~~_~ ii, G fi, 1JJ;M$M~ (Burdigalian) ~*~~R~{~:O Nephrolepidina praejaponica Matsumaru, n. sp. iI~96J! ~:h,~tIr:~:hl.:o *~fi N. japonica (Yabe) ~mJt~t;::.;j:§~-tGo~JLEmw&· *:ft~;=t-Trans. Proc. Palaeont. Soc. Japan, N.S., No. 156, pp. 270-285,7 Figs., December 30, 1989

888.

MIXED CONODONT ELEMENTS FROM HACHIMAN TOWN,MINO TERRANE, CENTRAL JAPAN*
HISAHARU IGO
Department of Astronomy and Earth Sciences,
Tokyo Gakugei University, Koganei, Tokyo 184

Abstract. Mixed conodont elements suggesting Early Permian to Late Triassic ages areabundant in a calcarenite that crops out near the Horikoshi Pass, Hachiman Town, Gujio
County, Gifu Prefecture, central Japan. This calcarenite occurs as fillings of fissuresdeveloped within a limestone belonging to the late Early Permian Akuda Formation.
Conodont elements seem to have been mixed by redeposition of washed out elements
together with calcareous sand-streams filling fractures developed on a submarine carbonate
cliff during late Norian to Middle Jurassic lime.
Thirty-three species, including six subspecies and four unidentified species of conodonts
belonging to six genera are discriminated herein. Of these Neogondolella bisecta, N.
polygnathiformis depressa and N. polygnathiformis magna are newly proposed herein.
Key words.

Mixed conodont, Permian, Triassic, Akuda Formation, Mino Massif.

Shimadani and Kuchibora Formations are
Triassic and that these units are olistostromes
including allochthonous blocks of Carboniferous to earliest Jurassic chert, limestone andgreenstone.
The Akuda Formation consists mainly ofwhite to pale gray massive limestone andgreenstone. Kanuma (1958a, b) describedfusulinaceans from this limestone, such as
Pseudofusulina ambigua (Deprat), Pseudoschwagerina uddeni (Beede and Kniker),
Min ojapa nella elongata Fujimoto andKanuma and others. These fusulinaceansindicate that the geologic age of the Akuda
Formation is late Early Permian.
Recently, Wakita (1984) mapped this area
and concluded that the Akuda Formation ishuge allochthonous blocks in his Jurassic
Nabigawa Formation.
I recovered abundant conodont elements
indicating Early and Late Permian and Earlyto Late Triassic ages from calcarenite fillingthe fissures developed within a limestone of
the Akuda Formation. This interesting

Introduction and acknowledgments
A thick series of limestone, greenstone,sandstone, shale and chert occurs widely in
Hachiman Town, Gujio County, Gifu Prefecture (Figure I). Geologically, this area is in
the central part of the Mino Terrane of the
Inner Zone of Southwest Japan. The geology and fusulinacean biostratigraphy of thisarea were studied by Kanuma (1958a, b, 1959,
1960) and the following stratigraphic succession was established:

Permian

Kayugawa
Formation
Shimadani
Formation
Akuda
Formation

Kuchibora
Formation

Subsequently, I restudied this area, using
conodont biostratigraphy to confirm that the
Kayugawa Formation and a part of·Received October 27, 1988; revised manuscript
accepted November 1, 1989
270

888.

Mixed conodonts from Mino

Figure 1.

27 1

Ma p showin g fo ss il locality.

~chertIF;'::,,, calcarenite/\
Horlkoshl Pass

Figure 2.

Rute map nea r fossil locality.

exposure crops out along the roadcut near the
Horikoshi Pass, about I km northeast of
Akuda (Figure 2). Calcarenite yielding
mixed conodont elements and radiolarian
chronology of the Nabigawa Formation provide dating of the deposition of thi s fissure
filling calcarenite as late Norian to early
Middle Jurassic.
The purpose of this paper is to discuss theorigin of mixed conodont elements and theirgeologic significance, and to describe someconodont elements.
Acknowledgments: Professor Hisayoshi
Jgo (University of Tsukuba) cooperated withme in the field , suggested the problem andcritically read this manuscript. Dr. Katsuo
Sash ida (University of Tsukuba) assisted mein the field . Professor Toshio Koike (Yoko-

Hisaharu /go272hama National University) gave me comments and suggestion for taxonomy. Dr.
Mitsuyoshi Kimata (University of Tsukuba)
identified mineral assemblage of calcarenitewith X-ray diffractometer.

4.

Geologic setting

5.

The conodont locality is about 2 km northof the Horikoshi Pass along the roadcut ofprefectural road bound for Kanayama from
Hachiman (Figure 1). A 550 m thicksequence including tuff and white to pale graymassive limestone of the Akuda Formation,and calcarenite, limestone conglomerate andradiolarian chert of the unnamed lithologic
units is exposed along this road. The following stratigraphic sequence is in ascendingorder but partly superficial:
1. Tuff; brown with a tint of green .....
........................... . morethan .. 20 m thick, so far as exposed.
2. Limestone; white to pale gray, massive, encrinal, including fragments ofbryozoans and rare fusulinaceans(Pseudojusulina sp.) ............... .
.................. about 90 m thick.
3. Calcarenite; fissure filling, red andbrown, conglomeratic at the southeast
side of outcrop, including frequently
clasts of limestone, well-laminatedcalcarenite and calcareous shale, a few

6.

~massive~Iimestone'" -,'.......
[ill...-.:....
:' ' •• ',.

7.

Mixed conodont elements are abundant in
the calcarenite (Unit 3 mentioned above) .
Figure 3 is a detailed sketch showing theoccurrence and lithology of this calcarenite in
the outcrop. There are many cracks andirregular shaped fissures in the uppermost
part of massive limestone (Unit 2) of the
Akuda Formation, and they are completely
filled with calcarenite. The boundary
between the massive limestone and calcarenite is marked very distinctly by color
differences and its irregularly undulated or
straight surface. The calcarenite exposed atk.· ••

calcarenite

centimeters to 50 em in diameter .....
.. thickness uncertain, but exposed in
6.5 to 10.5 m wide along the roadcut.
Limestone; white to pale gray, massive, encrinal, including fragments ofbryozoans.......... about 70 m thick.
Tuff; brown with a tint of green .....
........................ 15 m thick.
Limestone conglomerate; including
angular limestone clasts, several centimeters in diameter, and sporadically
including red to brown shale breccias.
................ about 200 m thick.
- - inferred fault-Chert; red to brown, thin bedded,
including an early Permian radiolarian(Pseudoalbaillella sp.) .............. .
.............. more than 20 m thick.

••lclasls of massive limeslone &calcareous shale.
'--....1..--.
.,oFigure 3,2m

Sketch showing outcrop of calcarenite.

888. Mixed conodonts from Mino

273

Figures 4a (left), b(below). Photomicrographs showing textureof calcarenite. a ; typical texture of calcarenite.
b; dolomitized pan.
Scale bars 0.5 mm .

the southeast side of the outcrop (right side of
Figure 3) includes many angular clasts of afew centimeters to 50 cm in diameter of white
to pale gray limestone, well-laminated calcarenite and sporadic red calcareous shale.
Under the microscope, calcarenite is poorly
sorted and allochems form tight compacted
fabric. It is made up largely of skeletal fragments, which are mostly crinoid columns andless commonly uncertain calcareous organisms, and small limestone clasts comprisingpeloid, micrite and compacted calcarenite.
The skeletal fragments and limestone clasts
are cemented with red to dark brown argillaceous matrix occasionally showing interlaminations. Skeletal fragments are variable
in size and up to 2.5 mm across. Hence both
calcarenite and calcirudite are present.
These bioclasts show crude size grading, withlarger ones irregularly distributed. Allochems are all fragmented and do not show
any roundness (Figure 4a) . Secondary
growth of dolomite rhombs, 0.05 to 0.15 mm
across, is mostly scattered, but the rhombs are
partly concentrated in patches (Figure 4b).
These dolomite rhombs are commonly zoned,
having a central portion clouded with inclusions and a relatively clear peripheral part.
The rhombs are ordinarily coated with thindark brown clay film . X-ray diffractometer
pattern indicates that argillaceous matrix consists mainly of hematite.
I recovered conodont elements from all
samples collected from the various points ofUnit 3. However, samples numbered
89091310 and 8909139 collected from thenorthwestern side of the outcrop (left side of
Figure 3), yield particularly abundantconodont elements. About 200 elements
were obtained from I kg sample; ramiform
elements are mostly fragmented , but
pectiniform elements are rather well-pre-Hisaharu Igo

274

served and do not show any attrition.
Observation of the etched surface of calcarenite with a scanning electron microscope
confirmed that the red hematitic matrixincl udes conodont elements. Recovered
conodont assemblages comprise elements indicating various geologic ages, but assemblages from different points have almost similar specific composition.
Mixed conodont elements and theirgeologic significanceAs noted above, conodont elements areabundant in calcarenite, but ramiform elements are mostly fragmented and their identification is almost impossible. Table 1
shows a list of pectiniform elements recoveredfrom samples 8909139 and 89091310 and theirsuggested geologic age.
Among the listed elements, Neogondolella
joliata (s.1.), which indicates a late Ladinian
to early Carnian interval, is most abundant.
Other elements indicating younger age thanthat of N. joliata (s.1.), such as N. polygnathijormis polygnathiformis, N. nodosa, Epigondolella echinata and E. spatulata, reduce
their number. Conodonts suggesting older
age than that of N. joliata (s.1.), such as
Carinella mungoensis, C. hungarica, N. excelsa and N. mombergensis are rather rare.
Misikella hernsteini, one of the latest survivors of conodont animals, is the most rare
species in the present sample.
The origin of this mixture is puzzling.
The occurrence of mixed conodont elements
has been reported from several places inJapan (Koike et al., 1974; Conodont Research Group, 1974; Koike, 1979; Watanabe et al., 1979; Koike, 1981). Koike etal. (1974) and Conodont Research Group(1974) reported a mixed conodont assemblage
from laminated limestone exposed in the
Kuzu area, Tochigi Prefecture. Thislaminated limestone crops out elsewhere at
the top of the Nabeyama Limestone Formation and fills fissures of the limestone, and it

also occurs as the matrix of limestone conglomerate including clasts of limestone andchert concretions derived from the N abeyama
Limestone. This laminated limestone andlimestone conglomerate were thought to be
the basal conglomerate of the Adoyama Formation. Mixture of abundant conodont elements suggesting Middle Permian to Late
Triassic occurs in the laminated limestone.
The Adoyama Formation consists mainly of
bedded chert yielding successively Upper
Triassic conodonts and Lower Jurassic
radiolarians at the type section (Igo andNishimura, 1984). Therefore, laminatedlimestone and limestone conglomerate
superficially underlying the Adoyama Formation should be separated from the latter as anindependent lithologic unit. Mixed conodont elements in this laminated limestone
were said to be reworked from limestone
dated as Middle Permian to Late Triassic.
Koike (1979) introduced Kinoshita's study(Kinoshita, 1974, MS) and mentioned theoccurrence of Triassic mixed conodont assemblages from the Morisawa area, north ofKuzu, Tochigi Prefecture. He interpreted
the origin of this mixing as redeposition oflimestone from a shallow sedimentary basin
to a deep basin. Koike (1979, 1981) also
documented the mixture of conodont elements in thin beds of conglomeratic limestoneintercalated with the Triassic Taho Limestone, Ehime Prefecture. His interpretationis very slow accumulation of reworked
conodont elements.
Watanabe et al. (1979) discussed the originof mixed elements in the Triassic Kamura
Limestone of Miyazaki Prefecture andpointed out two causes: condensed lag
deposits and reworking during deposition of
the basal conglomerate.
The field occurrence of the present calcarenite is similar to that of laminated limestonereported from the Kuzu area. However, adifference has been recognized between thepresent case and that of Kuzu. The distribution of calcarenite of the Hachiman area is

Table 1.

List of conodont elements recovered from samples 8909139 and 89091310 and their known range and relative abundance.
line indicates uncertain range. (A): abundant, (C): common, (R): rare, (VR): vary rare.
Permian
Low. Mid. Up.

SystemSeriesStage
Taxa
Neospathodus homeri (Bender) (R)N. waggeni Sweet (R)N. timorensis (Nogami) (VR)
Neogondolella subcarinata Sweet (R)N. changxingensis Wang and Wang (R)N. intermedia Igo (R)N. bulgarica (Budurov and Stefanov) (C)N. bifurcata (Budurov and Stefanov) (R)N. excelsa (Mosher) (VR)N. mombergensis (Tatge) (VR)N. aff. mombergensis (Tatge) (R)N. foliata foliata (Budurov) (A)N. foliata inc/inata (Kovlics) (A)N. sp. A (VR)N. sp. B (R)
N. sp. C (R)N. sp. D (R)Gladigondolella tethydis (Huckriede) (R)G. malayensis malayensis Nogami (R)Carinella mungoensis (Diebel) (R)C. hungarica (Kozur and VSga) (R)Neogondolella polygnathiformis (s.s.) (Budurov and Stefanov)N. aff. polygnathiformis (s.s.) (Budurov and Stefanov) (R)N. polygnathiformis magna Igo, n. subsp. (R)N. polygnathiformis depressa Igo, n. subsp. (C)N. bisecta Igo, n. sp. (R)N. nodosa (Hayashi) (C)N. aff. tadopole (Hayashi) (R)Epigondolella primitia Mosher (C)E. abneptis (Huckriede) (C)E. echinata (Hayashi) (R)E. spatulata (Hayashi) (C)E. postera (Kozur and Mostler) (R)Misikella hernsteini (Mostler) (VR)

Triassic
Middle

Lower
G.-D.

Smith.

DashedSpath.

AnisianUpper

Ladinian

Carnian Norian-t----- t--

~
~

- t-

~.

......

~

~

- -

...

g

;:s

I::l

-------_.

§;:s
1:;'

... --.-.--.

~

~

---

(C)

~
~.
I::l

------_ ... _.- ... _---------------- ---

--

-- -

-

- t-

r---

---

N
....,
V>

276

Hisaharu /govery restricted, whereas the laminated limestone of the Kuzu area can be widely traced
elsewhere at the top of the Nabeyama Limestone. Calcarenite in this area is characteristically red to brown and contains a considerable amount of hematitic argillaceous matrix,
but laminated limestone in Kuzu is gray incolor and does not contain any hematitic
argillaceous matrix.
According to my interpretation, the Permian Akuda Limestone was deposited on asubmarine bank or seamount whose basement
was basic volcanic rock and related hyaloclastics. This limestone constituted anabruptly elevated steep submarine cliff rising
above a deep basin and submerged beneath ashallow sea throughout Triassic times. This
shallow sea had a lime-sand shoal in which
repeated alternating sedimentation and denudation occurred. As a result, condensed thincalcareous sediments accumulated on theseafloor and incorporated mixed elements of
conodont animals that inhabited the sea.
Shallow carbonate sedimentation was mostly
continued in late Ladinian to early Carnianages, thus conodont elements indicating theseages, such as Neogondolella Joliata (s.1.), aremost abundant in the calcarenite.
The general sedimentary setting of thementioned model recalls that of carbonate
slopes of "by-pass margin" proposed byMcllreath and James (1979). A sudden
shock such as an earthquake or tsunami
caused the Triassic condensed sequence including conodont elements and the underlying Permian limestone near the submarine
cliff collapse into the deep basin and be
redeposited as peri-platform talus deposits.
Limestone conglomerate and limestone breccia exposed in the present section may havebeen deposited by the proposed rock-fall andgravity-induced downslope mass movement.
Calcarenite represents finer fractions of these
deposits, such as sand-streams, that filled thefissures of the submarine cliff composed of the
Akuda Limestone. Washout conodont elements suggesting an Early Permian to Late

Triassic interval were also redeposited
together with these calcareous grains andmuch finer argillaceous hematitic material.
This argillaceous material consisting ofmatrix of calcarenite seems to be originatedfrom residual soil, which was produced bychemical weathering of limestone and otherrocks under a tropical or subtropical climate.
Chert bearing early Permian radiolarians,
exposed in the northern part of this section,
represents basin deposits and is contemporaneous but heterotopic with the massive limestone of the Akuda Formation.
Paleontological notes on someinteresting species
The present mixed conodont elements contain many well-known cosmopolitan species,
which were repeatedly described by various
authors. Description of these species isavoided, but brief paleontological notes ofsome interesting species are given herein.
Epigondolella echinata (Hayashi) originally described from chert of the Adoyama
Formation of Kuzu, Tochigi Prefecture israther rare in the present calcarenite. This
species is distinguishable from the allied
species, E. abneptis (Huckriede), in its relatively longer free blade and shorter nondenticulated platform. Honeycomb structure is well developed on the platform of eachside of carina. This species also closely
resembles Neogondolella aff. tadpole (Hayashi) of this paper, but the latter possesses a
shorter free blade than that of the former.
Detailed synonyms and remarks of E.
echinata were given by Kovacs and Kozur(1980a, p. 569).
Epigondolella primitia Mosher is common
in the present locality and is similar to E.
abneptis, but the former has an elongate
quadrangle platform and 3 to 6 lateral nodes
on the anterior two half length of the platform. This species is also related to Neogondolella nodosa, but the latter possesses a sharp
pointed elongate anterior platform. Further-

888.

Mixed conodonts from Mino

Figure 5. 1, Neospathodus homeri (Bender), lateral view, TGU. 1906. 2, Neospathodus waggeni
Sweet, lateral view, TGU. 1913. 3-5, Neogondolella subcarinata Sweet, 4,5, oral views, 3, aboral view,
TGU. 1890- 1892. 6, Neogondolella sp. A, latera l view, TGU. 1901. 7,8, Neogondolella changxingensis
Wang and Wang, 8, oral view, 7, aboral view, TGU. 1807, 1808. 9a, b, Neogondolella sp. C, slightly lateraland oral views, TGU. 1903. lOa, b, Neogondolella sp. B, slightly lateral and oral views, TGU . 1902. 11,
Neogondolella intermedia Igo, slightly lateral view , TGU. 1845. 12,13, Neogondolella bulgarica (Budurov
and Stefanov), lateral views, TGU. 1798, 1799. 14, Neogondolella excelsa (Mosher), lateral view, TGU.
1811. 15,16, Neogondolella sp. D , slightly latera l views, TGU.1904, 1905. 17a, b, Neogondolella bifurcata(Budurov and Stefanov), latera l and slightly latera l views, TGU . 1796. All figures X 60.

277

278

Hisaharu Igo

more, N. nodosa has a keel with bifurcatedposterior end in mature specimens. Koike(1982, p. 18) gave detailed synonyms andremarks of this species.
Epigondolella spatulata (Hayashi) was
originally described from the Adoyama Formation of Kuzu, and its holotype selected by
Hayashi was an immature form. Koike(1982) described E. spatulata from the Taho
Limestone, Ehime Prefecture and showed
many SEM micrographs of immature to gerontic stages. This species closely resembles
E. abneptis but is characterized by a subcircular to triangular shaped platform. The
present specimens have a longer platform
than that of the holotype. The Taho specimens are characterized by a triangular platform or platform with bifurcated posterior
end. Recently, detailed synonyms anddescription were given by Vrielynck (1986, p.
153-154).
The specimens identified with Neogondolella bifurcata (Budurov and Stefanov) arebroken and more or less deformed, but theirdiagnostic character coincides with that of thespecimens described by Budurov andStefanov (1972). This species is very rare
and only three specimens are yielded from thepresent locality.
Neogondolella bulgarica (Budurov andStefanov) originally described by Budurov
and Stefanov (1975) has a highly arched basaledge of unit and also arched upper edge ofcarina, but some of their specimens have astraight line of upper edge of carina. Thismorphological variation is rather commonly
observed in most European specimens (e.g.
Kovascs and Kozur, 1980b, pI. 2, figs. 1,2 ;Pisa et al., 1980, pI. 60, figs. la, b; pI. 61, figs.
1-12). Koike (1982) described immature tomature stages of this species came from Kedahof western Malaysia. Most of his specimens
have a carina with weekly to highly arched
upper edge, and nearly straight basal edge ofunit. Similar morphological characters arealso observed in most of the present specimens. It is not certain that the above

mentioned morphological vanatlOn is only
restricted to the Asiatic specimens.
Neogondolella Joliata Joliata and N. Joliata
inc/inata are most abundant elements recovered from the present calcarenite. N. Joliata
was originally described by Budurov (1975)
as the genus Paragondolella. Subsequently,
Kovacs (1983) discriminated N. Joliata inc/inata from N. Joliata Joliata and pointed
out that the characteristic diagnosis of N.
foliata foliata in a straight basal edge of theunit anterior to pit. Furthermore, the upperedge of carina in foliata foliata is mostly
straight in the anterior two~thirds, and theplatform anteriorly tapers abruptly. He
claimed that N. foliata foliata evolved fromN. foliata inc/inata. Previously, Koike(1982) described N. foliata from Bukit Kechil, Malaysia and the Kamura Limestone ofMiyazaki Prefecture, Japan. His specimens
included the mentioned two subspecies.
N. foliata inc/inata (Kovacs) has an archedbasal edge, and the platform extends fulllength of unit. In mature stage, the anterior
part of platform margin is crenulated.
Koike (1982, pI. 2, figs. 19-22) and Kovacs(1983, pI. 1, figs. 1c, 2c, 3c) already noted presence of these crenulations. Most of the present specimens referable to this subspecies
have these crenulations. I consider that thesecrenulations are another important criterion
to distinguish this subspecies from foliata
foliata. Detailed synonyms and description
were given by Kovacs (1983, p. 110-112).
Neogondolella subcarinata Sweet is rare inthis collection. This species was originallydescribed as a subspecies of N. carinata(Clark) by Sweet (in Teichert et al., 1973). I
restudied N. asiatica, which was proposedfrom the Akuda Formation of this area (Igo,
1981), and inclined to believe that this species
is a junior synonym of N. subcarinata.

888.

Mixed conodonts from Mino

279

Figure 6. 1,2, Neogondolella aff. mombergensis (Tatge), slightly lateral views, X 120, TGU. 1916, 1917.
3, Gladigondolella tethydis (Huckriede), slightly lateral view, TGU. 1788. 4-6, Neogondolella Joliata
Joliata (Budurov), oral views, TGU. 1812-18 14. 7,8, Neogondolella Joliata inclinata (Kov:ics), oral views,
TGU. 1822, 1823. 9a, b, Neogondolella mombergensis (Tatge), b, oral view, a, lateral view, TGU. 1847. 10,
Gladigondolella malayensis malayensis Nogami, oral view, TGU. 1791. 11, Carinella mungoensis (Diebel),oral view, TGU. 1753. 12, Carinella hungarica (Kozur and Vega), oral view, TGU. 1754. 13-15,
Neogondolella polygnathiformis polygnathiformis (Budurov and Stefanov), 13, lateral view, 14, 15, oral views,
TGU. 1864- 1866. 16, 17. Neogondolella polygnathiformis magna Igo , n. subsp., oral views, 16, holotype,17, paratype, TGU. 1888, 1889.

All figures x60, except for 1,2.

Hisaharu Igo

280

Description of species
Genus Neogondolella Bender andStoppel, 1965
Neogondolella bisecta Igo, n. sp.
Figures 7-1,2Gondolella polygnathiformis Budurov and Stefanov;
Krystyn, 1973, pI. 2, figs. 1-3.

Diagnosis. - Posterior platform bifurcated.
Anterior half of platform anteriorly tapers
abruptly. Anterior one to three denticles
free blade.
Description. - In oral view, posterior endof platform bifurcated. Anterior half ofplatform anteriorly tapers abruptly and being
sharply pointed at anterior end. Two or
three node-like crenulations occur on anterior
inner lateral part of platform at mature stage.
Deep and narrow lateral furrows developedon anterior platform of each side of carina.
Honeycomb structure well observed all overplatform except for narrow lateral furrows.
Main denticle indistinct and lies at centerof platform. One or two node-like denticles
developed at posterior to main denticle.
Two low indistinct ridges stretch to inner andouter corners of posterior end of platform andform terminal node-like denticle.
In lateral view, oral surface straight andaboral surface step-like. Anterior carina
high and consist of sharply pointed denticles.
Posterior half of carina low and composed of
node-like denticles.
In aboral view, basal cavity elongate elliptical, shallow, and lies one-third anteriorly
from posterior end of platform. Keel narrow, high and extends to anterior end. Loop
low and remarkably bifurcated.
Remarks. - This new species closely
resembles Epigondolella triangularis (Budurov), but the latter bears characteristic marginal node and beams. N. bisecta is closely
related to N. polygnathiformis polygnathiformis, but it is easily distinguished from thelatter by relatively bifurcated flat posterior
platform.
Reg. nos. TGU. 1805 (holotype: Figure 71),1806 (paratype: Figure 7-2).

Neogondolella changxingensis Wang
and Wang
Figures 5-7, 8
Neogondolella subcarinata changxingesis Wang andWang, 1981a, p.I17-118, pI. 2, figs. 13-16;
Wang and Wang, 1981b, p. 230-231, pI. 1, figs. 67.
Neogondolella changxingensis Wang and Wang;
Clark and Wang, 1988, figs. 3-24.
Neogondolella gujioensis Igo, 1981, p.37-38, pI. 3,
figs. 1-19; pI. 4, figs. 1-6.
Non Neogondolella gujioensis Igo; Igo and Hisada,1986, p. 521, pI. 97, figs. 1-9.

Remarks. - This species was originallydescribed as a subspecies of Neogondolellasubcarinata (Sweet) from the Longtan andChanghsing Formations of Changxing, China(Wang and Wang, 1981a), and the samematerial was also described by the sameauthors (Wang and Wang, 1981b, in Teichert,
Liu and Chen 1981 b). Previously, I proposed Neogondolella gujioensis from a limestone conglomerate of the Akuda Formationof the present area (Igo, 1981). This species
has exactly the same morphological characterto N. changxingensis Wang and Wang, which
was proposed in the same year as the former,
but the latter takes priority.
Recently, Igo and Hisada (1986) described
N. gujioensis (= N. changxingensis) fromLower Permian limestone exposed at the
Ogawadani Valley, western part of Tokyo.
The specimens came from the Ogawadaniprobably represent early to middle growthstages of N. bisselli (Clark and Behnken).
Reg. nos. TGU. 1807,1818.
Neogondolella polygnathiformis depressa
Igo, n. subsp.
Figures 7-3,4

888.

Mixed conodonts from Mino

Diagnosis. - Platform wide and pointed
anteriorly. Posterior end of platform
rounded. Anterior carina high and bears
fused denticles, but posterior carina low andconsists of node-like denticles.
Description. - In oral view, platform
extends full length of unit. Anterior platform tapers and sharply pointed at anterior
end. Posterior end of platform rounded.
Posterior half of platform wide and almost
flat. Honeycomb structure well observed allover platform except for narrow furrows oneach side of carina. Widest part of platform
one-third posteriorly. Carina does notextend to posterior end of platform. Anterior carina high and bears fused denticles andreduces rapidly in height posteriorly. Posterior denticles discrete and node-like. Main
denticle indistinct.
In lateral view, platform arched. In aboral
view, basal cavity subcircular and shallow,
lies beneath main denticle and extends toanterior end of unit as a narrow groove.
Loop rectangular or bifurcated in mature
specimens.
Remarks. - This new subspecies is similar
to Neogondolella polygnathiformis polygnathiformis, but it is easily distinguished from thelatter in having an anterior free blade. Lateral margins of the central part of platform
turned up orally in this new subspecies. It isalso similar to N. foliata inclinata, but theformer has a wider flat posterior platform
than that of the latter.
Reg. nos. TGU. 1838 (holotype: Figure 73), 1839 (paratype: Figure 6-4).
Neogondolella polygnathiformis magna
Igo, n. subsp.
Figures 6-16,17

Diagnosis. - Unit large and elongate.
Posterior end of platform rectangular. Anterior half of platform tapered gradually.
Platform extends full length of unit. Basalcavity small and shallow. Loop low and281

bifurcated.
Description. - In oral view, unit large andelongate. Anterior half of platform tapers
gradually and anteriorly pointed. Posterior
half of platform keeps the same width. Posterior end of platform rectangular. Carina
extends to near posterior end and carries 14 to
15 denticles. Anterior half of carina composed of tall and fused denticles. Posterior
half of carina consists of node-like denticles,
and its height reduces posteriorly. Main
denticle lies at posterior end of carina but
rather indistinct. One node-like denticle
developed posterior to main denticle in one
specimen (Figure 6-17).
In aboral view, basal cavity elliptical andshallow. Loop bifurcated and low.
Remarks. - This new subspecies closely
resembles Metapolygnathus communisti
Hayashi morphotype A of Krystyn (1980, pI.
12, figs. 8-14), but the latter has a remarkable
free blade. N. polygnathiformis magna has
an anterior platform extending from the anterior terminal of carina. This subspecies isvery similar to N. polygnathiformis polygnathiformis, but the former has a larger unit,
more elongate platform and lower bifurcate
loop than those of the latter.
Reg. nos. TGU. 1888 (holotype: Figure 616), 1889 (para type: Figure 6-17).

Neogondolella intermedia Igo
Figures 5-11
Neogondolella intermedia Igo, 1981, p. 38, 39, pI. 4,
figs. 7-11.
Neogondolella err. intermedia Igo; Dong, Wang andWang, 1987, pI. 3, fig. 21.

Description. - Platform narrow, elongate
and anteriorly tapers gradually. Anterior
one-third of carina slightly high and being
gradually lower toward posterior. Platformmargin turned up orally. Anterior end of
platform pointed and its posterior end roundly square. Main denticle inconspicuous andlocated near posterior end. Basal cavity

282

Hisaharu [goFigure 7. 1,2, Neogondolella bisecta Igo, n. sp. , oral views, 1, holotype, 2, paratype, TGU . 1805, 1806.
3,4, Neogondolella polygnathiformis depressa igo, n. subsp ., ora l views, 3, holotype, 4, paratype, TGU. 1838,
1839. 5,6, Neogondolella nodosa (Hayashi), oral views, TGU. 1850, 1851. 7,8, Epigondolella abneptis(Huckriede), oral views, TGU. 1757, 1758. 9, Epigondolella echinata (Hayashi), ora l view, TGU. 1774. 10,
11, Neogondolella aff. tadpole (Hayashi), oral views, TGU. 1898, 1899. 12, Neogondolella aff. polygnathiformis polygnathiformis (Budurov and Stefanov), oral view, TGU . 1919. 13, 14, Epigondolella primitia
Mosher, oral views, TGU. 1778, 1779. 15, 16, Epigondolella spatulata (Hayashi), oral views, TGU . 1784,
1785. 17, Epigondolella postera (Kozur and Mostler) , oral view, X 120, TGU. 1775. 18,19, Misikellahernsteini (Mostler), lateral views, X 120, TGU. 1793, 1794. All figures X 60, except for 17- 19.

888.

Mixed conodonts from Mino283

small and elliptical, lies beneath main denticle. Keel broad and low. Loop low andelliptical or square.
Remarks. - The present material is identical with the original specimens obtained from
Ichinose and the Kuchibora Formation ofthis area. This species represents the evolutionary link between Neogondolella bisselli
and Neogondolella idahoensis (Igo, 1981).
Reg. no. TGU. 1845.

posterior terminal denticle. Keel fairly narrow and ending in loop.
Remarks. - This unidentified species isslightly similar to Neogondolella bulgarica,
but carina of the former does not extend toposterior end of platform and bears shorter
denticles and less prominent main denticle
than those of the latter. This unidentified
species is probably new to science.
Reg. no. TGU. 1902.

Neogondolella sp. A

Neogondolella sp. C

Figure 5-6

Figures 5-9a, b

Neogondolella sp. A, Igo, 1981, p. 39, pI. 4, fig. 12.

Description. - Unit small, elongate andarched. Anterior carina high and composedof four denticles. Posterior carina low andhaving sharply pointed denticles. In oralview, platform full length of unit and anterior
one-third length of unit slightly corrugated.
Posterior terminal carina located at posterior
end of platform. Posterior half length ofplatform edges turned up orally and observed
honeycomb structure on platform margins.
Posterior end of platform bluntly rounded.
In aboral view, basal cavity small andlocated beneath posterior terminal denticle.
Keel narrow and low, ending in small elliptical low loop.
Remarks. - The present unnamed species
is similar to Neogondolella constricta (Mosher
and Clark) and some other Anisian to
Ladinian species of Neogondolella, but theformer does not have any constriction on theposterior part of platform. This unnamed
species is probably a new species.
Reg. no. TGU. 1903.

Description. - Unit very small and elongate navicular shape. Carina composed of
low node-like subequal sized denticles. Platform extends full length of unit and widest
part at half length of unit. Honeycomb
structure observed all over platform except for
furrows of each side of carina. Basal cavity
small and lies beneath anterior to second
denticle from posterior terminal denticle.
Loop elliptical and keel low and inflated
laterally.
Remarks. - This unnamed species was
already described by the present author (Igo,
1981). I also refrained specific identification
this time because only one specimen is at
hand.
Reg. no. TGU. 1901.
Neogondolella sp. B
Figures 5-lOa, b

Description. - Unit small and slightly
arched. Anterior one-fourth of carina highand composed of fused denticles. Posteriorcarina low and having sharply pointed denticles. Posterior terminal denticle situatedanteriorly one-fifth from end of platform.
Anterior one-fourth length of unit free blade.
In oral view, posterior end of platform has
two rectangular corners. Anterior half
length of platform edges turned up orally.
In aboral view, basal cavity lies beneath

Neogondolella sp. D
Figures 5-15,16

Description. - Unit elongate and small.
In oral view, platform narrow. Anterior
one-third of unit free blade. Posterior endof platform rounded. Carina extends toposterior end and composed of fused denticles but their upper part discrete. Anterior

Hisaharu Jgo

284

three to five denticles being high free blade.
Height of carina reduces abruptly toward
posterior. Main denticle located at posterior
end of carina but not so conspicuous. Bothouter and inner sides of platform turn up
orally and make deep lateral furrows. Basalcavity small and shallow, lies near posterior
end. Loop elliptical. Keel narrow andhigh posteriorly.
Remarks. - This unnamed species closely
resembles Neogondolella bulgarica, but theformer is easily distinguishable in having free
blade. Platform of N. bulgarica is fulllength of the unit.
Recently, Clark and Wang (1988) illustrated N. denticulata Clark and Behnken camefrom the uppermost bed of the Changhsing
Formation of Changxing, China. The present unnamed species closely resembles N.
denticulata reported from China.
Reg. nos. TGU 1904, 1905.
Repository: All specimens treated in thispaper are deposited in the Department of
Astronomy and Earth Sciences, Tokyo Oakugei University with the prefix TOU.

References cited
Budurov, K., 1975: Paragondolella foliata sp. n.
(Conodonta) von der Trias des Ost-Balkans.
Re, Bulgarian Geol. Soc., vol. 36, part I, p.7981, pI. 1.
- - and Stefanov, S., 1972: Platform-Conodonten
und ihre Zonen in der Mittleren Trias Bulgariens.
Mitt. Ges. Geol. Bergbaustud, vol. 21, p.829852, pis. 1-4.
- - and - - , 1975: Neue Daten uber die
Conodontenchronologie der Balkaniden mitteren
Trias. Compt. Rendu. l'Acad. Bulgare, Sci.,
vol. 28, no. 6, p. 791-794, pI. I.
Clark, D.L. and Wang, c.Y., 1988: Permian neogondolellids from South China: significance for
evolution of the serrata and carinata groups inNorth America. Jour. Paleont., vol. 62, no. I, p.
132-138, figs. 1-4.
Conodonts Research Group, 1974: Conodonts at thePermian-Triassic boundary in Japan - Stratigraphy and faunas of the Nabeyama and Adoyama
formations in Karasawa area, southeast Ashio

mountains -. Earth Sci., vol. 28, no. 3, p.8698. (in Japanese with English abstract)
Dong, Z.Z., Wang, c.Y. and Wang, Z.H., 1987:
Carboniferous and Permian conodont sequencein Northwestern Yunnan. Act. Pal. Sinica, vol.
26, no. 4, p. 411-419, pis. 1-3. (in Chinese withEnglish summary)
Hayashi, S., 1968: The Permian conodonts in chert of
the Adoyama Formation, Ashio mountains, central Japan. Earth Sci., vol. 22, no. 2, p.63-77,
pis. 1-4.
Igo, Hisaharu, 1981 : Permian conodont biostratigraphy of Japan. Pal. Soc. Japan, Special Papers,
no. 24, p. I-50, pis. 1-12.
- - and Hisada, K., 1986: Lower Permian
conodonts from the Kawanori Formation of thesouthwestern Kanto Mountains, Tokyo. Trans.
Proc. Pal. Soc. Japan, N.S., no. 144, p. 516-527.
pis. 96-98.
- - and Nishimura, H., 1984: The late Triassic andearly Jurassic radiolarian biostratigraphy in the
Karasawa, Kuzuu town, Tochigi Prefecture (preliminary report). Bull. Tokyo Gakugei Univ.,
Sect. 4, vol. 36, p. 173-193. (in Japanese withEnglish abstract)
Kanuma, M., 1958a: Stratigraphical and paleontological studies of the southern part of the Hida
plateau and north-eastern part of the Mino
mountainland. Jubilee Publ. Comm. Prof. H.
Fujimoto, p. 1-48.
- - , 1958b: Ditto., part II, Paleontology, No.2.
Bull. Tokyo Gakugei Univ., vol. 9, p. 29-49, pis.
2-3.
- - , 1959: Ditto., No.3, Pseudoschwagerina,
Pseudofusulina and Parafusulina. Ibid., vol.
10, p. 59-107, pis. 4-9.
- - , 1960: Ditto., No.4, Ozawainellinae, Schubertellinae and Neoschwagerininae. Ibid, vol. II,
p. 55-83, pis. 10-13.
Kinoshita, T., 1974: Geology of the southern part of
the Ashio mountains (MS). Master thesis ofTokyo Gakugei University. p. 1-63. (inJapanese)
Koike, T., 1979: Conodont biostratigraphy in the
Taho Limestone (Triassic), Shirokawa-cho,Higashiuwa-gun, Ehime Prefecture. Mem. Vol.
Prof. Mosaburo Kanuma, p.115-126. (inJapanese)- - , 1981 : Biostratigraphy of Triassic conodonts inJapan. Sci. Repts. Yokohama Natl. Univ., Sec.
II, no. 28, p. 25-46, pis. 1-2.
- - , 1982: Review of some platform conodonts of
the Middle and Late Triassic in Japan. Ibid.,
no. 29, p. 15-27, pis. 1-3.
- - , Igo, H., Igo, H. and Kinoshita, S., 1974:
Gelogical significance of the unconformity
between the Permian Nabeyama and Triassic

888.

Mixed conodonts from Mino

Adoyama Formations in the vicinity of Kuzuu,
Tochigi Prefecture. Jour. Geol. Soc. Japan,
vol. 80, no. 7, p.293-306. (in Japanese withEnglish abstract)
Kovlics, S., 1983: On the evolution of excelsa-stockin the upper Ladinian-Carnian (Conodonta,
genus Gondolella, Triassic). Schrift. Erdwiss.
Komm. Osterr. Akad. Wiss., vol. 5, p. 107-119,
pis. 1-6.
- - , and Kozur, H., 1980a: Some remarks on middle and upper Triassic platform conodonts.
Recent Researches in Geology, vol. 5, p. 541-581,
pis. 1-5.
- - and - - , 1980b: Stratigraphische Reichweite
der wichtigsten Conodonten (ohne Zahnreihenconodonten) der Mittel-und Obertrias. Geol.
Palaont. Mitt. Innsbruck, vol. 10, no. 2, p. 47-78,
pis. 1-15.
Krystyn, L., 1973: Zur Ammoniten-und Conodonten-Stratigraphie der Hallstatter Obertrias(Salzkammergut,Osterreich). Verh. Geol. B.A.,
Jahrgang 1973, no. I, p. 113-153, pis. 1-5.
- - , 1980: Triassic conodont localities of the Salzkammergut region (Northern Calcareous Alps).
In Guidebook and abstract of ECOS II, Abh.
Geol. Bundesanstalt, vol. 35, p. 61-98, pis. 11-14.
Mcllneath, LA. and James, N.P., 1979: Facies
Models 12, Carbonate slopes. In Walker, R.G.
(ed.), Geoscience Canada, reprint series, Facies
Models. p. 133-143.
Mosher, C.L. and Clark, D.L., 1965: Middle Triassic
conodonts from the Prida Formation of northwestern Nevada. Jour. Pal., vol. 39, no. 4, p.

285

551-565, pis. 65-66.
Pisa, G., Perri, C. and Veneri, P., 1980: Upper
Anisian conodonts from Dont and M. Bivera
Formations, southern Alps (Italy). Riv. Ital.
Paleont, vol. 85, nos. 3-5, p. 807-828, pis. 60, 61.
Teichert, c., Kummel, B. and Sweet, W., 1973: Permian-Triassic strata, Kuh-E-Ali Bashi northwestern Iran. Bull. Mus. Compo Zool., vol. 145,
no. 8, p. 359-446, pis. 1-14.
Vrielynck, B., 1986: Conodonts du Trias peri mediterraneen. systematique, stratigraphie.
Docum. Lab. Geol. Lyon, no. 97, p. 1-301, pis.
1-15.
Wakita, K., 1984: Geology of the Hachiman district.
Quadrangle series, scale : 50,000. Kanazawa(10), no. 70, Geol. Surv., Japan. (in Japanesewith English abstract)
Wang, C.Y. and Wang, Z.H., 1981a: Permian
conodonts from the Longtan Formation andChanghsing Formation of Changxing, Zhejkiang
and their stratigraphical and paleontologicalsignificance. In selected papers on the 1st con-vention of Micropalaeontological Society of
China. p. 114-120, pis. 1-2. (in Chiense)- - and - - , 1981 b: Permian conodont biostratigraphy of China. Geol. Soc. America, Special
Paper, 187, p.227-232, pis. 1-2.
Watanabe, K., Kanmera, K. and Nakajima, K., 1979:
Conodont biostratigraphy in the Kamura Limestone (Triassic), Takachihocho, Nishiusuki-gun,Miyazaki Prefecture. Mem. Vol. Prof. Mosaburo Kanuma, p. 127-137. (in Japanese)

Akuda'tC),.EH. Hachiman i\~, Horikoshi Pass :!Jiili1'!!~. Kanayama ~J1J. Kayugawa ~JII.
Kuchibora Pi1"J. Nabigawa ml.ltJII. Shimadani ~:fr.
~¥l* j\~I!IJ;6, G£:1±l 1... t.: ::I / r:/ r 17)~:tE~~: fJJWl"/1..- A*c;6' GffWl-=~*ct;:.bt.:~::I/r:/rl7)~<I7)~~ • • • • m~mi\~I!IJI7).i1'!!~#~Kal±l~~~~~v~~r17)i1l\i'Jiz."'?< ~~iff-tjiJlt;ve'Jiflll;6'G~:tEL..-C37f((~G.:ht..:o ;:'17)~/1..-~ v~~ r fi.iff-iSz.

~1...~.~~b~~.<. E~~~.~~~I7)~~z.~~ fJJWl"~AeffWlI7)'tC),.EH~
I7)E~~K~.1...t.:M.:h§z.~~1...t.:l5~£:~z.~~~0::I/r:/rl7)~:tEI7).~~~

17) l 5 t.{jir~l1:;6~~:Z G.:h ~ 0 "II..- A *cffWl;6' G=1UcffWlt;:';6'H"~ 'tC),.EH ~I7)E~~17)~t;:.1=.[t..:~l'la-e. BR~jg~;6;Jt1lc~1tz.~I)]g1..., ::1/ r:/Hi.foJ~ct.e<l5t~'I±l~.:h?jlmJ 1... ~~tE 1... t..:o c < t;:.t;:.ffWl7 T -I .=. 7 :/;6' GfJJWl ~ -.=. 7 :/ Z.f~ff-~ ~ Neogon-

dolella foliata (s.l.) ;6~ftP. c .l:tti: 1... ~ 00 1$ f((;6; EEfftJi¥J t;:'37 ~,17) fi.. ;:'17)Jli!fWl t;:.Jt1l;6~1j!.i1'!! 1...
t.:tl7)c~G.:h~o ~~ fJJWl"~Ael7)::I/r:/r~'tC)"EH~K~*~~E~D~E~~~;6'Gtt..:G~.:ht.:tl7)-e.;b0 50 ffWl/ -!i 7 :/;6'G<pWlv;>. 7*c"i-C:·I7).;b~Jli!fWl
t;:.. ;:..:h G~tE~~z.~trE~7f..P~~~~~ve'Ji~;6, G t.e ~ml'laJtt'l¥.lHi.. l$tlllt.e c'l7)f@'fI!I.t.e-Y" o;J f7 t;:'l-:>~. l'laJ.t-emz.7fftffl(;1...~~,t.:'tC),.EH~I7)E~~t;:.ta-:>~~l'la:ll.ilG;6'G
sand-stream c t.e -:> ~VlE.:h T I). ~ II..- ~ V ~ ~ r c 1... ~ -t"l7)l1iU.:h § z.~~ 1... t..: t 17) c.lj.G.:h~o ::I /r fi.~ II..- ~ v ~ ~ r 17) c';:' z. C -:> ~ t m~1R.I [ l 5 tdll..lj.~b-l:!:l7)~tEz.
ff-1..., 6~. 6l11!~. 4*~~z.~tr34~;6~~.\JIj~.:ht..:;6;. -t"17)5'0I~t.eGV:t;:.2l11!~fi.

r:/

ff 1... < ~Pl§ 1... t..:o~~),.~

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 156, pp. 286-290,4 Figs., December 30, 1989

889.

GROWTH AND LIFE MODE OF A PLEISTOCENE BRACHIOPOD,
KIKAITHYRIS HANZAWAI (YABE)*KAZUYOSHI ENDO
Department of Geology, University of Glasgow
Glasgow GI2 8QQ, Scotland, U.K.

Abstract. The onset of sexual maturity in the Pleistocene free-living brachiopods
appears to be reflected in shell morphology. This interpretation is based upon the demonstration of a two phase relationship between shell length and shell convexity, and assumes
that the phase change is triggered by, or at least closely correlated with the first developmentof gonadal tissues. The results suggest that Kikaithyris hanzawai became sexually mature
prior to the adoption of a secondary free-living life habit. A similar relationship between
morphology and sexual maturity has been demonstrated in the Recent brachiopod Laqueus
rubel/us, which belongs to the same family as Kikaithyris hanzawai.
Key words.
life habit.

Brachiopoda, Laqueidae, Pleistocene, relative growth, gonad development,ogy of a secondarily free-living brachiopod is
also discussed.

Introduction

Gonads first develop in juvenile specimens,
extending greatly at the onset of maturity(Rudwick, 1965). Their presence in fossil
specimens is usually inferred from their traceson the inner shell surface (i.e. pallial sinuses,
see Williams, 1956). Recently, Endo (1987)
indicated that gonad development affects therelative growth pattern in an extant laqueid
species, which is represented as a diphasic
allometry between the shell convexity and theshell length with a turning point between thejuveniles and the adults. This relationshipbetween gonads and shell allometry could beapplied to fossil species, to discuss the average
size at which individuals achieve sexual
maturity.
This paper reports the analysis attemptedon Kikaithyris hanzawai (Yabe), a Pleistocene extinct laqueid. The life style of thisspecies which has the characteristic morpho 1-

Material
Among the Pleistocene biogenic carbonate
sediments of the Ryukyu Group which yield
Kikaithyris hanzawai (Yabe), the best preservation is seen at the type locality in theunconsolidated grainstone of the Wan Formation. The locality is about 500 metres
north of Kamikatetsu, Kikai Island, Kagoshima Prefecture, Japan. Forty-two complete specimens of various growth stages fromthe locality were used for the measurements,
while numerous fragmentary specimens fromthe same locality enabled the examination ofinternal features. The deposited environment is considered by Mori (1987) to havebeen a fore-reef in excess of 50 metres deep,
dated radiometrically at 82,000± 2,000 years
B.P. (Omura, 1983). The studied specimens
are from the collections of the University*Received Feburary 21, 1989: accepted November I,
1989
286

889.

Growth of a Pleistocene Brachiopoda

Museum , University of Tokyo (UMUT), andthe Institute of Geo logy and Paleontology,
Tohoku University , Sendai (lGPS).

Morphology and life habit
The shel l of Kikaithyris hanzawa i (Yabe)
was first described by Yabe (1932) and has
been subsequently described by Hata i (1940)
and Cooper (1957). Endo (1987) briefly
referred to the life habit of this species.
Adult shells of K. hanzawai are large andare disti ngu ished from j uveni les by posteriorly thickened shell and strongly incurved beakwith a relati ve ly minute mesothyrid foramen(Figures 1- 3). These features are characteris-287

tic of the seco ndary free-living life style ofmany specIes. The size of foramen shows
little increase with growth, while the curvature of ventral beak increases continuously(Figure 2). Spec imens larger than about 25
mm in shell length have the beak angle ofover 90 degrees , a nd also have differentiall yth ickened posterior shell. Th us the change
into free-living life is considered to haveoccurred at the shell length of about 25 mm.
The biconvex valves, which have a planar or
almost planar commissure (Figure 1) , become
posteriorly thickened (Figure 3). The small
foramen , incurved beak and po sterior thickening indicate a self-righting tumbler-likeposition similar to that described by Surlyk( 1972).
The diductor and the adductor muscle systems are readily recon structed from the evidence provided by muscle scars on the innershell surface, on the ventral median ridge, andthe cardinal process. However, the adjustor
muscle system of Kikaithyris hanzawai may
have d ege nerated in some adult individuals
becau se the stoutly thickened cardinalia ofadult shells provides very little space for the
adjustor mu scles (Figure 3) . This strongly

Figure 1. Dorsal (A) and lateral (B) views ofan adult specimen of Kikailhyris hanzawai (Yabe)
from the Wan Formation (Type locality). Specimen
UMUT CB 18196a in natural size.
140
~
~

e·OOf

120

..

., 100

...

80

Cl
C

'"
"".,'"
Cl

....

Oc:>k

"~4n(J l ()

Cl

~
~

5

.s

3

;;

.,

~

E

2
60

20

.. ,

. '" "+"'. :+ , +..t....

40

a

E

4

'"
.,c

"0

E

1

• 't'
;

~

0

u.

a
10

20

30

40

50

L(mm)

Figure 2. Ontogenetic change of the beak angle(squares) and the foramen diameter (crosses) of
Kikailhyris hanzawai . Sample UMUT CB18196,
N = 33.

o

VM

c

D

Figure 3. Interior of ve ntral (A) and dorsal (B)valves and median sections at sessi 1 (C) and free·living (D) growth stages. Sample CB 18196. Scalebar indicates 1 cm. Abbreviations: AM, adductor
muscle attachment; C, crus; CP, cardinal process ;DM , diductor muscle attachment; HT, hinge teeth ;MS, median septum ; SR, inner socket ridge ; TM,trace of muscle scar; YM, ventral median ridge.

Kazuyoshi Endo288

suggests that the pedicle of adult individuals,
if any, was hardly functional.

c-

1.2

A
r---------------,

.. .-

_o c
01

en .~ 1.1

01-

Shell size at sexual maturation~m 1.001 0
LIn a living laqueid species, Laqueus rubelIus (Sowerby), larger inidviduals with gonads
show positive allometry of shell convexity toshell length, while smaller ones without
gonads indicate isometrical relationshipbetween them (Endo, 1987). The size atsexual maturation would therefore be
revealed if the same relationship applied to a
fossil species.
Conventional dimensions of shell length(L) and shell height (H) were taken in
Kikaithyris hanzawai using vernier calipers.
Figure 4B shows size distribution plotted on adouble logarithmic scatter diagram. The
distribution pattern seems diphasic, with thepoint of inflection occuring at around 20 mm
in shell length. This is supported by a seriesof accumulative regressions. The reduced
major axis regression coefficient (a, the slopeof allometry in a log-log plot) between log L
and Log H was calculated using the smallest
and the second smallest specimens. The
third smallest specimen was then added to theregression, and the regression coefficient recalculated. By adding specimens of increasing size one by one, 41 regression coefficientswere finally obtained. Figure 4A gives thesevalues after the point of adding the 10thsmallest specimen the sub-sample of smaller
specimens indicates isometry at 95%
confidence level until the 18th specimen.
The regression coefficient with standard error
exceeds 1.0 at the 19th specimen, and it
increases gradually with fluctuation as the
addition of more specimens. Forty-two specimens are then divided into two groups of 18"juvenile" and 24 "adult" specimens. The
reduced major axes were obtained separately
for the two groups and superimposed on the
diagram. Both axes fit well to the plots, theslopes of them also appear reasonable:
almost 1.0 for the smaller specimens, indicat-

U

IInlIIIIhID:ll~·IlIIiInWlIII

isometry -0.9 L----1_....L_....L..._.L..----I_.....J.._....I----I
5
10
15
20
25
30
35
40
45
number of specimens

1.5 ,.:B~_ _ _ _ _ _ _ _ _ _ _ ___,

1.3

J:

'"

1.1

~

0.9

o

"juvenile" specimens•"adult" specimens

1mi. J.!
l-H-i

0.7
L=21.8 (mm)
0.5

0.9

1.1

1.3

1.5

1.7

log L

Figure 4. A. Relationship between the regression coefficients (with standard error bars) and thesample size of the "smaller specimens." For
explanation, see text. B. Double logarithmic allometric relationship between shell length (L) andshell height (H) in Kikaithyris hanzawai with bestfit reduced major axis regressions. The crossing
point of the two axes represents the average size ofsexual maturation. Nine specimens from sample
lOPS 29436 and 33 specimens from sample UMUT
CB18l96, all of which were collected from the type
locality of the Wan Formation.

ing "isometry", and 1.22 for the larger specimens, indicating remarkable positive allometry of H to L.
The diphasic pattern is similar to thatfound for L. rubel/us, which has been explained in terms of the gonad development(Endo, 1987). The shell length at the transition point is calculated as 21.8 mm, the probable size of onset of maturity in K. hanzawai
from this locality.

Discussion

Permanent free living forms
Species with similar life habit to Kikaithyris hanzawai have been cited by Rudwick

889.

Growth of a Pleistocene Brachiopoda(1970) and Surlyk (1972) as free living forms.
Bassett (1984) categorized the life stategies of
Silurian brachiopods, calling this life style"ambiotic liberosessile". These brachiopods
usually keep the anterior of the shell above
the sediment by means of the thickening of
the umbo, which shifts the center of gravity
posteriorly. Rudwick (1970) pointed outthat the importance and extent of the posterior weighting increases as the pedicle
becomes reduced to a mere "tether". Why
does the animal abandon the functional
pedicle- which is excellent to keep the feeding
position? I suggest that it would occur
when the available substrate is restricted tounconsolidated sediments. Recent brachiopods are not confined to rocky substrates,
but are also found on unconsolidated sediments. (Richardson, 1987). On unconsolidated substrates, e.g., shell fragments,
pebbles, coarse bryozoan sands, etc., evenpedunculate brachiopods often become
effectively free living, that is, the relatively
small substrate provides insufficient anchorage and suport for the adult shells. On such
sediments, the pedicle may function merely asa tether, and a specialized free living form
could be selectively advantageous. The
strong currents which govern these coarse
sediments may accelerate the selection ofdifferentially weighted shells (Richardson
and Watson, 1975); a conclusion supportedby the observation that K. hanzawai isalways found in coarse grained deposits.

Gonad development in Kikaithyris hanzawai
The observed diphasic growth pattern of
Kikaithyris hanzawai supports my supposition that gonad development explains the
positive allometry of shell convexity to shelllength in adult laqueids. Gonad development would require enough space to hostbands of gonads (Endo, 1987), or it would
require a larger enclosed volume for brooding
and ventilation.
An alternative explanation to the diphasic
growth pattern is possible considering the289

free-living mode of life: as the animal
becomes free living, a posterior shift in thecentre of gravity is advantageous to maintaina prefered orientation, thus the less elongatedshell form could have been selected. Terebra tel/a inconspicua (Sowerby) which is only
free-living by misadventure (see Lee, 1978)
also has a diphasic pattern when height isplotted against length, and the point of
inflection occuring at a shell length ofapproximately 15 mm corresponds well to
Doherty's first reported spawning at a lengthof 14 mm (Doherty, 1979).
The observation of Recent L. rubel/us
shows that gonads first develop at various
size, and plots of the juveniles and the adults
in the L-H diagram overlap around the turning point of the two phases (Endo, 1987).
Thus the separation of the larger and thesmaller specimens in K. hanzawai does notstrictly mean the separation of the adults andthe juveniles. However, as the transition
point in L. rubel/us corresponds to a biological minimum (first gonad development), so
the point in K. hanzawai is expected to give
an approximation to the biological minimum
within this population. In conclusion, thisspecies is inferred to have become capable ofreproduction slightly before the individuals
became free living at a length of 20 mm.
Summary

The morphological features of Kikaithyris hanzawai (Yabe) indicate the secondarily free-living mode of life, which is anadaptational form to the life on unconsolidated substrates.
2. The diphasic allometric trend in therelationship between the shell length and theshell height enables the approximation of thebiological minimum, or shell size at first
reproduction in this species.
1.

Acknowledgments

I wolud like to thank Prof. I. Hayami andKazuyoshi Endo

290

Associate Prof. K. Tanabe of the Universityof Tokyo, and Sir A. Williams, Dr. G.B.
Curry, Dr. M. Collins of the University ofGlasgow, for critically reading this manuscript. I am grateful to Prof. T. Nohara and
Dr. R. Tabuki, Ryukyu University for thekind guidance in the field survey. I am
indebted to Prof. K. Mori, Dr. K. Ogasawara
and Dr. Y. Iryu, Tohoku University for providing access to the type specimen of Kikaithyris hanzawai.
References
Bassett, M.G., 1984: Life stategies of Silurian brachiopods. Special Papers in Palaeontology,
vol. 32, p. 237-263.
Cooper, G.A., 1957: Tertiary and Pleistocene brachiopods of Okinawa Ryukyu Islands. U.S .G.
S. Professional Paper, 314-A, p. 1-20, pis. 1-5.
Doherty, P.J., 1979: A demographic study ofsubtidal population of the New Zealand articulate brachiopod Terebratella inconspicua.
Marine Biology, vol. 52, p. 331-342.
Endo, K., 1987: Life habit and relative growth ofsome laqueid brachiopods from Japan. Trans.
Proc. Palaeont. Soc. Japan, N.S., no. 147, p.
180-194.
Hatai, K., 1940: The Cenozoic Brachiopoda fromJapan. Sci. Rep. Tohoku Imp. Univ., Ser. 2,
vol. 20, p. 1-413, pis. 1-12.
Lee, D.E., 1978: Aspects of the ecology andpaleoecology of the brachiopod Notosaria ni-

gricans (Sowerby). Jour. Roy. Soc. N. Z., vol.
8, p. 395-417.
Mori, K., 1987: Intraspecific morphological variations in a Pleistocene solitary coral, Caryophyllia(Premocyathus) compressa Yabe and Eguchi.
Jour. Paleont., vol. 61, p.21-31.
Omura, A., 1983: Uranium-series ages of some solitary corals from the Riukiu Limestone on the
Kikai-jima, Ryukyu Islands. Trans. Proc.
Palaeont. Soc. Japan, N.S., no. 130, p.117-122.
Richardson, J.R., 1987: Brachiopods from carbonate
sands of the Australian shelf. Proc. R. Soc.
Vict., vol. 99, no. I, p. 37-50.
- - and Watson J.E. 1975: Form and function of
the Recent free living brachiopod Magadina
cumingi. Paleobiology, vol. I, p. 379-387.
Rudwick, M.J.S., 1965: Ecology and paleoecology.
pp. H199-H214 in R.C. Moore (ed): Treatise on
invertebrate paleontology. Part H, Brachiopoda.
927p. Geol. Soc. Am. and Univ Kansas Press,
Lawrence, Kansas.
- - , 1970: Living and fossil brachiopods. 199p.
Hutchinson, London.
Surlyk, F., 1972: Morphological adaptations andpopulation structures of the Danish chalk brachiopods (Maastrichtian, Upper Cretaceous).
Kongelige Danske Vidensk. Selsk. Bioi, Skrifter,
vol. 19, p. I-57, pis. 1-5.
Williams, A., 1956: The calcareous shell of the Brachiopoda and its importance to their classification. Cambridge Phi/os. Soc., Bioi. Reviews7
vol. 31, p.243-287.
Yabe, H., 1932: Brachiopods of the Genus Pictothyris Thomson 1927. Sci. Rep. Tohoku Imp.
Univ., Ser. 2, vol. 15, p. 193-197, pI. 1.

J!!fJT1!t~'@iJJiJJ Kikaithyris hanzawai (Yabe) O)Rlt~ C ~m~~: J!!fJTif9t~~~ff J: 9gg"t G Kikaithyris hanzawai ft, .."to)%i~a9%'f,( J: 9, =(jza9t;:.U!iI~~mtJ, i? EI El3~m"".fiLkc~~i?hGo ik, .00~~Kn"tG.0)~<i?~O)ffinRlt~tt, ~GRlt~.
IIft;:.:t,;~ '-C ~Rlt~tJ, i?filRlt~t;:.~{r."t Go Co O)=ffiO) /~ ? - :/ ft, Co O)fi c Ii'iJ C.f4t;:.~"tG Laqueus rubellus (Sowerby) O)m~fi"(" ~~ i?h, ~~rnJ~:O)96~ c M:iI L -C ~'G c ~ ~i?hG o K. hanzawai t;:.:t,;~'-C:;j(~i?.nt..:=ffiO)~.,~ft, CoO)fitJ~, =.(jza9E1 El3~mt;:';f$fi"t G J: 9 ilfj~;:.1j:a9t;:.Rlt~ L -C ~ ,t..: Co c ~7F~"t Go~~-fE

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 156, pp.291-295, 1 Fig., December 30, 1989

890. A NEW DEVONIAN CEPHALOPOD FROM THE NAKAZATOFORMATION OF THE SOUTHERN KITAKAMI MOUNTAINS*SHUJI NIKO
Department of Earth Science and Astronomy, College of Arts and Sciences,
The University of Tokyo, Komaba, Tokyo 153

Abstract. A new pseudorthoceratid species, Geisonocerella nakazatoensis Niko, is
described from the N3 Member of the Middle Devonian Nakazato Formation. This species
is characterized by its weakly annulated large shell with elliptical cross section, deeply
concaved septa, centrally located siphuncie, slightly suborthochoanitic septal necks andepiseptal-mural cameral deposits.
Key words. Cephalopoda, Geisonocerella nakazatoensis, Middle Devonian, Nakazato
Formation, Kitakami Mountains.

Introduction

the first record of the genus from East Asia.

The Middle to Upper Paleozoic strata inthe southern Kitakami Mountains serve as thestandard of reference for less complete marine
deposits in Japan. Among them, the Nakazato Formation has been attracting the attention of paleontologists as the fauna and flora
can provide a lot of information on the
Middle Devonian biostratigraphy and biogeography of Japan. Nevertheless, only cephalopods in this fauna have been little investigated by recent workers. Collections of
invertebrates, other than orthoceratids, fromthe formation have been described in works
by Sugiyama and Okano (1941), Okubo(1956), Kobayashi (1957), Kobayashi and
Hamada (1977), Minato and Kato (1977),
Copper et ale (1982), Kaneko (1984, 1985),
Kase and Nishida (1986), Tazawa (1988), andothers.
Geisonocerella nakazatoensis Niko, sp.
nov. described herein is the first orthoceratid
reported from the Middle Paleozoic strata of
the southern Kitakami Mountains, and also

Systematic paleontology
Specimens utilized in this report are stored
at the University Museum of the University ofTokyo with abbreviation UMUT.
Subclass Nautiloidea Agassiz, 1847
Order Orthocerida Kuhn, 1940
Superfamily Pseudorthocerataceae Flower
and Caster, 1935
Family Pseudorthoceratidae Flower andCaster, 1935
Subfamily Spyroceratinae Shimizu andObata, 1935
Genus Geisonocerella Zhuravleva, 1978

Type species: Zhuravleva, 1978.

Geisonocerella

mitis

Geisonocerella nakazatoensis Niko, sp. nov.
Figures 1-1-4Type specimen: - Ho10type, UMUT PM
18470, an unperfect phragmocone.

*Received April 13, 1989; revised manuscript accepted November 4, 1989
291

292

Shuji Niko

Diagnosis: - Weakly annulated large
orthocone with elliptical cross section anddeeply concaved septa. Siphuncular position central; septal necks slightly suborthochoanitic. Cameral deposits mainly episeptal-murai.
Description: - The holotype is an orthoconic shell, approximately 75 mm in length,
which consists of ten camerae with a deep
septal curvature (Figures 1-2, 3). It is elliptical in cross section; conch diameter is 24.3mm X 28.0 mm at the adoral end. Sutures are
not observable but they can be assumed, by
the septal shape, to be nearly transverse. The
shell surface is marked with widely spaced
annulations and lirae that run parallel to theannulet. The annulations are low and slightly oblique to the conch axis. The septal
spacing is close; the number of camera
ranges from three to three and one-half in
relation to the corresponding apical conch
diameter. The siphuncle occupies the central position of the shell; septal necks areshort and slightly suborthochoanitic (Figure1-4). Cameral deposits consist of episeptalmural deposits, and bosses which are in theepiseptal or hypo septal position in somecamerae. No endosiphuncular deposits areevident.
Discussion: - Although the preservationof the holotype is poor in that the connecting
rings are missing and the surficial ornamentation is obscure, it is referred to the genus
Geisonocerella because of the possession of
the slightly oblique annulations and lirae,
and the suborthochoanitic septal necks.
Geisonocerella nakazatoensis Niko, sp,nov. is closely allied to Geisonocerella pershinae Zhuravleva (1978, p. 113, pI. 13, figs. 3,4) from the Emsian of U.S.S.R. in that it has
an elliptical cross section of the shell andrelatively narrow annulations with fine transverse lirae. In the latter, however, the siphuncular position is considerably more
eccentric and the septa are shallower in comparison with the former. The present species
is somewhat similar in the overall shell form
to Geisonocerella mitis Zhuravleva (1978, p.
Ill, 112, pI. 13, figs. I, 2a-b) from theGivetian of U.S.S.R., but it is distinguishable
by the less distinct transverse lirae and narrower annulations. Geisonocerella vajgachensis Zhuravleva (1978, p. 112, pI. 13, figs.
5a-b, 6a-b) from the Gedinnian of U.S.S.R.
also resembles G. nakazatoensis, but differsfrom the latter in having a larger siphuncular
diameter to external shell width ratio.
A Devonian orthoconic cephalopod was
also recovered by Toshio Kawamura of
Miyagi University of Education from thesame formation in the Simosabukurazawa of
the Sabukura area, Sumita-cho. Unfortunately, this specimen is a natural mold anddoes not retain the internal structure. Thus,
convincing classification and a detailed comparison with the type specimen of Geisonocerella nakazatoensis Niko, sp. nov. cannot be
done.
With the exception of the present species,
the following species have been describedunder or assigned to Geisonocerella:Geisonocerella (?) bicingulata (Sandberger
and Sandberger) from the Emsian ofNovaya Zemlya, Rossiyskaya S.F.S.R. andthe Eifelian of the Rheinland, West Germany. (Kuzmin, 1965; Zhuravleva, 1978)
G. mitis Zhuravleva, 1978 from the Givetianof the Pai-khoi Mountains, Rossiyskaya S.
F.S.R.
G. (?) novosemelica (Kuzmin, 1965) from theEmsian of Novaya Zemlya, Rossiyskaya S.
F.S.R.

~ Figure 1. Geisonocerella nakazatoensis Niko, sp. nov., holotype, UMUT PM 18470. 1, lateral viewof silicone rubber cast from the external mold, coated with ammonium chloride. 2, interior view of the
septate conch, coated with ammonium chloride; cavities mainly represent impressions of the shell andcameral deposits. 3, polished median section of the conch, submerged in water. Arrow points to theposition of siphuncJe. 4, partial enlargement of Figure 3. Arrow indicates relatively well-preserved septal
neck. Scale bars represent 20 mm for Figures 1-3 and 5 mm for Figure 4.

890.

Devonian cephalopod from Nakazato Formation

293

294

Shuji Niko

G. orientalis Zhuravleva, 1978 from theGivetian of Kuzbass, the Rossiyskaya S.F.
S.R.
G. pershinae Zhuravleva, 1978 from the Emsian of the basin of the River Pechora,
Komi A.S.S.R.
G. vajgachensis Zhuravleva, 1978 from theGedinnian of Ostrov Vaygach, Rossiyskaya
S.F.S.R.
Although the information on the Devonian
cephalopods in East Asia is too limited tomake an accurate presumption of biogeography at that time, it seems that the occurrenceof the genus Geisonocerella has previously
been restricted to only the Old World Province as mentioned above.
Occurrence and age: - The holotype of
Geisonocerella nakazatoensis Niko, sp. nov.
and a specimen (UMUT PM 18471, a crushedinternal mold of the large body chamber) ofquestionable assignment to the species were
found by Atsushi Kaneko of Kyoto University from the upper portion (N3 Member) of
the Nakazato Formation. Although fossils
are rather poor in the Nakazato Formation, a
few intercalated thin sandstone beds in the
N3 Member yield a large quantity of brachiopods, trilobites and mollusks including
the present cephalopods. Both specimens
were collected at an outcrop in a small tributary of the Higuchizawa of the Hikoroichi
area, Ofunato City, southern Kitakami Mountains (141°40'8"E, 39°6'55"N), where a greenish gray colored fossiliferous sandstone bed(approximately 1 m thick) is intercalated
within thin alternating beds of tuffaceous
sandstone and sandy shale.
Biostratigraphic investigations of the fauna
offer a consensus favoring the Couvinian toGivetian (e.g., Kobayashi and Hamada,
1977; Kato and Minato in Minato et al.,1979). Recent research on the atrypoid brachiopod by Copper et a/., (1982) provided amore defined age determination, the middle
or late Eifelian. Similar conclusions werereached by Kaneko (1984, 1985) based on
trilobites.

Acknowledgments

The author would like to thank Drs. Takashi Hamada, !taru Hayami, and Kazushige
Tanabe (the University of Tokyo) for reading
and commenting on early drafts of the manuscript. Thanks are also due to Dr. Tamio
Nishida (Saga University) for access to thespecimens, and Mr. Atsushi Kaneko (Kyoto
University), who collected the cephalopod
fossils and assisted in the field research. Dr.
Toshiro Kawamura (Miyagi University of
Education) kindly provided a specimen fromthe Sabukura area. This study was supported in part by the Japan Academy throughEmeritus Professor Teiichi Kobayashi (theUniversity of Tokyo).
References
Copper, P., Tazawa, J., Mori, K. and Kato, M., 1982:
Atrypa (Devonian Barchiopoda) from Japan.
Trans. Proc. Pa/aeont. Soc. Japan, N.S., no.
127, p. 368-374, pI. 59.
Flower, R.H. and Caster, K.E., 1935: The stratigraphy and paleontology of northwestern Pennsylvania. Part II: Paleontology. Section A:
The cephalopod fauna of the Conewango Seriesof the Upper Devonian in New York and Pennsylvania. Bull. American Pa/eont., vol. 22, no.
75, p. 199-271.
Kaneko, A., 1984: A Middle Devonian trilobite
fauna from the Kitakami Mountains, northeast
Japan-I. The Lachidae. Trans. Proc. Pa/aeonto Soc. Japan, N.S., no. 136, p. 474-491, pis.
87-89.
- - , 1985: Ditto-II. The Calymenidae. Ibid., no.
138, p. 94-110, pis. 14-16.
Kase, T. and Nishida, T., 1986: A Middle Devonian
gastropod faunule from the Nakazato Formationof Kitakami, northeast Japan. Bull. Nat. Sci.
Mus., Ser, C, vol. 12, no. 3, p. 73-89.
Kobayashi, T., 1957: Notes on two Devonian
trilobites from the Kitakami Mountains in Japan.
Jour. Fac. Sci., Univ. Tokye, Sec. II, vol. II, p.
1-10, pI. 1.
- - and Hamada, T., 1977: Devonian trilobites ofJapan in comparison with Asian, Pacific andother faunas. Pa/aeont. Soc. Japan, Spec. Pap.,
no. 22, 202 p., 13 pis.
Kuzmin, A.M., 1965: Devonian cephalopods (Superorder Nautiloidea) from the southern islands of890.

Devonian cephalopod from Nakazato Formation

295

Gotlandian and Ordovician nautiloids. Shanghai Sci. Inst., Jour., Sec. 2, vol. 2, p. 1-10.
Sugiyama, T. and Okano, H., 1941 : On the discovery
of Phacops (s.s.) from the Nakazato Series (Middle Devonian) of the Kitakami Mountainland.
Japan. Jour. Geol. Soc. Japan, vol. 48, no. 574,
p.357-361.
Tazawa, J., 1988: Zdimir (Devonian Brachopoda)
from the Kitakami Mountains, northeast Japanand its paleo biogeographical significance.
Ibid., vol. 94, no. 12, p. 1013-1016 (in Japanese).
Zhuravleva, F.A., 1978: Devonian orthocerids-Superorder Orthoceratoidea-. Akademia
Nauk SSSR, Trudy Paleontologicheskogo Institut, vol. 168, 227 p. (in Russian).

Novaya Zemlya. Uchenye Zapiski NauchnoIssledovate'skii Institute Geologii Arktiki(NIIGA), Ministerstva Geologii SSR, Paleontologii i Biostratigrafii, vypusk 9, p. 8-40, pis. 1-8(in Russian).
Minato, M. and Kato. M., 1977: A reticulate speriferid from the Devonian Nakazato Formation of theKitakami Mountains, Japan. Jour. Fac. Sci.
Hokkaido Univ., Ser.IV, vol. 17, no. 4, p.619627.
- - , Hunahashi, M., Watanabe, J. and Katto, M.
(eds.), 1979: The Abean Orogeny. 427 p.,
Tokai Univ. Press, Tokyo.
Okubo, M., 1956: Same Devonian brachiopods andtrilobites of the southern Kitakami Mountainland. Japan. Jour. Geol. Geogr., vol. 27, p. 3745, pis. 1-3.
Shimizu. S. and Obata, T., 1935: New genera ofiR.

Higuchizawa ill I=lHikoroichi B iJJ:m, Kitakami Mountains ~tl:l.lJ:it!!, Nakazato <j:tlIl.. Ofuna to ::kf.}l!!!:. Ohno ::k!f, Sabukura *~. Simosabukura-zawa r*~iR.. Sumitacho {± EEl DIJ.
i¥HiB~tl:il.J!tB<j:tlIl.JIli£:T;f- :/iIlCiiJi..lEMQ)-*'i'fi: rtHm~tl:il.J!tBQ)::6=F~::kf.}t!tm B iJJ:m!tB.K~~~~<j:t$T;f-:/*<j:tlIl.JIlN3$JIll~i£:WLkiiJi..lEM(~~-f~N~~'~fiD Q)-*'i'fi, Geisonocerella nakazatoensis Niko a-~tI;~ ~ 0 :;f;:filt. *F9:ti\Q)iNWTOOaff- LiN~t;:.ilil~'~~i.J~~/Jb 1?:h~::k~fi1:~ Jffi(!lj~ ~~m. ~1*Q)<j:t{"t;:.{ftil':~ ~1*~,:bi'i.J't;:'!IE~/v ~ ~, ~~a-ff-~~m~, episeptal-mural3a:~F9rtJillt¥.oa-1f~~':t;:.l~M.~~I?:h~o
~~.~

<

c

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 156, pp.296-318, IS Figs., December 30, 1989

891. FOSSIL OSTRACODE ASSEMBLAGES FROM THE
PLIOCENE SASAOKA FORMATION, AKITA CITY, JAPAN-WITH REFERENCE TO SEDIMENTOLOGICAL ASPECTS' TOSHIAKI IRIZUKI
Institute of Geology and Paleontology, Tohoku University,
Aobayama, Sendai 980

Abstract. Two hundred sixteen species offossil ostracodes coming under 71 genera arerecognized in the Pliocene Sasaoka Formation distributed in the eastern part of Akita City,
northeast Japan. In general, cryophilic species which either live today in Japan or havebeen reported from the Plio-Pleistocene of that region are predominant in each sample, withsubordinate amounts of such circumpolar species as Acanthocythereis dunelmensis (Sars),
Hemicythere emerginata (Sars), Elofsonella concinna (Jones) and Palmenella limicola (Norman). In addition to such cold water species, warm water species inhabiting sea areas under
the influence of the Kuroshio current are contained in each sample, running up to a few
percent of the total.
Q-mode cluster analysis of ostracode occurrence data brings out four clusters of samples(A, B, C and D). The results from grain size analysis of sediments containing fossil
ostracodes are compared with the size of ostracode valves, the ratio of left to right valves, theratio of adult to total valves, species diversity and equitability, with intention of understanding these four clusters. In general, physical agents had a great influence upon the distribution of fossil ostracode assemblages in the Sasaoka Formation, thus the depositional
environment is to be assessed not only on the ecological side of ostracodes but also on thesedimentological side.
Key words. Ostracoda, Pliocene Sasaoka Formation, northeast Japan, cryophilic
species, Q-mode cluster analysis, grain size analysis.

paleoecologists are seeking to study theprocesses which give rise to post-mortem
modification of the remains of organisms.
There are two different ways in taphonomic
studies. One is laboratory experiments. In
relation to fossil ostracodes, for example,
Kontrovitz (1975) conducted flume experiments on their differential transportation andconcluded that carapaces (articulated valves)
are involved in a traction current at lower
velocities than are valves (disarticulated
valves) of the same species. Moreover,Kontrovitz and Nicolich (1979) showed thatthe shape of carapaces and valves is more
important factors than their size in undergoing transportation and suggested a high likeli-

Introduction

Paleontologists are often confronted withsome problems when inferring paleoenvironments by using fossils. One of these isdifficulties in distinguishing such microfossils
as ostracodes into autochthonous and allochthonous material. If the fossil assemblages
are in situ, their ecological aspects may beemphasized, and if they have been influenced
by physical, chemical and/or biologicalagents, sedimentological aspects are more
important in interpreting a paleoenvironment. Consequently, large numbers of'Received April 14, 1989; revised
accepted November I, 1989

manuscript

296

891.

Ostracodes from Sasaoka Formation

hood of success in predicting threshold velocities by using shape parameters. Whatley,
Trier and Dingwall (1982) indicated thatdurability of ostracode carapaces varies greatIy: some robust species have the greater
potential for preservation than fragile ones.
Another is carried out through comparisons
between living and subfossil assemblages in
the hope of guiding feasible interpretations offossil assemblages. Kilenyi (1969) studied
the living and death assemblages from theThames Estuary and assessed sorting effects
by using the ratios of carapaces to valves andadults to juveniles. Okada (1979) discussed
the degree of mixtures of ostracode communities by comparing the structure of fossil
assemblages from the Shibikawa and Anden
Formations with that of Recent communities.
Frydl (1982) also inferred the degree of sorting of fossil ostracode assemblages from theBoso Peninsula in Japan by means of community structures, the ratios of each instar to thetotal numbers and the left to right valves.
Izuka and Kaesler (1986) compared biotopes
based on ternary plots and cluster analyses ofliving ostracode assemblages with those from
subfossil assemblages from a small reef flatand showed that a mixing of algae-dwellingand sediment-dwelling ostracode assemblages
easily occurs and thin shelled species arelargely destroyed by biostratinomic agents.
Moreover, they mentioned that transportationof ostracodes does not completely homogenize subfossil assemblages, nor does it completely obliterate distributional patterns ofliving ostracodes. van Harten (1986) investigated living ostracode assemblages in the
Mediterranean and concluded that displaced
ostracode assemblages typically contain relatively few adult specimens and selective sorting leads to over representation of certain sizeclasses and may cause the ratio of left to rightvalves to shift from the original ratio of one
to one. Moreover, he inferred the paleodepth of the Prasas Marl sediments, taking
those results into consideration.
The purpose of this study is to delineate the297

depositional environment of the Pliocene
Sasaoka Formation, Akita City in Japan, bymeans of fossil ostracodes. Thus, as to infer
whether they have been subjected to selective
physical agents or not, it is important torecognize the relationships between sedimentgrain size and the composition of fossil
ostracode assemblages in addition to turning
to account the above-mentioned varied taphonomic knowledge of ostracode valves.
Ostracodes are of great advantage in conducting taphonomy because their growth stages
can be recognized even in fossil assemblages
and their carapace consists of two asymmetrical valves.
Geological setting
Late Cenozoic deposits in the study area,
the eastern part of Akita City, are classified,from the bottom upward, into the Onnagawa,Funakawa, Tentokuji, Sasaoka and Takaoka
Formations (Figure 1). These formations
are broadly folded into a syncline (Wada
Syncline), whose axis passes through the center of the study area from north to south.
Many geologists have investigated this area
(e.g. Huzioka et al., 1977; Ozawa et al.,1981). The stratigraphic scheme resulted
from the present survey is basically the sameas in previous investigations (Figure 2).
The Onnagawa Formation, resting conformably on the Sunakobuchi Formation which
consists of basaltic breccia and lava, is composed mainly of 420 to 600 m thick stratified
hard mudstone. Along the Sannaigawa
River, thick and massive rhyolitic tuff andtuff breccia called the Kamisannai Tuff Member of this formation, are well exposed.
The Funakawa Formation conformably
overlies the Onnagawa Formation and consists of dark gray massive mudstone. The
upper part distributed in the northern part iscomposed of massive pumice tuff and tuff
breccia.
The Tentokuji Formation, resting unconformably on the Funakawa Formation, con-

Toshiaki Irizuki
298

1@iJ1
r.::::.'12a~6~~t;::.:~ 2b \AAAj 7§§3ar~rr]8

891.

SW
AGE

Ostracodes from Sasaoka FormationNE

STRATIGRAPHY

THICK
NESS

terrace deposits
Takaoka Formation?

Sasaoka

300-

I:i:l

Z

600m

I:i:l
C)

0
......
~

p.,

Tentokuji
Formation

150620m

~

Z

~

C)

o......
:E

Formation

600m

Sunakobuchi
Formation
Figure 2. Stratigraphic units. S.A.: Souyakyo Andesite, K.T.: Kamisannai Tuff Member, T.
R.: Tsukushimori Rhyolite.

sists of an alternation of conglomerate andsandy siltstone (Katsurane facies) and siltstone. Such ostracodes as Acanthocythereis
dunelmensis (Sars) and Robertsonites
reticuliforma (Ishizaki) are also observed, but
are generally, not in abundance.
The Sasaoka Formation overlies the Tentokuji Formation conformably on both theeastern and western sides of the syncline, but
unconformably in the northern part where a299

few meter thick basal conglomerate is recognized. The formation in the southern partconsists mainly of tuffaceous silty sandstonewhich grades upward into fine sandstone. In
the northeastern part, the formation is composed maily of 300 to 600 m thick fine tomedium sandstone but silty sandstone grading upward into fine sandstone, and granuleconglomerate and pebbly sandstone are seenalong the Hatsutagawa River, and along theKogurosawagawa River and Hirasawa,
respectively. Some thin beds of white tocream colored fine tuff are widely traceable inthe study area. The formation yields large
quantities of calcareous fossils called theOmma-Manganji Fauna which originallyreferred to cold-water inhabiting molluscan
assemblages in the Pliocene of Japan (Otuka,1936). According to Maiya (1978), the lower
and middle parts of the Sasaoka Formation
represent the planktonic foraminiferal
Neogloboquadrina pachyderm a I Globorotalia
orientalis Zone (late Pliocene). However, its
upper part, which has not yielded any agecontrolling fossils, may run up in age to the
Pleistocene, judging from the great thicknessof 300 m.
The Takaoka Formation, resting unconformably on the Sasaoka Formation, is distributed only in the central part. It is composed of
30 to 100 m thick cross-laminated fine tocoarse sand and gravel with a thin lignite bed.
No marine fossils have been obtained fromthis formation. In consequence, the wholeformation may be of terrigenous origin.

Materials and methods
A total of 21 samples collected from the
Sasaoka Formation were used for ostracodeanalyses (Figures 3, 4). Eighty grams of~ Figure 1. Index and geological maps.
I: Takaoka Formation, 2: Sasaoka Formation, 2a: sandstone, 2b: conglomerate and pebbly sandstone, 3: Tentokuji Formation, 3a: mainly siltstone, 3b: alternation of conglomerate and silty sandstone, 4: Funakawa Formation, 4a: massive mudstone, 4b: pumicetuff, 5: Onnagawa Formation, 5a: stratified hard mudstone, 5b: rhyolitic tuff and tuff breccia (Kamisannai
Tuff Member), 6: Sunakobuchi Formation, 7: Souyakyo Andesite, 8: Tsukushimori Rhyolite, 9: dolerite,
10: key beds (fine tuff), II : Wada Syncline, 13: inferred fault.

Toshiaki Irizuki

300

IWAMISANNA I

IWA6T~WA7T

IWAST
IWA4T
IWA3T
IWA2T

"fIWA8T
IWA9T

T

IWA lOT

IWAIT

KOClT

!

o1...._L-_IL..---'----',
1.0
2;0 (km)Figure 3. Map showing fossil localities in the Tentokuji and Sasaoka Formations.
the location of samples barren of ostracodes but analyzed for grain size.

Asterisks show

891.

Ostracodes from Sasaoka Formation

Figure 4. Map showing fossil localities in the
Sasaoka Formation distributed around Kurosawa.

dried sediment were basically disaggregatedmaking use of a saturated sodium sulphate
solution and naphtha for rock maceration(Maiya and Inoue, 1973), washed through a
200 mesh sieve screen, and dried again. A
fraction coarser than 177 J.lm (80 mesh) wassieved and divided by a sample splitter into
aliquot parts, from which about 200 specimens of ostracodes were picked on an assemblage slide, when possible.

General features of ostracode specimens in
the Sasaoka Formation
Two hundred sixteen species belonging to
71 genera of ostracodes were discriminated in
the Sasaoka Formation. 20 samples with the
exception of JIN-1S were taken from the
middle and lower parts of the Sasaoka Formation distributed to the east of the synclinal
axis (Figures 3, 4). Specimens and species
are generally numerous. General features of
ostracode species are as follows.
Circumpolar species such as Palmenella
limicola (Norman), Hemicythere emerginata(Sars), Acanthocythereis dunelmensis (Sars)

301

and Elofsonella concinna (Jones), which havebeen known from the Arctic seas off British
Isles, eastern North America, Scandinavia
and Europe (Cronin and Ikeya, 1987), arecommon in each sample. There are many
cryophilic species such as Finmarchinella
spp., Robertsonites spp., Schizocythere okhotskensis Hanai, Howeina higashimeyaensis
Ishizaki, Hemicythere spp. and Urocythereis ?
spp., which either live today in cold waterseas around Japan or are reported from the
Plio-Pleistocene of that region. In contrast,
species which inhabit bay areas do not occur:
Bicornucythere bisanensis (Okubo),
Spinileberis quadriaquleata (Brady), and Pistocythereis bradyi (lshizaki), and warm water
species represented by Loxoconcha optima
Ishizaki, Cythere omotenipponica Hanai, andPacambocythere spp. run into a few percent
in every sample. As mentioned above theSasaoka Formation exclusively contains cryophilic and circumpolar species, and represent
a deposit in coastal environments, not in
embayment.

Analyses and discussiona)Species diversity and equitability
First of all, in order to comprehend thestructure of each of the ostracode assemblages
in 17 samples which yielded about 200 specimens, species diversity was examined by using
the Shannon-Weaver's information function:
H(S)= - J;pi In Ph where Pi means the proportion of the i th species in a sample. Incidentally, Buzas and Gibson (1969) expressed
equitability by the following formula: E =eH(S) / S, where S stands for the number of
species. It equals the formula, H(S)=ln(S.E) which plots the relationships among
the number of species, diversity andequitability on a graph (Figure 5). A basis
for comparison is constructed by using following literature data:
1 Inner Bay of Uranouchi (lshizaki, 1968)
2 Outer Bay of Uranouchi (lshizaki, 1968)
3 Nakanoumi Estuary (Ishizaki, 1969)

Toshiaki Irizuki

302
1

Nakanoumi Estuary (Ishizaki, 1969)

EOUITABILlTV(E)

2 Inner Bay of Uranouchi (Ishizaki, 1968)
3 Deeper section in Aomori Bay (Ishizaki, 1971)
4 Outer Bay of Uranouchi (Ishizaki, 1968)
5 Shallower section in Aomori Bay (Ishizaki, 1971)
6 East China Sea (Ishizaki, 1981)

1.0
0.9
0.8
0.7
0.6
0.5

4.0

0.4
0.3

>
Im

0.2

3.0

o HAT ISo HAT 2S
t:. HAT 3So HAT 4Sa:w

\l HAT 5S>

I> HAT 6S

Ci

0.1

m

2.0

w

<J HAT 7S

o TAl 2S
X TAl IS

c.J

• TAl
TKOS
~ KOS
~ KOS

w

~

m
1.0

• HIR
• HIR
• HIR
... HIR

3S
IS
2S
3S
IS
2S
4S
5S

0
0

20

40

60

60

100

NUMBER OF SPECIES

Figure 5. Diagram showing the positions of 17 samples from the Sasaoka Formation in relation to
species diversity, equitability, and number of species. Large ellipses show sample groups constructed byusing the data from Ishizaki (1968, 1969, 1971, 1981).

4

Shallower section in Aomori Bay (Ishizaki, 1971)
S Deeper section in Aomori Bay (Ishizaki, 1971)
6 East China Sea (lshizaki, 1981)
Ostracode assemblages in bay areas display
lower values of S, H(S) and E, but those inopen seas such as the East China Sea show
higher values. The equitability values of theassemblages in the Sasaoka Formation are
shown between 0.S-0.8 with the exception of
T AI-2S. Those diversity values are all relatively high, except for TAl - 2S, TAl - 3S, HIR4S, and HIR-SS. Generally all the examinedassemblages except in T AI-2S display
changes in diversity depending on the numberof species rather than equitability values andseem to be representatives of open sea areas.
Cluster analysis
As one of the useful ways to find out
biotopes based on similarities among theb)samples with respect to the composition of
ostracode species, Q-mode cluster analysis
was conducted by using NEAC-ACOSmodel 1000 computer in the Tohoku University Computer Center. The computer program used was written by Shiro Hasegawa.
Similarities are given by the Horn's overlap
index (Horn, 1966) between samples, andclustering is practiced by using the weighted
variable group method with arithmetic averages. 110 species which are represented bymore than three specimens in any of thesamples were used for this calculation. As aresult, four clusters (A, B, C and D) wererecognized in the dendrogram (Figure 6).
Cluster A: Localities - HA T -2S, HAT3S, HAT -4S, HAT -SS, HAT -6S, HAT -7S,
and KOS-IS
Main species - Cytheropteron sawanense
Hanai, Finmarchinella (Barentsovia) japonica (Ishizaki), Cythere boreokurila Schornikov, and Cornucoquimba moniwensis (Ishiza-

891.

Ostracodes from Sasaoka Formation

ki)
Cluster B: Localities - HA T -1 S, KOS2S, KOS-3S, HIR-lS, HIR-2S and HIR-4S
Main species - Howeina higashimeya0.0

c..

ct

...I

0:
W

>

o

0.5
Ll.

o
x

W

Q

Z

to

~~~~~~~~~~~~~~~~~»>-»0»»--00>---~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A

B

ensis, Sehizoeythere okhotskensis, and Cornueoquimba moniwensis
ClusterC: Localities-HIR-5S, TAI-2S
and TAI-3S
Main species - Uroeythereis? gorokuensis Ishizaki, Norman icy there japoniea Tabuki, Finmarehinella (Barentsovia) nealei
Okada, and Howeina higashimeyaensis
ClusterD: Locality-TAl-IS
Main species - Uroeythereis? gorokuensis, and Callistoeythere retieulata Hanai
The clusters A to D are disposed diachronouslly from northwest to southeast (Figure 7). Toward a better understanding ofthese clusters, examined are the relationships
between the size of fossil ostracode specimens
and sediment grain size, which may imply the
degree to which the original material has been
influenced by physical agents such as water
currents.
Grain size analysis
Twenty-two samples (19 ostracode-bearing
samples from the Sasaoka Formation, one
ostracode-bearing and two barren samples
from the Tentokuji Formation) were analyzed for the frequency distribution of grain
size by a settling tube which is able to measurec)

XO • • e>64<lvOO.,."o.

101 c 1

303

I

Figure 6. Dendrogram from Q-mode cluster
analysis. A, B, C and D show biotopes.
+TA135c~TAl 25<>(m).HIR 25100

HIR 15 •

,

,

o

0.5

SE

B
K05354,1.0 (km)

NW

Figure 7. Diagram showing the stratigraphic distribution of clusters determined by Figure 6 on aschematic cross section (Figure 9).

Toshiaki Irizuki

304

particles ranging in size from - 1 to 4.5 c/>(Minoura et al., 1988).
As a result, three types (I, II and III) wererecognized in grain size distribution (Figure8). Figure 9 is a cross section showing the
distribution of those three types of sediments.
Type I: The peak in frequency distribution of grain size is around 3.0 c/>. Sorting iswell to fair. Mud content is 6.9-35.0%.
Two subtypes are discriminated, i.e., Type lais characterized by the secondary peak aroundo c/> which is indiscernible in Type lb. Threesamples (KOS-3S, HIR-4S, HIR-5S) belong
to Type la and six samples (KOS-l S, KOS2S, HIR-lS, HIR-2S, TAl-IS, TAI-3S) to
Type lb.
Type II: The peak in distribution of grain
size is around 4.0 c/>. Sorting is poor. Mudcontent is 39.0-71.7%. Eight samples (HAT -TYPE la(HIR5S)

01

2

Figure 8.

3
PHI SCALE

4Frequency distribution of grain size.

1S, HAT -2S, HAT -3S, HAT -4S,HA T -5S,
HAT -6S, HAT -7S, T AI-2S) come under thistype.
Type III: The peak in distribution ofgrain size is beyond 4.0 c/>. Mud content is
58 and 74%. Two sterile samples from the
Tentokuji Formation (KUR-lT, SAR-lT)
belong to this type. SAR -1 T yielded such
benthic foraminifera as Euuvigerina juncea(Cushman and Todd), Epistominella pulchera
Husezima and Maruhasi, and Trifarina kokozuraensis (Asano), which represent the upper
to middle bathyal zones.
Types I and II sediments in the Sasaoka
Formation are comparable with modern sediments in the Sea of Japan off Nishi-Tsugaru
and off Kyogamisaki and in the Bay of
Mutsu. In addition, 3.0 c/> fractions which
dominate Type I sediments are recognized in
an environment where sediments are being
deposited under 20 to 30 cm/sec currents(Sundborg, 1967). Sediments with that grainsize, frequency distributions and mud contents are known to be distributed on theseafloor within 20 km both off Nishi-Tsugaru(lnouchi et al., 1979) and off Kyogamisaki(Katayama and Ikehara, 1988) on an almost
parallel with the coast. Type Ia sedimentswith a bimodal distribution may be a result
from two different agents: coarser fractions(around 0 c/» have been brought into mingle
with 3 c/> fractions through creeping. In the
Bay of Mutsu, Type Ia sediments arecharacteristically recognized in channel
deposits (Minoura et al., 1988). Namely,
Type I sediments are thought to have been
deposited in high-energy environments wherecoarser grains are to be supplied. Threesamples coming under this type belong toclusters Band C.
Type II sediments having high mud contents are being deposited both in more
offshore areas than those of Type I sediments
and in the mouth of small bays. Because 3.5
to 4.0 c/> fractions, which make a peak in TypeII sediments, are sensitive to the movement ofwater, it is thought that the fractions were891.

Ostracodes from Sasaoka Formation

305_...........................................................................................................................................................- .. - .. - .. - .. - .. .. -40 :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::,,:,:~~~Ei:-i.iit~;j~j

2: ~~~;;?~;~·~~~L3.I~j/ffi~Y>@4%Y!!!!!!!!!!!}!!!!!!!!!!!!!!~!!!J/~~:t;~!!%!!!!!!%!i~~.~:~;~f.i.~~.~.
o

0.5

,

"

1.0 (km)

TENTOKUJI

FORMATION(TYPE 11+111 or TYPE III)

Figure 9. Schematic cross section in the Sasaoka Formation constructed by using the result of grain
size analysis. Vertical axis represents thickness of the formation.

sediments settled out of suspension in stagnant and low-energy environments where
hardly any coarser grains will be supplied.
Most of the samples in cluster A come underType II sediments.
Besides those three types, medium types(Type I + II, Type II + III) are distinguished.
Two samples yielding a few fossil ostracodes(SUN-IS, SAR-IS) are grouped under Type
1+11. Type II+III comprises TAI-9T
which yielded the most fossil ostracodes of all
the samples from the Tentokuji Formation(50 specimens/80 g sediments).
d)

Measurement of ostracode shell
To investigate whether there are relationships between grain size and ostracodes shellsize, eight species which are common in 17
samples were selected for measurements of
their length and height: Cornucoquimba

moniwensis, Cythere boreokurila, Cytheropteron sawanense, Finmarchinella (Barentso via) hanaii Okada, Finmarchinella (Barentsovia) japonica, Schizocythere okhotskensis, Urocythereis? gorokuensis, and Urocythereis ? sp. A. If relationships are suggested,
ostracode valves are thought to have beensorted by water currents. The mean andstandard deviation of their size are shown in
Figure 10. Measured are either right or left
valves because most ostracodes have more orless asymmetrical valves. As for Cythere
boreokurila, left valves are measured with the
exception of HIR-2S and HAT -5S, in whichright valves are reluctantly used because mostleft valves are broken.
The valves of Urocythereis? gorokuensis
from samples belonging to sediment Type I(solid symbols) are larger than those of TypeII (open symbols) except for T AI-2S. An

Toshiaki Irizuki

306

(mm)

0.5

Urocythereis? sp

At--+-t-......_ _--1

(mm)

Urocy thereis?
gorokLiensis

0.5
0.4
0.4
0.3
0.3

0.2

0.4

0.6

1.0 (mm)0.8(mm) Sch izocythere okhotskensis

0.4

0.2

:T
0.3

0.4

1. 0 (mm)

0.8

0.6

( mm )

0 .35 Cythere boreokurila

T

0.2

0.30

0.2

0.3

0.4

0.6

0.5

.;::L.j

0.7
(mm)

(mm)

0.25

0.4
Finmarchinella (Barentsovia) hanaii

0.3

0.3

I

0.4

0.5

I

I

0.7 (mm)

0.6(m m) Cornucoquimba moniwensis

O. 4
0.2:~------.------.------,

0.4
(mm)

0.4

O. 3

ot:

Finmart;:hinella (Barentsovia) japonica

ifIW'!

0.3

O. 2

0.4

I I

0.5

0.6

0.7

0.4

Cytheropteron sawanense

I

0.2+-------~~---.------._----_,

0.3

0.4

0.5

0.6

TYPE

II

o HAT 1S

• TAl 3S)( TAl 15~ K0515(:,. HAT 3So HAT 4S'\l HAT 55
I> HAT 6S<I HAT 75
TAl 2S• K0525
I ... K0535• HIR15• HI R 25• HIR 45.. HIR 55

o

TYPE

1

0.7
(mm)

o HAT 25

0.8 (mm)

(mm)

0.3

1.1.

0.3

,II

0.4

I

0.5

I

0.6

(mm)

891.

Ostracodes from Sasaoka Formation

apparent break is recognized between sediment Type II and Type I for Urocythereis?
sp. A which has relatively large valves. As
to the remaining six species, Type I samples
contain larger valves than in Type II. As
valve sizes of Urocythereis? gorokuensis in
T AI-2S are not related to grain size, they may
not be influenced much by water currents.
Similar results were also obtained from astudy of age distributions of dominant species
in each sample (Figures II, 12). Frydl

~!.~
30(1)

Co.m.

Co.s.

Fi. j.

Ba.h.

Cy. h.

16( 3)

14( 0)

12(0)

9(0)

9( 0)

lliI ~A ill Dh

HAT 45Co.s.

Cy. s.

Co.s.

Fi. j.

Cy. b.

14(2)

13(1)

11 (0)

9( 0)

15(J)

~ [lL 11l ilL

C'l,j ~
HAT 35Cy.s. Co. s.

17[~
[fu
18(0)

HAT 25
Co.A. Co.m. Fi. j.
13( 1)

10(0)Fi. j.

Fi. j.

'8"'[[]I ':ttl.
AA

Co.m. Cy. b.
18( 2)

15( 0)

5c. o.
15( 0)

ITD. ~jhA

cill

TAl 25
Ur. g.

No. j.

Pa. t.

66( 19)36(3)

21 (21)

Pa. h. Pa. r.

HAT 75Cy.s!

17( 2)

12(7)

7( 3)

~ eLI

Co.m.

CY·b.

Fi. j.

Co. s.

17( 1)

14( 0)

12( 2)

11 (2)~ [1Jl dl J1 ~11( 1)

7(0)ill [h lli JJJ. J1L

HAT 15
Cy. s.

15(2)(1982) and van Harten (1986) inferred thedegree of sorting from their studies of age
distributions. Most ostracodes molt eighttimes from hatch to adult. Their castoff
carapaces are usually fragile and potentiallyless preservable as fossils. Therefore it seems
likely that each instar of fossil ostracodes
represents largely their time of death.
There are few or no adult valves but numerous juvenile ones in samples of Type II sediments. For example, valves of Cythere bor-

Co .. m.
Cy. s. Cy. b.
8( 1)

9( 0)

5c.o.

307

A -S"4-J..2-tA

dL

HAT 6S';'~A

Cy. s. Ur. g.

Ac.A.

Lo. s. Fi. j.

24( 6)1

16( 1)

11 (0)

17( 0),~ l Jill

11 (0)nJ1L

Figure 11. Histograms showing the abundance of various growth stages of dominant species present ineach sample of sediment Type II. The numerals show the number of total specimens and the numbers inparentheses stand for adult specimens. Shaded column and abbreviation A represent an adult stage, and-I, -2, ······for successive younger stages. Ac. A.: Acanthocythereis sp. A, Sa. h.: Baffinicythere howei,
Co. m.: Cornucoquimba moniwensis, Co. s.: Cornucoquimba saitoi, Co. A.: Cornucoquimba sp. A, Cy. b. :Cythere boreokurila, Cy. s.: Cytheropteron sawanense, Fi. j.: Finmarchinella (Barentsovia) japonica, Lo.
s.: Loxoconcha subkotoraforma, No. j.: Normanicythere japonica, Pa. h.: Paijenborchella hanaii, Pa. t. :Paijenborchella tsurugasakensis, Pa. r.: Patagonacythere robusta, Sc. 0.: Schizocythere okhotskensis, Ur.
g.: Urocythereis? gorokuensis.
~ Figure 10. Mean and standard deviation of the valve size of eight species which are common in 17
samples. Horizontal and vertical axes represent length and height, respectively.

Toshiaki Irizuki

308

TA~.35

HIR 25
Ho. h.

Sc. o. Ur. 8.

Fi. n.

22( 22)

12(0)

8(8)

5'1

HIR15
CO.
11( 11)12(2)CO. m.
8( 6)

Ur. g.
7( 1)

J

K053S
5c. o.

I

ITL Jil.

Pa. r.

,,~,;,

TAl 15
Ur. g.

21(ll~

Ho. h.
5( 5)

6( 1)

[L Au. IA.
II( 4)

Fi. h.
9(0)A

5e. h. 5c. o.
9(9)

~

A

9(0)

A

Mu. h.

9( 9)

7(7)

Ca. r.

Cy. s.

Cy.C. Pa. t.

8(8)

7( 3)

7(7)

I

[}

Ke. A.
8( 0)Ur.8.
19( 4)dIJ

Ne. j.

Fi. n.

Ca. s.

15( 13)14( 14)12( 1 0)J IJ

Ur. g.

Ur. 8.

Fi. n.

Ne. j.

Pa. h.

Am. k. 33(33)~

16(2)

14(2)

12(12)

11 (5)

8(6)

8( 2)

A

-1A

6( 6)

I I

HIR 4S
Ho. h.

I all J ~A

Ca. r.

1 O( 10)20( 20)~'il~~ ~~(:li ~~J ~J
22( 19)Ho. h.

14(6)HIR 55
Ho. h.

K0525

K0515
Cy. s.

Ur. g.

D1L[[[J.
CO. m. Cy. s.
Fi. j.

20~ '~ "]"(3~I JlI I I I

lL ~ I

Figure 12. Histograms showing the abundance of various growth stages of dominant species present ineach sample of sediment Type I. Abbreviations are the same as those on Figure II. Am. k.: Ambostracon
kitanipponica, Au. A.: Aurila sp. A, Ca. r.: Callistocythere reticulata, Ca. s.: Callistocythere setanensis,
Cy. c.: Cytherura sp. C, Fi. h.: Finmarchinella (Barentsovia) hanaii, Fi. n.: Finmarchinella (Barentsovia) nealei, Ho. h.: Howeina higashimeyaensis, Ke. A.: Keijella? sp. A, Mu. h.: Munseyella hatatatensis,
Ne. j.: Neomonoceratina japonica, Se. h.: Semicytherura henryhowei, Ur. A.: Urocythereis? sp. A, Ur. B. :Urocythereis? sp. B.

eokurila and Schizocythere okhotskensis areabundant, but few adult valves are containedin each sample: only one adult valve of theformer species is present in HAT -3S. As
Cythere boreokurila inhabits today largely
intertidal zones in the Kuril Islands (Schornikov, 1974), it seems that species in Type II
samples have been displaced at least in partfrom upper sublittoral zones. In this way
some small juvenile valves of certain species
are those displaced. In contrast, T AI-2S ofthe same Type II sediment is dominated by
specimens in A to A-4 instar of Urocythereis ? gorokuensis and Normanicythere japon-

ica, and A to A-I of Paijenborchella hanaii
Tabuki and Patagonacythere robusta Tabuki. Namely, these species in TAI-2S havenot been influenced much by water currents
and there is a possibility that they are in situ
ones.
Dominant species in samples of sedimentType I are represented by numerous adult andfew or no juvenile specimens. For example,
such species as Howeina higashimeyaensis in
HIR-IS, HIR-2S, HIR-4S, HIR-5S and
T AI-3S, Finmarchinella (Barentsovia) nealei
in HIR-4S, HIR-5S and T AI-3S, and Callistocythere reticulata in TAl-IS and TAI-3S

891.

TYPE

I

Ostracodes from Sasaoka Formationo HAT lSo HAT 2S

• TAl 3S)( TAl 15

o

•
•
•
•

l:> HAT 3So HAT 4S'Q HAT 55
I> HAT 6S<l HAT 7S
TAl 2S

influence upon the assemblages in Type I
sediments. Similar aspects are indicated in
Figure 13 where the relationship between thepercentage of adult valves in each sample andmud content are demonstrated. In this graphsamples containing adult valves of more than
50% can be distinguished from those of lessthan 30%. Adult valves are numerous, being
no less than 73.2% in T AI-3S (mud content is
the least (7.8%) and the reverse is generally
true in samples with high mud content.

• K0515• K0525~ K0535
HIR15
HIR 25
HIR 45
HIR 55

Cl

~

z
w
o
II:
W

e) The ratio of right to left valves
Another way to know whether shells havebeen influenced by physical agents is to test
the ratio of right to left valves. If ostracodes
are fossilized utterly in situ after death, theirratios of right to left valves should be 1 : 1.
Because their valves are more or less asymmetrical, however, it is likely that ostracodevalves are differentially sorted by water currunts and that their ratios may shift fromoriginal ones. Using the chi-square test,
whether the hypothesis (L: R= 1: I) is adopted or not was determined at the 5% level ofsignificance (Table I).
The following species were rejected bymeans of the chi-square test: Finmarchinella

II.

o

20

40

MUD

CONTENT (%)

60

Figure 13. Diagram showing the relationshipbetween mud content and percentages of adult valves.

are represented by only adult valves being
thick and strong. Juvenile valves of these
species may have been winnowed away.
There is also an over representation of A-I
instar in Type I samples due to selective sorting: Finm arch in ella (Barentsovia) hanaii in
KOS-I Sand KOS-2S, and Finmarchinella(Barentsovia) japonica in KOS-3S. As
mentioned above, physical agents had a great
Table 1.

Numbers of left and right valves and the result of chi-square testof dominant species in each sample. A to D show clusters.
Open and solid symbols represent sediments of Type II and TypeI, respectively. +: acceptance, / : rejection (at 5% level).

LOCALITYSPECIES
HAT-IS

(0,

(0,

L.V.

R.V.

5%

28

20

14

22

18

12

15

10

II

15

+
+
+
+
+

B)

Cytheropteron sawanense Hanai
Finmarchinella (Barentsovia) japonica (Ishizaki)
Cornucoquimba moniwensis (Ishizaki)
Cythere boreokurila Schornikov
Schizocythere okhotskensis Hanai
HAT-2S

309

A)

Cornucoquimba sp. A
Cornucoquimba moniwensis (Ishizaki)
Finmarchinella (Barentsovia) japonica (Ishizaki)
Cytheropteron sawanense Hanai
Cythere boreokurila Schornikov

6

13

10

10

9

8

8

7

6

7

+
+
+
+
+

(to be continued)

Toshiaki lrizuki

310

LOCALITYSPECIES
HAT-3S

(6.

L.V.

R.V.

5%

A)

CYlhere boreokurila Schornikov
Cylheropleron sawanense Hanai
Cornucoquimba saitoi (Ishizaki)
Finnmarchinella (Barenlsol'ia) japonica (Ishizaki)
Cornucoquimba moniwensis (Ishizaki)

34

37

20

21

+
+

Schizocythere okholskensis Hanai
HAT-4S

(0.

18

8

/

13

17

12

15

12

15

+
+
+

A)

10

+
+
+

II

3

/

7

9

+

23

30

+

2

16
Id

/
/

12

8

6

9

9

5

+
+
+

Cylhere boreokurila Schornikov
Cylheropteron sawanense Hanai
Urocythereis ? gorokuensis Ishizaki
Acanthocythereis sp. A

28

22

+

II

24

/

17

10

16

II

Loxoconcha subkolOraJorma Ishizaki
Finmarchinella (Barentsol'ia) japonica (Ishizaki)
Cornucoquimba moniwensis (Ishizaki)

4

II

+
+
+
+
+

Cornucoquimba sailOi (Ishizaki)
CYlheropleron sawanense Hanai
Cornucoquimba moniwensis (Ishizaki)
Finmarchinella (Barenlsol'ia) japonica (Ishizaki)
Cythere boreokurila Schornikov
HAT-5S

('17.

(C>.

II
10

13

A)

Cylheropleron sawanense Hanai
Cornucoquimba moniwensis (Ishizaki)
Cornucoquimba saitoi (Ishizaki)
Finmarchinella (Barenlsol'ia) japonica (Ishizaki)
BajJinicythere cr. howei Hazel
Cylhere boreokurila Schornikov
HAT-6S

15
14

2

A)

7

II

II

II

15

17

+

4

17

/

13

14

+

12

5

/

II

8

+

Cylheropteron sawanense Hanai

22

16

Finmarchinella (Barentsol'ia) hanaii Okada
Semicytherura henryhowei Hanai and Ikeya
Schizocythere okhotskensis Hanai
Paijenborchella hanaii Tabuki
Amboslrakon kitanipponica Tabuki

7

9

9

( <l. A)

HAT-7S

Cytheropteron sawanense Hanai
Cornucoquimba moniwensis (Ishizaki)
Cylhere boreokurila Schornikov
Finmarchinella (Baren/sol'ia) japonica (Ishizaki)
Cornucoquimba saitoi (Ishizaki)
KOS-IS

KOS-2S

(

....

(~.

A)

4

+
+
+

9

3

/

8

8

8

7

+
+

27

27

16

16

10

14

10

10

10

8

B)

Urocythereis ? sp. A
Schizocythere okhotskensis Hanai
Finmarchinella (Baren/sol'ia) hanaii Okada
Cytheropteron sawanense Hanai
Cornucoquimba moniwensis (Ishizaki)

+
+
+
+
+

(to be continued)

891.

Ostracodes from Sasaoka Formation

LOCALITY

311

L.V.

R.V.

5%

KOS-3S (~. B)
Sehizoeythere okhotskensis Hanai
Cornueoquimba moniwensis (Ishizaki)
Cy/heropteron sawanense Hanai
Finmarehinella (Barentsovia) japoniea (Ishizaki)
Aurila sp. A

20
II
13
14
9

15
15
14
6
II

+
+
+

HIR-IS (B)
Cornueoquimba saitoi (Ishizaki)
Cornueoquimba moniwensis (Ishizaki)
Uroeythereis ? gorokuensis Ishizaki
Patagonaeythere robusta Tabuki
Howeina higashimeyaensis Ishizaki

7
8
3
6
5

II
6
7
2
3

+
+
+

HIR-2S (B)
Howeina higashimeyaensis Ishizaki
Sehizoeythere okhotskensis Hanai
Uroeythereis ? sp. B
Peetoeythere quadrangulata Hanai

22
12
12
7

21
II
12
8

+
+
+
+

28
16
7
12

33
14
14

SPECIES..
..

HIR-4S (e. B)
Howeina higashimeyaensis Ishizaki
Uroeythereis? gorokuensis Ishizaki
Uroey/hereis ? sp. B
Finmarehinella (Barentsovia) nealei Okada
Neomonoeera/ina japoniea (Ishizaki)

/

+

6

9
II

+
+
+
+
+

C)
HIR-5S (Howeina higashimeyaensis Ishizaki
Uroeythereis? sp. B
Neomonoeeratina japoniea (Ishizaki)
Finmarehinella (Barentsovia) nealei Okada
Callistoeythere se/anensis Hanai

20
17
15
14
9

12
19
13
13
12

+
+
+
+
+

TAl-IS (x. 0)
Uroeythereis? gorokuensis Ishizaki
Keijella ? sp. A
Callis/oey/here retieulata Hanai
Cytherop/eron sawanense Hanai
Cytherura sp. C
Paijenborehella tsurugasakensis Tabuki

21
8
8
7
0
6

18
6
8
7
7
6

+
+
+
+

TAI-2S (0. C)
Uroeythereis ? gorokuensis Ishizaki
Normanieythere japoniea Tabuki
Paijenborehella /surugasakensis Tabuki
Paijenborehella hanaii Tabuki
Pa/agonaey/here robusta Tabuki

66
35
21
12
6

52
36
14
12
7

+
+
+
+
+

C)
TAI-3S (Finmarehinella (Baren/sOl'ia) nealei Okada
Uroeythereis ? gorokuensis Ishizaki
Howeina higashimeyaensis Ishizaki
Callistoey/here retieulata Hanai
Munseyella ha/ata/ensis Ishizaki

12
9
10
9
7

15
14
4
7
4

+
+
+
+
+

..

..

/

+

Toshiaki Irizuki

312(Barentsovia) japoniea (HAT -4S, HAT - 7S,
KOS-3S); Cornueoquimba moniwensis(HAT -5S, HT A-7S); Cornueoquimba saitoi(Ishizaki) (HAT -3S, HA T -5S); Cytheropteron sawanense (HAT - 6S); and Sehizocythere okhotskensis (KOS-l S).
It is notable to see that more species were
rejected in Type II than in Type I sediments.
f) The number of species, diversity andequitability in HAT -section
Successive changes of the number of
species, species diversity, and equitability
were examined in HAT-section where theSasaoka Formation in composed of 120 m
thick silty sandstone with rare intercalationsof granule conglomerate beds. Seven samples consist entirely of Type II sediments, ofwhich six (except for HAT-IS) belong tocluster A. Figure 14 shows density (specimens/I g sediments), the number of species,
species diversity (H(S)J, equitability, percentages of cold water species and shallow
water species, and mud content. Cold water

forms were selected from the large literature(Cronin, 1981; Cronin and Ikeya, 1987;
Hanai, 1970; Hazel, 1967, 1968; Ishizaki,
1966, 1971 ; Ishizaki and Matoba, 1985;
Neale, 1974a, 1974b; Neale and Howe, 1975;
Neale and Schmidt, 1967; Okada, 1979;
Schornikov, 1974; Siddiqui and Grigg,
1975; Swain, 1963; Swain and Gilby, 1974;
and Tabuki, 1986) as follows; Baffinieythere, Elofsonella, Finmarehinella,Hemieythere, Howeina, Muellerina, Normanieythere, Palmenella, Uroeythereis?,Cythere boreokurla, Cythere uranipponiea
Hanai, Callistoeythere setanensis Hanai,
Cytheropteron sawanense, Munseyella hokkaidoana Hanai, Patagonaeythere robusta
Tabuki, Sehizoeythere okhotskensis andSemieytherura subundata (Hanai). The following upper sublittoral forms were pickedout from such accounts as Ishizaki (1971),
Ikeya and Hanai (1982), and Tabuki (1986) :Aurila, Callistoeythere, Hemieytherura, Loxoeoneha, Pontoeythere, Robustaurila, Xestoleberis, Neonesidea mutsuensis (lshizaki),

T-7S

Em1

~4

~2

~5

m3 B6

3
10
15 60 70 80 903.0 3.5 4.00.5 0.6 0.7 50 40 30
10
20 3040 50 60 70 (%)
NUMBER OF
NUMBER OF
H(S)PERCENTAGES PERCENTAGESMUDINDIVIDUALS/lg
SPECIESEQUITABILITYOF
OF
CONTENT
COLD-WATER SHALLOW-WATERSPECIESSPECIES

Figure 14. Vertical changes of various aspects of ostracode faunas and mud content in HAT-section.
I : well-sorted fine sandstone (Type I), 2: silty sandstone (Type II), 3: alternations of Type I and Type II,
4: well-sorted granule conglomerate, 5: mudstone, 6: shell beds.

891.

Ostracodes from Sasaoka Formation

Pistocythereis bra dyform is (lshizaki),
Schizocythere kishinouyei (Kajiyama), andSemicytherura miurensis (Hanai). They are
dwellers on algae and sand bottoms at depths
less than about 10 to 20 m.
Excepting mud content, six of the parameters correlate to each other: samples which
include many shallow water species and few
cold water species are represented by highvalues of density, H(S), equitability andlarge numbers of species. Certainly, theseassemblages in HAT-section display changes
in diversity and equitability depending on thenumber of species. Such consistencies leadto the following three hypotheses: I) Relative decreases in number of cold water species
and high values of H(S) have resulted fromperiodic inflows of warm water masses; 2)
The value of H(S) and relative frequencies ofshallow water species have fluctuated inaccordance with sea level changes resulting
from isostatic or tectonic movements; 3)
Depth changes were negligible, and relative
quantities of displaced specimens from shallower into deeper areas brought about
fluctuations of H(S).
It is necessary to discuss these hypotheses so
as to figure out the most working one. It is
certain that there were periodic inflows ofwarm water masses, as indicated by the occurrence of Globorotalia injlata (d'Orbigny).
Unlike any other group such as molluscs orforaminifers, benthic ostracodes have no planktonic life even in their larval stages, thus
their ability of dispersion seems to be lower.
Small percentages of warm water species[Loxoconcha optima, Pacambocythere spp.,
Proteoconcha spp., Kangarina spp.,
Schizocythere kishinouyei, and Xestoleberis
sagamiensis (Kajiyama )J are not enough tobring about fluctuations of the number of
species. Mud contents of six samples except
for HAT -I S are about 40-60%. These samples resemble each other and are assigned toType II sediments. Adult specimens occurring along HAT-section are less than 20% in
HA T -3S and HAT -SS, less than 30% in the313

others. That is to say, the continuation of
the same sediment type and the dominantoccurrence of small and juvenile valves showthat the third hypothesis is more probablethan the second.
Depositional environment of the Sasaoka
Formation

On the basis of the results mentioned
above, the depositional environment of the
Sasaoka Formation will be discussed in thefollowing lines (Figure IS). Six samples
belonging to cluster A are under Type II
sediments (massive silty sandstone), and characterized by a large number of species, fewer
adult valves than those of any other clusters,
and dominant species with ratios of right toleft valves significantly different from I: 1.
Argilloecia spp. and Propontocypris spp.
which inhabit largely outer sublittoral silty
sediments and Robertsonites reticuliforma
which is commonly contained in the Tentokuji Formation are recognized. Fossil
assemblages in cluster A contain fragile juvenile valves. According to Whatley (1983),
their percentages are comparable with thoseof biocoenosis. However, it is certain that
there are both upper and lower sublittoral
species, and as the result of chi-square test,
some small valves are thought to have beentransported in the state of suspension fromhigh-energy environments into relatively deepand stagnant areas in which are being preserved original assemblages containing small
juveniles to adults because of low-energy. It
seems that such displacement from upper
sublittoral areas and preservability of in situ
valves led to a large number of species.
Five samples in cluster B are under Type I
sediments, and are characterized by highspecies diversity and equitability, relative tomoderate numbers of species, and containdominant large hard valves and only a small
number of juvenile valves. This shows thatthe valves may have been lag material behindstrong currents - the majority of juvenile

Toshiaki Irizuki

314

-

".-

// "

1/

1/
II

ClusterA
B

C

0

Sediment
Type

No. ofH(S)species

HAT 253545
HAT 556575
K0515
K05 2535
H IR 152545
HAT15

MainlyTYPE II58 - 92

MainlyTYPE I

50 -76

HIR 55
TAl 35TYPE I

44 -47--------TAl 25TYPE II43

2.66 0.33

CommonTAilS

TYPE I66

3.71 0.62 Abundant

Sample------ --------

E

3.70 0.57
II

4.13 0.72

'X}

Large
valves

test

Few

X

Lower
subl ittoral

3.42 0.58

Paleodepth

I

I

Abundant0

Lower
sublittora I

I

I

Abundant0

Uppersublittoral

3.91 0.77
3.32 0.63

3.46 0.68---- fo---- ---------Upper00sublittoral
Upper
sublittoral

Figure 15. Idealized diagram showing the formative process of ostracode biotopes (A, B, C and D) in
the Sasaoka Formation. Broken and solid arrows represent suspension and rotation, respectively and show
relative abundances of displaced ostracodes. 0: Acceptance X: Rejection

valves may have been transported into deeper
places. As the species with thick carapaces,coming under, for example, Cornueoquimbaand Uroeythereis? have strong hinges, they
were preserved in the state of intact carapaces
rather than valves, thus their ratio of right toleft valves is close to 1 : 1.
T AI-3S and HIR-5S in cluster C are underType I sediments with main peaks at less than
3 tP and mud contents of 7.8 and 11.1%,
respectively. These values are lower thanthose of many samples in cluster B and show
strong current conditions. Those two samples are characterized by lower values of
species diversity and a smaller number of
species than those of clusters A and B, and bya large number of adult valves (73.2% in T AI3S and 63.4% in HIR-5S). There exist no
such deep water species as Robertsonites
retieuliforma but Callistoeythere spp. in abundance in both samples, which inhabit upper
sublittoral sandy sediments. Fossil assem-

891.

Ostracodes from Sasaoka Formation

blages in both T AI-3S and HIR-5S are represented only by valves more resistant against
physical agents than those in cluster Bandmay have remained selectively on the upper
sublittoral area, leading to lower species
diversity and numbers of species. T AI-2S inthe same cluster C is, however, different fromthose two samples in age composition andsediment grain size. It belongs to Type II(silty sandstone) and contains not only fragile
juvenile valves but also large adult valves.
The most dominant species, Urocythereis?
gorokuensis (66/207 total specimens), isabundant on shallower mud to silty mud in
Aomori Bay (lshizaki, 1971). The su bordinate species, Paijenborchella tsurugasakensis(21/207 total specimens), also inhabits bay
areas (Hanai and Yamaguchi, 1987). About
70% of specimens in T AI-2S are dominatedby five species (142/207 total specimens). It
seems, therefore, that fossil assemblage in
T AI-2S may have inhabited a calm sea andhas not been modified in comparison withthose in any other samples. Namely, suchspecies as Urocythereis? gorokuensis,
Normanicythere japonica, and Paijenborchella tsurugasakensis dominated largely theirown ecological niches, and into this low
equitability assemblage, some species weretransported from high-energy environments,
leading to 40 species. Such being the case,cluster C spans two types of sediment whichyield different compositions of fossil assemblages.
Cluster D is very different from other clusters. The dominant species such as Pontocythere spp., Callistocythere spp. and Loxoconcha optima and abundant in coastal
shallow areas. The sample in this cluster
belongs to Type I sediments which have themain peak at 3 cP and a mud content of 13.4%,
presenting the shallowest area where coastal
currents were relatively strong, and possibly,
large valves of such species as Urocythereis?
gorokuensis and Paijenborchella tsurugasakensis were transported from a calm sea tomix with those sand dwellers.

315

The above results show shallowing of depositional environments of the Sasaoka Formation upward in the sequence and southeastward (Figures 7, 9). It is noteworthy that
our inference of depositional environments
has to be made both on the sedimentologicaland ecological sides of ostracode assemblages
because the assemblages in all samples except
for those of T AI-2S were under strong
influences of current winnowing. The valuesof species diversity and equitability, determined in this study, are those modified owing
to physical agents, and do not involve much
ecological meaning.
Concludng remarks

Three conclusions reached through cluster
analysis of fossil ostracode data obtained
from the Sasaoka Formation, examination ofvaried parameters with respect to ostracodeassemblages, and grain size analysis of sediments containing fossil ostracodes are as follows:
1) Fossil ostracode assemblages in the
Sasaoka Formation are characterized, in general, by circumpolar and cryophilic species
which are common in the Omma-Manganji
Fauna in Japan (Cronin and Ikeya, 1987).
2) Sedimentological and ostracode faunalanalyses show that the Sasaoka Formation
was deposited under cold and upper to lower
sublittoral environments, where high-energy
currents largely modified the original (in situ)
ostracode assemblages.
3) In interpreting depositional environments by using fossil ostracodes, a factor that
seems to be of prime importance is theirindigenity which should be assessed fromboth sedimentological and paleontologicalaspects.
Acknowledgments

The author expresses his deep gratitude toProfessors Yokichi Takayanagi and Kunihiro
Ishizaki, of the Institute of Geology andToshiaki Irizuki

316

Paleontology, Faculty of Science, Tohoku
Univerity, for advice and continuous encouragement throughout the course of the present
study and critical reading of the manuscript.
Deep appreciations are also expressed to Dr.
Shiro Hasegawa of the same institute and Dr.
Kyu-Kui lung, a former graduate student at
the same institute, for constructive discussions
and suggestions. The author is muchindebted to Professor Koji Minoura and Mr.
Toshiaki Susaki, of the Institute of Geology
and Paleontology, Faculty of Science, Tohoku University, and Mr. Kazutoshi Fujioka
of Takigashira Elementary School, for helpful advice and discussion concerning sedimentology.

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Ostracodes from Sasaoka Formation- - and Nicolich, M.l., 1979: On the response of
ostracode valves and carapaces to water currents.
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Ozawa, A., Kano, H., l\1aruyama, T., Tsuchiya, N.,
Ito, M., Hirayama, J. and Shinada, S., 1981:
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Gubik Formation, Arctic coastal plain, Alaska.
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Ostracoda from the Pacific coast of North andCentral America. Micropaleontology, vol. 20,
no. 3, p. 257-352, pis. 1-7.
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to palaeoenvironmental analysis. In Maddocks,
R.F., ed., Applications of Ostracoda. Department of Geosciences, University of Houston, p.
51-77, Houston.
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Ellis Horwood Limited, Chichester.

Bonjigawa ~T)II, Funakawa 1J{})II, Hatsutagawa j\EE)II, Hirasawa ~iR, Iwamigawa!6Ji!.)II, Iwamisannai !6Ji!.=::.Ii3, Iwamisugisawagawa !6Ji!.t~IR)II, Jinnaigawa fillli3)lI, Kainosaw a ~ / iR, Kamikitate J:~t-=F, Kamisannai J:=::.Ii3, Katsurane tEfft Kogurogawa 'h~)11, Kogurosawagawa 'hW<iR) 1I, Kurosawa ~iR, Kyogamisaki l\?E?" i111jl, Noda !!!fEE, Obarino:7d~!!!f, Omma-Manganji *~- nD:~, Onnagawa:9:)II, Sannaigawa =::.Ii3)11, Saraminaizawa .DIl.Ji!.li3iR, Sasaoka tftllUJ, Shimokitate T~t-=F, Souyakyo i111l.1:l'~, Sunakobuchi 1i'YT~J,
Taiheigawa ::k~)II, Takaoka ~1lUJ, Tentokuji 7(~~, Tsukushimori ~~~, Wada ;fOEE.
~EE*tftllUJ~.~~~~E5.-~~~~.OO~~~~~-:~EE*.EK~~~~tft
llUJ~iJ'l? 71 ~ 216 ~~~~~{r.Ez..1:±:l LI-:o t..tLl?fi.~IlD-c~~l*1t~~\"5.H1inJ(;~ ~o -~t:::.:mtE B::ifi:Jli:w,

317

btlfittJT- ]l!tJT~iJ' I?~~, tif~~~~ ~, ~t~f,!11;llt:::.m1:.

Toshiaki Irizuki

318

i" G Acanthocythereis dunelmensis (Sars), Hemicythere emerginata (Sars), Elofsonella
concinna (Jones), Palmenella limicola (Noman) tt. c' i7;.r¥-~i" G 0.::h I? Q)*V1E*:fi~;::1Jrl:t, ~iI~w--n::.1:..~ i" G1B!V1E*:fii7~, I. 'T:hQ) -tj-:/ 7' IV~;:: ~,~ % ~!jHl~"!:h G t)J:Q) J'iJ~.!R{r.E~~~ Q ~ - f? '77-. !J -?t;tJf 1.... tdi§* 4 "?Q)? '7
7-.!J- (A,B,C,D) i7;~,gIj~:ht.:o '::h~~c~;::tQ:jlliJJ!Q):It.~~~1!E~1....t.:o -tQ)~,{r.E c 1.... -cf*;ff: ~:h G"! -e~;::~H-t.:¥.oI1l~~~, -t :h~;:: J: -? -C 1:. t: tdl~~.~Q)~{r.~~lti" Gt.:/Jb, :It.¥lJQ)*,.:'l!l?t;tJf~rrtt.I.', -tQ)~* ~~*Q) J'lJ~.!F.W!:Q)-tj-1~, leW!:~mtQ).l:~*, .Ql(;{;$:mtQ)~tl1t, :fi~~!l' ~lI!lQ)~{r.H~~ 1...., q!(/Jb-C 4 "?Q)? '77-.!J ~~~ 1.... t.:o -~jIH;::, ¥lJI1l~~~i7;Jt~.!R{r.E~~Q)?t;(Pt;::~*tt.~W~~:t -C:to IJ, :It0cc.~~Q)M;tJf~;::~t.: IJ, Jt~.!F.Q)1:.~~~{JItllIDQ)~tt.I?T, :It.~~{JIUlID~ ~~li~;::I.':htt.H-:hlitt.1? tt. HfHJH7U~7f-i" 0
AJ:! ~~

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 156, pp. 319-342, 13 Figs., December 30, 1989

892. SYSTEMATICS OF THE AMMONITE GENUS TETRAGONITESFROM THE UPPER CRETACEOUS OF HOKKAIDO*Y ASUNARI SHIGET A
Geological Institute, University of Tokyo,
Tokyo 113, Japan

Abstract. The ammonite genus Tetragonites (Lytoceratina, Lytocerataceae) from theUpper Cretaceous (Turonian to Maastrichtian) of Hokkaido includes three species: T.
glabrus (Jimbo), T. minimus, n. sp. and T. terminus, n. sp., based on the shell size, apertural
shape and early internal shell structure. Although the three species are similar in external
shell shape, they are clearly distinguishable from one another on the basis of the above
characters without any intermediate form.
T. glabrus, occurring in the Middle Turonian to the Upper Campanian, exhibits
remarkable variation in shell form, and the previously described species T. sphaeronotus(Jimbo), T. crassus (Jimbo), T. popetensis Yabe and T. glabrus problematicus Matsumoto
should all be regarded as synonyms of this species. The specimens illustrated as T.
superstes Van Hoepen and T. epigonus Kossmat from Hokkaido are also identified with thisspecies. T. glabrus shows a chronocline in which the sizes of initial chamber and ammonitella decrease with time. T. minimus, n. sp., occurring from the Lower Turonian to theUpper Campanian, is much smaller in adult shell size (less than 30 mm in diameter) than T.
glabrus, and shows also a chronocline of miniaturization in adult shell size and of narrower
umbilicus toward later forms. T. terminus, n. sp., restricted to the Lower Maastrichtian, has
an unusually large embryonic shell and a peculiar early internal shell structure.
Key words.
shell structure.

Tetragonites, Upper Cretaceous, Hokkaido, variation, aperture, internal

Maastrichtian sequences of the Yezo Groupor Yezo Supergroup (Okada, 1979, 1983) in
Hokkaido, and are relatively common in theTuronian to the Campanian horizons (e.g.
Matsumoto, 1942a, 1943; Tanabe et ai.,1977).
In spite of the seemingly conservative shellcharacters, this genus includes many "species"
based on the external shell characters (i.e.
whorl shape and ornamentation). However,taxonomic validity of these characters has notbeen confirmed by studies of large samples.
Furthermore, more critical characters such as
early internal shell features have little been
investigated in Tetragonites.
In this paper, I evaluate the taxonomic
validity of various morphological characters

Introduction

The genus Tetragonites, established by
Kossmat in 1895, is considered to be one ofthe derivatives from the lytoceratid main
stock (Murphy, 1967b). It was defined by
the suture formula ELU 2 U 3 ( = S)U lIs, irregularly bifid or trifid termination for the firstlateral saddle (EjL), and nearly symmetricallobe (L) (Drushchits and Mikhailova, 1976;
Krivoshapkina, 1978). Tetragonites ranges
from the Late Aptian to the Early Maastrichtian, having an almost world-wide distribution (Collignon, 1956). Specimens of thisgenus occur in the Albian to the Lower'Received May 15, 1989; revised manuscript accepted
November 18, 1989
319

Yasunari Shigeta

320

in specimens of Tetragonites from horizons in
the Upper Cretaceous of Hokkaido, anddiscuss the systematics of Tetragonites.
Previous studies
Haboro area

Japanese species of Tetragonites were firstdescribed by Jimbo (1894) from the Upper
Cretaceous Yezo Group of Hokkaido. He
distinguished three species based on umbilical shape and ornamentation: Lytoceras
glabrum, L. sphaeronotum and L. crassum.
One of the two syntypes of L. sphaeronotum
was later regarded by Matsumoto (1942b) as avariety of Epigoniceras glabrum (Jimbo).
Tetragonites epigonus Kossmat was proposedby Spath (1925) as the type species for the
genus Epigoniceras, but Howarth (1958)
pointed out that this genus is a synonym of
Tetragonites. The other syntype of L.
sphaeronotum is a deformed specimen of
Desmophyllites cf. diphylloides (Forbes)(Matsumoto, 1942b, 1963).
Yabe (1903) pointed out that the holotypeof L. crassum could be an immature example
of T. glabrus (Jimbo). Later, this specimen
was regarded by Matsumoto (1942b) as avariety of E. glabrum (Jimbo). Matsumoto( 1942b ) also described a varietal form of thisspecies from Sakhalin as E. glabrum var.
problematica, but later he regarded it as asubspecies, T. glabrus problematicus (Matsumoto, 1959). The fourth species was described by Yabe (1903) as T. popetensis.
Afterwards, Matsumoto (1942b) reported avarietal form of this species as E. pope tense
var. frequence, but detailed description andillustration of the shell were not presented.
Several specimens of Tetragonites from theYezo Group were hitherto referred to thefollowing species that were originally described from abroad: T. epigonus Kossmat
reported by Yabe (1903) and T. superstes
Van Hoepen by Matsumoto and Miyauchi(1984).

Nukibetsu area

o

100km

~

Figure 1. Map showing the distribution ofCretaceous deposits in the central zone of Hokkaido(dotted) and sampling areas of the specimens
examined.

Material and methods
Material: A total 320 specimens belonging to 48 samples of Tetragonites were
examined in this study (Table 1). These
specimens were collected from the Upper
Cretaceous (Turonian to Maastrichtian)deposits of Soya, Saku, Toyoshimizu, Haboro, Kotanbetsu, Tappu, Tomiuchi andNukibetsu areas from north to south of
Hokkaido (Figure 1).
Specimens in each sample were extracted
from several calcareous nodules at the same
horizon in an outcrop (AWlOOIA, AWlO03,
SM1048 and SFl104) or from a single nodule(remaining samples). The localities andbiostratigraphic ages of the samples examined
are summarized in Table 1. All specimens
are kept at the University Museum, Universityof Tokyo (UMUT).
Analysis of external shell morphology:
A total 229 specimens (Table 1) were used
for the biometric analysis of the shell

892.

Systematics of Tetragonites from Hokkaido

321

Table 1.

List of material. Specimens used in SEM observation are shown in parentheses. For details ofsampling localities with the following prefixes see the following papers; Hand T (except for
TI220): Matsumoto (1942a), W: Matsumoto and Miyauchi (1984), Nk: Kanie et al. (1981),
RH, RK and RO: Toshimitsu (1988), R: Tanabe et al. (1977), and T1220: Sekine et al.
( 1985).

SampleN Registered number

SM10488SM1041
3
SF1104
6
AW1001A 110
AW1001B
3
AW100318
AS2038A
7AS2038B
9AS3027A
3
AS3027B
1
AS3014P
1
AS-TYl3
SN1001
2
SN2001
1
TP422
2AH3064
7
AH4032
3
AH10182
AH6033P
1
AK1029A
1
AK1029B
4
AK1033
3
AK10182
AT-AR1A
1
AT-AR1B
2
AT802514
AT8026
1
AT151410AT8023
1
AT7067
1
AH40872
AT6003
2
AT1551
1
AS10006AT1206
3
AT1201A 15
AT1201B
3
AT1207
6
AT1208
11
AT1214
2
AT1202
5
AT1103
13
AT1575
5
AT1578
7
AT1577
1
AT15622
AW2001P
2
AT21004

Locality

UMUT MM18635 [1-6,(7,8)]
Tomiuchi,H12d
UMUT MM18636 [(1-3)]
Tomiuchi,H12a
UMUT MM18637 [1-3,(4-6)]
Tomiuchi,Tonaizawa.R.
UMUT MM18638 [1-90, (91-110)] Soya,W7A
Soya,W7A
UMUT MM18639 [1-3]UMUT MM18640 [1-15,(16-18)] Soya,W7C
UMUT MM18641 [1-6,(7)]Saku,T313
UMUT MM18642 [l-5 j (6-9)]
Saku,T313
UMUT MM18643 [1-3
Saku,T205
UMUT MM18644 [1 ]Saku,T205
UMUT MM18645 [1]Saku,T208
UMUT MM18646 [(1-3)]
Toyoshimizu,Teshio R.
UMUT MM18647 [l j 2]
Nukibetsu,Nk11
UMUT MM18648 [1Nukibetsu,Soushibetsu R.
UMUT MM18649 [1,2]Tappu,Akanosawa R.
Haboro,RH1262
UMUT MM18650 [1,(2-7)]
Haboro,RH4032
UMUT MM18651 [1,(2,3)]
Haboro,RH5036
UMUT MM18652 [lj2]Haboro,RH5107
UMUT MM18653 [1Kotanbetsu,RK0043
UMUT MM18654 [1]Kotanbetsu,RK0043
UMUT MM18655 [l-3 j (4)]Kotanbetsu,RK0046
UMUT MM18656 [1-3
Kotanbetsu,RK0030
UMUT MM18657 [1~2]Tappu,Arakizawa R.
UMUT MM18658 [lJ
Tappu,Arakizawa R.
UMUT MM18659 [1,(2)]Tappu,R2663
UMUT MM18660 [1-13,(14)]Tappu,R2665
UMUT MM18661 [1]Tappu,Kawakami
UMUT MM18662 [1-10]
Tappu,R2662
UMUT MM18663 [1]Tappu,R2185
UMUT MM18664 [1]Haboro,RH2131
UMUT MM18665 [(1,2)]
Tappu,R2144
UMUT MM18666 [(1,2)]
Tappu,T1220
UMUT MM18667 [1]Saku,T679
UMUT MM18668 [1-5,(6)]Tappu,R4016
UMUT MM18669 [1,(2,3)]
Tappu,R4018
UMUT MM18670 [l-4 j (5-15)]
Tappu,R4018
UMUT MM18671 [1-3Tappu,R4019
UMUT MM18672 [1,2,(3-6)]
Tappu,R4020
UMUT MM18673 [1-5, (6-11)]
Tappu,R7001
UMUT MM18674 [(1,2)]
Tappu,R4017
UMUT MM18675 [1-5]UMUT MM18676 [1-10, (11-13)] Tappu,R4001
Tappu,R2115
UMUT MM18 6 77 [(1-5)]
Tappu,R2110
UMUT MM18678 [1-4,(5-7)]
Tappu,R2113
UMUT MM18679 [1]Tappu,R2129
UMUT MM18680 [1,2]Soya,Higashiura
UMUT MM18681 [1,2]Tappu,R6394
UMUT MM18682 [1-4]form. Shell diameter (D), umbilical diameter(U), whorl height (H) and whorl breadth (B)were measured with the aid of a slide caliper(accuracy, ± 0.05 mm) and two geometric

HorizonL. Maast.
L. Maast.
L. Maast.

Up. Camp.
Up. Camp.
L. Camp.
L. Camp.
L. Camp.
L. Camp.
L. Camp.
L. Camp.
L. Camp.
L. Camp.
L. Camp.
Up. Santo
L. Sant.
L. Santo
L. Sant.
L. Santo
L. Santo
L. Santo
L. Santo
L. Santo
L. Sant.
L. Santo
L. Santo
L. Santo
L. Santo
L. Sant.
L. Santo
Con.
Con.
Con.
Up. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
Mid. Tur.
L. Tur.
L. Tur.

parameters: relative umbilical size (U /D) andrelative whorl thickness (B/H), were calculated for each specimen (abbreviations used in
the text are shown in parentheses) (Figure 2).

Yasunari Shigeta

322

c

B

A

adapicalt

Diameter~concave adoral' -_ _ _ _.-/ straightpreserved shell~ convex

adoral~adoralkeel-like elevation
primary constriction

1/

E

D
venter----.-----::;;:00--__ peripheral
shoulderflank-- umbilical edge............. umbilicale wall

Figure 2. Morphology and measurements of Tetragonites. A. Lateral view. B. Ventral view.
Apertural margin on the venter. D. Whorl cross section. E. Early whorls in median section.

Additionally, 7 specimens (UMUT MM
18638-1-4, MM 18642-5, MM 18678-4, MM
18637-3) were selected and prepared in thefollowing manner for ontogenetic study of theshell form. Every specimen was cut andpolished along the median plane, and subsequently the "median-sectioned" specimen
was also cut along a plane perpendicular tothe polished surface at the base of the caecum.
The cross-sectioned surface was etched with
10% acetic acid for two to three minutes, andthen an acetate peel was prepared by pressing
a sheet of triacetylcellulose film (25 pm inthickness) onto the etched surface while it isflooded with acetone. The four portions (D,U, H, B/2) were measured at intervals of a
halfvolution (90°) on the peeled cross section

C.

using a digital micrometer (accuracy± 1 pm)
attached to a profile projector (Nikon Model
V-16D).
Analysis of early internal shell morphology: A total 236 specimens (Table 1) wereused for observations of early internal shellmorphology. For this purpose every specimen was cut and polished along the medianplane, and the internal features of early
whorls in median section were observed
under a binocular microscope with magnification of 20 times. Moreover, 91 specimens
among them were prepared in the following
manner for scanning electron microscopy.
The polished median plane of each specimen
was etched with 5% acetic acid for one to two~
Figure 3. Diagrams of early internal shell structural types of Tetragonites in median section. A; IA
type. Band C; IB type. D and E; IC type. Terminologies from Branco (1879-80), Grandjean (1910),
Drushchits and Khiami (1970). am: ammonitella, amw: ammonitella wall, c: caecum, f: flange, ic:
initial chamber, icw: initial chamber wall, na: neck-like attachment, pc: primary constriction, ps: proseptum, psh: prosiphon, sp: siphunclar tube.

892.

Systematics of Tetragonites from Hokkaido

323

B

A
am

\

na

c

E

324

Yasunari Shigeta

minutes, and the etched surface was thencoated with platinum using an ioncoater(Eiko Engineering Model IB-5). The earlyinternal features of each specimen were thenobserved by means of a scanning electron
microscope (SEM) (Hitachi Model S-430).
The following three characters were measured
on the enlarged SEM photograph (X 100- X
500): maximum initial chamber size, ammonitella size and ammonitella length (Figure 2).
Shell morphology of Tetragonites
External shell morphology: As shown
diagrammatically in Figure 2, most of thespecimens examined possess a round to subrectangular whorl section and a fairly narrow(U/0=0.20) to wide (U/0=0.37) umbilicus
in the middle to late growth stage. The
umbilicus is surrounded by a nearly verticalto subvertical wall, and has a subangular toabruptly rounded shoulder. The outer shellsurface is nearly smooth throughout the postammonitella stage, and is marked only withfine and dense growth lines and rib-like weakelevations. Some specimens have a keel-likeelevation on the venter in the middle to late
growth stage. In many specimens the apertural margin is strongly prorsiradiate on theflank and possesses an adorally concave sinus
on the venter. Some specimens, however,
have an ado rally convex aperture on theventer. These two apertural types are distinct, with any intermediate form between
them.
Internal shell structure: The early
whorls of Tetragonites consist of initial chamber (= "protoconch"), proseptum, caecum,prosiphon, flange, septa, siphuncular tube
and outer shell wall (Figure 3, for details ofthese structures, see Ohtsuka, 1986), as inother Mesozoic Ammonoidea. The earlyinternal features of the specimens can bedivided into three types; here named lA, IB
and IC types (Figure 3).

IA type (Figures 3A and IIA-B) - The
initial chamber is nearly circular in mediansection. Caecum is subellipsoid with aweakly constricted base at the connected
portion with proseptum. One to three short,adorally concave prosiphons extend from theadapical portion of caecum to the inner sideof initial chamber. Initial chamber wallconnects with pro septum at the dorsal side of
caecum, forming an indistinct short flange.
Siphuncle occupies a central position in theearliest portion of the first whorl near theproseptum, but rapidly shifts toward the ventral side near the second or third septum.
Thereafter, it retains a ventral position.
IB type (Figures 3B-C and IIC-O) - The
initial chamber is nearly circular in mediansection. Caecum is hemispherical with astrongly constricted base; hence the shape ofthe earliest portion of the caecum-siphuncle
system is like a mushroom. It is linked with
the inner surface of the initial chamber wallby one to three short, ado rally concave prosiphons. Flange is short as in IA type, and issometimes obscure in some specimens. Siphuncle is initially located at a central position in the early portion of the first whorl,and subsequently shifts its position gradually
toward the venter. The marginal approximation of siphuncle is completed at the end of
the first to second whorls.
IC type (Figures 30-E and liE-F) - The
initial chamber is nearly circular in mediansection. The caecum is elongate and subelliptical, without a conspicuous constrictedbase. It is connected with the inner surface
of initial chamber by a relatively long andnearly straight prosiphon. Proseptum resting on the ventral side of initial chamber wall
is long, and acutely projects toward the
caecum. Early portion of the first whorl
swells markedly as a result of discordantunderlay of the ammonitella wall with theinitial chamber wall. Siphuncle is initiallylocated at dorsal side. At the middle part of
the first camera it makes an abrupt turninward, and thereafter it immediately approx-

892.

Systematics of Tetragonites from Hokkaido

imates to the ventral side within the secondthird camerae. The first septum is adorally
concave, but subsequent septa are adorally
convex.
The above characteristic features of theearly internal shell structure are consistent inall the examined specimens of each type, andno intermediate forms have been found.

share the same apertural shape. Diagnostic
features of each group other than the earlyshell structure are summarized below.
Group A: Specimens of this group possess
the early internal morphology of IA type andado rally concave sinus of aperture on theventer. They exhibit wide but continuous
variation in overall shell shape; a round to
subrectangular whorl section and a fairly
narrow to wide umbilicus. Specimens of thisgroup were collected from the Middle Turonian to the Upper Campanian of many areas of
Hokkaido. Morphologic variation in thespecimens from various horizons is summarized as follows.
Variation in juvenile stage - Specimens of
this group show wide variation in the sizes of
initial chamber and ammonitella in mediansection, ranging from 475 to 875 J-lm and from
900 to 1,700 J-lm in diameter, respectively

Grouping of specimens

The 236 specimens studied in median section can be classified into three groups, A, B,
and C, based on the characteristic features inthe early internal shell structure and apertural
shape (Table 2). The 84 specimens used forobservations of external morphology can also
be classified into the above three groups byusing the differences in adult shell size andapertural shape, because the specimens withthe same early internal shell structural type
Table 2.
Sample325

Classification of 236 specimens of Tetragonites based on the early internal shell morphology andapertural shape. CC: adorally concave, CV: ado rally convex.
No.

MM18638 (1-110)
AW100lMM18640 (9-18)
AW1003
AS2038A MM18641 (1-7)
AS3027A MM18643 (1-3)
MM18646 (1-3)
AS-TYlMM18650 (2-7)
AH3064
MM18651 (2,3)
AH4032
MM18660 (5-14)
AT8025
MM18665 (1,2)
AH4087
MM18666 (1,2)
AT6003
MM18668 (1-6)
AS1000MM18669 (2,3)
AT1206
AT1201A MM18670 (5-15)
MM18672 (3-6)
AT1207
MM18673 (4-11 )AT1208MM18674 (1,2)
AT1214
MM18675 (1-5)
AT1202
MM18676 (1-13)
AT1103
MM18677 (1-5}
AT1575
AS2038B MM18642 (3-9)
AS3027B MM18644 (1)AT-AR1B MM18659 (1,2)
AK1029B MM18655 (4)MM18678 (2-7}
AT1578MM18635 (7,8)
SM1048MM18636 (1-3)
SM1041
MM18637 (4-6)
SF1104

N

110
10
7
3
3
6
2
10
2
2
6
2
11
4
8
2
5
13
5
7
1
2
1
6
2
3
3

Internal morEhology
Ie
IB
IA

x
x

AEerture
ev
ee
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

Group A

X
X
X
X
X

X
X
X
X
X
X
X
X

X
X
X

Group

Group B

Group eYasunari Shigeta

326

contrast, less variable than the ammonitella
size. The sample mean of the Turonian specimens is larger by 10° than that of theCampanian specimens, but the difference is
not significant statistically (Figure 9).
Variation in the middle to late growthstage - Wide variation in the shell shape is(Figure 8). The extent of variation of thetwo measurements is, however, reduced in
specimens selected from a stratigraphic interval, and furthermore both sizes tend to
decrease upwards in stratigraphic succession(Figure 8).
The spiral length of the ammonitella is, in
Up. Campanian

0.4 N=90
UfO..

.... . ~.....
.., ..
•~...

.. . ••••....•• ••... •,:• . ••

0.3

~.

•

• •
•

•
.....
••
• •

••

L. Santonian (lower part)

N=25

•
••

•

•

•

0.2

0.4

•

• • •••.: ... • •

..

•

•

• • •
•

L. Campanian

N=28

UfO

0.3

•

••

•

0.2

0.4

L. Santonian (upper part)

N=13

N=2

• ••
• I y •y ..

• • •••••

Up. SantonianMid. Turonian

N=30

UfO

•

•

0.3

•

.~

• ••••
••

•

0.2

10

20

30 4050

D ameter

(m m)

.

•
• '\
• • ••

•
100

10

20

30 4050

Diameter

100

(m m)

Figure 4. Semi-logarithmic diagram showing the relationship between umbilicus/diameter ratio (U/D)
and shell diameter (D) for middle- to large-sized specimens of Group A from different horizons. Turonianand most Santonian specimens tend to become narrowly umbilicate with growth. Campanian specimens
exhibit wide variation in U/D ratio, even in the middle to late growth stages.

892.
1.4

,
.. . ."'...... ..
.....
••
• ••
•

N=90

8tH

......".:.. ..
·.. ...
· .. 'r·. ·•L. Campanian

••

...'.

••

.~

•

•

,•

••

1.0

•

•

•
••

•

••
••

•
•••••

•• ••
•
• •

•

Up. Santonian

N=2

L. Santonian (lower part)N=25••• • •
•

•

1.2

1.4

•
• • • • ••
•
•

•

N=28

•

•

••

· •te···:·-.
•••
•

327

L. Santonian (upper part)

N=13

•

: --

•

1.0

8tH

Up. Campanian

~

1.2

1.4

Systematics of Tetragonites from Hokkaido• ••• • •
I
I;. •
•
•
• ••
••
•
•• •
•• •

1.2

•

•

Mid. Turonian

N=30

8tH

•

•

•

1.0

10

20

30 40 50

Diameter

(mm)

100

10

20

30 40 50

D ameter

100

(mm)

Figure 5. Semi-logarithmic diagram showing the relationship between breadth/height ratio (B/H) andthe shell diameter for middle- to large-sized specimens of Group A from different horizons. The specimensof each horizon exhibit wide variation in this parameter.

recognized in the middle- to large-sized specimens of this group (Figures 4 and 5). The
Turonian specimens are narrowly umbilicate(UjD=0.20-0.2S) with more or less roundwhorl sections (BjH=l.l-1.3) in the growthstages of more than 30 mm in diameter.
Almost all specimens lack conspicuous ribs

and a keel-like elevation.
Although the sufficient Coniacian specimens could not be observed, their shell shapeand surface ornament essentially resemble
those of the Turonian specimens.
Most Santonian specimens have also anarrow umbilicus (UjD=0.IS-0.25) and a

328

Yasunari Shigeta

round whorl section (B/H = 1.0-1.3) withouta keel in the middle to late growth stage (D >30 mm), but two specimens (UMUT MM
18652-1, MM 18654-1) from the upper Lower
Santonian and one (UMUT MM 18649-1)
from the Upper Santonian have a relatively
wide umbilicus (U/D=0.30-0.35) even in thestage of more than 40 mm in diameter. In
such specimens the whorls are subrectangularin cross section, with a keel-like elevation on
the relatively flat venter.
Shell shape variation is conspicuous in theCampanian specimens, especially in the Late
Campanian ones (UMUT MM 18638-1-90).
Even in the specimens of similar size, theshells are widely to narrowly umbilicate (U /D=0.20-0.37) with a round to subrectangularwhorl section (B/H = 1.0-1.3). A keel-likeelevation is fairly common in the Early
Campanian specimens, although the state ofdevelopment varies from specimen to specimen. Such a morphotype is rare in the Late
Campanian specimens.
Ontogenetic shell variation - At about 2
mm in diameter, every specimen has a wide
umbilicus in relation to shell diameter (U /D = 0.4) (Figure 7). Thereafter the shell
becomes narrowly umbilicate up to 10 mm indiameter. In the stage larger than 10 mm indiameter the whorl umbilication is fairly
variable from specimen to specimen.
In every specimen the whorl cross-section isrelatively depressed in the early stage (B/H=
1.2-1.4) (Figure 7). Except for specimen no.
4 in Figure 7 (UMUT MMI8638-3), it generally becomes more compressed (B/H = 1.051.15) in growth stages of more than 20 mm indiameter.
Group B: The specimens belonging to thisgroup are small in size, less than 30 mm indiameter even in the adult stage, being characterized by the early internal morphology ofIB type, adorally convex aperture on theventer, round to subrectangular whorl section
and fairly narrow to wide umbilicus. They
are found less commonly in the Middle

Turonian to the Lower Campanian sequenceof the Yezo Group. Although sufficientmaterial could not be analyzed, the morphological features of this group are summarized below.
Variation in juvenile stage - Initial chamber size, ammonitella size and its spiral length
in median section are from 500 to 600 pm,
from 900 to 1,050 pm and 320 to 340·, respectively (Figures 8 and 9). The ranges of variation of these characters among the specimensof different stages largely overlap one
another.
Variation in the middle to late growthstage - Both Turonian and Coniacian specimens have a wide umbilicus (U/D=0.270.36) and a round whorl section (B/H = 1.11.3) with a keel-like elevation in the stage of
0.4

C

'"

......
::>

'" '"

"'",

0.3

.0..0..0.

/::I.

o ~%" x'"

00'6'0

g. xx

'"

x

'"

'"

xxx

x

0.2

o

10

20

30

40

20

30

40

1.4

:c
ED
1.2

o
1.0

o

10

Diameter (mm)Figure 6. Double scatter plots of umbilicus/
diameter ratio (U/D) and breadth/height ratio (B/H) versus shell diameter (D) for specimens of Groups
Band C. Triangle: Turonian and Coniacian specimens of Group B. Circles: Santonian and Campanian specimens of Group B. Cross mark: Specimens of Group C. Both Turonian and C'oniacian
specimens of Group B have a relatively wider umbilicus than the Santonian and Campanian specimens of Group B.

892.

Systematics of Tetragonites from Hokkaido

UfD

BfH

0.5

1.6

0.4

1.4

IX

0.3

"

,"

x

\

329

4

1.2
3

3

2

2

x

0.2

1.0
1

2

3

4 5

Diameter

10

20 30 40

(m m)

1

2

3

4 5

Diameter

10

20

3040

(m m)

Figure 7. Ontogenetic changes of umbilicus/diameter ratio (U/D) and breadth/height ratio (B/H)
versus shell diameter (D) for specimens of Groups A, Band C. Black circle: Specimens of Group A (I :UMUT MM18638-1, 2: UMUT MM18638-2, 3: UMUT MM 18638-4, 4: UMUT MM18638-3, sample
AWlOOIA, the Upper Campanian). White circle: Specimens of Group B (5: UMUT MM18642-5, sample
AS2038B, the Lower Campanian; 6: UMUT MM18678-4, sample ATl578, the Middle Turonian). Cross
mark: Specimen of Group C (7: UMUT MM18637-3, sample SFl104, the Lower Maastrichtian).

more than 10 mm in diameter (Figure 6).
Diagnostic features of an adult stage, such as
approximation of the last two septa, andthickening of the last septum, are observable
at 20 mm in phragmocone diameter of somespecimens.
The Santonian and Campanian specimens
are narrowly umbilicate (U /0 =0.24-0.29)
with more or less round whorl section (B/H = 1.0-1.3) at the middle to late growth stage(0) 10 mm) (Figure 6). The phragmocone
diameter in adult stage is usually 10 mm,
which is smaller than those of Turonian andConiacian specimens. Also the state ofdevelopment in a keel-like elevation is lessconspicuous in comparison with that of theTuronian and Coniacian specimens.
Ontogenetic shell variation - In the earlystage of about 2 mm in diameter, the two

specimens are widely umbilicate, but thereafter they become narrowly umbilicate (Figure 7). Decreasing of U /0 ratio versus
diameter (D) for specimen no.6 (UMUT
MMI8678-4) in Figure 7 is smaller than thatfor specimen no.5 (UMUT MMI8642-5).
In both specimens, BjH ratio decreases from
1.7 to 1.1 as the shells grow, and the whorl
becomes higher than broad in the adult stage.

Group C: The specimens of this grouppossess early internal morphology of IC type,ado rally concave ventral sinus at aperture,round to subrectangular whorl section, flat
venter, rounded umbilical shoulder and fairly
narrow umbilicus. The shell surface isgenerally smooth but some specimens havenumerous rib-like elevations. A keel-likeelevation on the venter is obsent. All speci-

Yasunari Shigeta

330

in the stage of more than 5 mm III diameter(Figure 6).

mens possess an unusually large initial chamber (925-1,050,um in median diameter) andammonitella (1,700-1,900,um in diameter)(Figure 8). Ammonitella length ranges from
330 to 345" (Figure 9). The specimens of thisgroup are restricted to the Lower Maastrichtian.
The shell at 3 mm in diameter is widely
umbilicate (U /D = 0.35) but it becomes narrowly umbilicate (U/D=0.24) with growth(Figure 7). The relative whorl thickness (B/H) is initially large (= 1.6), but gradually
decreases with growth up to 5 mm in diameter(Figure 7). The parameter remains constant

Maas!.

Group A: All specimens of this genus
hitherto described from Hokkaido and Sakhalin are characterized by the possession ofan ado rally concave aperture on the venter, around to subrectangular whorl section andfairly narrow to wide umbilicus (Table 3).
Such features agree with the characteristics ofGroup A. As already stated, the specimensof this group exhibit remarkably wide varia-

~

L.

~

Up.

Camp.

Taxonomic relationship

L.

~

San!.

cC---..

• cO

L.

I

[1

Con.

Tur.

Mid.

400

-

500

Initial

Maas!.

b
600

700

chamber

800

900

size

(Vm)

B
c

1000

1100

~

Up.
~

L.

~
L.

Con.

~
~

- JJ

I

c::::::=:::J

~
Tur.

•
~

L.

Camp.

San!.

D A

CJ

Up.

-

N=5

Mid.

800

DA

CJ

... 6
1000

1200

N=5

•

B

~c

1400

1600

1800

Ammonitella

size

(pm)

2000

2200

Figure 8. Variation in initial chamber size and ammonitella size for specimens of Groups A, Band C
from different horizons. In Group A both sizes tend to decrease toward the upward sequence.

892.

Maast.

~

L.

~

Up.

Camp.

Systematics of Tetragonites from Hokkaido-

Ciiii~

L.
I Up.

Santo

~-

L.

Con.

~
Up.

Tur.

I

N=5

CJ

~

Mid.

300 0

320 0

340 0

OA
•

B

~c

360 0

380 0

Ammonitella length

Figure 9. Variation in ammonitella length for
specimens of Groups A, Band C from different
horizons. There is no significant difference in theammonitella length among the three groups.

tion in the external shell shape. They cannot
be divided into subgroups by the shell form
ratios because of the wide and continuous
range of the variation. Sample A W1001A
from the Upper Campanian of Soya area is a
Table 3.

331

typical example showing wide shell shapevanatlOn. Furthermore, the shell form ratios(U 10, B/H) of the type and previously illustrated specimens are mostly included in therange of variation of the specimens in thesample (Figure 10). This evidence strongly
suggests that these specimens merely represent
the variants in a single species. Although
the internal structure of these specimens cannot be examined, all the previously described
species, T. glabrus (limbo), T. sphaeronotus(Jimbo), T. crassus (Jimbo), T. popetensis
Yabe and T. glabrus problematicus Matsumoto, show an ado rally concave aperture on
the venter. These species should be, therefore, treated as synonymous, and are all included in Group A. The oldest species
name, T. glabrus, is used here for these specimens in Group A. Judging from the apertural features and shell sizes of the figured specimens, T. cf. epigonus (Kossmat) and T.
superstes Van Hoepen illustrated respectively
by Yabe (1903) and Matsumoto and Miyauchi (1984) can also be identified as T. glabrus.
Group B: This group is represented bysmall-sized specimens with an adorally con-

Measurements (in mm) of previously described or illustrated specimens of Tetragonites from theUpper Cretaceous of Hokkaido.

D

U

B

H

U/D

B/H

Remarks(1) Lytoceras glabrum
51.1
40.8
(2) L. shaeronotum
24.9(3) L. crassum
35.0(4) Tetragonites glabrus
Yabe(1903)
65.0(5) T. glabrus
145.0(6) T. shaeronotus(7) T. shaeronotus
68.9
34.0
(8) T. popetensis
20.5(9) T. pope tens is
34.4(10) T. cf. epigonus(11) Epigoniceras glabrum var.
Matsumoto87.0
problematica(1942b)41. 3
T.
superstes
Matsumoto & (12)66.6
T.
pope tens is
Miyauchi(1984)(13)

11. 3
8.9
6.8
8.0
14.0
30.0
13.5
10.5
5.5
9.4

21. 5
21.6
13.2
19.0
36.0
72.0
36.7
15.0
9.0
16.1

24.2
19.8
11.6
17.0
32.0
70.0
34.3
14.5
9.0
14.7

0.22
0.22
0.27
0.24
0.22
0.21
0.18
0.31
0.27
0.27

1.09
1.17
1.14
1.17
1.12
1.02
1.07
1.03
1.00
1.09

MM7513MM7494
MM7515MM7461

21.0
11.2
21. 2

37.3
18.6
27.0

40.7
12.7
26.4

0.24
0.28
0.32

0.92
1.05
1.02

MM5529MNH.502
MNH.501

Authors
Jimbo(1894)

No.

SpeciesMM7540MM7460MM7541
MM7459Yasunari Shigeta

332

•

0.35

•

@

-

(§!

0.30

c

@.

®
0.25

®
®

0.20

0.15~

____

~

CD

______

~

•

••• •
•
•
®>. • •@.
•
• @!
•
•

·as• ®

____

1.0

~~

____- L_ _ _ _ _ _1.1~_ _ _ _~

1.2

B/H
Figure 10. Scatter plot of umbilicus/diameter ratio (U/D) versus breadth/height ratio (B/H) for 22
specimens of Group A (black circle; more than 30 mm in diameter) in the Upper Campanian sample
AWlOOIA from Soya area and 13 previously described or illustrated specimens of Tetragonites from
Hokkaido (white circle). Number in each white circle corresponds to that in Table 3. The shell form ratiosof type and illustrated specimens largely overlap with those of the specimens in the sample AWlOOIA.

vex aperture on the venter. Such a morphotype has not yet been described from theUpper Cretaceous of the North Pacific region
including Hokkaido. Although the adultshell form and size more or less differ between
the specimens from the Turonian - Coniacian and those from the SantonianCampanian, because of the similarity in othershell characters, it is considered that thedifference should be attributed to the phyletictransition within a lineage. A new species
name, T. minimus, n. sp., is therefore given tothis group.
Group C: Matsumoto (1942b, 1943) listed

Epigoniceras poptense var. frequence from theLower Maastrichtian of Tomiuchi area.
Judging from Matsumoto's (1942b, p.673)
description, this variety appears to resemble
some specimens of Group C in having numerous rib-like elevations on the whorls and afairly narrow umbilicus. However, he did
not describe the diagnostic characters of thevariety, nor illustrated any material. Therefore, Group C is treated as a new species, T.

terminus, n. sp.
Phylogeny
Although the phylogenetic relationships ofthe post-Cenomanian Tetragonites species
have not been studied, those of Aptian to
Cenomanian species have been discussed by
Murphy (1967a) and Wiedmann (1973).
Murphy (1967a) classified seventeen species
into three morphological groups, based on
their apertural shape, suture line and shellform. The T. timotheanus group was characterized by species with an adorally convex
aperture on the venter, and has as its ancestor
the Upper Aptian species, T. subbeticus.
This group includes T. timotheanus from theUpper Albian, and T. spathi from the Lower
Cenomanian.
T. minimus, n. sp. also possesses an adorally convex aperture on the venter, and therefore, according to Murphy's classification, it
belongs to the T. timotheanus group.
Furthermore, the Turonian specimens of thisspecies resemble T. spathi, in having a wide

892.

Systematics of Tetragonites from Hokkaido

umbilicus and a keel-like elevation on theventer. Therefore, T. minimus is considered
to have originated from a species of thisgroup, and its probable ancestor is T. spathi.
Other morphological groups proposed by
Murphy (1967a) are the T. rectangularis
group and the T. kichini group, both ofwhich are represented by species with anadorally concave sinnous aperture on theventer. The former group was possibly thedominant stock of Tetragonites, and includes
most species of mid-Cretaceous representatives. According to Murphy's (l967a)
definition, T. glabrus can be assigned to thisgroup. Many Albian and Cenomanianspecies of this group have been described byprevious authors (e.g. Wiedmann, 1962;
Kennedy and Klinger, 1977), but details of
the intra- and interpopulational variation ofshell form and phylogenetic relationships
have not yet been realized. T. glabrus seems
to have originated from a species of thisgroup. However, it is at present difficult to
identify its ancestor.
Santonian and Campanian Tetragonites
having an adorally concave sinuous apertureon the venter consist ofthe following species:
T. margaritatus Marshall, T. simplex (Marshall), T. marshalli (Collignon), T. superstes
Van Hoepen, T. mitraikyensis Collignon, T.
beantalyensis Collignon, T. garudus Forbes,
T. epigonus Kossmat and T. glabrus (limbo)(Collignon, 1956; Kennedy and Klinger,1977). T. terminus, n. sp., with the same
apertural type, may have been derived from a
species of this group. The exact ancestor ofthis species is, however, unknown because of
the insufficiency of data on intra- and interpopulational variation and exact stratigraphical distribution for the above foreign
species.
On the other hand, the three species of
Tetragonites examined are well defined bytheir unique early internal shell features.
The significance of early internal shell structure in the major classification of the Mesozoic Ammonoidea have been demonstrated

333

by several paleontologists (Druschchits andKhiami, 1970; Druschchits and Doguzhayeva, 1974; Zakharov, 1974; Druschchits
et al., 1977; Tanabe et al., 1979; Tanabe
and Ohtsuka, 1985; Ohtsuka, 1986).
According to Ohtsuka (1986), theGaudryceratidae are characterized by the following early internal morphology in mediansection: nearly circular initial chamber,semi-circular caecum with a weakly constricted base, one to three short prosiphons andventrally located siphuncle in most of the
post-ammonitella growth stages. Such features are commonly observed in T. glabrus.
The Tetragonitidae are now regarded as having been derived in the Aptian from theGaudryceratidae (Wiedmann, 1962; Murphy,
1967b). If this interpretation is correct, it isapparent that T. glabrus preserves moreancestral characters in the early stage than T.
minimus and T. terminus. The present
study also suggests that T. terminus, n. sp.
and T. minimus, n. sp. might have been
derived from the stock with the early internal
morphology ofIA type including T. glabrus.
Because of the similarity of apertural shapes,
such a stock may correspond to the T. rectangularis group of Murphy (1 967a).
According to Wiedmann (1973), Tetragonites rapidly diversified throughout the
Tethyan realm during the Albian andCenomanian, and thereafter had a distinct
decline from Turonian to Maastrichtian.
However, in Hokkaido in the northwestern
Pacific region generally, the diversity of the
Albian and Cenomanian members remained
nearly constant until the end of Campanianor Maastrichtian.
Concluding remarks
This study reveals that the intrapopulational variation of shell form in Tetragonites
glabrus is relatively wide, especially in the
middle to later growth stage, and that manyof the previously described species under thename of Tetragonites are synonymous with

Yasunari Shigeta

334

T. glabrus. Moreover, the seemingly small
variability of shell form in the previously
described "species" was a result of extreme
taxonomic splitting. More than twenty
species of Tetragonites have hitherto been
described from the Aptian to Cenomanian of
the world. Their taxonomic and phylogenetic relationships should be re-examinedby adequate evaluation of taxonomic characters from the viewpoint of population concept.
The smooth and featureless external morphology in Tetragonites causes difficult problems for phylogenetic reconstruction. However, three morphological types of early internal shell structure are clearly distinguished in
Tetragonites. It is believed that such early
characters are stable within a given species
irrespective of time and may be strongly
controlled by phylogenetic (genetic) factors.
They may serve as a key for phylogenetic
reconstruction not only in Tetragonites but
also in other ammonoids.
Systematic description
Order Ammonoidea Zittel, 1884
Suborder Lytoceratina Hyatt, 1889
Superfamily Tetragonitaceae Hyatt, 1900
Family Tetragonitidae Hyatt, 1900
Genus Tetragonites Kossmat, 1895

Type species. - Ammonites
Pictet, 1848

timotheanus

Tetragonites glabrus (limbo)
Figures IIA-B, 12
Lytoceras glabrum limbo, 1894, p. 180, pI. 22, figs. 2,2a.
Lytoceras sphaeronotum limbo, 1894, p. 181, pI. 22,

fig. 4.
Lytoceras crassum limbo, 1894, p. 181, pI. 22, figs. 5,5a,5b.
Tetragonites glabrus: Yabe, 1903, p. 43, pI. 7, figs. 2,
5; Tanabe and Kanie, 1978, p.8, pI. I, figs.2a,2b.
Tetragonites sphaeronotus: Yabe, 1903, p.45, pI. 7,
figs. I a, lb.
Tetragonites popetensis Yabe, 1903, p. 48, pI. 7, figs. 4,6; Matsumoto and Miyauchi, 1984, p. 52, pI. 23,
figs. 3a, 3b.
Tetragonites cf. epigonus: Yabe, 1903, p. 49, pI. 7, fig.
3.

Epigoniceras glabrum var. problematica Matsumoto,
1942, p. 672, fig. 1.
Tetragonites superstes: Matsumoto and Miyauchi,
1984, p. 52, pI. 23, fig. 2.

Type. - The holotype (UMUT MM7513;
limbo, 1894, pI. 22, figs. 2, 2a) is a large-sized
specimen with a deformed body chamberfrom the Upper Cretaceous of Ikandai, Urakawa area.
Material. - In addition to the holotype,267 specimens [UMUT MM18638 (N = 110),
UMUT MM18640 (N=18), UMUT
MM18641 (N=7), UMUT MM18643 (N=3),
UMUT MM18645 (N = 1), UMUT MM18646(N=3), UMUT MM18647 (N=2), UMUT
MM18648 (N = 1), UMUT MM18649 (N =2),
UMUT MM 18650 (N = 7), UMUT MM 18651(N=3), UMUT MM18652 (N=2), UMUT
MM18653 (N = 1), UMUT MM18654 (N = 1),
UMUT MM18656 (N=3), UMUT MM18557(N = 2), UMUT MM 18658 (N = 1), UMUT
MM18660 (N = 14), UMUT MM18661 (N =1), UMUT MM 18662 (N = 10), UMUT
MM1863 (N = 1), UMUT MM18664 (N = 1),
UMUT MM18665 (N=2), UMUT MM18666(N=2), UMUT MM18668 (N=6), UMUT
MM18669 (N=3), UMUT MM18670 (N=15), UMUT MM18672 (N=6), UMUT
MM18673 (N=ll), UMUT MM18674 (N=~ Figure 11. Scanning electron micrographs of the early internal shell structure of three Tetragonites
species in median section. Scale bars in A, C and E: 200 pm. Scale bars in B, D and F: 50 pm. A-B.
Tetragonites glabrus (limbo), the Coniacian, Haboro area, Sample AH4087, UMUT MM 18665-1. C-D.
Tetragonites minimus, n. sp., the Lower Campanian, Saku area, Sample AS2038B, UMUT MM I 8642-6,
paratype. E-F. Tetragonites terminus, n. sp., the Lower Maastrichtian, Tomiuchi area, Sample SM1041,
UMUT MMI8636-2, paratype.

892.

Systematics of Tetragonites from Hokkaido

335

336

Yasunari Shigeta2), UMUT MM 18675 (N = 5), UMUT
MM18676 (N = 13), UMUT MM18677 (N =5), UMUT MM 18679 (N = 1), UMUT
MM18680 (N =2)J are referable to the present
species. The localities and ages of them aresummarized in Table 1.
Diagnosis. - Large-sized species of
Tetragonites characterized by ado rally concave sinuous aperture on venter, nearly circular initial chamber in median section, subellipsoid caecum with weakly constricted
base, and ventrally located siphuncle except
for earliest first to fourth chamber stage.
Description. - Shell large, sometimes,
exceeding 80 mm in diameter, rather evolute
to moderately involute, with a fairly narrow
to wide umbilicus even in the stage of morethan 30 mm in diameter. Whorl round to
subrectangular in cross section, with arounded to flat venter, nearly flat to gently
convex flanks, subangular to rounded umbilical shoulder and nearly vertical to subverticalumbilical wall. Shell surface nearly smooth,with fine and dense growth lines, and infrequent conspicuious rib-like elevations.
They are prorsiradiate on the flanks, curved
adapically at the peripheral shoulder andcross the venter with a shallow backward
sinus. A keel-like elevation sometimes
occurs in middle to late stage of theSantonian and Campanian specimens. Initial chamber nearly circular in median section. Caecum subelliptical in lateral view
with a weakly constricted base, and its
adapical end connects with the initial chamber wall by one to three short, ado rally concave prosiphons. Flange weakly developed.
Siphuncle occupies a central position near theproseptum, and then immediately shifts
toward the venter in second to forth chamber
stage. Thereafter it keeps a ventral position.
Initial chamber and ammonitella medium- tolarge-sized (ranging 475-875 pm and 9001",700 pm in median diameter, respectively),both showing a clear chronocline in size
decrease in the Upper Cretaceous seqeunce of
Hokkaido. Variation of ammonitella lengthis rather small (310 to 350' in volution), nevermarking a conspicuous historical trend.
Dimensions. DUB

Holotype

H

(mm)

(mm)

(mm)

(mm)

51.1

11.3

26.5

24.2

U/D
0.22

B/H
1.10

F or the measurements of other specimens, see
Figures 4,5, 7, 8 and 9.
Remarks. - In overall shell morphology
T. glabrus (Jimbo) closely resembles someforeign species such as T. epigonus Kossmat(1895, p. 135, pI. 17, figs. 4, 5, 10), T. superstes
Van Hoepen (1921, p.lO, pI. 2, figs. 17-20),
T. garudus (Forbes) (1846, p. 102, pI. 7, fig.
1), T. mitraikyensis Collignon (1956, p.86,
pI. 11, fig. 2), T. beantalyensis Collignon(1956, p. 83, pI. 10, fig. 1), T. marshalli (Collignon) (1956, p. 86), T. margaritatus Marshall (1926, p. 151, pI. 20, fig. 5, pI. 30, figs. 5,6) and T. simplex (Marshall) (1926, p. 150, pI.
20, figs. 11, IIa, pI. 32, figs. 3,4). The narrowest and the widest umbilicate forms of T.
glabrus also suggest affinities with Pseudophyllites indra Forbes (1846, p. 105, pI. 11, fig.
7) and Saghalinites nuperus (Van Hoepen)(1921, p. 13, pI. 3, figs. 3,4).
The taxonomic relationship between T.
glabrus and the above foreign species is,however, at present uncertain because of
insufficient data on the intra- and interpopulational variation and exact stratigraphical distribution of the later.
Occurrence. - This species occurs abundantly from the Middle Turonian to theUpper Campanian of the Yezo Group in
Hokkaido and south Sakhalin. This species
is also known from the Turonian-Campanianof California (Matsumoto, 1959).

Tetragonites minimus, n. sp.
Figures lle-D, 13-1-7b

Type. - A small-sized specimen (UMUT
MMI8667-I) from the Coniacian outcrop
exposed along the middle course of the Obirashibe River (Loc. Tl220 of Sekine et al.,

892.

Systematics of Tetragonites from Hokkaido

la

Ib

337

2a

4

6

7a

7b

Figure 12. Telragoniles glabrus (limbo) . For loca li ties see T a ble I. la - b. UMUT MMI8662 - 5,
Sample AT1514, the lower Lower Santonian , Tappu area, x O.8 . 2a - b. UMUT MMI 8653- 1, Sample
A H 6033P, the upper Lower Santonian , Haboro area , x O.8. 3. UMUT MMI8638 - 16, Sample AWIOO IA ,the Upper Campan ian, Soya area, X 1.0. 4. UMUT MMI8638- 15, Sample AWIOOIA , the Upper
Ca mpanian , Soya area, X 1.0. 5. UMU T MMI 8638- 13, Sample AW IOO IA , the Upper Campa ni an , Soyaarea, X 1.0. 6. UMUT MM 18640- 3, Sample A W 1003, th e Lower Campania n, Soya area , x 0.8. 7a - b.
UMUT MMI8654- 1, Sample AKI029A, th e upper Lower Santonian , Kotanbetsu area, x O.7 .

338

Yasunari Shigeta

1985), Tappu area, northwestern Hokkaido isdesignated as the holotype.
Material (Paratypes). - In addition to the
ho1otype, 35 specimens [UMUT MM18639(N = 3), UMUT MM 18642 (N = 9), UMUT
MM18644 (N = 1), UMUT MM18655 (N =4),
UMUT MM18659 (N =2), UMUT MM18671(N=3), UMUT MM18678 (N=7), UMUT
MM18681 (N =2), UMUT MM18682 (N =4)J
from various localities of Hokkaido are usedin the following description. Their localities
and ages are summarized in Table 1.
Diagnosis. - Small-sized species of Tetragonites characterized by adorally convex
aperture on the venter, nearly circular initialchamber in median section, hemisphericalcaecum with strongly constricted base, andcentrally to sub-centrally located siphuncle in
the first to second whorls.
Description. - Shell rather small, less than
30 mm in diameter, rather evolute to moderately involute, with a fairly narrow to wide
umbilicus. Whorl rounded to subquadrate
in cross section with a round venter, nearlyflat to gently convex flanks, round umbilicalshoulders and a nearly vertical umblilicalwall. Shell surface sculptured with regularly
spaced fine and dense growth lines and lessfrequent, inconspicuous rib-like elevations.
In the middle to late stage, a keel-like elevation appears on venter. Apertural margin
markedly prorsiradiate on the flanks, recurves
at peripheral shoulder and adorally convex
on the venter. Initial chamber nearly circular in median section. Caecum hemispherically shaped with a strongly constrictedbase. Its adapical end connects with initialchamber wall by one to three short, adorally
convex pro siphons. Flange weakly developed. Siphuncle initially occupies a central
position at the earliest portion near proseptum, but gradually shifts toward the venter
during the growth of first-second whorls.
Initial chamber size, ammonitella size and its
spiral length in median section range from500 to 600 J-lm, 900 to 1,050 J-lm and 320 to340', respectively.
Dimensions. DUB
Holotype

H

(mm)

(mm)

(mm)

(mm)

28.1

8.9

12.3

1l.0

U/D B/H
0.32 1.12

For the measurements of paratypes see Figures 6-9.
Remarks. - T. minimus, n. sp. resembles
T. spathi (Fabre) (1940, p.214, pI. 6, fig. 1)
from the Lower Cenomanian of Cassis (France), and T. timotheanus (Pictet) (1848, p. 295,
pI. 2, fig. 6, pI. 1, fig. 9) from the Upper Albian of the French Alps near Geneva in having
an ado rally projected or nearly straight aperture on the venter, but it is distinguished fromthese taxa in having an arch-shaped apertural
margin on the venter.
Occurrence. - This species ranges from theLower Turonian to the Upper Campanian of
the Yezo Group in Hokkaido.

Tetragonites terminus, n. sp.
Figures llE-F, 13-8-10

Type. - The holotype (UMUT MM186351) is a small-sized specimen from the lower
Maastrichtian of the Ichiyanagi-no-sawa--+ Figure 13. 1-7: Tetragonites minimus, n. sp., X 1.5. For localities see Table 1. 1. UMUT
MMI8642-1, Sample AS2038B, the Lower Campanian, Saku area, paratype. 2a-b. UMUT MMI8655-1,
Sample AK1029B, the upper Lower Santonian, Kotanbetsu area, paratype. 3a-b. UMUT MMI8678-1,
Sample AT1578, the Middle Turonian, Tappu area, paratype. 4a-b. UMUT MMI8667-1, Sample AT1551,
the Coniacian, Tappu area, holotype. 5a-b. UMUT MMI8671-1, Sample A T1201B, the Middle Turonian,
Tappu area, paratype. 6a-b. UMUT MMI8682-1, Sample AT2100, the Lower Turonian, Tappu area,
paratype. 7a-b. UMUT MMI8681-1, Sample AW2001P, the Lower Turonian, Soya area, paratype. S-10: Tetragonites terminus, n. sp., X 1.5. Sa-b. UMUT MMI8635-1, Sample SM1048, the Lower
Maastrichtian, Tomiuchi area, holotype. 9. Sectional view, UMUT MMI8635-2, Sample SM1048, theLower Maastrictian, Tomiuchi area, paratype. lOa-b. UMUT MMI8635-4, Sample SM1048, the Lower
Maastrichtian, Tomiuchi area, paratype.

892.

Systematics of Tetragonites from Hokkaido(Loc. H 12d in Matsumoto 1942a), Tomiuchi
area, southern central Hokkaido.
Material (Paratypes). - In addition to theholotype, 7 specimens [UMUT MM 18635-2

33 9-8 J from the type locality and 9 specimens[UMUT MM18636 (N = 3) , UMUT
MM18637 (N = 6)J from other localities areused in the following description. Their

2a

5b

5a

6a

8a

6b

8b

9

lOa

lOb

Yasunari Shigeta

340

localities and ages are summarized in Table 1.
Diagnosis. - Small-sized species of
Tetragonites characterized by adorally concave sinuous aperture on venter, unusuallylarge-sized initial chamber, elongate subellipsoid caecum without any conspicuous constriction at its base, relatively long andstraight prosiphon, and abrupt shift of siphuncular position from dorsum to venter
within the first camera.
Description. - Shell rather small, less than
20 mm in diameter even in adult, involute,with a fairly narrow umbilicus. Whorls
round to subrectangular in cross section, witha flat venter, gently convex flanks, roundedumbilical shoulder and subvertical umbilicalwall. Shell surface seemingly smooth, but
ornamented with fine growth lines and widespaced rib-like elevations, both of which areprorsiradiate on the flank, recurve near the
peripheral shoulder and cross the venter witha shallow backward sinus. Initial chamber
elliptical in median section. Subellipsoid
caecum lacks a conspicuous constricted base.
Its adapical end connects with the inner· surface of initial chamber by a long and nearlystraight prosiphon. Pro septum is relatively
long and acutely projects toward the caecum.
Early portion of the first whorl swells remarkably as a result of discordant underlay of theammonitella wall with the initial chamberwall. Siphunde initially occupies a dorsal
position within the first camera, and then
immediately shifts its position toward theventral side. Marginal approximation iscompleted in the third camera, and thereafter,
it retains a ventral position. The first septum
is adorally concave, but subsequent septa areadorally convex. Median diameter of initialchamber, and maximum diameter and spirallength of ammonitella range from 925 to
1,050 pm, 1,700 to 1,900 pm and 330 to 345',
respectively.
Dimensions. DUB
Ho1otype

H

(mm)

(mm)

(mm)

(mm)

U/D B/H

19.4

5.2

10.1

8.6

0.27

1.17

F or the measurements of other paratypes see
Figures 6-9.
Remarks. - T. terminus, n. sp. resembles
the narrowly umbilicate form of T. glabrus(limbo) in the external shell shape, but thetwo species are easily distinguished by thedifference in the early internal shell features.
Occurrence. - This species is restricted to
the Lower Maastrichtian of the Yezo Groupin the Tomiuchi area.
Acknowledgments

I wish to thank Professor Itaru Hayami(University of Tokyo), Associate Professor
Kazushige Tanabe (University of Tokyo), Dr.
Tatsuo Oji (University of Tokyo) and Dr.
Graeme R. Stevens (New Zealand Geological
Survey) for many helpful suggestion during
the course of this study, and for critical reading of the manuscript. I am much indebted
to Emeritus Professor Tatsuro Matsumoto(Kyushu University), Dr. Haruyoshi Maeda(Kochi University), Dr. Tomoki Kase
(National Science Museum) and Mr. Toshiya
Miyauchi (Natural History Collection of
Northern Hokkaido) for providing somespecimens. Critical discussion was provided
by Dr. Takashi Okamoto and other colleagues at the Paleobiological Laboratory of
the University of Tokyo, to whom I express
sincere gratitude.
References
Anderson, F.M., 1958: Upper Cretaceous of the
Pacific Coast. Mem. Geo!. Soc. Amer., vol. 71,
p. 1-378, pis. 1-75.
Branco, W., 1879-80: Beitrage zur Entwickelungeschichte der fossilen Cephalopoden. Pa!aeontographica (Stuttgart), Bd.26, p. IS-50, pls.4-13(1879); Bd.27, p. 17-81, pis. 3-11 (1880).
Collignon, M., 1956: Ammonites neocretacees duMenabe (Madagascar). IV. Les Phylloceratidae; V. Les Gaudryceratidae. VI. Les
Tetragonitidae. Ann. Geo!. Servo Mines, vol.
23, p. 1-106, pis. I-II.
Drushchits, V.V. and Doguzhayeva, L.A., 1974:
Some morphogenetic characteristics of892.

Systematics of Tetragonites from Hokkaido

phylloceratids and Iytoceratids (Ammonoidea).
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- - and - - , 1981: Ammonites under the electron
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- - , - - and Mikhaylova, LA., 1977: The structureof the ammonitella and the direct development ofammonites. Paleont. J., 1977, no. 2, p. 188-199,
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Fabre, S., 1940: Le Cretace superieur de la BasseProvence occidentale. I. Cenomanien et Turonien. Annis. Fac. Sci. Marseille, (2) 14, 355
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Henderson, R.A., 1970: Ammonoidea from the Mata
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Cretaceous of the Kaminukibetsu area, southerncentral Hokkaido. Sci. Rept., Yokosuka City
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Kossmat, F., 1895-1898: Untersuchungen tiber die
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Krivoshapkina, V.S., 1978: The ontogeny of thesuture in late Cretaceous tetragonitids from Sakhalin. Paleont. J., 1987, no. I, p. 64- 70.

341

Marshall, P., 1926: The Upper Cretaceous ammonites of New Zealand. Trans. N.Z. Inst., vol.
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Murphy, M.A., 1967a: The Aptian-Cenomanian
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Kaseki (Fossils). Palaeont. Soc. Japan, no. 38,

Yasunari Shigeta

342

p. 1-15 (in Japanese with English abstract).
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Jamaica. Geol. Mag., vol. 62, p.28-32.
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deposits in the Obira area, northwestern Hokkaido. Sci. Rep., Dept. Geol. Kyushu Univ.,
vol. 12, no. 3, p. 181-202 (in Japanese with English abstract).
- - and Kanie, Y., 1978: Colour markings in two
species oftetragonitid ammonites from the Upper
Cretaceous of Hokkaido, Japan. Sci. Rep.,
Yokosuka City Mus., no. 25, p. 1-6, pI. 1.
- - , Obata, 1., Fukuda, Y. and Futakami, M., 1979:
Early shell growth in some Upper Cretaceousammonites and its implications to major taxonomy. Bull. Nat. Sci. Mus. Tokyo, Ser. C(Geol.), vol. 5, no. 4, p. 153-176, pis. 1-6.
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Toshimitsu, S., 1988: Biostratigraphy of the Upper
Cretaceous Santonian stage in the northwestern

Hokkaido. Mem. Fac. Sci., Kyushu Univ.,
Ser. D, Geol., vol. 26, no. 2, p. 125-192, pis. 2329.
Van Hoepen, E.C.N., 1921 : Cretaceous Cephalopoda
from Pondoland. Ann. Transv. Mus., vol. 8, p.
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Wiedmann, J., 1962: Ammoniten aus der Vaseogothisehen Kreide (Nordspanien). 1. Phylloceratina, Lytoceratina. Palaeontographica, Bd.
118A, p. 119-327, pis. 8-14.
- - , 1973: The Albian and Cenomanian
Tetragonitidae (Cretaceous Ammonoidae) withspecial reference to the circum-in die species.
Ec/og. Geol. Helv., vol. 66, p. 585-616, pis. 1-8.
Yabe, H, 1903: Cretaceous Cephalopoda from Hokkaido. Part 1. Jour. Coli. Sci., Imp. Univ.
Tokyo, vol. 18, no. 2, p. 1-55, pis. 1-7.
Zakharov, Y.D., 1974: New data on internal shellstructure in Carboniferous, Triassic andCretaceous ammonoids. Paleont. J., 1974, no.
1, p. 25-36.

**Ei-,

Kotanbetsu J!1ftliU, Nukibetsu Jt~liU, Obira IJ\3JL, Saku
Haboro ;:j3l1\!!'/;, Ikandai
Soya
Tappu )i;ffi, Tomiuchi 1i1.'P'l, Toyoshimizu :am7.K, Urakawa OOM.

ttI:~,*:e:,;ltrla:@:J::fffiBl!Ii:~,gE Tetragonites ~ 7 /" ~ -r 1 r 0)7t~: ;ltrla:@:O) Bl!Ii:~~~II~ J: '?
,gElfj-t G Tetragonites ~ T / ~ -r 1 r t;::v:;>\, '-C, ~ff~O)m:i:t·~~ll*a-1JQ.:tI.::a1i1.'tJ::ll*a-~ ct;::~%1tO)7t~~i¥J~flHia-IT·::d.:o .:to)*6*t;::£-:)~, T. glabrus (Jimbo) a-:pJ~~-t Gee ~ t;:: 2 ~~a-OOtliU L, T. minimus, T. terminus Cfrr~ L ~tx: L 1.:0;::.h I? 3 ~lt1}JlUm!1:{;$:P'lfffi~~~~ I=l~O)%tJ:: c>Fjj~tJ::%1tt;:: J: '? -C~£t;::OOtliU~.h
GoT. glabrus vt 7- "" - p :=. 7 /"1lf!:j:lfffiiJ, I? 7J /" /~ :=. 7 /"1lfJ::{ffit;::,gE L, .~O)%~~iID~~tJ::c·t;::*~tdrJ~iJ;'~.I?.hGo :ftt*~tx:~.ht.: T. sphaeronotus (Jimbo), T. crassus(Jimbo), T.popetensis Yabe tJ::Dt*~P'lO)~A~c.l,o.tJ::-ItGo T. minimus It/J\~O)~"t",7- "" - p :=. 7 /"IlfTfffiiJ' I? 7J /" /~:=. 7 /"1lfJ::fffit;::,gE-t Go T. terminus It ~ A r !I l:: 7- 7 /"IlfTfffiO).l,o.~,gEL, §*~fi~a-~-tGo

.mad

343

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ra~f-J 650 lJpj ~~ ~ L 1t~ * 9 0~ hl;l:~~O)t§'~~;:- AGf:> t.: I) ~1iffi 6,000 pj~$O) tI:l!l&!jo/.J~ ~~ I) ~ L1t~ ~ ~ i::~;::>d: I) * 9 0~:b)~, *~0)1f.~.1;l:, ftl!O)~~~;:.tt~Lt:k:~ L~1t~ i:: I;l:~;z T, ~~t;t~.0)C6t)E (f@:.Llj) 1;l:~jJi!!Htt.: 1t~ i::~;z L ~ I) * 9 0~ ~ -r, ~~;:!&.L·9:b~, 9'f.OOO)S~~:b~1T-::>L1t~~ J: ~ ~;:, *~-r~~~olbtO)~J~~O)t§'~O)§~:>d:~.~~J:~.~(.M~~~O)~.-rm~$~~~,~.
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344

Palaeontological Society of Japan, Special Papers
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No.9 (1962): 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
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No. 16 (1971): Tertiary Molluscan Fauna from the Yakataga
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No. 17 (1973, reprinted 1980): Revision of Matajiro Yokoyama's Type Mollusca from the Tertiary and Quaternary of
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No. 22 (1978): Bibliography of Palaeontology in Japan, 19611975. By K. Kanmera and H. Ujiie (ed.)
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Transactions and Proceedings of the PalaeontologicalSociety of Japan

December 30, 1989

New Series No. 156

CONTENTS
TRANSACTIONS
887. Kuniteru Matsumaru and Koshi Kimura: Larger foraminifera from the
Eocene Shimizu and Miocene Misaki Formations in Tosa Shimizu City, Kochi
Prefecture, Japan .................................................... 255
888. Hisaharu Igo: Mixed conodont elements from Hachiman Town, Mino Terrane, central Japan .................................................... 270
889. Kazuyoshi Endo: Growth and life mode of a Pleistocene brachiopod, Kikaithyris hanzawai (Yabe) .............................................. 286
890. Shuji Niko: A new Devonian cephalopod from the Nakazato Formation of
the southern Kitakami Mountains ...................................... 291
891.

892.

Toshiaki Irizuki: Fossil ostracode assemblages from the Pliocene Sasaoka
Formation, Akita City, Japan - with reference to sedimentological aspects..................................................................... 296
Yasunari Shigeta: Systematics of the ammonite genus Tetragonaites from theUpper Cretaceous of Hokkaido ........................................ 319