ISSN 0031-0204

Transactions and Proceedingsof thePalaeontological Society of Japan
New Series

1'10.

159

Palaeontological Society of Japan
September 30,

1990

Co-Editors

Hisayoshi Igo, Hiroshi Noda and Kei Mori
Editorial Board

Y oshikazu 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 ofTokyo), Tsunemasa Saito(Tohoku University), Kazuhiko Uemura (National Science Museum), Akira Yao (Osaka City University)

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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. 159, pp. 541-553, 7 Figs., September 30, 1990

903. TAXONOMIC AND PALEOZOOGEOGRAPHIC SIGNIFICANCEOF CENOZOIC HUNCH-BACK LIKE VENERIDSPART I. GIGANTOCALLISTA, GEN. NOV. (MOLLUSCA: BIVALVIA),A NEW ENDEMIC VENERID GENUS FROM THE PLIOCENETATSUNOKUCHI FORMATION, SENDAI CITY,MIYAGIPREFECTURE,NORTHEASTERNJAPAN*
TOSHIO TAKAGI
Suncoh Consultants Co., Ltd., 1-8-9,
Kameido, Koto-ku, Tokyo 136

Abstract. A new genus of hunch-back like Bivalvia, Giganlocallisla, is proposed andPilar sendaica Nomura is designated as the type-species. The genus is monotypic and may
have evolved from the Miocene genus Neogenella. Giganlocallista sendaica occurs only in
the Pliocene Tatsunokuchi Formation, and may reflect localized zoogeographic or
paleoecological conditions within the Pliocene Paleo-Sendai Bay.
Key words. Hunch-back like shell, Giganlocallista, Tatsunokuchi Formation, Tatsunokuchi Fauna, Pliocene.

and Uozumi, 1954; Tanaka, 1961 ; Iwasaki,
1963; Iwai, 1965; Masuda, 1966; Zhidkova
et al., 1968, 1972; Itoigawa, et al., 1974;
Itoigawa et al., 1981a, b; Amano, 1983,
1986; Gladenkov, 1984; Menner, 1984).
Though this type of venerid has long been
included in PitaI', its dentition is clearly
different from PitaI' Romer (Iwasaki, 1963).
The taxonomic position of this venerid has
not been settled to many authors yet, whoeither include the above-mentioned "PitaI'''
species in Romer's PitaI', or in Pseudamiantis
Kuroda (1933). Krishtofovich (1955, fide
Zhidkova et at., 1968) proposed Neogenella
as a subgenus of PitaI' Romer and someauthors included this type of "PitaI''' in his
subgenus. But as already mentioned by
Iwasaki (1963), its dentition is not of Pitartype, so this type of "PitaI''' should not be
included in the genus PitaI'.
These so-called PitaI' species are biogeographically significant. They and their allied

Introduction

The extraordinary group of PitaI' (Hayasaka and U ozumi, 1954), or "the so-called
Tertiary PitaI''' (Iwasaki, 1963) is a veneridwith an unusually thick hunch-back likeshell. In Japan, PitaI' okadana (Yokoyama), P. itoi Makiyama, P. hokkaidoensis
Nomura, and P. sendaica Nomura have been
included in this above-mentioned "Pitar"group (Iwasaki, 1963). This group of PitaI'
has long been well known from Miocene andPliocene deposits of Japan, Korea, Sakhalin
and Kamchatka. Particular attention has
been paid to this type of PitaI' because of its
biostratigraphic value as well as its unusualmorphology (Makiyama, 1926, 1936; Yokoyama, 1932; Nomura, 1935, 1938, 1940;
Slodkewitsch, 1938; Nomura and Hatai,
1936, 1937; Uozumi, 1953, 1962; Hayasaka'Received September 27, 1989; revised manuscript
accepted Septem ber I, 1990
541

Toshio Takagi

542

species are known only in eastern Asia,
although significant changes in their geographic distribution have occurred during the
Neogene. In Miocene time they inhabited
Korea, Honshu, Hokkaido, Sakhalin andwestern Kamchatka, but in Pliocene time they
were confined only to Sendai Basin (Takagi,
1987, 1989 MS).
The present writer was recently given theopportunity to re-examine the extraordinarygroup of Pitar from the Miocene and the
Pliocene deposits of various localities in
Hokkaido, Honshu, Korea, and western
Kamchatka. He proposed a new genus,
Gigantocallista, based upon Pilar sendaica
Nomura (1938) and included Miocene
species, P. okadana, P. itoi, and P. hokkaidoensis in the genus Neogenella Krishtofovich.
In this paper, the writer discusses the taxonomic and paleozoogeographic positions of
the new genus Gigantocallista. The taxonomic and paleozoogeographic problems of
Neogenella will be discussed in anotherpaper.

Systematic description
Order Veneroida H. and A. Adams, 1858
Superfamily Veneracea Rafinesque, 1815
Family Veneridae Rafinesque, 1815
Genus Gigantocallista Takagi, gen. nov.

Type species.- Pitar sendaica Nomura,
1938, by original designation. Pliocene Tatsunokuchi Formation, Sendai, Miyagi Prefecture, Japan.
Diagnosis.- Hunch-back like Callista-typegenus with high and strong hinge plate, peculiar cardinals and laterals; Neogenella-likecardinals in right valve and A-shape strong
cardinals of (2a)-(2b), and remarkably large
and heavy lateral in left valve.
Description.- Shell large, test thick,trigonalovate, strongly inflated; lunule wide,
cordate, obscurely impressed; escutcheon indistinct; sculpture consisting of incremental(:i h)

2 (A-TYPE)

3 (B-TYPE)

Figure 1. Hinge area of Gigantocallista. I:
right valve; (I): middle cardinal, (3a): anteriorcardinal, (3b): posterior cardinal, (AI) and (AIlI) :anterior lateral lamellae, N.: nymph. 2-3: left
valve; (2a): anterior cardinal, (2b): middle cardinal, (4b): posterior cardinal, (All): anterior lateral.
Hinge of right valve: consisting of 3 cardinals andtwo anterior laterals; the anterior (3a) and middle(I) cardinals almost perpendicular to the hinge
margin, middle (I) one heavy; the anterior (3a) one
short, posterior (3b) one bifid, anterior lateral lamellae (AI) and (AIII) indistinct and flanking a deep
socket, (AIlI) almost parallel to middle (I), cardinal.
Hinge of left valve: consisting of 3 cardinals and one
anterior lateral; anterior (2a) one rather thin; themiddle (2b) one very heavy, posterior (4b) one slender and almost joined to the nymph, anterior (2a)narrowly continuing to middle (2b) one and making
A-shape, anterior lateral (All) heavy, conical, andbifid, the base of (All) extending toward the beak.
The type species of Gigantocallista, G. sendaica
exhibits dimorphism in anterior lateral (All); mostof specimens have large thickened and strongly
inflated anterior lateral All (A-type), but one specimen, large but thinner than A-type and distinctly
bifid one (B-type).

growth lines and very weak radial striae;
hinge plate high, thick; hinge of right valve
consisting of 2 indistinct anterior laterallamellae (AI and AlII) flanking a deep
socket, and strong 3 cardinals, the anterior(3a) and middle (I) ones almost perpendicular to hinge margin, the middle (1) one heavy,
the anterior (3a) one short, the posterior one
bifid; hinge of left valve consisting of aheavy, conical, bifid anterior lateral (All) and3 cardinals, the anterior one (2a) rather thin,
the middle one (2b) very heavy, the posterior
one (4b) slender and almost joined to nymph,
the base of All extending toward beak; pal-

903.

Gigantocallista, a new venerid genus

lial sinus deep; ventral margin smooth.
Comparison.- Gigantocallista, gen. nov.
differs from all other venerid genera in possessing a high and strong hinge plate, and peculiar cardinals and laterals; Neogenella-likecardinals in right valve, A-shaped strong cardinals of (2a)-(2b), and a remarkably large
and heavy lateral in the left valve (Figure I).
Above mentioned dentition of Gigantocallista is dissimilar to that of Pitar, but of
Callista.
Callista Poli (1791, fide Cox et al., 1969)
resembles the present genus by having Ashaped cardinals of (2a)-(2b) and beak-side
stretched All in the left valve, which arecommon characters of the subfamily Callistinae N ordsieck ( 1969 ; fide Cox et al.,1969). However, the present genus differsfrom Callista in possessing a thin and lessinflated shell, a lower and thinner hinge plate,
and a smaller and thinner anterior lateral in
the left valve.
Nomura (1938) applied the genus Pitar
Romer (1857) to his new species sendaica,
designated as Gigantocallista herein, because
its teeth arrangement is of Pitar and its large
and heavy shell may be placed in Megapitaria. However, at that time, he had only worn
and imperfect specimens to examine. However, Pitar differs from Gigantocallista inpossessing a low and thin hinge plate, bridged
cardinals of (2a)-(2b) that are almost parallelto the hinge margin anterior lateral in the left
valve. The subgenera of Pitar, Pitarina
lukes-Browne (1913, fide Cox et al., 1969),
Lamelliconcha Dall (1902) and Hyphantosoma Dall (1902), have similar dentition, butdiffer from Gigantocallista.
Hysterochoncha Dall (1902) and Costel/ipitar Habe (195 I) also have Pitar-type dentition as mentioned above except for theirposterior cardinal in left valve and can beeasily distinguished from Gigantocallista by
having low and thin hinge plate, and bridged
cardinals of (2a)-(2b).
Nomura (1938) also discussed the relationof Pitar sendaica with Megapitaria Grant

543

and Gale (1931), and Amiantis Carpenter(1864, fide Grant and Gale, 193 I). However,Megapitaria, which was raised from the subgenus of Pitar to generic rank by Hertlein and
Grant (1972), differs from the present genus inpossessing a thinner shell, a low and thinnerhinge plate, bridged cardinals of (2a)-(2b),and a thinner anterior lateral in the left valve.
Amiantis resembles Gigantocallista in having large and heavy shell, but differs from thelatter in possessing a low and thin hinge
plate, a thin and short (3a) cardinal in its
right valve, bridged cardinals of (2a)-(2b)and an isolated long anterior lateral in theleft valve, that is almost parallel to hinge
margin.
Macrocallista Meek (1876 fide Grant andGale, 1931; Korobkov, 1954) resembles
Gigantocallista in having a large shell andA-shaped cardinals of (2a)-(2b) in the left
valve, but differs from the latter in possessing
a thin and elongated shell, a low and thinhinge plate, and a thin anterior lateral in theleft valve.
Ezocallista Kamada (1962) resembles thepresent genus in having a large shell, andA-shaped cardinals of (2a)-(2b) in its left
valve, but differs from Gigantocallista inpossessing independent cardinals of (2a) and(2b), and a thin anterior lateral in its left
valve.
Saxidomus Conrad (1897, fide Grant andGale, 1931) resembles the present genus inhaving rather distinct concentric lines on its
surface, and A-shaped cardinals of (2a)-(2b)in the left valve, but differs from Gigantocal!ista in possessing a thin shell, a low and thinhinge plate, and an anterior denticle joined to(3a) cardinal in its right valve.
Pseudamiantis Kuroda (Kuroda, 1933;
Iwasaki, 1963; Habe, 1977) resembles thepresent genus in having a large shell andsimilar dentition in the right valve. Chinzei
and Iwasaki (1967) applied the generic name
Pseudamiantis Kuroda (1933), without
description or remarks, to the type-species ofthe present genus and some authors followedToshio Takagi

544

them (e.g., Chinzei, 1978; Masuda, 1986;
Matsui, 1988). But Pseudamiantis differsfrom Gigantocallista in possessing low andthinner hinge plate, bridged cardinals of (2a)(2b), isolated (= not joined to nymph) (4b)cardinal in the left valve, distinct radial
threads on the surface, and a thinner shell(Figure 7-5).
Neogenella Krishtofovich (1955, fide Zhidkova et al., 1968) resembles Gigantocallista
in having a high and thick hinge plate and a
thick hunch-like shell. Amano (1983) included the type-species of the present genus in
Neogenella, but it differs from the present
genus in possessing bridged cardinals of (2a)(2b) in the left valve, and large middle cardinals (1) and short anterior (3a) one in theright valve (Figures 6-5a-b and Figure 7-6).
Gigantocallista is represented only by the
Pliocene G. sendaica (Nomura) from theTatsunokuchi Formation in Miyagi Prefecture and may be restricted to the Pliocene
Paleo-Sendai Bay (Chinzei and Iwasaki,
1967; Masuda and Ogasawara, 1981). Fromthe peculiar hunch-back like shell, high andthick hinge plate, and similar dentition except
Table I.

for anterior and middle cardinals in left valve,
Gigantocallista may have evolved from the
Miocene Neogenella. The relation of bothgenera with the taxonomic problem ofBeak Position

I
L•

Lengtht-Dc p t h~~~~~.....L~
Figure 2.
daica.

Measurement of Gigantocallista sen-

Measurements (in mm) of G. sendaica from the Tatsunokuchi Formation. B.P.: Beakposition (= distance anterior end to beak); Ds: depth of sinus; V: valve; R: right; L:
left; CON: conjoined. Locality; Goroku: G6roku Cliff, Sendai City; Sendai: unknown,
but in Sendai City; Chuo-5: Chl16 5-chome, Sendai City. SHK: Saito Ho-on Kai Museum
register number; UH: University of Hokkaido register number; * I : Masuda's collection at
Miyagi University of Education, 2: single valve %.

*

No.

Loc.

Meg. No.

LengthHeight

Depth

B.P.

Os.

H/L%

D/H%*2

BP/L%

V.

00-1
00-2
00-3
00-4
00-5
00-6
00-7
00-8
00-9
Se-I
Cu-I
Cu-2
Cu-3

OorokuOorokuOorokuOorokuOorokuOorokuOorokuOorokuOorokuSendaiChuo-5Chuo-5Chuo-5

SHK 4017
SHK 4017
SHK 4017
SHK 4017
SHKcl6131

66.0
96.0
74.0
69.0
82.0
96.5
58.0
72.0
86.0
90.2
96.0
86.2
81.6

55.0
78.0
61.0
57.0
78.0
84.2
47.0
62.8
72.8
77.0
90.0
78.0
76.6

22.0
33.0
27.0
25.0
64.0/2
71.6/2
17.0
21.5
26.0
51.4/2
28.9
25.5
27.9

15.1
22.4

19.8

83.3
81.3
82.4
82.6
95.1
87.3
81.0
87.2
84.7
85.4
93.8
90.5
93.9

40.0
42.3
44.3
43.9
41.0
42.5
36.1
34.2
35.7
33.4
32.1
32.6
36.4

22.9
23.3

R

35.6
29.0
29.7
33.3
31.2
28.8
27.9
29.6
31.9

CON.
CON.
L

*'
UH 31000
UH 31001
UH 31002*'
UH 31003
UH 31004
UH 31005

29.4
28.0
17.2
24.0
26.9
26.0
26.8
25.5
26.0

21.5
28.2
20.0

L
L
R

L

L
CON.
R
R
L

903.
Neogenella will be discussed
paper.

Gigantocallista, a new venerid genusIn

another3, lOa-b.
Pilar sendaica monstrosa Nomura, 1938, p. 259, pI.
35(3), figs. 8a-b, 9a-b.

Gigantocallista sendaica(Nomura, 1938)

Remarks: - The present writer reexamined the specimens of this species fromthe Tatsunokuchi Formation including
Nomura's type specimens in the Saito Ho-on
Kai Museum. Measured specimens are not

Figures 6-1-4b; 7-1-4

Pilar sendaica Nomura, 1938, p. 258, pI. 35(3), figs. 1-

1 0

60

545

90

H II

IOOmm
LengthFigure 3. Relation between height/length and length of Gigantocallista sendaica(Nomura). H/L %: height/length %; I: specimens from Goroku Cliff, Sendai City; 2:
specimens from Sendai City (locality unknown); 3: specimens from ChQo 5-chome, Sendai
City; 4: type-specimen of Pilar sendaica monslrosa Nomura.

1>/119'
5 0

0

0

o
o

4 0

0

o

0
0
30

50

60

1 0

H II

90

95mm

He I g h t

Figure 4. Relation between depth/height and height of Gigantocallista sendaica(Nomura). D/H %: depth/height %; symbols are the same as in Figure 3.

Toshio Takagi

546

III' /L"
3 5

0

A
3 0

0
A

0

0

t:.
A

2 5

o

o

20J-----r----r----.---~----,_----~--_r----~---,

60

7 0

80

lOOmm

90
LengthFigure 5. Relation between beak position (= distance from anterior end to beak)/length and length. BP /L %: beak position/length %; symbols are the same as in Figure 3.

so many because most of materials at hand
are imperfect. Statistically useful measured
data, therefore, will be needed for discussing
the strict variation of this species. Examining all material at hand, the writer recognizeda variation of height/length ranging from 81 %to 95% (Figure 3), and a variation of depth/
height ranging from 32% to 44% (Figure 4).
Generally speaking, the most common proportion is about 80-88% in the former, and in
the latter, 32-38%, both being observed inboth immature and adult shells. The present
species exhibits dimorphism in the anterior
lateral of the left valve (Figure I). Most
specimens have an A-type lateral, which islarge, thickened and strongly inflated. But
one specimen has a B-type lateral, which islarge, but thinner than the A-type, and distinctly bifid. The B-type lateral may beabnormal form of this species.

Nomura (1938) described Pitar sendaica
monstrosa based on specimens from the same
locality as Pitar sendaica, and noted that thissubspecies can be distinguished from sendaica (s.s) by "having more inflated valves,
beaks placed slightly more anteriorly with amore convex, or somewhat hump-back curvature along the postero-dorsal border". But
the type specimens of Nomura's P. sendaica(s.s) have more inflated shells (42.3-44.3% in
depth/height) than those of P. sendaica
monstrosa (41 %), and the proportion of beakpoint/length of Gigantocallista sendaica
from the Tatsunokuchi Formation grades
continuously from 27.9% to 36.3% (Figure 5).
Since they occur form the same place and can
not be divided from each other by morphological characters, Nomura's P. sendaica
monstrosa may be considered herein to be ajunior synonym of P. sendaica (s.s). Similar~
Figures 6-1 - 4b. Gigantocallisla sendaica (Nomura) 1-3, hinge area of left valve, I : U.H. Reg. No.
31006, X 1.35; 2: U.H.Reg.No.31007, Xl; 3: U.H.Reg.No.31008, xl; 4a-b: dorsal (4a) and right(4b) views, Prof. Masuda's collection in Miyagi University of Education, X I ; 1 - 3, Tatsunokuchi
Formation, ChOo 5 chome, Sendai City; 4, Tatsunokuchi Formation, Goroku Cliff, Sendai City. 5a - b,
Neogenella okadana (Yokoyama), interior and exterior views of left valve, for comparison, U.H. Reg. No.
31011, X I, Tachikaraushinai Formation, Utanobori-chou, northern Hokkaido.

903.

Gigantocallista, a new venerid genus

547

Toshio Takagi

548

morphological variation IS observed in its
related species Neogenella okadana (Yokoyama). Over 80 specimens of this species
are measured and examined, the writer recognized that some old large specimens of
Neogenella okadana tend to have more
inflated or somewhat hump-back curvature
along the postero-dorsal border, in general.
This species from the type locality has large
varietal form and ranges from typical hunchback like N. okadana form to low convex
even including N. hokkaidoensis form. The
variation and its relation to geological andgeographical distributions of this species will
be discussed in another paper.
Geologic and paleozoogeographic
distribution of Gigantocal/ista
The hunch-back like shells of the Miocene
Neogenella species and Pliocene Gigantocal!ista sendaica, may be closely related to eachother genetically and ecologically. Manydistinctive morphological characters are shared by these species and they also show aremarkably crowded occurrence in coarsegrained sandstone. Based on associated fossils and substrate, they evidently lived onshallow, sandy, and level bottoms (Chinzei
and Iwasaki, 1967). In Miocene time,
Neogenella was distributed widely in eastern
Asia, including Korea, Honshu, Hokkaido,
Sakhalin, and western Kamchatka. Duringlate Middle to Late Miocene time, Neogenella
lived in Hokkaido, Sakhalin and western
Kamchatka, but not to the south in Honshu
and Korea. During this period, the Wakkanai and Atsunai-Togeshita Faunas occupied in those northern areas. It seems that

this faunas lived in water which was cooltemperate, but still slightly warm, because
they were associated with intermingled cooland warm elements (U ozumi, 1962; Zhidkova et af., 1968; Amano, 1983, 1986;
Gladenkov, 1984; Menner, 1984).
Another hunch-back like venerid, Gigantocallista, was restricted geologically and geographically to the Pliocene Tatsunokuchi
Fauna in the "Paleo-Sendai Bay" (Chinzei
and Iwasaki, 1967; Masuda and Ogasawara,
1981). Though the Tatsunokuchi Fauna has
been recognized to be composed of cool waterelements, this fauna also includes some warm
water elements such as Trachycardium goro-kuense, Meretrix parameretrix, Anisocorbula
venusta, and Neverita kiritaniana (Nomura,1938). Since this fauna is composed of intermingled cool and warm elements, the Tatsunokuchi Fauna seems to have lived in waterthat was cool-temperate, but still somewhat
warm.
In Pliocene time, the Takikawa-Honbetsu
Fauna lived in Hokkaido, Sakhalin andKamchatka, but not in the Miyagi Prefecture
and its south. It seems that this fauna lived
within cool-water currents, similar to those of
the present day along the Pacific coast ofeastern Hokkaido (Uozumi, 1962; Takagi,
1982; Uozumi et al., 1986). In addition,
Dosinia tomikawensis Takagi, one of thecharacteristic species of the TakikawaHonbetsu Fauna, was distributed in Aomori,Hokkaido, and southern Sakhalin, but not in
the Sendai Basin and further south (Takagi,
1986; Uozumi et al., \986).
The Tatsunokuchi and the Kakegawa
Faunas were intermingled in the southernarea of Sendai (= the Ishiguma Formation of~
Figures 7-la - 4. Gigantocallista sendaica (Nomura), la - b, exterior and interior views of rightvalve, U.H. Reg. No. 31004, X I; 2 - 3, hinge area of right valve, 2: U.H. Reg. No. 31009, X 1.2; 3: U.H.
Reg. No. 310 I0, X I ; 4, exterior view of the right valve, U.H. Reg. No. 3100 I, X I ; la - 3: Tatsunokuchi
Formation, Chuo 5 chome, Sendai City; 4: Tatsunokuchi Formation, Goroku Cliff, Sendai City. 5,
Pseudamiantis tauyensis (Yokoyama), interior view of the right valve, for comparison, U.H. Reg. No.
31012, X I, Upper Ikeda Formation, Obihiro City, eastern Hokkaido. 6, Neogenella okadana (Yokoyama),
hinge area of right valve, for comparison, U .H. Reg. No. 310 13, X I, Oiwake Formation (= upper Iwamizawa
Formation), Iwamizawa Cily, central Hokkaido.

903.

GiganlOcal!isla , a new venerid genus

549

550

Toshio Takagi

Futaba and Tomioka Formation of Hirono,
Futaba-gun, Fukushima Prefecture). In
these mixed fauna, Fortipecten takahashii(Yokoyama) or F. kenyoshiensis Chinzei,
and cool-water elements, such as Puncturella

nobilis, Ariadnaria insignis, Turritella Jortilirata, Velutina plicatilis cryptospira, Cryptonalica janthostoma, Nucella lamellosa, Nucellalapillus, Neptunea arthritica, Japelion pericochlion, AulacoJusus periscelidus, Obestoma
simplex, A cirsa ochotensis, Glycymeris yessoensis, Limatula vladivostokensis, andSpisula polynyma are associated with warm
Kakegawa faunal elements (e.g., Suchium
giganteum yamamotoi, Neverita didyma,
Adusta onyx, Sydaphera spengleriana, Turritella ikebei, Glycymeris cf. nakamurai,
Chlamys miurensis, Chlamys satoi, CrYPlopecten vesiculosus, Nemocardium samarangae, and Anisocorbula venusta) (Hayasaka
and Hangai, 1966; Masuda and Ogasawara,
1981; O'Hara and Nemoto, 1988; Noda,
Kikuchi and Nikaido, 1989). Though it
contains cool-water elements, this fauna of
the Ishiguma and Tomioka Formations
seemed to live in warm-temperate habitat,
warmer than that of the Tatsunokuchi Fauna
and the Takikawa-Honbetsu Fauna (Hayasaka and Hangai, 1966; Takahashi, 1986;
Noda, Kikuchi and Nikaido, 1989).
Though this fauna includes FOrlipeClen, themolluscan fauna of the Ishiguma and Tomioka Formations is more similar to the southern
Kakegawa Fauna than to the Tatsunokuchi
and Takikawa-Honbetsu Faunas.
The Tatsunokuchi Fauna, which includes
Gigantocallista, lived in distinctive conditions, which resemble those of the late
Middle-Late Miocene of Hokkaido, Sakhalin
and western Kamchatka. These distinctive
conditions are reflected in the many endemic
species of shallow, sandy, level-bottom
dwellers that lived only within the Pliocene"Paleo-Sendai Bay". Such species include
GZvcymeris gorokuensis Nomura, Chlamys
sendaiensis Masuda, Ostrea palaeodenselamellosa Nomura, "EI)'cina" sendaiensis

Nomura, Trachycardium gorokuense Nomura, Dosinia tatunokutiensis Nomura, Meretrix
parameretrix Nomura, "Venerupus" hirosegawana Nomura, Tellina sendaica Nomura,
ZilJaea hataii Masuda and Noda, Relusa
gorokuensis Nomura, Batillaria shataii
Nomura, Caecum yotume Nomura, Lacunaihayasakai Nomura, Ch/orostoma yabei
Nomura, Sukenea basilirata Nomura, andGigantocallista sendaica (Nomura) (Nomura,
1938; Masuda, 1962; Hayasaka and Hangai,
1966; Masuda and Noda, 1969; Takagi,
1986; Masuda, 1986). These characteristic
species in the Tatsunokuchi Fauna imply an
unusual specialization under the influence ofintermingled cold and warm currents causedby special zoogeographical conditions(Nomura and Hatai, 1936; Hayasaka andHangai, 1966; Matsui, 1988; Noda, Kikuchi
and Nikaido, 1989). As mentioned above,
such a water condition was restricted geologically and geographically to the Pliocene,
which is why Gigantocallista lived only
within the Pliocene Paleo-Sendai Bay.

Acknowledgments
I am grateful to Prof. S. Uozumi of Hokkaido University, and Dr. L. Marincovich of
U. S. Geological Survey, for their continuous
encouragement during the present study andfor critical reading of the manuscript.
Thanks are also due to Dr. M. Akamatsu of
the Historical Museum of Hokkaido, forproviding information about his studies on
Pleistocene faunas in Hokkaido. Prof. K.
Masuda of Miyagi University of Education
and Assoc. Prof. K. Ogasawara of Institute ofGeology and Paleontology, Tohoku University are thanked for furnishing some venerid
specimens from the Tatsunokuchi Formationand for making the arrangements necessary
for the author's re-examination of venerid
fossils at Saito Ho-on Kai Museum andTohoku University. Thanks are due to Mr.
M. Honjo of the Ohyochisitsu Company at
Sendai Branch, for offering information on

903.

Gigantocallista, a new venerid genus

venerid specimens from the Tatsunok uchi
Formation in Sendai.

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Kanky6d6, Korea. Mem. Coil. Sci., Kyolo
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- - , 1936: The Meisen Miocene of North Korea.
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Masuda, K., 1962: Tertiary Pectinidae of Japan.
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characteristics of Japanese Cenozoic Molluscs.
Monogr. Mizunami Fossil Mus., no. 6, p.I-22,
pis. 7-10. (in Japanese with English abslracl)- - and Noda, H., 1969: Pliocene boring shells andtheir burrows from the environs of Sendai, Japan.
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552

Toshio Takagi

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beds in the vicinity of the town Tanagura,
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- - and - - , 1937: A list of the Miocene Mollusca
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Itoigawa, J. and Chinzei, K. eds., Faunal characteristics of Japanese Cenozoic Moll uscs.
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Formation. Bull. Fac. Educ., Shinshu Univ.,
no. 12, p. 61-97, pis. 1-2.
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Japan, Special Papers, no. 29, p. 211-226, pis.
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In, Noda, H., Kotaka, T., Masuda, K., Itoigawa,J. and Chinzei, K. eds., Faunal characteristics ofJapanese Cenozoic Molluscs. Monogr. Mizunami Fossil Mus., no. 6, p. 75-90, pis. 8-11. (inJapanese with English abstract)
Yokoyama, M., 1932: Tertiary mollusca from coalfield of Uryu, Ishikari. Jour. Fac. Sci., Imp.
Univ. Tokyo, Ser. 2, vol. 3, pt. 6, p.221-247.
Zhidkova, L.S., Kuzina, LN., LautenshHiger, F.G.
and Popova, L.A., 1968: Atlas of molluscs from903.

Gigantocallista, a new venerid genus

the Upper Miocene and Pliocene, Sakhalin.
Acad. Sci .• USSR. Siberian Section, p.I-176,
pis. I-50. (in Russian)- , Vevz, V.E., lIyina, A.P., Krishtofovich, L.V.,

553

Neverova, T.!., Savitsky, V.O. and Scherement'
eva, G.N., 1972: Atlas of Neogene Molluscs ofKuril Islands. Ibid., p.I-166, pis. 1-48. (inRussian)Tatsunokuchi ~ / I:J, Sendai 1wiJ', Miyagi -g~, Wakkanai ~P'.], Atsunai-Togeshita iJP'.]-wtT, Takikawa-Honbetsu fitJII-*BIJ. Aomori W~, Hokkaido ~ti'ia~, Ishiguma E~~.
Futaba ~~, Fukushima &;J1I" Kakegawa
Ikeda ifuB3. Obihiro *$, Utanobori lIfI.:
1t, Poroshin 1JI¥6m', Numata i'BB3, Oiwake ~7t, Iwamizawa:;'fi ~tR..

mJII.

*

Gigantocallista, -g~lIf<1wiJ'mO)~m't!t~ / I:J ~ Veneridae f4 (=-:tll~.) O)-m'~:f./)O) CPm't!t;J:Q.t lf~m't!t.t 1J.il:-t G~~t.dlJ~z. t 0t 'nl1> G Pitar ~t.:. ~~ I?.h "( ~ t.:~1tEO)~Wz.rrt', -g~lIf<1wiJ'mO)~/ l:J~iI'I?.il:-tG Pitar sendaica Nomura z.t c
I':'m'~ Gigantocallista z.~~I§-t Go *~Ii.~ L.. <*~-('.t <~1?A.,f':iJH~l(:, m:iJtJ:~t1R,~~O)~t!'r~-c-~~"'::Htl?.hGo Gigantocallista Ii., -to):Jfj~EfJ~~ (~t.:.~t1R. ~t$) iI~
CPm't!tt.:.$ <.il:-t G Neogenella ~I':'N <~1tI. L.., lltr~Ii.~~iI' 1?iJR:1=. L.. t.:;: c iI~5ffi <~~~.hGo it.:, *~0)7t;fpIi.~m't!to)t'nI1>GE1wiJ'~I.:.IlRI?.hG;: c~. ;J:l<.il:-tG~~
1tE t *~ c [liJ~O)lF.ft~EfJ, i1l!~EfJ7t;fpz.~-t t o)iI~~ L.. <~t,;: c ii, I? Gigantocallista
Ii., ~m't!to)~/ I:JtIJ!Io/.JtWO)i1l!~EfJ· ~~EfJtJ:~Af1z.~-ttO)c~*-I?.hGo ~*~~

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 159, pp. 554-561, 3 Figs., September 30, 1990

904.

EARL Y CARBONIFEROUS (VISEAN) CEPHALOPODSFROM THE HIKOROICHI FORMATION,
SOUTHERN KITAKAMI MOUNTAINS*SHUJI NIKO
Faculty of Integrated Arts and Sciences,
Hiroshima University, Hiroshima 730

Abstract. A new Early Carboniferous cephalopod fauna is described from the
Hikoroichi Formation of the southern Kitakami Mountains, northeast Japan. The faunaconsists of five species including three new taxa: Mooreoceras kinnoi, sp. nov., Neocycloceras (?) sp., Adnatoceras onimarense, sp. nov., Dolorthoceras (?) sp. and Slieroceras nishimllrai, sp. nov. These are the first Carboniferous orthocerids from northeast Japan.
Key words.

Hikoroichi Formation, Kitakami Mountains, Visean orthocerid fauna.

Introduction

Systematic paleontology

Carboniferous nautiloids from the Kitakami Mountains have been little investigated.
To date only a single form, Coelonautilus sp.
from the Lower Carboniferous of the Setamai
area, Iwate Prefecture has been previously
reported (Hayasaka, 1954). However, recent
collections by the staff members of the
Onimaru Quarry in the Hikoroichi area,
I wate Prefecture clarify the presence of adiverse molluscan fauna including cephalopods in the Lower Carboniferous Hikoroichi Formation at this quarry. Based mainlyon this material, five species of orthocerid
nautiloids including three new species aredescribed herein.
Specimens utilized in this report are stored
at Geological Section of Ofuna to City
Museum, Iwate Prefecture (OCM) or the
University Museum of the University ofTokyo (UMUT).

Order Orthocerida
Superfamily Pseudorthocerataceae
Flower and Caster, 1935
Family Pseudorthoceratidae
Flower and Caster, 1935
Subfamily Pseudorthoceratinae
Flower and Caster, 1935
Genus Mooreoceras Miller,
Dunbar and Condra, 1933

'Received October 3, 1989: revised
accepted Septem ber I. 1990

Type

species. - Mooreoceras

normaleMiller, Dunbar and Condra, 1933, from theMiddle Pennsylvanian of Kansas.

Mooreoceras kinnoi Niko, sp. nov.
Figures 1-1-3, 5Material.- Holotype, OCM G-SNOI, animperfect phragmocone.
Diagnosis.- Mcoreoceras with ornamentation of lattice pattern; siphuncle consists ofbarrel- shaped to pyriform connecting ringsand cyrtochoanitic septal necks with very

manuscript

554

904.

Carboniferous cephalopods from Kitakami

short brims.

555

Devonian of Pennsylvania.

Description.- The holotype is an orthoconic shell with a subcircular cross section,
70.5 mm in length. The shell surface ismarked by fine cancellate ornamentation of
longitudinal and transverse lirae. Sutures
are oblique and faintly sinuous. Septa are
relatively deep; approximately five camerae
occupy the corresponding dorsoventral shell
diameter. The siphuncle is situated centrally
and composed of barrel-shaped to pyriform
connecting rings and cyrtochoanitic septal
necks; dorsal necks are abruptly recurved(Figure 1-5). Siphuncular segment heights
range from 2.5 to 3.3 mm; maximum segment
expansion is 3.0 mm in width. Width[max.Jjheight ratio of siphuncular segments
ranges from 0.93 to 1.10. Brims are very
short. Camerae and endosiphuncle lack evident biogenic deposits.
Remarks.- The sinuate and oblique
sutures, broadly inflated connecting rings,
and absence of both cameral and siphonal
deposits suggest that the new species belongs
to the genus Mooreoceras Miller, Dunbar andCondra, 1933. Other species of Mooreoceras, however, lack conspicuous surface ornamentation, whereas M. kinnoi has cancellate
markings of lirae.
Occurrence and age.- This species wasrecovered from a calcareous sandstone bed of
the H2 Member (Kawamura, 1983), Hikoroichi Formation at the Onimaru Quarry (loc.
NSM-PCL6-53-3, see fig. I in Kase, 1988).
The calcareous sandstone bed has been regarded as Visean in age, based on the
productid brachiopods (Tazawa, 1984) andgastropods (Kase, 1988).
Etymology.- The species is named inhonor of S. Kinno, who discovered this cephalopod.
Genus Neocycloceras
Flower and Caster, 1935Type

species.- Neocycloceras

obliquum

Flower and Caster, 1935 from the Upper

Neocycloceras (?) sp.
Figure 1-4

Material.- One figured specimen, UMUT
PM 18784.

Remarks.- A single deformed and fragmentary shell, 28.4 mm in length, is tentatively referred to the genus Neocycloceras Flower
and Caster, 1935 based on its slender shell
shape, and slightly oblique and scatteredannulations. The shell surface is also sculptured by transverse lirae; each interspace ofannulation is marked by five to six transeverse
lirae. The internal structure is not preserved.
The surface ornamentation of the present
species is most similar to Neocycloceras harrisi Flower and Caster, 1935 from the Upper
Devonian of Pennsylvania. However, N.
harrisi differs from this species in having acloser spacing of annulations and lirae. The
present species can be distinguished from
Cycloceras dombarense Shimansky, 1968
from the Lower Namurian of southern Urals,
U.S.S.R., in that the latter possesses a lessslender shell.
Occurrence and age.- Same as Mooreoceras kinnoi Niko, sp. nov.
Subfamily Spyroceratinae
Shimizu and Obata, 1935
Genus Adnatoceras Flower, 1939

Type species.- Orthoceras spissium Hall,
1879 from the Middle Devonian of New
York.
Adnatoceras onimarense Niko, sp. nov.
Figures 2-2-5

Material.- Holotype, UMUT PM 18785,
an imperfect phragmocone.
Diagnosis.- Adnatoceras characterized byslowly expanding shell of elliptical cros.s .section and subcentral siphuncular position.

556

Shuji Niko

1

4

904.

Carboniferous cephalopods from K itakami

Cameral deposits episeptal-mural and hyposeptal type which form pseudoseptum in ventral side. Endosiphuncular deposits form
continuous lining on ventral wall.
Description.- The holotype is a slowly
expanding phragmocone, 47.0 mm in length,with an elliptical cross section and smooth
shell surface. Diameter of the conch is 6.0 X
4.5 mm at the apical end and expands up to
approximately 7.5 mm (dorsoventral diameter) over the length of the fragment. Septa
are moderately curved; approximately two
and one-half to three camerae occupy thecorresponding dorsoventral shell diameter.
The siphuncle occupies a subcentral position,and consists of cylindrical connecting ringsand subcyrtochoanitic septal necks; connecting rings are abruptly contracted at the septal
foramen (Figure 2-4). Siphuncular segment
heights range from 1.4 to 2.4 mm; maximum
segment expansion is I. I mm in width.
Width [max.] /height ratio of siphuncular segments ranges from 0.54 to 0.67. The area ofadnation is nearly equal to the width ofbrims. Cameral deposits are well developed.
On the ventral side of the siphuncIe, deposits
can be differentiated into episeptal-mural andhypo septal deposits, and they form pseudoseptum. Dorsally, biogenic carbonates consistof episeptal-mural deposits. Endosiphuncular annulus deposits are restricted to theventral side, and fusing to form continuous
lining.
Remarks.- Adnatoceras onimarense, sp.
nov., most resembles A. ichinotaniense Nikoand Hamada, 1987 from the upper Bashkirianof the Ichinotani Formation, central Japan,
in that both taxa possess a slender shell withsmooth surface and hyposeptal deposits.
The former species, however, does not exhibit
a rapid siphuncular shifting to the venter as
the shell growth, unlike A. ichinotaniense.
+---

557

Furthermore, the latter species has a lesselliptical cross section than that of the former.
A. araskense Gordon, 1957 from the middle
to upper Visean of Alaska, is also similar tothe present species in the siphuncular structure, but di ffers in having a circular crosssection of the shell and more rapid shell
expansion. In addition, A. araskense lacks
hyposeptal deposits. A. kipchakense
Shimansky, 1968 from the lower Visean of
Kazakhstan, U.S.S.R. is easily distinguishedfrom A. onimarense by its larger shell expansion ratio.
Occurrence and age.- Same as Mooreoceras kinnoi Niko, sp. nov.
Etymology.- The species is named for theoccurrence at Onimaru Quarry.
Genus Dolorthoceras Miller, 1931

Type

species.- Dolorthoceras

circulare

Miller, 1931, from the Upper Carboniferousof the Karakoram Mountains, India.

Dolorthoceras (?) sp.
Figure 2-1

Material.- Figured specimen, UMUT PM
18787, an imperfect phragmocone.
Remarks.- A single orthoconic phragmocone of moderately expanding shell represented by a cast and silicified connecting
ring. The specimen is 37.0 mm in length andincreases in diameter from 4.5 to 8.7 mm overthe fragment. There is no obvious external
ornament. Septa are gently to moderately
curved, forming straight and slightly oblique
sutures. The siphuncIe shifts slightly ventral
side in the adoral part; its segment is expanded in camerae. Cameral deposits consist of
L-shaped episeptal-mural type.

Figure 1. 1-3,5, Mooreoceras kinnoi Niko, sp. nov., holotype, OeM G-SNOI, 1, ventral view, X
1.5; 2, silicon rubber cast, showing surface ornamentation, X 5.0; 3, dorsoventral thin section, venter left, X
3.0; 5, partial enlargement of Figure 1-3, showing siphuncular structure, X 8.0. 4, Neocycloceras (?) sp.,
UMUT PM 18784, lateral view, X 2.5. 6, 511eroceras nishimllrai Niko, sp. nov., partial enlargement of Figure
3-5, showing siphuncular structure, X 8.0.

Shuji Niko

558

Figure 20 1, Dolorthoceras (?) sp. , UMUT PM 18787, weat he red lateral v iew ve nter right, X 3.0.
2 - 5, Adnaloceras onimarense Niko , sp. nov. , holorype, UMUT PM 18785; 2, lateral vie w of silicone
rubber cast, venter left, X 2.0 ; 3, cross thin section near apical e nd of the specimen , ve nter down , X 8.0 ; 4,p artial enlargement of Figure 2- 5, show ing siphuncular structure, X 15.0 ; 5, dorso ventral thin secti o n , vente r
left, X 4.0.

These features are characteristic of typicalpseudorthoceratids such as Dolorthoceras
Miller, 1931 but poor preservation of theinternal structure makes taxon o mic assign ment of the specimen equivocal.
Occurrence and age . - Sa me as MOOloeoceras kinnoi Niko , sp. nov.

Type species.- Sueroceras irregulare Riccardi and Sabattini , 1975, from the Carboni ferous of Chubut , Argentina.

Genus Sueroceras Riccardi
and Sabattini , 1975

Malerial.- Holotype , OCM G234, an Imperfect phr ag mocone. Para type s, OCM
G235 , a sma ll fragment of external shel l ;Sueroceras nishimurai Niko , sp. nov.
Figures 1- 6, 3- 1- 6

904.

Carboniferous cephalopods from K itak ami

559

4

Figure 3. Sueroceras nishimurai Nik o , sp. nov., 1 - 3, 5, ho lo type, Oe M G234, 1, parti a l en largementof Figure 3- 2, show in g surface orna mentati o n, X 5.0 ; 2, dorsa l v iew , x 2.0 ; 3, la tera l view, ve nter left , x
2.0 ; 5, dorsoventral polished sectio n, ve nter ri ght , X 3.0. 4, para type, OeM G236, weatherd shell , ap ica lend of the specime n, X 3.0. 6, para type , OeM G235 , latera l view, ve nter rig ht , X 2.0.

560

Shuji Niko

OCM G236, a deformed phragmocone withpartial body chamber.
Diagnosis.- Sueroceras with relatively
rapid shell expansion, subcircular cross section, sinuous transverse lirae, and fine longitudinal lirae which disappear on ventral sidein advanced growth stages. Siphuncular
position subcentral; septal necks very shortand partly cyrtochoanitic. Connecting rings
strongly contracted at septal foramen.
Description.- The holotype is an orthoconic phragmocone, 62.1 mm in length, with
subcircular cross section. The shell diameterof the apical end is 15.7 X 14.2 mm. The
surface ornamentation exhibits reticulate pattern; it is composed of considerably sinuoustransverse lirae, and fine longitudinal lirae of
which spacing shifts dorsal ward to close.
Sutures are straight and slightly oblique.
Septa are moderately curved; approximately
three camerae occupy the length of apicalconch diameter. The siphuncle is subcentral
and circular in cross section; it consists ofsuborthochoanitic to cyrtochoanitic septal
necks, and cylindrical connecting rings which
are strongly and abruptly constricted at the
septal foramen (Figure 1-6). Siphuncularsegment heights range from 5.2 to 5.5 mm ;maximum segment expansion is 3.5 mm inwidth. Width[max.J/height ratio of siphuncular segments is approximately 0.59. Brims
are very short. Biogenic carbonates are notpreserved in the present material.
One of the paratypes (OCM G235, Figure3-6) is a fragment of the shell wall, approximately 40 mm in length. The shell surface issculptured by sinuous and closely spacedtransverse lirae that are replaced by coarse
transverse lirae with broad salients in adoralshell, and dorsal ornamentation of longitudinal lirae.
The other paratype (OCM G236, Figure 34) is a natural mold of flattened orthoconic
shell, approximately 110 mm in length, andthis represents earlier growth stages than theholotype and the other paratype. Approximately one-half of the shell is a body chamberthat bears transverse and fine longitudinallirae. Connecting rings are cylindrical andconstricted at the septal foramen.
Remarks.- The present species is placedin the genus Sueroceras Riccardi and
Sabattini, 1975, because of the characteristic
reticulate surface markings with Dolorthoceras-like internal structure.
Eight species from the Lower Carboniferous to Permian had been referred or tentatively assinged to Sueroceras. Among them thisspecies is most similar to S. irregulare Riccardi and Sabattini, 1975 in general morphologyof the siphuncle. It differs from S. irregulare
by having a more rapidly expanding conch,
cyrtochoanitic septal necks with abruptly
contracted connecting rings, and closer septal
spacing. Moreover, longitudinal lirae of thepresent new species are coarser than in S.

irregulare.
Occurrence and age.- Same as MOOl'eoceras kinnoi Niko, sp. nov.
Etymology.- The species is named inhonor of S. Nishimura, who discovered thiscephalopod.

Acknowledgments
The author thanks Messrs. S. Nishimura, S.
Kinno (Onimaru Quarry Limited) and A.
Kaneko (Kyoto University) for providing thematerial utilized. In addition, Drs. T. Kase
(National Science Museum) and T. Kawamura (Miyagi University of Education) assisted him with field work and discovered several
fossils. Thanks are also due to Dr. K. Mori
(Tohoku University) and Mr. E. Sato (Ofunato City Museum) for access to some important
specimens. He also acknowledges to Drs.T.
Hamada and K. Tanabe (University ofTokyo) for critical reading of the first draft.
This research was supported by grants fromthe Japanese Ministry of Education, Science
and Culture (No. 01790346).

904.

Carboniferous cephalopods from Kitakami

References
Flower, R.H., 1939: Study of the Pseudorthoceratidae. Palaeontographica Americana, vol. 2, no.
10, p. 1-214, pIs. 1-9.
- - and Caster, K.E., 1935: The stratigraphy andpaleontology of northwestern Pennsylvania.
Part II: Paleontology. Section A: The cephalopod fauna of the Conewango Series of theUpper Devonian in New York and Pennsylvania.
Bull. American Paleont., vol. 22, no. 75, p. 199271.
Gordon, M., 1957: Mississippian cephalopods ofnorthern and eastern Alaska. U.S. Geol. Survey Prof. Paper 283, p. 1-61, pIs. 1-6.
Hall, J., 1879: Descriptions of the Gastropoda, Pteropoda and Cephalopoda of the Upper Helderberg, Hamilton, Portage and Chemung Groups.
N. York Geol. Survey, Palaeont. New York, vol.
5, pt. I, xv +492 p., pt. 2, 113 pIs.
Hayasaka, I., 1954: Younger Paleozoic cephalopods
from the Kitakami Mountains, Japan. Jour.
Fac. Sci., Hokkaido Univ., Ser. 4, vol. 8, no. 4,
p. 361-374, pIs. 22,23.
Kase, T., 1988: Early Carboniferous (Visean) gastropods from the Hikoroichi Formation of theKitakami Mountains, northeast Japan. Trans.
Proc. Palaeont. Soc. Japan, N.S., no. 149, p.
361-370.
Kawamura, T., 1983: The Lower Carboniferous formations in the Hikoroichi region, southern Kitakami Mountains, northeast Japan (Part I).

561

Stratigraphy of the Hikoroichi Formation.
Jour. Geol. Soc. Japan, vol. 89, no. 12, p.707722. (in Japanese with English abstract)
Miller, A.K., 1931 : Two new genera oflate Paleozoic
cephalopods from Central Asia. Amer. Jour.
Sci., Ser. 5, vol. 22, no. 131, p.417-425.
- - , Dunbar, C.O. and Condra, G.E., 1933: The
nautiloid cephalopods of the Pennsylvanian System in the Mid-continent region. Nebraska
Geol. Survey, Ser. 2, Bull. 9, p.I-240, pIs. 1-24.
Niko, S. and Hamada, T., 1987: Adnatoceras from
Middle Carboniferous of the Ichinotani Formation, Fukuji district, central Japan. Trans.
Proc. Palaeont. Soc. Japan, N.S., no. 148, p.
223-227.
Riccardi, A.C. and Sabattini, N., 1975: Cepalopoda
from the Carboniferous of Argentina. Palaeontology, vol. 18, pt. I, p. 117-136, pIs. 22-24.
Shimansky, V.N., 1968: Kamennougolnye Orthoceratida, Oncoceratida, Actinoceratida i Bactrida.
Academia Nauk SSSR, Trudy Paleontologicheskogo Institut, vol. 117, p. I-lSI, pIs. 1-20. (inRussian)Shimizu, S. and Obata, T., 1935: New genera of
Gotlandian and Ordovician nautiloids. Shanghai Sci. Inst., Jour., Sec. 2, vol. 2, p. 1-10.
Tazawa, J., 1984: Occurrence of Gigantoproductus(Carboniferous Brachiopoda) from the lower
Hikoroichi Formation, Kitakami Mountains andits significance. Earth Sci. (Chikyu Kagaku),
vol. 38, no. 2, p. 132-134, pI. I. (in Japanese)

Hikoroichi B~m, Ichinotani -rJ);fr, Kitakami Mountains ~U::illJt!!, Ofuna to ::kJiJ(}l1t,
Oimaru Jlb1L, Setamai ilt EH*.

m$~~illJt!!B~m~.E_eMM(~~-ilt)a~.:m$~~illJt!!rJ)~*~::kJiJ(}l1tmJlb1Ll*E~~.::.ltlli-t G T1l1lE_* f3 ~m~rJ) H2 $~ (~~ -ilt) iJ· Ga~.>a:'~tr~.~.~.~~EW>a:'.lli-tG~t~, ~l*E~rJ)~M., .ff.~reGrJ)~ • •*KlI) IjJl GiJ'l.::.t.(.-0t.: o *glfi-elt, 3 fJT1m>a:'1l;tr:;t/L-- 'J ~ '7 A § rJ)a~. 5 f.i>a:'§C.:tH.. t.: o .:ttL
G ft, Mooreoceras kinnoi, sp. nov., Neocycloceras (?) sp., Adnatoceras onimarense, sp.
nov., Dolorthoceras (?) sp., Sueroceras nishimurai, sp. nov.
*~~ B*iJ· GrJ)E_*c:;t Iv'J ~ '7 A §a~ • • llirJ)1JJ~c~t t.(.G o
YC.T~~-e,Trans. Proc. Palaeont. Soc. Japan, N.S., No. 159, pp. 562-586,9 Figs., September 30, 1990

905.

LOWER JURASSIC RADIOLARIANZONES OF SW JAPAN*
RIE HORI
Department of Geosciences, Faculty of Science,
Osaka City University, Osaka 558

Abstract. Four Lower Jurassic radiolarian assemblage-zones and four subzones are
established on the basis of radiolarian biostratigraphic data from the Inuyama and threeother areas of SW Japan. These zones are as follows in ascending order: the Parahsuum
simp/um (divided into Subzone I to IV), Mesosaturnalis hexagon us (newly proposed),
Parahsuum (?) grande and Hsuum hisuikyoense Assemblage-zones. These zones range inage from latest Triassic/earliest Jurassic (Rhaetian/Hettangian ?) to early Middle Jurassic(Bajocian). This age assignment is based on comparison with Early to Middle Jurassic
radiolarian biostratigraphy established in North America and Turkey.
Key words.

Lower Jurassic, radiolarian assemblage-zones, SW Japan.

scribed in this paper represents approximately
half a 10 m.y. time span and the zonal framework is derived from the assemblage-zones
proposed by Yao (1982) and Yao et al.
( 1982).

Introduction
Studies of Jurassic radiolarian biostratigraphy have advanced rapidly during the past
two decades. In Japan, a pioneer study on
Jurassic radiolarian zonation was made by
Yao et al. (1980) in the Inuyama area ofcentral Japan. At that time, each radiolarianzone represented an average of 10 m.y. interval. Needs for radiolarian zones spanning
shorter time ranges than those hitherto established has increasingly been felt for undertaking more precise analysis of stratigraphic
sequences. Since then, many workers haveproposed various zones which were summarized by Yao (1986). These zonations, however, produced some confusion.
The purpose of this paper is to revise andrearrange the radiolarian zones that had been
established for the Lower Jurassic of Japanand to discuss their ages through a comparison with radiolarian data from North America and Turkey. Each radiolarian zone de-Geologic setting
The Lower Jurassic radiolarian zones described in this paper are based upon biostratigraphic data obtained from continuous
sequences of Upper Triassic to Middle Jurassic strata in SW Japan. These sequences all
share almost the same lithostratigraphy, inwhich the lower part is composed of bedded
chert and the upper part of clastic rocks.
These units generally occur in a pile of imbricate tectonic slices and/or blocks in the
Mesozoic subduction-accretion complexes.
Eleven measured sections have been chosen
for the present biostratigraphical study.
These sections are located in four distinct
areas in SW Japan: six in the Inuyama area
and one in the Mt. Norikuradake area of the
Mino Belt, two in the Kuzuu area of the'Received October 30, 1989; revised manuscript
accepted September I, 1990.
562

905.

/

Lower Jurassic Radiolarian Zones

563

36~
"

~o

SEA OFJAPAN// [[J Mino Belt

/ 0

PACIFIC OCEAN

Chichibu Belt
I

100lm
I

IJ81:

Figure 1. Localities of the Kuma, Inuyama, Mt. Norikuradake andKuzuu areas of Japan.

Ashio Belt, and two in the Kuma area of the
Chichibu Belt in Kyushu (Figure 1).
A. Inuyama area (lat. 3Y, 25±2'N, long.
136°, 58±2'E)
The sedimentary complex exposed in thisarea comprises bedded cherts and clastic sedimentary rocks forming a large synform called
the "Sakahogi Syncline" (Mizutani, 1964),
and its lithologic distribution was studied indetail by Kondo and Adachi (1975), however,both stratigraphic and tectonic interpretations of the Triassic conodont occurrences incherts underlie or overlie clastic rocks, whichyield ammonite and plant fossils of Jurassic
age had not been fixed. Yao et al. (1980)
carefully examined the distribution ofradiolarians and conodonts in chert and clastic sedimentary rocks and found that imbricate slices composed of Triassic to Lower
Jurassic chert and Middle Jurassic (and possibly much younger) clastic sedimentaryrocks, were tectonically repeated at least fourtimes (Figure 2).
A generalized col umnar section of the chertand clastic sedimentary rocks in this area isshown in Figure 3. The section consists ofthe following six lithologic units in ascendingorder; 1) pale-green and black claystone
with pyrite nodules, thin chert layer anddolomite; 2) varicolored bedded chert; 3)
red and green siliceous mudstone; 4) black
mudstone with thin sandstone layer; 5) massive sandstone; 6) sandstone with mudstonelayer and tuff. The age of these rocks ranges
from Middle Triassic or Early Triassic '?
(Mizutani and Koike, 1982) to Middle or
Late Jurassic (Adachi, 1988). Six chert sections were measured and sampled for thisradiolarian study and their locations areshown in Figure 2.
Katsuyama (UF) Section: This is one of
the most complete sections of Upper Triassic
to Lower Jurassic strata (ca. 32 m thick)available in this area. Nakaseko and Nishimura (1979) described Late Triassic
radiolarians from a chert in the lower part ofthis section. Fragments of Mesozoic plantfossils were obtained from sandstone overlying the chert (Nishida et al., 1974). A late
Bathonian-early Callovian ammonite,
Choffatia (Subgrossouvia) sp. was reported
from a black siltstone float near this section(Sato, 1974; Sato and Westermann, 1985).
This ammonite was probably derived from a
mudstone facies of the clastic slice resting564

Rie Hori

1km",====;;;;;1'

CLJ clastic rocks
Figure 2. Geological sketch map of the I nuyama area (modified from Kondo andAdachi , 1975: Yao el at. , 1980) and location s of measured sections.

upon the chert unit (CH-3?).
Iw ayakannon (lY) Section: This section is
located at the chert unit, CH-4 of Yao et al.
(1980) , and consists of an approximately 25 mof bedded chert that is Early Jurassic in age(Hori , 1988). The chert is coherent with a
Middle Jurassic mudstone at the top , though
there is a stratigraphic break between the two.
This break is equivalent to the Hsuum hisuiky oense Assemblage-zone of Yao and Matsuoka (1981).
Kurusu (KU) Section: This section represents a complete sequence of Upper Triassic
to Lower Jurassic strata including theTriassic-Jurassic boundary. It is composedof a 35 m thick sequence of rhythmicallyinterbedded chert and mud stone (Hori , 1988) .
Teishyoji (PT) Section: Thi s section is
located above the chert unit CH -4 and structurally eq uival ent to the IY Section
mentioned above. At the top of this section ,the chert which represents the Parahsuum (?)

grande Assemblage (Yao et al. , 1982) iscoherent with sa ndstone (Matsuda et al. ,1981 ).
UC Section: The section is compo sed of arhythmically in terbedded sequence of chertand mudstone (Hori , 1986). The upper partof this section corresponds to th e section
studied by Iso za ki and Matsuda (1985a).
UA Section: This section corresponds tothe uppermost part of the section studied by
Yao et al. (1980) and Yao (1982). Hori
(1986) documented stratigraphic distributionof selected radiolarian species. The chert ofthis section includes the stratotype of the
Parahsuum simp/urn Assemblage (Y ao ,1982).
B. Mt. Norikuradake area (Iat. 36°, 8± I'N ,long. 13T, 37 ± l'E )The Mesozoic sedimentary complex of thisarea is called Yukawa Complex and can becorrelated with that of the Inuya ma area

905.

Lower Jurassic Radiolarian Zones

sandstone wi thmudstone layer
and tuff

u
(/)
(/)

oL

::J

--,

sandstone

Ilil-?Am

black mudstone----siliceousmudstone

565

Triassic to Lower Jurassic radiolarians from acontinuous chert sequence of the "Adoyama
Formation" in this area. They recognized
four radiolarian assemblage-zones for theUpper Triassic to Lower Jurassic interval.
Two sections, KuA (KA) and KuB-C-D(KD) were examined in this study. The KA
Section corresponds to the upper part of theSection C of Igo and Nishimura (1984) andconsists of a dark gray bedded chert of about
8 m in thickness. The other section, KuB-Co (KD) is the upper part of the Section B
reported by Igo and Nishimura (1984). It
consists of a rhythmically interbedded
sequence of chert and mudstone approximately 35 m in thickness, which is overlain bysandstone. Immediately below the chertsandstone contact, Brachyoxylon (silicifiedwood) was found (lijima et al., 1988).
Radiolarians obtained from this section are
Early to Middle Jurassic in age.

L.:

--,
varicoloredradiolarian chert

claystone-loL.Tr.?

Figure 3. Generalized columnar section of theInuyama area. Lithologic units and ages are basedon conodont and radiolarian data. W: stratigraphic position of fossil fragments of petrified Mesozoic
wood. ? Am: possible stratigraphic position of alate Bathonian-early Callovian ammonite.

based on similarities in the lithologic succession (Otsuka, 1988). The NK Section located I km northwest of Kanayama in the Norikura highlands consists of bedded chert andsiliceous mudstone. Hori and Otsuka (1989)
reported the stratigraphic distribution ofwell-preserved radiolarians from this section.
C. Kuzuu area (lat. 36°, 26±4'N, long. 139°,
35±4'E)
Igo and Nishimura (1984) reported Upper

D. Kuma area (lat. 32°, 21±4'N, long. 130°,37±4'E)
Late Paleozoic and Mesozoic radiolarians
from this area were studied by Nishizono etal. (1982), Nishizono and Murata (1983),
Sato and Nishizono (1983), Sato et at. (1986)
and others. Sato et al. (1986) established 13
radiolarian zones for the Lower Triassic toUpper Jurassic interval in this area. Twosections, the Kaiji (KG) and Kajiki (KS)Sections were investigated in this study.
The lithology and correlation of all measured sections are shown in Figure 4. The
distribution of· representative radiolarianspecies in these sections studied are shown in
Table I.
Radiolarian zonation
Four radiolarian assemblage-zones in theUpper Triassic to lower Middle Jurassic of
the studied areas are described in this paragraph. These zones are the Parahsuum simplum (Ps), Mesosaturnalis hexagonus (Mh),Parahsuum (?) grande (Pg), Hsuum hisui-

u.
0'>
0'>

sw

NE

KS

Pg

Mh

:::t!

li;.

~
;::;.
UA

~mudstone[[[] chert['mFigure 4. Lithology and correlation of the sections studied (see text for section names), showing selected sample
localities, which yielded those radiolarian species listed in Table I. Hh: Hsuum hisuikyoense Assemblage-zone; Pg:
Parahsuum (?) grande Assemblage-zone; Mh: Mesosaturnalis hexagonus Assemblage-zone; Ps: Parahsuum simp/um
Assemblage-zone; Ct: Canoptum triassicum Assemblage-zone. All the assemblage-zones are described in the text with the
exception of the Ct Assemblage-zone proposed by Yao (1982).

Occurrence of radiolarian species listed in Figure 5 and a conodont species in samples from SW Japan.
present, Open square: absent. (continued)

Table I.

~_SAMPLE LOCALITIES~-RA0 TOLA R 1 AN SPEe T ES

KG Section
I
KS SectionI
UF Section
I 1 O'-I.:I:..'.:..:!:.
OJ_IN!ML~11~!~~a>,,,o~!~[1I~I~ II,....!m ~l~:;....;i~~:.:;:::..;::..I
IoUNIMI.,I~I~j~Ia>!",oll
I I I I r-. ~1~-'o-NM~~~~a>",o-N. . . I_ ..............
. . . -t' ......
0'1""" ...................................................

~ I:..... N M ~ V'\>D:r;!~

N N_N!M:-:r LI)<C!

c f.

I

I

so. B

-+-

-,--t-

=-

--I

I

R

I

•

sp.A

lo.Sy.rif1R.ocapsa coliforme
I 2 . B1 Pe d 1 ~0- ............................................................ N N N N+ ...~.~,J-j+H+H+H--H-+-l+H+H+I-++I-++-l--l-~-l+I~-I"H+H+t-r-t-I-I-+-++I-l..,LII-++I++-++I-+-H!-I--H+H-i-H..J-jk III ens c

7.G. aff. gongy oideum
B.Dictyonlitrelln sp.C

1 1. S.

IY Section:~ I!a:J o-NM~~~~a>",o-NM~I§

NN N_ N M -:t V"III:) ......

I•~: ~~ r~! ~~ i ~~ ll~ ~~~ 1 oid eum

9.XenorumCO~~,~~~~:~I~~~I~!~!~!~;~I~~;;:~ ~ ~,~I~!~I~I~~~:;::;~l~I~!~~'~;a:;a~,~*~~,~j~!~g;Ig;\g;I~g;g;g;g;g;g;g;g;g;g;g;g;g;g;g;g;;:;::;:;;:;:;:;;:I::::::;:;::;::;::;::;:;:;;:;;::;:;;::;::;:;::

l.Deflandrec rtium sp.A
L.Snuinabolella?
SD.C
3.Pantancllium cf. rothwelli
4 . P.

N .... iN!M!-:t!LI"'I!\O

Solid square:_____,_

I..J.J..JL.I--+-I-W-I--I-I-~ P. A-i-H-l.H+I-++I-+-H-i--H-i-+-'.I-+-H..-H-l-H-i-W++-+-HI-H......+-1-+-+-.+-1.I-+-H~-H-l-+-+-l-W++-+-H!-H=tt:jjjt:li~±tt±tJ.".".itt~""'''''"""H-i-+-++I-+~!-

1 • B. S P • 11
15.P.
simoium
1 4 .pa.fnhSllum
nCt.

Ion

iconicum____ __..

~afUJj~Efll:I-1-+-H
IB~B~~!afUJj~E'8!afUJj~Ei8!BB..+4i1

1 7 • C; 1 g aff.
i s p fl'--~----------I+H-I-H--H+H+H+H--HH--H+H+H+I+-H+H+H+H-+I-I-I
r8.G.
Custis

16. P. ovnl e rf.
.1_9.Knlromnbicornus

20.K. "p.N
2 I • K.

~-H++-++I""I'~I-+-H~-H-i-+-+-l-+-++I-+-I--I-H

k u r II s tJ ens i s~~~~H+I-++I--~-H-I--+-l+H-I--~~-I--I--~+~_ -~l--I--I-+14+I-+-I..I~"".H-+I-++I-++-l+H+H+I-++I-+-H'-f-.LJ

22.Bagotum spp.
23. Za r t u 5 s P p.
24.0urnitrirOlclla (?) sp.A2').Ares('!)~ 6 . Pan tan ell ill m c f. dan a ens e2_~~~~J'~_~ell\lm (?)
28.Nilpora spp.

l-

I

sp.D

_.-~11tat~Ejat.tat~E±~±Etet~trn
I -1'-H',_.
CD
I
Ii

L

I

f-L!--fE~~: ~;Ir ~~! ~~ f ~-i nson i

nosthernstpini_~~_==C)~j

I-1- =tI:

L

~

t"-<

\:)

~...,
~
~
~

;::;0

::tI

I::l

I::l...

CO

i::l
~.

;::;

~

;::;

~

-=t:j=tt:jit:t±b......lllttlt.

r-L_H+I-++H-+-IH-H+

grande~Uc~~t~:~;~~~~~~

1"'---+H--HH-+-t+I-

L=~_

46.Nassell~ria
en. etindct.X
47 . Un urn n (S PJl •48. And romeda sp. D
49.Hsllum aff. hisuik~oens~?O.Stichocaps? nrf. Japonlca
51.Lilxlorum (?~ ]lIrassicum
52 . L. ("') hie his 0 ens e

CONODONT: Misikella'I--~---tf-:-tl~-t=lr-:):1-~+=1-tf-+r=-t1=1-:):I=I:Jqtl=):tl=):~~~-~+4__~-~~I-

42. Mesosa til rna 1 is hexagonus
43.Transhstlum medium
44.Archicapsa pachyderma

T'

'

j.J

I=R-r

1m 1 n i
37.PnrahsuumI1?l aff. magnum
38.HslIum 5 l.H:l9.PnrahsulIm transicns~(Y:Parvicing~lil 1l00lloconica
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905.

Lower Jurassic Radio/arian Zones

kyoense (Hh) Assemblage-zones in ascendingorder. Furthermore, four subzones of the Ps
Assemblage-zone are proposed on account ofspecies composition. The Mh Assemblagezone is newly proposed herein.
A. Definition of zone
Radiolarian zones are defined by the presence of a characteristic species or a pair ofsuch species and in practice, taking maximum
ranges of characteristic species into consideration. This concept is similar to the radiolarian zonation based on the Unitary Associations method (e.g., Baumgartner et a/., 1980;
Baumgartner, 1984). Because which species
among the Lower Jurassic radiolarians is
endemic or pandemic is not known, there is aproblem of selecting a species pair suitablefor establishing a zonation by the use of U.A.
method. Thus, further work is required toapply the U.A. method to a Lower Jurassic
radiolarian zonation.
The upper boundary of four zones isdefined as the level which corresponds to thelower boundary of the superjacent or overlying zone. These four zones are described
below beginning with the lowest.
l. Parahsllum simp/um (Ps) Assemblagezone (Yao, 1984, emended)
The base of this zone is defined by thelowest occurrence of P. simp/wn in association with Dictyomitrella sp. C.
The present author selected the U F Section(UF6-16) of the Inuyama area as thestratotype of this assemblage-zone and thefollowing species including two diagnostic
species, Parahsuum simp/um Yao, P. ovale
Hori and Yao, are characteristic in this zone.
These species are: Ares (?) sp. D (= Parares
sp. of Takemura, 1986), Bipedis sp. A, B. sp.
B, Dictyomitrella sp. C of Yao (1982),
Dlimitricaella (?) sp. A, Eucyrtidiellum (?) sp.
C group of Nagai (1986), Gigi aff. Justis De
Wever, Gorgansium gongy/oideum Kishida
and Hisada, G. aff. gongy/oidellm, Katroma
kllrusuensis Hori, K. cf. bicornlls De Wever,
Pantanellillm cf. k/uense Pessagno and

569

Blome, P. aff. kluense, P. cf. danaense Pessagno and Blome, Parahsuum aff. longiconicum Sash ida, Syringocapsa co/iforme
Hori, S. sp. B of Yao (1982), Trillus e/khornensis Pessagno and Blome, Xenorum sp. A,
Bagotum spp., Napora spp., and Zartus spp.
The geologic range of this zone is theuppermost Triassic to middle Lower Jurassic(upper Pliensbachian to Toarcian?).
Remarks: The Dictyomitrella sp. CArchaeodictyomitra sp. A Assemblage was
first proposed from the Inuyama area by Yao
et a/. (1980). Subsequently, Yao (1982)
renamed it as the Parahsuum simp/um (Ps)
Assemblage. A biostratigraphic unit assignable to the Ps Assemblage was first describedby Yao (1984) from the Kii-Yura area of the
Chichibu Belt.
This assemblage-zone is subdivided into
four (I-IV) subzones in ascending order suchas: the Parahsuum aff. /ongiconicum,
Katroma kllrusuensis, Eucyrtidiellum (?) sp.
C, and TI'illus e/khornensis Subzones.
Subzone I (Parahsuum aff. /ongiconicum
Assemblage-zone)-The following species are
obtained from this subzone: Bipedis sp. A,
B. sp. B, Dictyomitrella sp. C of Yao (1982),
Gigi spp., Gorgansium gongy/oideum, G. aff.
gongy/oideum, Pantanellium aff. kluense, P.
cf. k/uense, Parahsuum ova/e, P. simp/um, P.
aff. /ongiconicum, Syringocapsa coliforme, S.
sp. B of Yao (1982), and Xenorum sp. A.
Among them, Gorgansium gongy/oideum, G.
aff. gongy/oideum, Xenorum sp. A andPantanellium aff. k/uense are dominatedspecies. The range of these species extends
downwards into the Canoptum triassicum(Ct) Assemblage-zone (Yao, 1984).
The geologic range of this subzone is theuppermost Triassic (Rhaetian) to lowest Jurassic (Hettangian to Sinemurian ?).
Subzone II (Katroma kurusuensis Assemblage-zone)- This zone yields Ares (?) sp. D(= Parares sp. of Takemura, 1986), Bagotum
spp., Bipedis sp. A, B. sp. B, Dictyomitrella sp.
C of Yao (\ 982), Dumitricaella (?) sp. A, Gigi
aff. Justis, Katroma kurusuensis, K. cf. bicor-

570

Rie Hori

nus, K. sp. N of Hori (1988), Pantanellium
cf. danaense, Parahsuum ovale, P. simplum,
Syringocapsa coliforme, S. sp. B of Yao(1982), Xenorum sp. A, and Zartus (?) sp.
This subzone is defined by the co-occurrenceof K. kurusuensis and G. aff. Justis. Many
specimens of taxons belonging to the genus
Katroma (e.g., K. kurusuensis, K. bicornus
and K. sp. N) are found in this zone. Rare
specimens belonging to the species of thegenus Bagotum are observed in the chert
sequences, but this genus is also common, andoccasionally abundant, in a mudstone facies,
e.g., Kaiji Section of Kyushu.
The range of this subzone is the Lower
Jurassic (Sinemurian to lower Pliensbachian ?).
Subzone III (Eucyrtidiellum (?) sp. C
Assemblage-zone) - This zone is characterized by the following species: Ares (?) sp. 0(= Parares sp. of Takemura, 1986), Bagotum
spp. (e.g., B. modestum Pessagno andWhalen), Eucyrtidiellum (?) sp. C group of
Nagai (1986), Katroma kurusuensis, Napora
spp., Parahsuum ovale, P. simplum Yao,
Dumitricaella (?) sp. A, and Zartus spp.
The base of this zone is defined by the lowest
occurrence of Eucyrtidiellum (?) sp. C group.
Near the base of this zone, the following
species make their apparent final occurrences;
Bipedis sp. A, B. sp. B, and Gigi aff. Justis.
The geologic range of this zone is theLower Jurassic (lower Pliensbachian? toupper Pliensbachian).
Subzone IV (Trillus elkhornensis Assemblage-zone)- This subzone yields the following species: Bagotum spp., Dumitricaella (?)
sp. A, Eucyrtidiellum (?) sp. C group of Nagai(1986), Katroma kurusuensis, Napora spp.,
Parahsuum ovale, P. simplum, P. aff. longiconicum, Trillus elkhornensis, and Zartus
spp.
The base of this zone is marked by thelowest co-occurrence level of T. elkhornensis
and species of the genus Katroma. In some
sections, it is often difficult to distinguish
Subzone IV from Subzone III.

The range of this zone is the Lower Jurassic(upper Pliensbachian to Toarcian?).
2. Mesosaturnalis hexagonus (Mh) Assemblage-zone (new)The base of this zone is defined by thelowest occurrence of Mesosaturnalis hexagonus (= Acanthocircus hexagonus Yao) in
associated with Parvicingula nanoconica
Hori and Otsuka. This assemblage-zone is
proposed for the interval between the Ps
Assemblage-zone and the Pg Assemblagezone.
The present author selected the IY Section(IYII-17) of the Inuyama area as thestratotype of this assemblage-zone and thefollowing species including two diagnostic
species, M. hexagonus and P. nanoconica,
are characteristic in this zone. These are:Ares (?) sp. 0 (= Parares sp. of Takemura,1986), Hsuum altile Hori and Otsuka, H. sp.
B of Hori and Otsuka (1989), H. sp. X of
Hori and Otsuka (1989), H. (?) sp. Y of Horiand Otsuka (1989), Parahsuum simplum Yao,
P. lransiens Hori and Yao, P. (?) aff.
magnum Takemura, P. (?) sp. B of Hori andOtsuka (1989), Parvicingula cf. gigantocornis
Kishida and Hisada, Transhsuum medium
Takemura, Trillus elkhornensis Pessagno andBlome, Napora spp., Tripocyclia spp., andZartus spp.
The range of this zone is the Lower Jurassic(Toarcian) to lower Middle Jurassic(Aalenian ?).
Remarks: This zone was formerly named
the Acanthocircus hexagonlls Assemblagezone (Hori, 1987, 1988). An assemblage reported from the Mt. Norikuradake area (Horiand Otsuka, 1989) is typical of this zone. In
addition to the zonal index species, M. hexagonus, this zone is characterized by a nassellarian assemblage consisting mainly of thegenera HSllllm, Parahsllllm (?) and Parvicingula (s.I.). The first recorded occurrence ofParvicingula (s.l.) is observed at the base ofthis zone. These assemblages were reportedby Matsuda and Isozaki (1982), and Kishida
and Sugano (1982). Based on the co-905.

Lower Jurassic Radiolarian Zones

occurrence of conodonts and radiolarians,
they tentatively assigned a latest Triassic toearliest Jurassic age. The recent radiolarian
data indicate that this fauna is a late Early toearly Middle Jurassic age.
3. Parahsuum (?) grande (Pg) Assemblage-zone
The base of this zone is defined by thelowest occurrence of Parahsuum (?) grandeHori and Yao in association with P. transiens Hori and Yao.
The present author selected the IY Section(IYI8-24) and PT Section (PTS-8) of theInuyama area as the stratotype. This
assemblage-zone is characterized by the following species incl uding a diagnostic species,
Parahsuum (?) grande (= P. sp. D of Yao etal., 1982): Andromeda sp. D of Yao et al.
(1982), Archicapsa pachyderma (Tan Sin
Hok), Ares (?) sp. D (= Parares sp. of Takemura, 1986), Laxtorum (?) hichisoense Isozaki and Matsuda, L. (?) jurassicum Isozaki
and Matsuda, Parahsuum simplum Yao, P.
transiens Hori and Yao, P. (?) aff. magnum
Takemura, P. nanoconica Hori and Otsuka,
Stichocapsa aff. japonica of Yao et al.
(1982), Transhsuum medium Takemura,
Hsuum sp. B of Hori and Otsuka, H. aff.
hisuikyoense Isozaki and Matsuda, Nassellaria gen. et sp. indet. X, Mesosaturnalis hexagonus (Yao), Napora spp., Tripocyclia spp.,
Unuma (?) spp., and Zartus spp.
The range of this assemblage-zone is theupper Lower Jurassic (Toarcian ?) to lower
Middle Jurassic (Aalenian ?).
Remarks: Yao et al. (1982) first reported
the Parahsuum sp. D (= P. grande) Assemblage from the Inuyama area of the Mino Belt
and the Kurosegawa area of the Chichibu
Belt in SW Japan. Several species are common to the Mh Assemblage, however, the Pg
Assemblage is distinguished by the occurrence of multisegmented nassellarians with alarger test, such as Parahsuum (?) grande andLaxtorum (?) jurassicum.
4. Hsuum hisuikyoense
blage-zone(Hh)

Assem-

571

The base of this zone is defined by thelowest occurrence of H. hisuikyoense Isozaki
and Matsuda in association with L. (?) jurassicum Isozaki and Matsuda. The top coincides with the base of the Unuma echinatus
Assemblage-zone.
According to Yao et al. (1982) and others,
this assemblage-zone is characterized by thefollowing species including three diagnostic
species, Hsuum hisuikyoense Isozaki andMatsuda, Laxtorum (?) jurassicum Isozaki
and Matsuda, and L. (?) hichisoense Isozaki
and Matsuda: Archicapsa pachyderma (TanSin Hok), Dictyomitrella aff. kamoensis
Mizutani and Kido, Eucyrtidiellum unumaense (Y ao), Parvicingula sp. C of Yao et al.
(1982), Mesosa turn alis hexagon us (Yao),
Stichocapsa aff. japonica Yao, Tricolocapsa(?) fusiformis Yao, T. cf. ruesti Tan Sin Hok,
Trillus elkhornensis Pessagno and Blome,
Unuma sp. A ofYao (1984), Unuma sp. C of
Yao et al. (1982), Zartus sp. A ofYao et al.
(1982), and Zartus cf. dickinsoni Pessagno
and Blome.
The range of this assemblage-zone is thelower Middle Jurassic (Aalenian? to Bajocian).
Remarks: The Hsuum sp. B (= H. hisuikyoense) Assemblage was first recognized by
Yao and Matsuoka (1981) in a siliceous
mudstone of the Inuyama area. Yao et al.
(1982), Yao (1983, 1984), and Isozaki andMatsuda (198Sa, b) subsequently examined
this assemblage and listed various characteristic species. Yao (1984) defined this assemblage-zone in the Kii- Yura area of the Chichibu Belt.
Age of assemblage-zones
In SW Japan, Lower and lower Middle
Jurassic radiolarian fossils are very rarely
associated with age-diagnostic species ofother micro- and macro-fossils. Ages ofradiolarian zones therefore are based on comparison of the Japanese faunas with otherwell dated radiolarians in North America andTurkey by taking into account their faunal or
B.

Rie Hori

572

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15
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16
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11
18
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-19
19Kat roma cf. bicornus De \·,1e\'er, 1982
20
2OK. s p. N---21
21K. kurusuensis Hori ,1988"llBago tum spp.
22
- --- --232ar tus spp.
24Dum i tricael1a (?) sp.A
24----- --15A re s(?) sp.D of Yao et a1.(1982)
25
16Pan tane11ium cf. danaense Pessilg1l0 & Blome,1980-1 26
21Eue yrtidiellum(?) sp.C grotl!) of NFlgai(1986)
21--- 'ldNap ora spp.
-19
29Bag otum modestum Pessagllo & Whall'n,1982
JOTr i llus e1khornensis Pessagno & Blome,1980
1--31
31Pan'icingula cf. gigantocornisKishida & Hisada,1985-'!IPar ahsuum(?) sp.B of lIori & Dtsuka(1989)
f--32
33Hsu um a1tile Hori & Otsuka,l989
33
34-.14H. s p.X of Hori & Otsuka(1989)
35H. ( ?).
sp.Y of Hori & Dtsuka( 1989)
t--P5
362ar tus aff. imlayi Pess;lgno & Blom(',1980f--~631
31Par ahsuum(?) aff.magflumnf lIori & Otsuka(1989)
38
38Hsu um sp. S of lIori & Dtsuka( 1989)
39
39Pa r ahsuum transiens 1101' i & YilO, 1988
-40Pa r vicingula nanoconica Ilori & OL~uka, 1989--- -<llTr i pocyclia spp.
2Mes osaturnalis hexagonus(Yao, 1972)- r--- 43Tra nshsuum medium Takemura, 1986
Arc hicapsa pachyderma(Tilll Sin lIok,1927)
45Par ahsuum (?) grande liar i & Yao. 1988
f-t--46Nas sellaria gen. et sp. indel.X-<l1Unu ma ( ?) s'p p •....8And romeda sp.D of Yao et a1.( 1982).... 9Hsu urn aff. hisuikyocnse lsozak i & Natsuda,1985
f---- 505t i chocapsa aff. japonica of Yao et a1.(1982)- f---- 51Lax torum (?)jurassictlm lso;l,aki & Natsud<l,1985r--- 52L. ( ?) hichisoenseI~()z;1ki & MilLsuda, 1985
f---- 53Hsu um matsuokai lso;l.ak i & Matsuda. 1985r--- 5411. hisuikyoense IS();I,nki & ~laLsudil.1985
f---- 552a r tus cf. dickinsoni Pessagno & Blome,1980

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4 P. c f. kluense Pessagno & Blome,1980
5 P. a ff. kluense Pessagno & Blome,1980
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905.

Lower Jurassic Radiolarian Zones

specific compositIOn and relative stratigraphic positions.
When those four assemblage-zones described above are compared with radiolarianfaunas from Lower and lower Middle Jurassic
formations of the Queen Charlotte Islands in
British Columbia, Canada, and those fromeast-central Oregon, U.S.A., three criticalbiohorizons can be dated. These are, (I) thebase of the Ps Assemblage-zone; (2) the baseof the Mh Assemblage-zone; and, (3) the topof the Hh Assemblage-zone.
Parahsuum simplum Assemblage-zone:
The Ps Assemblage-zone is probably dated asa Rhaetian/Hettangian?- late Pliensbachian and early Toarcian? age.
The base of the Ps Assemblage-zone can beplaced in the Hettangian or lower horizon(Rhaetian) because of the following threeconstraints; I) The lowest co-occurrence
horizon of Parahsllum simplum Yao and
Diclyomilrella sp. C of Yao (1982) (= thebasal boundary of this zone) lies below the
first occurrence horizon of the genus
Kalroma Pessagno and Poisson emend. De
Wever. According to Pessagno et al. (1987),
its first occurrence defines the base of radiolarian Zone 04 where radiolarians are associatedwith lower Sinemurian ammonites in the
Kunga Formation (= Sandi lands Formationof Cameron and Tipper, 1985), Queen Charlotte Islands. These facts indicate that thebase of this zone probably lies in the lower
Sinemurian or lower. 2) The basal boundary of this zone lies a few meters above thefinal occurrence horizon of conodonts. In
continuous chert sequence in the Inuyama
area which crosses the T riassic-J urassic
boundary, the lower limit of this zone isalways observed a few meters above the highest occurrence horizon of conodonts; this isrepresentative the final occurrence of Axiolh-ea posthernsteini (= Misikella posthernsteini
Kozur and Mock) that occurs with such
Triassic radiolarians as Defiandrecyrtillm
Kozur and Mostler and Squinabolella Kozur
and Mostler. The highest occurrence of A.

573

posthernsteini was reported from the Choristoceras marshi Zone (uppermost Triassic;
Rhaetian, or upper Upper Norian of Tozer,1980) by Mostler et al. (1978). It is, therefore, highly probable that the basal boundaryof this zone is within the Rhaetian or lowest
Jurassic. 3) The basal boundary is below thefinal occurrence level of Pantanellium afr.
kluense Pessagno and Blome. According toPessagno and Blome (1980), P. afr. kluense
occurs from the Rhaetian (?)/Hettangian partof the Kunga Formation (= Sandi lands Formation of Cameron and Tipper, 1985) of the
Queen Charlotte Islands.
Hori (1986) and Yao (1986) noted theco-occurrence of some characteristic species
in this zone, Bagotum spp., Canoptum spp.,
Katroma spp., Pantanellium cf. danaense
Pessagno and Blome and Trillus spp., andcorrelated this assemblage-zone with a interval from a part of the Sinemurian to Pliensbachian. Additionally, the base of the superjacent Mh Assemblage-zone is considered to
be a middle Toarcian age, as discussed below.
The top of the Ps Assemblage-zone, therefore,
may extend upward to an early Toarcian age.
Mesosaturnalis hexagonus Assemblagezone: Hori and Otsuka (1989) discussed theage of the Mh Assemblage. They inferredthat its age ranges from late Early to early
Middle Jurassic, at least including a certain
interval of the Toarcian, based on their examination of a fauna representative of the Mh
Assemblage which was recovered from the
Mt. Norikuradake area.
Based on the following criteria, the Mh
Assemblage-zone is assignable to a time interval between the Toarcian and Bajocian withits base definitively beginning the middle
Toarcian.
Near the base of this zone, Parvicingula (s.
1.) and Mesosaturnalis hexagonus make theirfirst appearances. According to Carter et al.
(1988), species of the gen us Parvicingula (s.l.)
are not found in the upper Pliensbachian tolower Toarcian Fannin Formation, but occur
in the middle Toarcian Whiteaves Formation,

574

Rie Hori

the middle to upper Toarcian and Aalenian
Phantom Creek Formation, and the lower
Bajocian Graham Island Formation, all of
the Queen Charlotte Islands. They suggestthat the first appearance of Parvicingula (s.l.)in the Queen Charlotte Islands occurs in
middle Toarcian strata that are approximately equivalent to the Hildoceras bifrons Zone.
On the other hand, Mesosaturnalis hexagonus first occurs in the upper middle Toarcian part of the Phantom Creek Formation(upper Haugia variabilis to lower Grammoceras thouarsense Zones, in Carter et al.,1988) of the Queen Charlotte Islands. Theseradiolarian data indicate the base of this zone
to lie probably in the middle Toarcian.
The top of the Mh Assemblage-zone probably lies in the Middle Jurassic (Aalenian
and/or Bajocian) because it always occupies
a stratigraphic position between the underlying Ps Assemblage-zone (Rhaetian/Hettangian ?- upper Pliensbachian) and the overlying Pg Assemblage-zone (possibly older
than Bajocian age, as mentioned below) in all
the continuous sequences in the Inuyama andother areas of SW Japan.
Parahsuum (?) grande Assemblage-zone:
The exact age of the Pg Assemblage-zone isdifficult to determine from a direct comparison with North American faunas due to thescarcity of species common to both theseareas. Only the stratigraphic position of thiszone, higher than the Mh Assemblage-zone
and lower than the Hh Assemblage-zone,
enables us to determine its approximate age.
The Mh Assemblage-zone is probably correlatable with an upper Lower Jurassic tolower Middle Jurassic interval, at least including the middle Toarcian. The upper limit of
the Hh Assemblage-zone may lie in the Bajocian (Isozaki and Matsuda, 1985b and in
this paper). Thus, its age may be assigned to
an interval from the middle Toarcian to
Aalenian?
Hsuum hisuikyoense Assemblage-zone:
According to Isozaki and Matsuda (I 985b),
the lower part of the Hh Assemblage-zone isprobably of late Early to middle Middle
Jurassic. The present author narrows a possible age of this zone to a shorter time interval
between Aalenian? and Bajocian because of
the following reasons. The Unuma
echinatus (Ue) Assemblage, an assemblage
immediately overlying the Hh Assemblage, isinterpreted to be either Bajocian or Bathonian in age (Mizutani and Koike, 1982;
Yao, 1986; Yokota and Sano, 1986, etc.).
The upper limit of the Hh Assemblage-zone
therefore can be datable as Aalenian or Bajocian in age. Tricolocapsa (?) fusiformis
Yao is a characteristic species that occurs
both in the Hh and Ue Assemblages-zones.
According to Carter et al. (1988), this species
is not found in the Pliensbachian to lower
Aalenian Maude Group but occurs in thelower Bajocian part of the Yakoun Group(Ovalis Zone to lower? Laeviuscula Zone) of
the Queen Charlotte Islands. Considering
the stratigraphic data of these component
taxons, the top of Hh Assemblage-zone can be
drawn within an upper Aalenian to lower
Bajocian interval.
On the other hand, the age of its base isdifficult to place on the basis of faunal content. Because the Hh assemblage has few
species in common with the late Toarcian to
Aalenian fauna reported from North America, its stratigraphic position provides the
only clue its age. This zone lies stratigraphically above the Pg Assemblage-zone.
The Pg Assemblage-zone has not been dated
precisely. The age of the subjacent Mh
Assemblage-zone, however includes at least
middle Toarcian time. Thus, the base of the
Hh Assemblage-zone is believed to postdate
the middle Toarcian.
C. Age of Subzones I-IV of the Parahsuum
simplum Assemblage-zone
The age of Subzones I-IV ranges fromlatest Triassic/earliest Jurassic (Rhaetian/Hettangian ?) to Early Jurassic (late Pliensbachian to Toarcian ?). The base of the Ps
Assemblage-zone agrees with the base of

I
Al

2
BI

3

A2

A3

A4

Kishida and
THIS STUDY

Matsuoka and

Yao (1986)

Kishida andSugano (1982)

0:

::E

Sash ida, Tonishi

A6

B3

Salo andNishizono (1983)

Sato, Murata

Nishizono andand Yoshida

Igoand Nishimura

and Igo (1986)(1985.1986)(1984)

Sashida and

Murata (1983)

Igo (1985)

N ishizono, Ohishi

Sashida (1988)( 1986)

Salo and
Murata (1982)
Southwest

Southwest

Japan

Japan

Hsuum
hisuikyoense

Laxtorum (?)

jurassicum-?
POTahsuum (1)grandeArchicapsa
pachyderma

Mesosaturnalis

u

5
B2

Hisada'"0..:~

4
A5

hexagon us

<n
Vl
..:

Sakawa area
Chichibu Belt

Uena-mura area

Kuzuu area

Kanto region

Itsukaichi a.

Kuma area

Kuma area

Chichibu Belt

Ashio Bell

Chichibu Belt

Chichibu Belt

Chichibu Belt

Chichibu Bell

Zarlus jurassicus

Hsuum sp. G

Archaeodictyomitra
sp. C

1

Spongocapsu/a (?)
sp. ASpongocapsu/a (?)
sp. A

'?

Laxlorum ('!)
jurassicum

Hsuum minoralum

~
~

t"'-

o

f---??-

Parvicingula ('!)
-sp. A
Parvicingula (?)
sp. B

Parvicingula?

gigantocornis~....
Droltus (?) sp. A

HSllum minoratum

1

~

-

~

Dro/lus (?) sp. G

r;'

?

'~"

Parahsuum sp.
-

IV

r-III

Parahsuumt--simp/urn

Panlanellium sp.

r---r--?

Parahsuum
ovale

Pahlanellium

BagolUm sp. A

Parahsuum
takarazawQt'nse~.. Archaeodiclyomitra"
directiporata.. Eucyrtidium" sp. A

Parahsuum
directiporala

~

s.s.

."'ii

;:s

~

"''0~"

11..JParahsuum simp/um~

Gorgansium
sp. A

o'

....~

;:s

Wrangellium

E
~

!

$::l

~

!So

I-?

sp. B

-

I

-

[

Gigi sp .

E~

Parahsuum simp/urn

Parahsuum
simp/um.. Archaeodiclyomitra"
sp. A

-

~
Para hsuum sp. A

Triassocampe sp. A~~'" I - - - ' ! -I

Kalromaelliptica~-

Figure 6. Correlation of radiolarian zonations established for the Lower Jurassic of Southwest Japan.
Al-A6: Assemblage-zones, Bl-B3: Range-zones and Interval-zones.
V.

-.-J

v.

Rie Hori

576

Subzone I, while the upper boundary of thePs Assemblage-zone coincides with the upper
limit of Subzone IV. Other mutual boundaries between these subzones are marked by
the first occurrences of some characteristic
species belonging to the genera Bagotum,
Katroma and Trillus. The oldest species of
Bagotum, B. erraticum Pessagno andWhalen, is known from the Sinemurian partof the Kunga Formation (QC 549) (Pessagno
and Whalen, 1982). Thus, the base of Subzone II is probably in the Sinemurian.
According to Pessagno and Poisson (1981),
and Pessagno and Blome (1980), the lowest
horizon of co-occurrence of Trillus elkhornensis and species of the genus Katroma wasfound in the upper Pliensbachian Nicely
Formation (Amaltheus margaritatus ZonePleuroceras spinatum Zone) (OR536) in eastcentral Oregon. The base of the Subzone IV,
therefore, can lie in the upper Pliensbachian.
On the basis of these age constraints, Subzones I to IV are assigned to the following
ages; I: RhaetianjHettangian?-Sinemurian?, II: Sinemurian-early Pliensbachian?,
III: early Pliensbachian ?-Iate Pliensbachian,
IV: late Pliensbachian-early Toarcian?

Correlation of Lower Jurassic
radiolarian zones
A.

Correlation in Japan
In Japan, various radiolarian zones havebeen proposed for the Lower Jurassic interval
after the first zonal description of Yao et al.
(1980). Eight distinctive zonation schemes,
five using assemblage-zones, (A2-A6) andthree using other radiolarian biozones (B 1B3), are shown in Figure 6 along with thezonation presented in this paper (A 1).
I. Correlation with zones of Matsuoka
and Yao (1986): They proposed three
radiolarian zones in the Lower Jurassic of
SW Japan defined by biohorizons of the firstor last appearance of characteristic species(Figure 6, BI).
The base of their Parahsuum sp. C (= P.

ovale) Zone roughly coincides with that ofthe present Ps Assemblage-zone. The P.
ovale Zone seems to be a long-ranging zone
and correlative with a combined intervals of
the present Ps and Mh Assemblage-zones.
Concerning the next younger Archicapsa
pachyderm a Zone, A. pachyderm a (Tan Sin
Hok) is found in the Pg Assemblage-zone but
it lacks in the Mh Assemblage-zone. Matsuoka and Yao's this zone is a short ranging
zone and correlated with a part of the Pg
Assemblage-zone. Their Laxtorum (?) jurassicum Zone is correlative with the upper
part of the Pg Assemblage-zone and the entire
Hh Assemblage-zone.
2. Correlation with zones of Kishida andSugano (1982), and Kishida and Hisada(1985, 1986): Kishida and Sugano (1982)
studied some continuous sequences of chertand clastics in the Sakawa area in Shikoku of
the Chichibu Belt and recognized four successive assemblage-zones for the uppermost
Triassic and Lower Jurassic (Figure 6, A2).
Subsequently, Kishida and Hisada (1985,
1986) revised these zones on the basis of earlyJurassic radiolarian data obtained from asedimentary complex in the Ueno-mura areaof the Chichibu Belt. They recognized threeassemblages and two subassemblages for the
Lower Jurassic (Figure 6, A3).
Their Bagotum pseudoerraticum Assemblage-zone can be correlated with the Subzones I, II and III of the Ps Assemblage-zone
based on its faunal composition. The
Katroma elliptica Subassemblage-zone intheir zonation is roughly attributable to the
Subzone I because this subassemblage-zone
contains G. gongyloideum, P. afr. simp/um
and species of the genus Gigi and lacks
species of the genus Katroma. In theirclassification, the genus Gigi includes species
belonging to the genus Katroma, e.g., K.
elliptica. The Wrangellium (s.s.) Subassembiage-zone can be correlated with the Subzones II and III of the Ps Assemblage-zone
judged by the presence of species of the gen us
Katroma and the absence of Trillus e/khor-

905.

Lower Jurassic Radiolarian Zones

nensis.
Their Parvicingula gigantocornis Assemblage-zone which is synonymous with theirprevious Parvicingula (?) sp. A- Parvicingula(?) sp. B Assemblage-zone, can be correlated
to the Mh and a part of Pg Assemblage-zones
on the basis of the first occurrence of thegenus Parvicingula (s.1.).
The base of their Spongocapsula (?) sp. A
Assemblage-zone can lie within the upper
part of the Pg Assemblage-zone because S. (?)
sp. A (= Laxtorum (?) jurassicum) firstoccurs in the upper part of the Pg
Assemblage-zone. Kishida and Hisada(1986) equated the top of this zone with thebase of the Ue Assemblage-zone (= the top of
the Hh Assemblage-zone), however, it is questionable that the S. (?) sp. A Assemblagezone can be correlated to the whole of the HhAssemblage-zone due to lacking of characteristic species obtained from the upper part of
the Hh Assemblage-zone.
3. Correlation with zones of Igo andNishimura (1984): They documented fourradiolarian assemblage-zones for an Upper
Triassic to Lower Jurassic chert sequence ofthe "Adoyama Formation" in the Kuzuu
area. They recognized two Lower Jurassic
radiolarian assemblage-zones (Figure 6, A4).
Their Parahsuum simplum- Gigi sp.
Assemblage-zone is correlative with the lower
part of the Ps Assemblage-zone on the basisof species composition. Because their Parahsuum sp.-Pantanellium sp. Assemblage-zone
was not fully documented in their paper, its
upper boundary can not be correlated exactlywith the zones presented in this paper.
4. Correlation with zones of Sashida andIgo (1985), Sashida et al. (1986) and Sashida(1988): Sashida and Igo (1985) and Sashida
et al. (1986) recognized three successive
radiolarian assemblage-zones for Lower Jurassic strata in the Kanto region of the Chichibu Belt (Figure 6, A5). Sash ida (1988)
later revised them and proposed four zones
based on the radiolarian distribution in three
sections in the Itsukaichi area of the Kanto

577

Mountains (Figure 6, B2).
Their Parahsuum simplum Zone is correlatable with the Subzones I and II of the Ps
Assemblage-zone of this paper jUdging fromits species composition and stratigraphic position.
Sash ida's (1988) P. takarazawaense Zone
which corresponds to the Bagotum sp. A
Zone includes Trillus aff. elkhornensis andEucyrtidiellum sp. A (= Eucyrtidiellum (?) sp.
C group in this paper). Thus, it can becorrelative with the Subzones III and IV of
the Ps Assemblage-zone.
His Hsuum minoratum Zone as defined by
the first occurrence of H. minoratum at thebase is roughly correlated with the Mh and apart of Pg Assemblage-zones, because abundant species of the genera Hsuum and Parvicingula are present.
The Laxtorum (?) jurassicum Zone of
Sashida (1988) is considered to be coeval with
the Laxtorum (?) jurassicum Zone of Matsuoka and Yao (1986).
5. Correlation with zones ofNishizono etal. (1982), Nishizono and Murata (1983),
Sato and Nishizono (1983) and Sato et al.
(1986): Nishizono et al. (\982), Nishizono
and Murata (1983), and Sato and Nishizono(1983) investigated a radiolarian biostratigraphy of a Permian to Cretaceous sequence inthe Kuma area of Kyush u and recogn ized 16
assemblages. Two radiolarian assemblagesof Early Jurassic age were discriminated (Figure6, A6).
Based on their species composition andstratigraphic position, their "Archaeodictyomitra" sp. A- Triassocampe sp. A Assemblage-zone and the "Archaeodictyomitra"
directiporata -"Eucyrtidium" sp. A Assemblage-zone can be correlated with the combined intervals of the Subzone I and the lower
part of Subzone Ill, and that of the part ofSubzone III and Subzone IV of the Ps Assemblage-zone. For examples, the latter assemblage-zone is characterized by species ofsuch genera Napora, Trillus and Zartus,"Eucyrtidium" sp. A and B (=Eucyrtidium

V>

-...J
00

EAST

.~
~
ro

AMERICA

NORTH

ASIA

....

'J
~

'M

<::
=0

~

THIS STUDY

Tikhomirova(1988)

Southwest JapanFa r Eas t U. S. S. R.

Vishinevskaya( 1988)
Fa r East U. S. S. R.

Murchey( 1984)
California

Pessagno et a 1.
( 1987)
Composite
Zone IB( pa r t)
SubzoneSuper-

i

MH-2

r--?

Parahsuum(?) grande,

Zone

t

1

Mesosaturnalis?

hexagonus

IV

s::J

III

"'<
Q,

Trilluse1 khornensis

Zone

T

Eucyrtidiellum(?)

sp.C group

....s

.L
Bagotum modestum

R:3

01

Droltus hecatensis

'00"

....

c:::
~

~

1A
Subzone

5

lA2

4

3
2

I

Toa
M

I

I

-u

L

Subzone 01B
Subzone 01A

U

C/l
C/l

«

U

-

0::

Plb

::>
~

L

- -

Jl

s::J

Zone 03

U

::J
I/]

.,
.,

Aal

?

I/]

.c:
L.

Baj

i.

6

Zone 02

i

U

~

MH-1

-

c
c
....

,;;;

v

Zone

( pa r t)

J~

i

i

IA1

0

7

J2

Hsuum hisuikyoense

Ul

Carter et a 1.
(1988)
Queen Charlotte Is.

Katroma (?) cf.

Katroma

II

'"

R:2
kurusuensis

bicornus- Sin

Zone 04

Ll'
I

Parahsuum af f .

longiconicum

R: 1

--

Archecyrtum sp.A
Archetypum sp.A

Het

Zone 05

Figure 7. International correlation of Lower Jurassic radiolarian zones in the circum-Pacific region.
phic units after Westermann (1985). The arrow represents possible range of zone.

Chronostratigra-

0::
UJ

~
0
....J

~

Ri'

~
....

-.

905.

Lower Jurassic Radiolarian Zones(?) sp. C group) and "Archaeodictyomitra"
directiporata (= Parahsuum ovale Hori andYao, 1988).
Subsequently, Sato et al. (1986) proposed
13 new radiolarian zones for Lower Triassic
to Upper Jurassic strata based on radiolarian
data accumulated from Kyushu (Figure 6,
B3). In their zonation, three range zones andone interval zone were defined for a Lower
Jurassic to lower Middle Jurassic interval.
The Parahsuum sp. A and Parahsuum directiporata Zones are equivalent with theirprevious "Archaeodictyomitra" sp. A- Triassocampe sp. A Assemblage-zone and the"A rchaeodictyomitra" directipora ta -" Eucyrtidium" sp. A Assemblage-zone, respectively. The former zones, therefore, can be correlated with the lower part of the Ps
Assemblage-zone (Subzones I, II and a part ofIll) and the latter zone is correlatable with theupper part of the Ps Assemblage-zone (Subzone IV and a part of Subzone III) in thispaper.
The Droltus (?) sp. A-Droltus (?) sp. G
Zone is correlatable with the Mh and thelower part of the Pg Assemblage-zones basedon this stratigraphic position.
Near the base of the Hsuum sp. G Zone,
Spongocapsula (?) sp. A (= Laxtorum (?)
jurassicum) makes its first appearance. The
Hsuum sp. G Zone can, therefore, be correlated with a part of the Pg Assemblage-zone andthe Hh Assemblage-zone.
B.

International correlation
Several radiolarian zones proposed for a
Lower Jurassic interval in the circum-Pacificregion, particularly, zones established in the
Queen Charlotte Islands and east-central
Oregon are well dated by ammonites andother age diagnostic fossils. An international correlation of those Lower Jurassic
radiolarian zones of Japan with those of East
Asia and North America is summarized in
Figure 7.
1. Correlation with zones of Pessagno etal. (1987): They established six radiolarian579

zones for a Lower to lower Middle Jurassic(Hettangian to Aalenian?) interval, namely
Zones 05,04,03,02,01, and lA, in descending order.
The base of the Zone 05 is coincident withthe first appearance level of Pantanellium
kluense and the last that of P. rothwelli. In
Japan, the highest co-occurrence of P. cf.
kluense and P. cf. rothwelli is immediately
below the base of the Ps Assemblage-zone.
The base of the Zones 04 and 0 I is defined by
the first appearance of Katroma spp. and
Trillus elkhornensis, respectively; these biohorizons correspond to the base of subzones
II and IV of the Ps Assemblage-zone. The
Zone 05, therefore, is correlated with the
Subzone I, and the Zones 04 to 02 can becorrelatable with the Subzones II and 111 of
the Ps Assemblage-zone in SW Japan. The
top of the Zone 01 is defined by the final
appearance of Praeconocaryomma parvimamma as well as the first appearance of Parvicingula (s.I.), therefore, the Zone 01 can becorrelatable with the Subzone IV of Japan.
The base of the Zone I A is defined by the
first appearance of the gen us Parvicingula(s.I.). Judging from its stratigraphic position
and radiolarian components, the Zone I A
can be correlated with the Mh Assemblagezone and a part of the Hh Assemblage-zone ofpresent study.
2. Correlation with zones of Carter et al.
(1988): They proposed seven radiolarianzones, Zones I to 7, for upper Pliensbachian
to lower Bajocian strata in the Queen Charlotte Islands. These zones have a short timespan and their ages are well controlled byammonite evidences. Because of the scarcityof species common to both Japan andCanada, these zones are occasionally difficult
to correlate with the Japanese assemblagezones. However, the Zones I and 6 may becorrelative respectively with the Subzone IVof the Ps Assemblage-zone and with the HhAssemblage-zone, based a comparison on thegenus level.
The Zones 2 to 5 interval can be roughly

580

Rie Hori

equated to the Mh Assemblage-zone based on
the first occurrence of Parvicingula (s.I.). andMesosaturnalis hexagonus.
The co-occurrence of Trieoloeapsa (?)
Jusiformis and Zartus jurassieus was reported in the Zone 7. Therefore, it is probably
attributable to the Hh Assemblage-zone.
3. Correlation with zones of Murchey(1984): She described seven radiolarianassemblages (Marin Headland Assemblages;
MH-I to MH-7) from a Jurassic-Cretaceouschert sequence in the Franciscan Complex,
northern California, U.S.A.
The assemblage MH-I includes species of
the genera Katroma, Napora and Eueyrtidium (?), and Bagotum aff. modestum. In
the upper part of this assemblage-zone, thefirst occurrence of T. elkhornensis is recognized. Hence, the MH-I Zone is correlatedwith the upper part of the Ps Assemblagezone (Subzones III to IV) in SW Japan.
The assemblage MH-2 includes Parvicingula sp. A (= P. nanoeoniea), Mesosaturnalis hexagonus, Hsuum sp. B (= H. altile),
T. elkhornensis, Napora spp. and underlies
the MH-3 Assemblage which is correlatedwith the Unuma eehinatus Assemblage.
On the basis of its radiolarian compositionand stratigraphic positIOn, the MH-2
Assemblage-zone can be correlated with the
Mh Assemblage-zone, the Pg Assemblagezone and a part of Hh Assemblage-zone of
SW Japan.
4. Correlation with zones of Tikhomirova(1988): Tikhomirova (1988) identified 12
radiolarian assemblages from Lower Jurassic
to Lower Cretaceous strata along the Amur inthe Khabarovsk region, central Sikhote-Alin

and in Primorye, Far East U.S.S.R. The
following four assemblage-zones, R: I, R : 2,
R: 3 and R : 4, were established for an interval from Lower Jurassic to the lowest part of
Middle Jurassic.
The R: I is characterized by Areheeyrtum
sp. A and Arehetypum sp. A belonging to
the family Archecyrtiidae Tikhomirova, 1987.
These species have not been recognized in theLower Jurassic strata in Japan, thereby making it difficult to correlate the R: I withJapanese zones. According to Tikhomirova(1988), the assemblage-zone is Hettangian inage based on its stratigraphic position, hence,
it is tentatively correlated with the Subzone Iof the Ps Assemblage-zone.
The R : 2 is characterized by Katroma (?)
cf. bieornus, Gigi Justis and others. Speciesof the genera Katroma and Gigi, such as
Katroma cf. bieornus and Gigi aff. Justis,co-occur in the Subzone II of the Ps
Assemblage-zone of Japan, hence, the R : 2 iscorrelated with the Subzone II of the Ps
Assemblage-zone.
The R: 3 is characterized by Bagotum
modestum and Droltus heeatensis. B. modestum occurs in the Subzone III of the Ps
Assemblage-zone of this paper. The R: 3,
therefore, is roughly correlative to the upper
part of the Ps Assemblage-zone, namely the
Subzones III and IV. The R: 4 situatedabove the R: 3 is characterized by Unuma
typieus and by lacking species of Canoptum,
Katroma, Gigi, Bagotum, and Droltus.
Therefore, the R : 4 can not be correlated withLower Japanese ones because of the lacks ofcommon species.
5. Correlation with the zones of Vishnevs-~
Figure 8. Scanning electron micrographs of late Triassic to Early Jurassic radiolarians from theMesozoic complex of SW Japan. Figure number corresponds to taxon number of I to 30 in Table I and
Figure 5. Scale bar= 200 J.lm for all figures except for 17 (= 300 J.lm), 4, 23, 26, 29 (= 133 J.lm), and 3, 22 (=100 J.lm). 1: Defiandrecyrtium sp. A, 2: Squinabolella (?) sp. C, 3: Pantanellium cf. rothwelli, 4: P. cf.
kluense, 5: P. aff. kluense, 6: Gorgansium gongyloidellm, 7: G. aff. gongyloideum. 8: Dictyomitrella sp. C,
9: Xenorum sp. A, 10: Syringocapsa coliforme, 11: S. sp. B, 12: Bipedis sp. A, 13: B. sp. B, 14:Parahsullm aff. longiconicum, 15: P. simplum, 16: P. ovale, 17: Gigi sp., 18: G. aff. justis, 19: Katroma
cf. bicornlls, 20: K. sp. N, 21: K. kurllsuensis, 22: Bagotum sp., 23: ZarlllS sp., 24: Dllmitricaella (?) sp.
A, 25: Ares (?) sp. D, 26: Pantanellium cf. danaense, 27: Eucyrtidiellum (?) sp. C group, 28: Napora sp.,
29: Bagotum modestum, 30: Trillus elkhornensis.

905.

Lower Jurassic Radiolarian Zones

581

582

Rie Hori

905.

Lower Jurassic Radiolarian Zones

kaya (1988): She established several radiolarian zones in the Jurassic to Paleocene formations of the Far East U.S.S.R. She recognized two Lower Jurassic radiolarian zones,
Ji and Ii. Because both zones include speciesof the genera Bagotum and Hsuum, theboundary of J1 and Ji lies within the Pliensbachian. Judging from their radiolariancontent, the J1 Zone can be correlatable with
the Subzones II, III and part of IV of the Ps
Assemblage-zone. The Ji Zone correlateswith an interval from the uppermost part of
the Ps (upper part of Subzone IV) to the Pg
Assemblage-zones.
Conclusions
Four radiolarian assemblage-zones andfour subzones are described for an uppermost
Triassic/lowest Jurassic to lower Middle Jurassic interval. These are the Parahsuum
simplum Assemblage-zone (divided into Subzones I through IV), Mesosatllrnalis hexagonus Assemblage-zone, Parahsuum (?)
grande Assemblage-zone, and HSllllm hisuikyoense Assemblage-zone (Figure 5). A correlation of these four zones with those
proposed by earlier workers for the Japanese
Lower Jurassic sequence is summarized in
Figure 6.
The Parahsuum simplum Assemblage-zone
is long-ranging spanning an interval from the
Rhaetian? or Hettangian to early Toarcian?
In this assemblage-zone, four subzones (I, II,
III and IV) are distinguished on the basis ofradiolarian composition. They are correlat-583

ed with other Lower Jurassic radiolarianzones proposed for the circum-Pacific region,
for example the North American Zones 01
through 05 of Pessagno et al. (1987).
The Mesosaturnalis hexagonus Assemblage-zone, newly proposed in this paper, isan important Lower Jurassic biozone because
its base coincides with the first appearance
level of the genus Parvicingula (s.I.), which
can be traced internationally.
One of the other zones, the Hsullm hisuikyoense Assemblage-zone is characterized by
the fauna of the Middle Jurassic rather thanthe Lower Jurassic
The age of each zone is discussed bycomparing them with the North American
and Turkish faunas. Each zone spans anaverage interval of 5 m.y. within a time period
from the latest Triassic/Early Jurassic to early
Middle Jurassic.
Acknowledgments
The author wishes to thank Dr. Akira Yao
of Osaka City University for his kind advice
and guidance on this study. Sincere thanks
are due to Dr. Yukio Isozaki of Yamaguchi
University for his encouragement and helpful
criticism of the manuscript. The author expresses her thanks to Dr. Atsushi Matsuoka of
Niigata University and Dr. Tsutomu Otsuka
of Shinshu University for their advice, discussion, and help in sampling. Special thanks
are due to Dr. Elizabeth S. Carter for her
valuable advice on the manuscript.

~
Figure 9. Scanning electron micrographs of Early Jurassic to Middle Jurassic radiolarians, and a Late
Triassic conodont (56) from the Mesozoic complex of SW Japan. Figure number corresponds to taxon
number of 31 to 55 in Table I and Figure 5. 56: Axiolhea poslhernsleini (Kozur and Mock). Scale bar=
200 Jim for all figures except for 41,42 (= 300 Jim), 31-35,38, 40, 55 (= 133 ,urn), and 44,47,50,56 (= 100,urn). 31: Parvicingula cf. giganlOcornis, 32: Parahsuum (?) sp. B, 33: Hsuum allile, 34: H. sp. X, 35:
H. (?) sp. Y, 36: Zarlus aff. imlayli, 37: Parahsuum (?) aff. magnum, 38: Hsuum sp. B, 39: Parahsuum
transiens, 40: Parvicingula nanoconica, 41: Tripocyclia sp., 42: Mesosaturnalis hexagonus, 43: Transhsuum medium, 44: Archicapsa pachyderma, 45: Parahsuum (?) grande, 46: Nassellaria gen. et sp. indet.
X, 47: Unuma (?) sp., 48: Andromeda sp. D, 49: Hsuum aff. hisuikyoense, 50: Slichocapsa aff. japonica,
51: LaxlOrum (?) jurassicum, 52: L. (?) hichisoense, 53: Hsuum malsuokai, 54: H. hisuikyoense, 55:
Zarllls cf. dickinsoni. All the figured specimens in Figures 8, 9 were registered and deposited at the
Department of Geosciences, Osaka City University.

Rie Hod

584

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Inuyama :f\:W, Iwayakannon ;'EH~~1f. Kaiji 1tattr, Kajiki ;jf*, Katsuyama mw, Kuma
Kurusu ~:fi!!i. Kuzuu ~j::, Teishyoji Jli:~~.

~~.

imjfJ B *I::':NH' G "F$-./ ~ '7 *:DJ(Itt£R.{~n*: imjfJ B *0) 7- -\' - r :&Lf~BiI- I? t.t: G:i;tm:~ff:rtffrnil::':N\,,-C:DJ(Itt£R.{~nO)*@:7t;(Pz.WSJ1!tL, 4~~*c 4!11!~~*z.Jiltl:$ r V
7 ~*iJ-I?<j:t$-./ ~ '7*"F$O)ra'I::'~~ ·§C.~Lt.:o §C.~Ltd~n*It.. "F{ftJ: IJ Parah-suum simplum ~~*:&Lf-f:O) 4 !II!~~* (Subzones I-IV) c, Mesosaturnalis hexagonus~~* (~fJi1:P~), Parahsuum (?) grande ~~*, Hsuum hisuikyoense ~~*-C ~ Go 7/-t' 7'1 r {~n*c@:~~;frc:;0)0 ~t*~ r 1)...:2 0)7- 11 c O).I:ttel::'J: IJ, ~~~*O)if:<

ttlt.. Rhaetian/Hettangian ii- I? Bajocian i -cO)ra, I::.-f: n.:fn{ft~":JH' I?n G ~t.: I::'~~
L t.: Mesosaturnalis hexagon us ~~*I:I:., Pafl'icingula ~ ($~) 0) tf:lm~~~t.t:/N~~l~:/x
Nassellaria O)il:tf:l-C%'iJ":JH'l?n. imjfJ B *t':H'-ct.t: <~t*I::':N\"-C ~ *~~*I::.mt-t0

G{~n*iI~mltBIj~nGo

WI tU*

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 159, pp. 587-602,4 Figs., September 30, 1990

906.

JURASSIC EUCYRTIDIELLUM (RADIOLARIA) IN
THE MINO TERRANE*HIROMI NAGAI
Nagoya University Furukawa Museum,
Dating and Materials Research Center, Nagoya 464-01
andSHINJIRO MIZUT ANI
Department of Earth Sciences, Nagoya University, Nagoya 464-01

Abstract. Jurassic Eucyrtidiellum in chert, siliceous shale and manganese carbonate
rock in the Mino terrane of central Japan was studied together with that of the Snowshoe
Formation of Oregon with the result that eighteen species are recognized in the early Late
to Upper Jurassic formations. Of all these species, Eucyrtidiellllm disparile, E. lInlimaense,
E. pllstu!alUm, E. semifactllm and E. ptyclUm are most prevalent. These species aremorphologically related with each other, and show an evolutionary trend composed of twoconsecutive steps of change, early in shell structure of abdomen, represented by transition
from E. disparile to E. unumaense and later in superficial plication of abdomen, represented
by transition from E. puslU!atum through E. semifactum to E. ptyctum. On the basis ofoccurrence of E. pustulalUm in the upper Bathonian part of the Snowshoe Formation,
radiolarian biostratigraphical correlation for the Japanese Jurassic formations is discussed.
Two new species, Eucyrtidiellum disparile and E. semifactum, are described in this paper
together with other species relevant to them.

Key words. Eucyrtidiellum, Jurassic, Mino terrane, Snowshoe Formation, radiolarianbiostratigraphy, central Japan.

(Mizutani and Koike, 1982). Other speciesof older ages are also detected by Nagai(1988). In addition to our specimens, we
also examined Eucyrtidiellum from the Snowshoe Formation of Oregon as a reference
specimen whose horizon is biostratigraphically controlled by ammonites, and compared itwith that of Japan. This paper summarizes
all the data of Eucyrtidiellum available for us,
and discusses its evolutionary trend found in
Jurassic time.

Introduction
We studied Jurassic radiolarians in the
Mino terrane of central Japan, and recently
focussed our attention upon morphologicalvariation of Eucyrtidiellum in Middle to Late
Jurassic time. Many species of this gen us arecommonly found in the following threeassemblages, i.e., Late Jurassic Mirifusus
baileyi assemblage (Mizutani, 1981), late
Middle Jurassic Dictyomitrella (?) kamoensis-Pantanellium Joveatum assemblage(Mizutani and Kido, 1983) and middle Middle Jurassic Unuma echinatus assemblage

Materials and localities
Skeletons of Eucyrtidiellum have been
extracted from chert, siliceous shale and'Received November 7, 1989; revised manuscript
accepted September I, 1990.
587

Hiromi Nagai and Shinjiro Mizutani

588

manganese carbonate rock collected from theMino terrane of the Paleozoic-Mesozoic
disrupted sedimentary complex in central
Japan.
Rock samples of siliceous shale of Middle
Jurassic age were obtained from Kutsuwano,
Gifu Prefecture (13TO'46"E, 35'32'37"N)(Figure I). Nagai (1987) extracted 281 specimens of Elicyrtidiellum from them. Theserock samples were taken from a measured
section about 10 m thick, in which Pantanellium Joveatum Mizutani and Kido, Dictyomitrella (?) kamoensis Mizutani and Kido
and Tricolocapsa plicarum Yao arecontained. Tricolocapsa conexa Matsuoka
is found in the lower part of the section.
This siliceous shale is biostratigraphicallyreferable to the Dictyomitrella (?) kamoensisPantanellillm Joveatum assemblage zone of
Mizutani and Kido (1983).
Nagai (1986) also studied four rock sam-

36 N

136 E

5

10 km

Figure 1. Sample localities in the Mino Terrane, central Japan. Dotted area: PaleozoicMesozoic disrupted sedimentary complex.

pies of manganese carbonate nodule embedded in siliceous shale ofInuyama at the southeastern bank of Kiso River, Aichi Prefecture(l36°S7'SI"E, 35'23'43"N) (Figure I) andobtained 64 specimens of Eucyrtidiellum
together with Unuma echinatus Ichikawa
and Yao, Zartus dickinsoni Pessagno andBlome and others. The biostratigraphic
horizon of these samples is believed to beequivalent to the manganese carbonate rockoccurring at the northwestern bank of Kiso
River, which was investigated by Mizutani
and Koike (1982) to be correlative with the
Unuma echinatus assemblage zone of the
Middle Jurassic zonation.
Nagai (1988) also extracted 66 specimens of
Eucyrtidiellum from a chert sample containing manganese micronodule exposed at
Kamiaso, Gifu Prefecture (137747"E, 35'32'
S2"N) (Figure I). This rock sample contains Laxtorum (?) jurassicum Isozaki andMatsuda, L. (?) hichisoense Isozaki andMatsuda, Hsuum hisuikyoense Isozaki andMatsuda, H. (?) matsuokai Isozaki andMatsuda and other radiolarians, all of them
being indicative of late Early Jurassic or early
Middle Jurassic age (lsozaki and Matsuda,1985).
We also examined and comparatively studied many SEM photographs of Eucyrtidiellumin the Rad File of Nagoya University whichwere reported mainly from the Mino terraneof central Japan.
In addition to our specimens, we studied
North American radiolarians in a filtrated
residue obtained after chemical treatment ofrock sample (OR-SOle: provided by Pessagno of the University of Texas at Dallas).
It was collected from the Snowshoe Formation, east central Oregon (Pessagno andBlome, 1982; Pessagno et al., 1984), now
registered in the Rad File of Nagoya University as JMP1617.
The Snowshoe Formation (Lupher, 1941 ;Dickinson and Vigrass, 1964, 1965) occurs in
the Izee terrane (Silberling et al., 1984),
which is equivalent to the coherent terraneTable I.
LOCALITY

Eucyrtidiellum

"*

.a.

E. disparile Nagai andNumber of fossil bodies of Jurassic Eucyrtidiellum examined in this paper.

I KAMIASONagai

ISNOWSHOE
OR-501C( 1988)INUYAMA
Nagai( 1986)

KUTSUWASO
KUTSUWANO(lower)(upper)Nagai (1987)

39

-

-

-

-

68

107

-

-

-

6

11

3

42

218

316

6

124

70
28

211

12
28

24

othersin Mino I total
terraneMizutani, n. sp.

E. gujoensis (Takemura and5-Nakaseko

E. quinatum Takemura
E. unumaense (Yao)
E. pustulatum Baumgartner
E. semifactum Nagai andc......

53
11

75

104

Mizutani, n. sp.

E. nodosum Wakita
E. ptyctum (Riedel and Sanfilippo)
E. pyramis (Aita)
E. ozaiense (Aita)
E. sp. at (Nagai, 1986)
E. sp. a, (Nagai, 19!!6)
E. sp. a, (Nagai, 1986)
E. sp. d (Nagai, 1986)
E. sp. f (Nagai, 1987)
E. cf. nodosum (Nagai, 1988)
E. sp. A (Aita and Okada, 1986)
E. sp. C Group (Nagai, 1986)
E. sp.
total number of bodies

~
?~

~

~
r:;.
~

~

2

10
4

5

2
3
2

21

3
66

64

12

15

257

32

~
...

~
1\;.
:::::
~

3
1

3

33
9

40

~

9

~

2

5

IS

15

5

9

3

24

30

30

71

75

602

1016

1

!:l

!:l..

c·
...is"'

~

V>

00
~

590

Hiromi Nagai and Shinjiro Mizutani

distinctly separated from the central melange
terrane in the Blue Mountains province ofeast Oregon (Dickinson and Thayer, 1978).
The biostratigraphic position of OR-SOl ismost concisely summarized by Pessagno andBlome (1982) and by MacLeod (1988). In
their locality descriptions, Pessagno andBlome (1982) wrote that OR-SOIA, Band C(the Upper member) are dark gray mudstone
with common limestone nodules. Samples
were taken from the limestone nodules immediately below the contact with overlying
Trowbridge Formation. Imlay (1981) concludes in his discussion on the age of theSnowshoe Formation that the ammonite biostratigraphy makes possible a definite late
Bathonian age assignment for the uppermost
part of the Snowshoe Formation.
All these materials and their localities are
summarized in Table I for ready comparison.
In this table, the Kutsuwano samples areconveniently divided into two groups according to their stratigraphic position marked by
the first appearance of E. ptyctum. The
lower part does not include E. ptyctum. Of
all the specimens of Eucyrtidiellum extracted
from the Kutsuwano section, nine specimens
were excluded in the present study, because
their inner cephalic structure is quite different
from that of Eucyrtidiellum (N agai, 1989),
even though their abdominal forms bear someresemblance to that of E. disparile.
A radiolarian fossil is always labeled like44246/1543; the numerator indicates the registered number of SEM photograph of theradiolarian fossil and the denominator expresses the registered number of the rocksample from which the fossil was separated.
Morphological evolution of Eucyrtidiellum
Nagai (1988) summarized all the JapaneseJurassic species of Eucyrtidiellum so far described, and identified the following eightspecies to be included in this genus:
Eucyrtidium (?) ptyctum Riedel and
Sanfilippo (Riedel and Sanfilippo, 1974).

E. (?) unumaense Yao (Yao, 1979)
E. pustulatum Baumgartner (Baumgartner,
1984)
E. (?) ozaiense Aita (Aita and Okada,
1986)
E. (?) pyramis Aita (Aita and Okada,
1986)
E. quina tum Takemura (Takemura, 1986)
E. gujoensis (Takemura and Nakaseko)(Takemura and Nakaseko, 1986)
E. nodosum Wakita (Wakita, 1988)
As will be described in the later section, thefollowing two new species are also regarded
as the Jurassic Eucyrtidiellum:
Eucyrtidiellum disparile Nagai and
Mizutani, n. sp. (Figures 3-6-8).
E. semifactum Nagai and Mizutani, n. sp.
(Figures 3-1-4).
Although they have not been exactly
defined yet, the following five species, provisionally reported by Nagai (1986, 1987), also
belong to the Jurassic Eucyrtidiellum: E. sp.
ai' E. sp. a 2 , E. sp. a 3 , E. sp. d and E. sp. f.
Eucyrtidiellum sp. a\ resembles E. disparile,
but it has very small relict pores on its abdomen. E. sp. a 2 is also similar to E. disparile,
but it has shorter ridge on the upper portionof its abdomen. E. sp. a 3 has an abdomenwith an oblique ridge up to the upper part,and this species is comparatively large in size.
E. sp. d is very similar in its surface morphology to E. nodosum of the Upper Jurassic, but
it differs in having pores on its entire abdomen. E. sp. f (Figure 4-8) has polygonal,
usually hexagonal, pore frame on its abdomen and thorax. Nagai (1988) also reported
many species of E. nodosum group (=E. cf.
nodosum in Table I). They are very similar
to E. nodosum, but more or less differ inhaving more distinct nodes and having more
spherical cephalis. We have the other groupof Jurassic Eucyrtidiellum, such as E. sp. A(Aita and Okada, 1986, pI. 6, figs. 6-7), which
is characterized by its conical shape and anannular and short abdomen, and E. sp. C
group (Nagai, 1986, pI. 2, figs. 10-12), which
has a different shell form. Since these seven

Jurassic

Radiolarian

Ass e m b I age. s

Mizutani (1981), Mizutani et al.(I98 I), Kido et al. (1982)
Mizutani and Kido (1983)

Matsuoka and Yao (1986)e:Pseudodictyomitra
primitiva

Cinguloturri~tica

Jurassic E u c y r tid i e I Tum

e: .2 e:1--------.2 - (.) - ::J~ ~ t.2CI) - CIl-Q.
e: ~-- --I

Miri{usus baileyi

1 _ ___ _ __2.1

Stylocapsa ( ~1PjraJiS
Tricolocapsa
Tricolocapsa

conexapJicann

C/)

~

0.

uj

~

Dictyomitrella('1) kamoensis - Pantanellium (oveatum- - -- --- - - -- - - - ---- - _. ---- - -- - - - - - -- - - - -- - - ----- -I----

;::;
~

r;'

Unuma echinatus

tl')

~

Laxtorum (') jurasscum
Archicapsapachydenna

~
i?
fi)-

Parahsuum
sp. C

semifactum

~

~

-;:;
i::)

E. pustulatum

i::l...

0'E. unumaense
0. 1

mm

§"

~

E. disparile
Figure 2. Jurass ic Eucyr/idie/lum and its mo rphol og ic a l change in rel a tion to th e radiolari a n assemba lge zo ne in Ja p a n.
E. disparile (14773 / 194, Imaj o a rea , after N a ga i, 1986, pI. I, fig. 5), E. unumaense (52833 / 1302 , Inu yama, N aga i, unpubli shed) , E. pus/ula/um (44240/ 1543 . Kutsuw a no , Nagai , unpubli shed ), E. semifac/lim (44002 / 1531 , Kutsuw a no , thi s paper,
Figure. 3- 4a), a nd E. p/yc/lim (3498/ 108. Hid a-Kan aya m a. after Mizutani , 198 1, pI. 64, fig. la) . Evo luti o nary tre nd of (i)change of she ll stru cture o f a bd o me n fr om E. disparile to E . lInlimaense in late Ea rl y Jura ss ic to middle Middl e Jurass ic
interva l. a nd (ii) development of superfic ial plica ti o n in a bd o me n fr o m E. unumaense to E. p/yc /lim in middl e Middl e tola te Jurass ic interval.
vo
'Cl

592

Hiromi Nagai and Shinjiro MizlIlani

species are relatively poorly found in theJurassic radiolarian association, their mutual
morphological relationship has not beenclarified.
According to the Baumgartner's description, ElIcyrlidiellllm has a poreless thorax;
however, there are many species which have ashell very similar in its external form to thetype species (Eucyrtidiellum unumaense), buthave pores in their thorax. These radiolarians are treated as Eucyriidiellllm in thispaper, because of the similarity of their wholeexternal form.
Thus, 18 species above cited are regarded asJurassic ElIcyrlidiellum, and their abundancein the Mino terrane is summarized together
with that of the Snowshoe Formation I\1
Table 1.
When arranged according to similarity ofthe external shell form of Eucyrtidiellum, twoconsecutive steps of morphological change(Figure 2) are recognized as was discussed
previously by Nagai (1986): (1) change ofshell structure of abdomen represented bytransition from Eucyrlidiellum disparile to E.
unumaense occurring in late Early Jurassic tomiddle Middle Jurassic interval, and (2)change of superficial plication in abdomen
represented by transition from E. unumaense
to E. plyclum occurring in middle Middle toLate Jurassic interval.
The external shell form of E. disparile andthat of E. unumaense are almost identicalwith each other, but they have different
abdominal shell structure. The former has
circular pores regularly arranged along two
diagonal lines in its abdomen, whereas thelatter has an abdomen of poreless and solid
shell with smooth surface. An intermediate
form between E. disparile and E. lInlimaense
seems to be E. sp. a 1 as reported by Nagai(1986). This species resembles E. dispa rile ,but it should be noted that E. sp. a 1 has verysmall relict pores on the surface of abdomen.
E. disparile is commonly contained in the late
Early or early Middle Jurassic sample ofKamiaso (Nagai, 1988). E. sp. a 1 coexists

with E. disparile, but E. unumaense is notfound there. On the other hand, E.
lInlimaense is most prevalent in the middle
Middle Jurassic sample of Inuyama (Nagai,1986). A few bodies of E. sp. a 1 also coexist
with it. Occurrence of these species and theirmorphological properties reveal a successivechange of shell structure particularly in its
abdominal part.
The following six species were confirmed tooccur together in the late Middle Jurassic
section of siliceous shale in Kutsuwano, Gifu
Prefecture: E. pustlilatum, E. semifactum,
E. unumaense, E. nodosum, E. plyclllm andE. sp. f as shown in Table 1. The external
shell form of E. puslulatum resembles that of
E. unumaense, but E. pustulatum has proximal portion of abdomen with nodes andpustules; its distal portion of abdomen issmooth. Similarly, the external shell form of
E. semifactum resembles that of E. ptyctum,
but E. semifactum has sixteen longitudinalshort plicae on the upper one-fifth to twothirds of the abdominal surface, and its plicae
gradually die out downward leaving asmooth surface, while E. plyclum has longitudinal plicae from the upper to the distal
portion on the surface of abdomen. E.
unllmaense is abundant in the middle Middle
Jurassic sample of Inuyama, but it is lessabundant in the lower part of the Kutsuwano
section and much less in the upper one (TableI). E. pus{lllatum is prevalent in both partsof the K utsuwano section, but E. semifactumis rare in the lower part and common in theupper one, where a few bodies of E. ptyctum
appear.
This evidence supports above-mentioned
morphological change of superficial plication; i.e. after the acme stage of E.
unumaense, E. pustulatum proliferated andthen it was replaced by E. semifactllm andsucceedingly by E. ptyctum. Morphologicaldevelopment of the other species is not so
distinct as this group, probably owing to arandom or spasmodic variation of their surface ornamentation.

906.

Jurassic Eucyrtidiellum (Radiolaria)

Radiolarian biostratigraphical correlation
In the Snowshoe sample, Eucyrtidiellum
pustulatum (Figures 4-4-5) is a common
and only identifiable species of Eucyrtidiellum; a single body of E. sp. f (Figure 4-8)
was detected in addition to E. pustulatum inthe present study (Table I). Since the geological age of the Snowshoe Formation has
been defined as the late Bathonian by a comparative study of ammonites (Imlay, 1973,1981), E. pustulatum is inferred to haveproliferated in a stage of the late Bathonian in
North America. This implies that the geological age of the Japanese formations where
E. pustulatum is commonly included may
well be assigned to the late Bathonian. As
shown in Table I, E. unumaense is very
abundant in the Inuyama samples, and E.
pustulatum has never been observed in them
(Nagai, 1986). Judging from the occurrenceof Eucyrtidiellul11 in the Unuma echinatusassemblage, it seems likely that E. pustulatum
proliferated after the acme stage of E.
unumaense, and the Japanese formation corresponding to the upper Bathonian lies above
the Unuma echinatus assemblage zone.
The Kutsuwano section contains theradiolarian of the Dictyomitrella (?) kamoensis-Pantanellium fovea tum assemblage accompanied with, in the order of relative abundance, E. pustulatum, E. semifactum, E.
unumaense, E. nodosum, E. ptyctum, and E.
sp. f (Nagai, 1987). The K utsuwano andOregon samples contain both of E. pustulatum and E. sp. f, but neither E. semifactum nor E. ptyctum was found in the
Oregon sample. This suggests that E. semifactum and E. ptyctum proliferated at laterages. In fact, the upper part of the Kutsuwano section includes E. semifactum andE. ptyctum. Consequently, we conclude
that the upper Bathonian part of the Japanesesuccession is located above the Umana
echinatus assemblage zone and below or in
the lower portion of the Dictyomitrella (?)
kamoensis-Pantanellium fovea tum assem-

593

blage zone.

Conclusions(I) Eighteen species of Eucyrtidiellum arerecognized in the Jurassic Eucyrtidiellum in
the Mino terrane, of which the following fiveare relatively abundant and identifiable: inthe order of relative age, E. disparile, E.

unumaense, E. pustulatum, E. semifactumand E. ptyctum.
(2) On the basis of the morphologicalvariation of Eucyrtidiellum, an evolution
composed of two consecutive steps is found, i.
e., from E. disparile to E. unumaense, andthereafter, from E. unumaense to E. pustulalum, E. semifactum and up to E.

plyctum.
(3) On the basis of the fact that E. pustulatum is exclusively found in the upper
Bathonian part of the Snowshoe Formation,
radiolarian biostratigraphical correlation canbe made for the Japanese Jurassic formations
as follows: the Unuma echinalus assemblage
zone is lower than, and the lower part of the
Dictyomitrella (?) kamoensis-Pantanellium
fovea tum assemblage zone is correlative with,the upper Bathonian.

Systematic description
Subclass Radiolaria MUlIer, 1858
Order Polycystina Ehrenberg, 1838,
emended Riedel, 1967
Suborder N assellaria Ehrenberg, 1875
Polycystina incertae sedis
Family Eucyrtidiellidae Takemura, 1986
Genus Eucyrtidiellum Baumgartner, 1984

Type species.- Eucyrtidium (?) unumaensis Yao, 1979 (p. 39, pI. 9, figs. I-II).
Remarks.- Before Eucyrtidiellum wasdefined by Baumgartner (\ 984), the Mesozoic
species belonging to this genus had beenquestionably regarded and denoted as Eucyrtidium (?), because they bear no exact resemblance to the type species, Eucyrtidium

594

Hiromi Nagai and Shinjiro Mizutani

acuminatum Ehrenberg. According to theoriginal description of Eucyrtidium (Foreman and Riedel, 1972), its test has segmentswith two or more strictures, and the typespecies (Eucyrtidium acuminatum) has eightsegments. Contrary to this morphologicaldefinition, most, if not all, of the Mesozoic
species have only three or four segments.
Baumgartner (1984) wrote in his originaldescription that the shell of Eucyrtidiellum iscomposed of four segments, while Takemura(1986) noted that the shell is made up of morethan four segments. The first segment, cephalis, is small, spherical or subspherical andporeless with an apical horn that is either
straight or slightly curved and mostly small insize. The second segment, thorax, is domeshaped and poreless in almost all species, andhas ornamentation consisting of irregularridges with depressions, nodes or plicae.
There are many pores at the stricture
between the second and third segments. The
third segment, abdomen, is inflated annular tohemispherical. Surface of the abdomen is
generally smooth, but varies according to
species; it is, for instance, pored or plicate.
Post-abdominal segment is mostly cylindricaland may have a row of large pores on thestricture. There are only a few extant examples of the post-abdominal structure, because
this segment is extremely delicate and easily
disrupted.
Eucyrtidiellum disparile Nagai
and Mizutani, n. sp.
Figures 3-6-8a, b, C

Eucyrtidium (?) sp. a, Kido, 1982, pI. 5, fig. 5 ;Yamamoto, 1985, pI. 2, fig. 3.
Eucyrtidium (?) sp. A, Hattori and Yoshimura, 1982,
pI. 4, fig. 2; Kojima, 1982, p. 83, pI. 1, fig. 12.
Eucyrtidium (?) sp. B, Hattori and Yoshimura, 1982,
pI. 4, fig. 3.
Eucyrtidium (?) sp., Hattori and Yoshimura, 1983, pI.
9, fig. 11.
Eucyrtidiellum sp. A, Mizugaki, 1985, pI. 45, fig. 9;
Hattori, 1987, pI. 12, figs. 1-2; Hattori, 1988a, pI. 8,
fig. D.

Eucyrtidiellum sp. a, Nagai, 1986, pI. 1, fig. 5; Nagai,
1988, pI. 1, figs. 1a -d, 2.
Eucyrtidiellum sp. a" Nagai, 1986, pI. 1, fig. 6.
Monosera unumaensis Takemura and Nakaseko,
1986, p. 1022, figs. 4.9.
Eucyrtidiellum (?) sp. X, Hattori, 1987, pI. 12, fig. 16.
Eucyrtidiellum sp., Hattori, 1988b, pI. 1, fig. J.

Diagnosis.- Abdomen has circular pores
regularly arranged along two diagonal lines
on its whole surface.
Description.- This species has a test whichis composed generally of three segments, cephalis, thorax and abdomen. Cephalis issmall, spherical with a medium-sized apicalhorn. Sutured pores are arranged at a stricture between thorax and abdomen. Thorax
truncated-conical with closed pores and irregular hexagonal meshworks on the whole surface. Abdomen is relatively large andinflated-hemispherical, with circular pores
regularly arranged along two diagonal lines
on its whole surface.
Measurements.- (in ,um, based on 10 specimens): height of apical horn, 3-13 (average8); height of entire body incl uding cephalis,thorax and abdomen, 67-100 (average 79);height/width of cephalis, 5-19 (average 13)/
8-21 (average 17); height/width of thorax,
14-23 (average 18)/31-38 (average 35);height/width of abdomen, 41-66 (average
48)/48-77 (average 71).
Remarks.- External shell form of Eucyrtidiellum disparile is almost identical withthat of E. unumaense, but differs in having
pores on its entire abdomen. Many specimens of Eucyrtidiellum have been provisionally described as Eucyrtidium (?) sp. or
Eucyrtidiellum (?) sp., just because of thepresence of opened pores in their abdomen.
Etymology.- Derived from Latin adjective"disparilis, -e", which means "unlike" or"dissimilar".
Occurrence.- Common in siliceous shaleof late Early Jurassic to Middle Jurassic ageof Kamiaso, Gifu Prefecture.
Repository.- Holotype, HNHK05-C3-46(Figures 3-8a, b, c; 45946/1467, 45948/1467,

906.

Jurassic Eucyrtidiellum (Radiolaria)

50409/1467), Paratype, HNHK05-C3-41(Figure 3-6; 45932/1467), and HNHK03A3-44 (Figure 3-7; 42536/1467); stored in
the Rad File, Nagoya University.

Eucyrtidiellum semifactum Nagai
and Mizutani, n. sp.
Figures 3-1-4a, b

Eucyrtidium (?) sp. b, Kido et al., 1982, p. 20 I, pI. 4,
figs. 10-11 ; Yamamoto, 1985, pI. 2, fig. 9.

Eucyrtidium (?) sp. A, Wakita, 1982, pI. 3, fig. 2.
Eucyrtidium? sp. aff. E.? ptyctum Riedel and
Sanfilippo, Sato et al., 1982, pI. 4, fig. 4.
Eucyrtidiellum sp. b, Nagai, 1986, pI. 2, fig. 6; Nagai,
1987, pI. 3, figs. la, b, 2; Nagai, 1988, pI. 2, figs. 3a,b.
Eucyrtidiellum sp. b l , Nagai, 1986, pI. 2, fig. 3.
Eucyrtidiellum sp. b 2 , Nagai, 1986, pI. 2, fig. 4.
Eucyrtidiellum sp. b 3 , Nagai, 1986, pI. 2, fig. 5.
Eucyrtidiellum sp. B, Hattori, 1987, pI. 12, fig. 8.
Eucyrtidiellum sp. B2 , Hattori, 1987, pI. 12, fig. 9.
Eucyrtidiellum sp., Kojima and Mizutani, 1987, fig. 4;
14-15; Kojima, 1989, pI. 2, 6a, b.

Diagnosis.- Abdomen has sixteen longitudinal but short plicae on the upper one-fifth
to two-thirds of the surface.
Description.- Test usually composed ofcephalis, thorax and abdomen. Cephalis issmall, spherical with a small or medium-sizedapical horn. Thorax truncated-conical withclosed pores on the whole surface. Sutured
pores are arranged at a collar stricture
between thorax and abdomen. Third segment, abdomen, is poreless having sixteen
longitudinal but short plicae on the upper
one-fifth to two-thirds of the segment. The
plicae gradually die out downward leaving asmooth surface, with a few very small pores at
distal portion.
Measurements.- (in ,urn, based on 10 specimens): height of apical horn, 5-18 (average9); height of entire body including cephalis,thorax and abdomen, 56-82 (average 72);
height/width of cephalis, 8-15 (average 11)/
10-21 (average 15); height/width of thorax,
13-21 (average 16)/26-33 (average 29);
height/width of abdomen, 36-49 (average

595

46)/62-69 (average 67).
Remarks.- This species resembles E.
ptyctum, but differs in having shorter plicae
on its abdominal surface. E. semifactum isfound not infrequently in the Jurassic of theJapanese Islands.
Etymology.- Named after Latin adjective"semifactus, -a, -um" meaning "half-done"or "half-finished".
Occurrence.- Siliceous shale of Middle
Jurassic age of Kutsuwano, Gifu Prefecture.
Repository.- Holotype, HNHK05-B4-52(Figures 3-1a, b; 44246/1543, 44245/1543),
Paratype, HNHK05-B4-55 (Figure 3-3 ;44249/1543), HNHK05-BI-35 (Figures 3-2a,b; 44132/1540,44131/1540), and HNHK04D5-62 (Figures 3-4a, b; 44002/1531, 44001/
1531); stored in the Rad File, Nagoya University.

Eucyrtidiellum ptyctum (Riedel
and Sanfilippo, 1974)
Figures 3-5a, b

Eucyrtidium ptyctum Riedel and Sanfilippo 1974, p.
778, pI. 5, fig. 7, pI. 12, figs. 14-15; Baumgartner
and Bernoulli, 1976, p. 617, figs.lle-g; Baumgartner et al., 1980, p. 53 pI. 3, fig. 13; Aita, 1982, pI. 2,
figs. 8, 9a, b; N ishizono et al., 1982, pI. 2, fig. 12 ;Yao, 1984, pI. 2, fig. 30.
Eucyrtidium (?) ptyctum Riedel and Sanfilippo, Pessagno, 1977, p. 94, pI. 12, fig. 7; Foreman, 1977, pI.
2, fig. 5; Mizutani, 1981, p. 182, pI. 64, figs. I a, b2; Adachi, 1982, pI. 3, figs. 7-8; Okamura andUto, 1982, pI. 6, fig. 18; Mizutani et al., 1982, p.
57, pI. 4, fig. 5; Ishida, 1983, pI. 9, fig. 4; Nakaseko et al., 1983, fig. 2: 12; Yamamoto, 1983, pI. I,
fig. 4; Takashima and Koike, 1984, pI. 2, fig. 5 ;Aita, 1985, fig. 7: 14; Matsuoka and Yao, 1985,
pI. 2, fig. 8; Matsuoka and Yao, 1986, pI. 2, fig. 10;
Tanaka et al., 1985, pI. I, fig. 16; Aita and Okada,
1986, p. 109, pI. 6, figs. 14-17, pI. 7, figs. 3a, b.
Eucyrtidium? ptyctum Riedel and Sanfillipo, Nishizono and Murata, 1983, pI. 4, fig. 7; Ishida, 1985,
pI. 3, fig. 15.
Eucyrtidiellum ptyctum (Riedel and Sanfilippo)
Baumgartner, 1984, p. 764, pI. 4, figs. 1-3; Matsuoka, 1986, pI. 2, fig. 10; Nagai, 1986, p. 14,15, pI. 2,
fig. 7; Aita, 1987, pI. 4, figs. 12a, b, pI. 10, fig. 14,
pI. 14, fig. 3; Kojima and Mizutani, 1987, p.260,
fig. 4: 12-13; Nagai, 1987, pI. 3, figs. 5a-c, 6;

596

Hiromi Nagai and Shinjiro Miz ulani

906.

Jurassic Eucyrtidiellum (Radiolaria)

Nagai, 1988, pI. 2, figs. 4a, b; Wakita, 1988, pI. 4,
fig. 28, pI. 5, fig. 17; Koj ima, 1989, pI. 2, figs. 7a, b.
"Elicyrtidillm" ptyctum Riedel and Sanfilippo, Pessagno et al., 1984, p. 30-31, pI. 4, figs. 12-14.

Eucyrtidiellum pustulatum Baumgartner
Figures 4-1-5a, b, c

Elicyrtidiellllm pllstulatum Baumgartner, 1984, p. 765,
pI. 4, figs. 4-5; Yamamoto et al., 1985, pI. 4, figs.
4-5; Nagai, 1986, p. 14, pI. 2, fig. 2; Aita, 1987, pI.
4, figs. 13a-14b, pI. 10, figs. 15-16; Nagai, 1987, pI.
2, figs. 2a-c, 3a, b, 4a, b; Nagai, 1988, pI. 2, figs. 2a,b; Wakita, 1988, pI. 4, figs. 26-27.
Elicyrtidilim sp., Sashida et al., 1982, pI. I, fig. 3.
Elicyrtidilim (?) lInlimaense Yao, Aita, 1985, fig. 7 :15-16.

Eucyrtidiellum unumaense (Yao, 1979)
Figures 4-6-7

Stichocorys sp., Ichikawa and Yao, 1973, pI. I, figs. 34a, b.
Elicyrtidilim (?) lInlimaensis Yao, 1979, p. 39, pI. 9,
figs. I-II; Sugano et al., 1980, pI. 4, fig. 3;
Hattori and Yoshimura, 1982, pI. 4, fig. I ; Kido etal., 1982, pI. 4, fig. 9; Kojima, 1982, pI. I, fig. II ;Sashida et al., 1982, pI. 2, fig. 3; Wakita, 1982, pI.
3, fig. I ; Wakita and Okamura, 1982, pI. 8, fig. 7 ;Saka, 1983, pI. 5, figs. 6, 7.
Elicyrtidiellllm IInlimaensis (Y ao), Baumgartner,
1984, pI. 4, fig. 6; Yamamoto et al., 1985, pI. 4, fig.
6; Mizugaki, 1985, pI. 45, fig. 10; Takemura, 1986,
p.67, pI. 12, figs. 10-12; Nagai, 1986, p.13,14, pI.
I, figs. I a-c, pI. 2, fig. I ; Gorican, 1987, p. 182, pI.
3, figs. 9-10; Hattori, 1987, pI. 12, fig. 7; Wakita,
1988, pI. 3, fig. 15; Hattori, 1988a, pI. 8, fig. I.
Elicyrtidilllll (?) IInlllllaense Yao, Mizutani el al.,1984, pI. I, fig. 8; Yamamoto, 1985, pI. 2, fig. 4.
Elicyrtidielllllll IInlimaense (Yao, 1979), Kojima and597

Mizutani, 1987, p.260, pI. 4, fig. 16; Nagai, 1987,
pI. 2, figs. la-c; Yao, 1987, p. 95; Nagai, 1988, pI.
2, figs. I a, b; Wakita, 1988, pI. 4, fig. 25; Kojima,
1989, pI. 2, figs. Sa, b.
Monosera lInlimaensis (Yao), Takemura and Nakaseko, 1986, p. 1021, fig. 4.8.
Unnamed nassellariinid, Jones et al., 1980, pI. 2, fig.
14.

Eucyrtidiellum sp. f
Figure 4-8

Nagai, 1987, pI. 2, figs. 5a, b; Nagai, 1988, pI. 2, figs.
8a, b.

Descriptive remarks.- Cephalis small,
spherical with a small apical horn. Thorax
truncated-conical. Hexagonal pore frame
developed on thorax and abdomen on thewhole surface. This species is characterized
by its distinct poreframe; it may well bedefined as a new species of Eucyrtidiellum.
However, the species is relatively rare in our
rock-samples, and hence it is tentatively described in this paper as that of Nagai (1987).
Result of measurements is as follows (in ,urn,
based on 3 specimens): height of apical horn,
3-10 (average 4); height of cephal is, thorax
and abdomen, 54-69 (average 62); height/
width of cephalis, 8-15 (average 10)/15-18(average 17); height/width of thorax, 13-18(average 15)/31-36 (average 33); height/
width of abdomen, 33-38 (average 36)/59-72(average 64).

+- Figure 3. 1-4, Elicyrtidiellllm semifactum Nagai and Mizutani, n. sp. from Kutsuwano. 1,(Holotype, HNHK05-B4-52), la, Upper oblique view (after Nagai, 1987, pI. 3, fig. I b, 44246/1543) X 500, 1b,
Lateral view (Ibid., pI. 3, fig. la, 44245/1543) X 390. 2, (Paratype, HNHK05-BI-35), 2a, Upper oblique
view (44132/1540) x500, 2b, Lateral view (44131/1540) X 390. 3, (Paratype, HNHK05-B4-55), Lateralview (Ibid., pI. 3, fig. 2, 44249/1543) X 390. 4, (Paratype, HNHK04-05-62), 4a, Lateral view (44002/
1531) X 390, 4b, Upper oblique view (44001/1531) X 500. 5, Elicyrtidiellllm ptyctum Riedel and Sanfilippo
from Kutsuwano. Sa, Lateral view (Ibid., pI. 3, fig. Sa, 43892/1528) X 390, Sb, Upper oblique view (Ibid.,
pI. 3, fig. 5b, 43893/1528) x500. 6-8, Elicyrtidiellllm disparile Nagai and Mizutani, n. sp. from Kamiaso.
6, (Paratype, HNHK05-C3-41), Lateral view (45932/1467) X 390. 7, (Paratype, HNHK03-A3-44), Lateralview (42536/1467) X 390. 8, (Holotype, HNHK05-C3-46), 8a, Closeup of cephalic structure (after Nagai,
1988, pI. I, fig. Ic, 45946/1467) X 1770, 8b, Upper oblique view (Ibid., pI. I, fig. Id, 45948/1467) X 500, 8e,Lateral view (50409/1467) x390.

598

Hiromi Nagai and Shinjiro Mizutani

906.

Jurassic Eucyrtidiellum (Radiolaria)

Acknow ledgmen ts

We are very grateful to Professor Emile A.
Pessagno, Jr., the University of Texas at
Dallas, for his kindness to provide the sampleof east Central Oregon (OR-501C) which isone of the main samples dealt with in thispaper. Data base management of the Rad
File and data processing of this study weredone in and through the Nagoya University
Computation Center (Registration Nos.
A40227B and A40539A).
A part of the expense of this study has been
defrayed by the Grant-in-Aid for Scientific
Research given to us by the Ministry of
Education, Science and Culture of theJapanese Government (Grant No. 01304008,
Project Leader: S. Mizutani) for which wewould like to record our sincere thanks.
References
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2, fig. 2b, 43952/1530) X 500, 2b, Lateral view (Ibid., pI. 2, fig. 2a, 43952/1530) X 390. 3a, Upper oblique
view (44023/1532) X 500, 3b, Lateral view (44022/1532) X 390. 4-5, Eucyrtidiellum pustulatum Baumgartner from the Snowshoe Formation (OR-501C). 4a, Lateral view (48374/1617) X 390, 4b, Upper oblique
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(44059/1532) X 500. 8, Eucyrtidiellum sp. f from the Snowshoe Formation (OR-501C). Lateral view
(48384/1617) X 390.

Hiromi Nagai and Shinjiro Mizutani

600

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906.

Jurassic Elicyrtidieflllm (Radiolaria)

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Radiolarian fauna from the Paleozoic and Mesozoic formations, distributed along the midstream of Kuma River, Kyushu, Japan. Newsof Osaka Micropaleonl., Spec. Vol., no. 5, p.
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602

Hiromi Nagai and Shinjiro Mizutani

abstract)
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radiolarians of the Mirifusus baileyi Assemblage
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sedimentary complex of the Mino Terrane in thesouthern Neo area, Gifu Prefecture and the Mt.
Ibuki area, Shiga Prefecture, central Japan.
Ibid., vol. 91, p. 353-369, pIs. 1-2. (in Japanesewith English abstract)- - , Mizutani, S. and Kagami, H., 1985: Middle
Jurassic radiolarians from Blake Bahama Basin,West Atlantic Ocean. Bull. Nagoya Univ.
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Japan. Part II: Nassellaria I. Jour. Geosci.,
Osaka City Univ., vol. 22, p. 21-72, pIs. 1-12.
- - , 1984: Subdivision of the Mesozoic complex in
Kii-Y ura area, Southwest Japan and its bearing
on the Mesozoic basin development in the Southern Chichibu Terrane. Ibid., vol. 27, Art. 2. p.
41-103, pIs. 1-5.
- - , 1987: Radiolaria and geological history ofJapan. In, Science of Fossil, Palaeont. Soc.
Japan, p. 94-95. (in Japanese)

Inuyama :::k:LlJ, Kamiaso J:fliI;:!t. Kutsuwano ~!f. Mino ~~.
~~*Cl)liJlf{£E. {~E Eucyrtidiellum: $'ifll B *~~*Cl) 7- i' - ~. f111{J'{:fi. '7:/ 7/:/ J:R.
l!i5€tiK:fi tJ, G~ G.:h t..: Eucyrtidiellum C T 1/ ::{:/ 1+1 Cl) Snowshoe J~lh&J: 'ifll~M$ Cl).:.t.:h ~liJf§tL"C?XCl)*I'i:lI~:~~t..:o ll1rltJj,;. '" '7*c1&MtJ'G1&M';' '" '7*cK.tJ'V1"C. ;:Cl)~v':'vi 181]1tJ;
g;i!,1sb G .:h 0 0 .:.t Cl) ? i? Eucyrtidiellum disparile. E. unumaense, E. pustulatum, E.
semifactum, E. ptyctum Cl) 51]1 tJ;J'& >b ~ \, ' 0 ;:.:h G Cl)1]1 fiMi~i¥J v.:.;toE: \" v.:. 1* \" M;@; ~>b -:>"C\""C. vi [Isbv':' E. disparile tJ'G E. unumaense "'Cl)~{~f':'d,>.G.:h0 J: ? t,c1m'ifllCl))D(:~€Cl)~{~. --::J\, ,-e, E. unumasense tJ, G E. pustulatum, E. semifactum ~~"C E. ptyctum
V.:.\, ,t..: 0 ~{~K-d,>. Gt1.. 0 J: ? t.e!t\!$Cl)~:lIDtl!H~Cl)9EJt C \" ? 2 fjU/§'tJ, G t.e 0~?J.:~{b~f§1~~-r- 0 Snowshoe ~Cl) J:$/~ 'j .:=. 7 :/t;1ttJ, G fiW G E. pustulatum tJq'l!.t±l ~.:h 0 ;: C tJ, G
B *Cl)';' '" '7 *c~ (.:. --::J\, '''C Cl):!t~ 1'f~i¥Jxt .t~~~d,>. t..:o i't.ehi? Unuma echinatus M~*
fiJ:'ifll/~ 'j .:=. 7 :/t;1t J: I) vi""H.:., it..: Dictyomilrella (?) kamoensis-Pantanellium foveatum
M ~ * Cl) T'ifll vi J: 'ifll /~ 'j .:=. 7 :/ t;1t (.:. xH~ ~ *1.. Q 0 2 ~ 1]1 Eucyrtidiellum disparile c E.
semifactum ~~cllOCL. M;@;1]1v':'--::J\""C>b~WLt..:o:ik#V-0~' 7J\.fr1$w&~

Trans. Proc. Palaeont. Soc. Japan, N.S., No. 159, pp. 603-606, 3 Figs., September 30, 1990

SHORT NOTES24.

DIMORPHISM AND GEOGRAPHIC DISTRIBUTION OFTWO PHENOTYPES OF A WEST ATLANTIC STALKED
CRINOID ENDOXOCRINUS PARRAE (GERVAIS)*TAT SUO on
Geological Institute, University of Tokyo, Tokyo 113

Polymorphism in crinoids is thought to berare, and while several examples of sexual
dimorphism in stalkless crinoids have beenreported (Clark, 1921, p.369), no definite
shape polymorphism has previously been
described in stalked crinoids. The present
paper describes dimorphism in the western
Atlantic isocrinid Endoxocrinus parrae (Gervais). The geographic distribution andabundance of the two phenotypes are also
discussed.
Endoxocrinus parrae (Gervais) (FigurelA) is a common stalked crinoid in the tropical to subtropical western Atlantic; it has
been collected many times in the Strait ofFlorida, the Bahamas and the West Indies, theCaribbean Sea off Cuba and the Yucatan
Channel. The distribution also extends to
San Luis, Brazil (Meyer et al., 1978), andprobably off Rio Grande, Brazil (Tommasi,
1969, as Diplocrinus maclearanus). This
species lives at depths of 154 to 971 m, and it
is most commonly collected between about
500 and 600 m (Meyer et al., 1978).
Endoxocrinus parrae has a second morph,Endoxocrinus prionodes, previously described as a separate species by H.L. Clark(1941) (Figure. 1B). This species was distinguished from E. parrae by having projecting
distal edges of the brachials, especially theproximal brachials of the finials. This fea-

ture gives the proximal finial arms a conspicuously serrate appearance. Meyer et al.
(1978) suggested that E. prionodes is perhaps
synonymous with E. parrae. Characteristics
other than the proximal brachial morphology, such as stalk morphology, general size,
number of arms, and kind and position of theligamentary articulation, are similar in these
two forms; however, the forms were thought
to differ in some characteristics, such as thenumber of internodal plates and the numberof arms.
Material.- A total 165 specimens, housedin the National Museum of Natural History(USNM), Smithsonian Institution, Washington, D.C. were examined. There were 115
specimens of normal E. parrae, 44 specimensof the serrate form ("E. prionodes"), and six
intermediate specimens.
Two different species or intraspecificdimorphism ?- For the sake of convenience,
I abbreviate the typical form of Endoxocrinus
parrae as P A and the form with the strongly
serrate series of brachials PRo Most specimens of the two forms are usually clearly
separated by the morphology of the brachials(smooth versus serrate), otherwise they cannot
be separated (Figure 1). However, sometimes there are intergradations, and several
specimens cannot be readily classified aseither form. Moreover, recent collection
records show that both types occur from thesame stations. These lines of evidence seem

"Received January 29, 1990; revised manuscript
accepted Septem ber I, 1990
603

604

Tatsuo Oji

Figure 1. A: Endoxocrinlls parrae (Gervais). No. E33406, U.S. National Muse um. Collected at
so uth of Rock Port, Great Abaco, Bahama Islands (2S0S9' 30" N, 7T 4'06" W , 287 m). B: "En doxocrinlls
prionodes H.L. Clark ", here referred to a phenotype of E. pal"l"ae. No. E32644, U.S. Nationa l Muse um.
Collected at west of Wood Cay, Great Abaco, Baham a Isla nd s (26°4' 48" N, 79°09' 30" W, 624- 618 m).
Scale bars are I cm.

to support the conclusion that the two types
are morphs of a single species, rather than two
independent species.
Geographic cline.- J subdivide the mainarea of distribution , from the Lesser Antilles
to the Yucatan Channel, into six subareas.
These are, I. off the Yucatan Peninsula, 2.
around the western to central part of Cuba, 3.
the Strait of Florida to the northern Bahamas,
4. the central Bahamas, 5. the eastern Bahamas
to western Haiti , 6. eastern Haiti , Dominica
to the Lesser Antilles.
Figure 2 shows the sa mple sizes of thisspecies a nd the proportion of the two
phenotypes (plus that of indeterminable type)in these six subareas. PR is generally abundant in the northern part of the range. In
subarea 3, the northernmo st subarea , PR comprises almost half the total. The proportionof PR in subarea 3 is significantly higher thanthat in subareas 3 to 6 (G = 29.05, df= I, p <.001) . There are no PR individuals in subarea 6. Furthermore, all seve n specimens

collected off San Luis are PA. Therefore,
PR is a phenotype which appears to exist in
populations nea r the northern periphery of
the species' distribution.
Bathy metric distribution .- PR see ms tooccur slightl y deeper than PA (Figure 3).
The null hypothesis that the bathymetricdi stributions of PR and P A are the sa mecannot be rejected (G = 40.48, df = 3, p < .OOI).
Discussion.- This is the first documentation of the presence of shape polymorphismin li ving stalked crinoids. The phenotype
PR dominates in the northernmo st distribution a rea and it lives significantly in rather
deeper water than the phenotype PA . Suchdi stribution pattern suggests that the PR isadapted to deeper habitat than the PA .
Because the two phenotypes are often foundfrom the same station , the two phenotypes
prob a bly form the same popUlation in suchplaces .
Man y western Pacific isocrinids have a very
wide distribution , yet there is no significant

Short Notes 24.

Dimorphism of stalked crinoid605~ Phenotype PAoPhenotype PR~ Indeterminable

SA Subarea

+

+

+

N=4

SA 1 ,SA 2(9
---~~

N=2\

SA 6

@ \ ..

+.

++

c:t- 0:i+200.... '"
'if>"

+

+

+

+

\}

~+
0
(l

:

+.

0

10

60

Figure 2. Distribution and proportion of the two phenotypes of Endoxocrinus parrae in the
Caribbean region. The distribution is subdivided into six subareas. The proportion of the phenotype
PR increases toward the north.

geographic variation in such species as Endoxocrinlls alternicirrlls and Hypalocrinlls
naresianlls (Oji, 1989). While the present
result appears superficially to contrast withsuch morphologic stability, it also suggeststhat there may be actually unrecognizedpolymorphisms in the Pacific isocrinids, especially in the much diversified and possibly
oversplit species of Metacrinlls and Saracrinlls.

Acknowledgments: I thank Richard Aronson, Itaru Hayami, David Pawson and Jean
Vannier for critical reading of the manuscript
and improvement of the English. I also

thank David Pawson for allowing me to use
USNM crinoid specimens for this study, andCynthia Ahearn for her various help during
my visit to the National Museum of Natural
History. Thanks are also to David Meyer for
the information of the stations of RjVs Pilsbury and Gerda. Rich Mooi kindly sent me
an important reference. Examined material
includes many specimens collected recently
by submersible dives made by the Harbor
Branch Oceanographic Institution Inc. submersible programme. I thank John Miller
for allowing me to study these well-preserved
specimens. Contribution No. 18- Studies
on bathyal echinoderms of the Bahama

606

Tatsuo Oji

....

N

Islands, J.E. Miller (Harbor Branch Oceanographic Institution), Principal Investigator.

PA PR

D± SD

PA: 439.2±123.8m

References

PR: 540.3± 76.3m

20

100
I

I

I

I

I

I

199

299

399

499

599

699

D (depth, m)

Figure 3. Bathymetric distribution of the two
phenotypes of En doxocrin us parrae from the
Caribbean-West Indies area. Specimens with collection records of more than 100 m depth ranges areomitted.

Clark, A.H., 1921: A monograph of the existing
crinoids, vol. I, The Comatulids, pt. 2. U.S.
Nat. Mus., Bull., S2, p. 1-795.
Clark, H.L., 1941: The Echinoderms (other thanholothurians). Rept. sci. results "Atlantic" Exp.
to the West Indies. Mem. Soc. Cuban a Hist.
Nat., vol. 15, no. I, 153 p.
Meyer, D.L., Messing, e.G. and Macurda, D.B., Jr.,
1978: Zoogeography of tropical western Atlantic Crinoidea (Echinodermata). Bull. Mar.
Sci., vol. 2S, no. 3, p.412-441.
Oji, T., 19S9: Distribution of the stalked crinoids
from Japanese and nearby waters. In, Ohba, I.,
Hayami, I. and Mochizuki, K., eds., Current
Aspects of biogeography in West Pacific andEast Asian Regions. Univ. Mus., Univ. Tokyo,
Nature and Culture I, p. 237-43.
Tommasi, L.R., 1969: Nova contribuil;ao a \ista dos
crin6ides recentes do Brazil. Contr. Inst.
Oceanogr., Univ. Sao Paulo, ser. Ocean. BioI.
17: p.I-S.

Appendix
Registered numbers of the specimens used in this study are listed below. The numbers arefollowed by parentheses indicating the number of individuals contained in the same lot under thesame registered number. All the specimens are housed in the National Museum of Natural
History, Smithsonian Institution (USNM).
Subarea I: E IS033(1) E IS05S( I).
Subarea 2 : 12545(1), E I 7920( I), E21063( I), E21OS3( I).
Subarea 3: EI7514(3), EI7516(2), EI7517(4), EI7950(1), EI79SI(I), EI79S9(6), EI7990(3),EI7991(2), EI7996(2), EISOOS(I), EIS009(1), EIS023(1), EIS030(3), EIS032(2), EIS047(1),EIS04S(I), EIS050(2), E21004(1), E21005(2), E21012(1), E21020(9), E21024(l), E21037(5),E21052( I), E21071 (I), E21072(2), E210S4( I), E2590S(3), E26002( 13), E32644(2), E32655(l),E32656( I).
Subarea 4 : E32636( I), E32637( I), E32638( I), E32640( 4), E32641 (I), E32642(l), E32643(l),E32653( I), E32657(2), E32660( I), E32661 (I), E32664(3), E32666( I), E33403(2), E33406(2).
Subarea 5 : E IS035(23), E32639(1), E32654(1), E3265S( I), E32659( I), E32662(1), E32663(1),E33404( I), E33405( I).
Subarea 6: EI7994(2), EIS020(2), EI9967(1), EI996S(I), EI9969(l), E210IS(4), E21022(1),E21076(2), E2600I(l).

607

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Shallow Tethys 3.
Eocene crinoids from Seymour Island, Antarctica andNew members approved at the Council Meeting on June 29, 1990
Hideaki Machiyama
Yukiko Kamada
Masato Kosugi
Koichi Yamamoto
Kiyoko Kuwahara
Kiyoshi Kawabata
Chiharu
Suzuki
YukitoKurihara
Mayumi Koshio
Yuzo Tachibana
Noritoshi Suzuki
Ryuichi Uchimura
Hidehiko
Asai
Takashi Matsubara
Iginio Dieni
Mika Shigei
Seceding members:Hideo Urata
Kuniko Tasaka
Minoru Saito
Deceased members:
Nobuo Kobatake

Kouhei Tsumura
Takako Iwaki
Arabian Oil Co.

Kiyoshi Masatani
Jun Ando

Naoaki Aoki

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Transactions and Proceedings of the PalaeontologicalSociety of Japan

September 30, 1990

New Series No. 159

CONTENTS
TRANSACTIONS
903 .

Toshio Takagi: Taxonomic and paleozoogeographic significance of Cenozoic
hunch-back lik e venerids.

Part 1.

Gigantocallista, gen . nov. (Mollusca:

Bivalvia), A new endemic venerid genus from the Pliocene Tatsunokuchi
Formation, Sendai City, Miyagi Prefecture, northeastern J apan ... . ... ..... 541
904.

Shuji Niko: Early Carboniferous (Visean) cephalopods from the Hikoroichi
Formation , southern Kitakami Mountains . . .. . ..... . . . ... . .. .. . . . . ... . . 554

905 .

Rie Hori: Lower Jurassic radiolarian zones of SW Japan .... .. . . . . .. .. .. 562

906.

Hiromi Nagai and Shinjiro Mizutani : Jurassic Eucyrtidiellum (R adio laria) in
the Mino Terrane . ..... . ... . . . ......... . . .. . ...... . .......... . .... . .. 587

SHORT NOTES
24.

T a tsuo Oji: Dimorphism and geographic distribution of two phenotypes of awest Atlantic crinoid Endoxocrinus pm'rae (Gervais)

PROCEEDINGS. . . .... .. . ..... . . ... 603. .. .. ... . ... . .... .. . . ..... . .. . . . ..... . . . . . ....... . ....... . 607