ISSN 1346-2040

No.21
2022

Bulletin of the Tohoku University Museum
Editors
Ryusaku NGAOAKA

Professor of Art History
Department of Integrated Human Sciences, Graduate School of Arts and Letters, Tohoku University

Atsushi FUJISAWA

Professor of Archaeology
The Tohoku university Museum, Tohoku University

Yoshitaka KANOMATA

Professor of Archaeology
Department of Japanese Studies, Graduate School of Arts and Letters, Tohoku University

Reishi TAKASHIMA

Professor of Geology and Stratigraphy
The Tohoku university Museum, Tohoku University

March, 2022
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Cover image: Body design of Final Jomon Pottery drawn by the technigue of “erased-overcord impressions” . Original photograph by Miki Kikuchi.

Contents
Shuji Niko, Royal H. Mapes and Barbara Seuss : Virgilian (Late Pennsylvanian) coiled
nautiloids from the Finis Shale Member of the Graham Formation in Texas, southern 1Midcontinent North America

Masayuki Ehiro : Middle Permian cephalopods of the Takakurayama Formation in the 

21

Yaguki area, the southwestern margin of the South Kitakami Belt, Northeast Japan

Masayuki Ehiro : Early Anisian (Aegean) ammonoids from the Fukkoshi Formation (Inai 

39Group) with special reference to the Olenekian/Anisian boundary in the South Kitakami
Belt, Northeast Japan

Shunichi Kinoshita : Studies of large benthic foraminifers using microfocus X-ray CT85

Bull. Tohoku Univ. Museum. No. 21, pp. 1‒19, 2022
© by The Tohoku University Museum

Virgilian (Late Pennsylvanian) coiled nautiloids from theFinis Shale Member of the Graham Formation in Texas,
southern Midcontinent North America
Shuji Niko*, Royal H. Mapes** and Barbara Seuss****Department of Environmental Studies, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima
739-8521, Japan, **American Museum of Natural History, Central Part West at 79th Street, New York 10024-5192, U.S.A.,***GeoZentrum Nordbayern-Paläoumwelt, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Loewenichstraße 28,91054 Erlangen, Germany
Abstract: Nine species of Virgilian (Late Pennsylvanian) coiled nautiloids are described from theFinis Shale Member of the Graham Formation in north-central Texas, southern Midcontinent of North
America. They include Tainoceras monilifer Miller, Dunbar and Condra, Metacoceras quadratum sp.
nov., Endolobus sturgeoni sp. nov., Domatoceras tuckeri sp. nov., Titanoceras sp., Solenochilus
jackense sp. nov., Liroceras liratum (Girty), Peripetoceras bridgeportense Tucker and Mapes, andEphippioceras ferratum (Cox). The habitat of the nautiloid assemblage was the low latitudes in the
Marginal Sea of the Panthalassic Ocean. Strong biotic linkage between the Marginal Sea and thesouthern Late Pennsylvanian Midcontinent Sea is confirmed.

Introduction
The Finis Shale Member, introduced by Plummer andMoore (1922), is an early Virgilian (Late Pennsylvanian =latest Carboniferous) unit in the Graham Formation, Cisco
Group. It varies between 15−60 m in thickness and consists
mainly of shale characterized by the abundant presenceof ironstone concretions; it also contains sandstone andlimestone in its basal part (Plummer and Hornberger,
1936). This member outcrops in north-central Texas near
the Oklahoma border and west of Dallas on the southern
Midcontinent of North America (McGowen et al., 1972;
Barnes et al., 1987). A diverse marine fauna, including
foraminifers, sponges, cnidarians and mollusks, is recorded
from the member, and exceptionally well-preserved
cephalopod specimens provide material for taxonomic (Miller
et al., 1933; Plummer and Scott, 1937; Miller and Downs,
1950; Furnish et al., 1962; Hansman, 1965; Mapes, 1979;
McKinzie and McLeod, 2003; Doguzhaeva et al., 1999,
2006; Niko and Mapes, 2010, 2011; Mutvei et al., 2012;
Mutvei and Mapes, 2018), biostratigraphic (Boardman etal., 1994), and bionomic (Mapes, 1987; Mapes et al., 1995;
Mapes and Chaffin, 2003; Wani et al., 2012) studies. Adding
to these, the present paper analyzes coiled nautiloids as thethird fascicle in our recent studies describing non-ammonoid
cephalopods of the member and discusses their faunalsignificance.
Fossil material used in this serial project was recoveredfrom dark gray (to brownish-yellowish in weathered parts)
shales near Jacksboro, north-central Texas at 16 localities.
These comprise exposures (Figure 1) at pond dams (TXV34, 84), on hill sides (TXV-36, 78), at barren glades withgrooves, gullies to ravines (TXV-40, 54, 55, 56, 61, 120),at road sites (TXV-60, 62), on the east slope of Lost Creek(TXV-63), at the Old Lake Jacksboro Dam and spillway(TXV-69), near an abandoned oil well pad excavation(TXV-92), and at the excavation that serves as emergency
spillway for Lost Creek Lake (Lake Jacksboro; TXV-200).
Repository.―The specimens examined in the present
paper are reposited in the paleontological collections of
the American Museum of Natural History in New York City
(prefixed AMNH) and the Tohoku University Museum in
Sendai (prefixed IGPS).
Systematic Paleontology
Subclass Nautiloidea Agassiz, 1847
Order Nautilida Agassiz, 1847
Superfamily Tainoceratoidea Hyatt, 1883
Family Tainoceratidae Hyatt, 1883
Genus Tainoceras Hyatt, 1883
Type species.―Nautilus quadrangulus McChesney, 1859.

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Shuji Niko, Royal H. Mapes and Barbara Seuss

Figure 1. Map showing the geographic positions of
non-ammonoid cephalopod localities in the Finis Shale
Member near Jacksboro, north-central Texas.
Tainoceras monilifer Miller, Dunbar and Condra, 1933
Figure 2
Tainoceras monilifer Miller, Dunbar and Condra, 1933, p.
148–151, pl. 10, figs. 1–5, text-fig. 23; Unklesbay, 1962, p.
31–33, pl. 2, fig. 10; Tucker, 1976, p. 59, pl. 1, fig. 7, textfigs. 1a, b.
[not] Tainoceras monilifer; Miller and Unklesbay, 1942a,
p. 142, 143, pl. 4, figs. 1–3 [figs. 1, 2 = T. sexlineatum
Tucker, 1976; fig. 3 = T. sp. nov.]; 1947, p. 322, 323.
Tainoceras sp., Mapes and Chaffin, 2003, figs. 4A, 4D, 4F;
McKinzie and McLeod, 2003, p. 88, fig. 4-32 top.
Description.―Conchs moderate in size, having 140
mm in reconstructed diameter, discoidal and evolute with

gradual whorl expansion; umbilicus perforated; except forembryonic to juvenile shell indicating subcircular whorl
sections, more adoral shells have dorsoventrally depressedand subquadrate whorl sections with width/height ratios of
1.3–2.1; profiles of adoral whorls consist of weakly inflated
venter with a median groove, straight flanks, straightumbilical zone obtusely converging to dorsum and shallowly
rounded impressed area; apex corn-shaped. Shell surface
ornamented by oblique lirae in embryonic to juvenile shell,
then these lirae become subdued and nodes are added
on venter and at ventrolateral and umbilical angles; ventral
nodes closely spaced, laterally elongated, forming two rows
due to separation by a median groove; nodes at ventrolateralangles are strongly protruded. Septa shallow forming
sutures with sub-triangular to broadly rounded ventral lobes,
weak ventrolateral saddles, and relatively deep lateral lobes;
siphuncle central to faintly subcentral in position.
Material examined.―AMNH 5998–6014, 6016–6080,
6474–6483.
Occurrence.―The holotype of Tainoceras monilifer wascollected from the Finis Shale Member near Jacksboro,
Texas (Miller et al., 1933). Specimens of this species arealso known from the Upper Pennsylvanian of the Iatan
Limestone in Nebraska (Miller et al., 1933), the Lawrence
Shale, the Kereford and Burlingame Limestones in Kansas,
and the Vamoosa Formation in Oklahoma (Unklesbay,1962).
Localities of each examined specimen in this study are
as follows; TXV-34 (AMNH 5998–6010, 6474–6483), TXV55 (AMNH 6011), TXV-56 (AMNH 6012–6014, 6016–6022),
TXV-120 (AMNH 6023–6025), TXV-200 (AMNH 6026–6080).
Discussion.―Miller and Unklesbay (1942a) assigned
three specimens, Carnegie Museum cat. nos. 149, 10.434,
and 22.299, from the Upper Pennsylvanian Conemaugh
Formation of Pennsylvania to Tainoceras monilifer. Tucker(1976) reexamined them and concluded that 1) the former
one is undoubtedly assignable to T. monilifer and 2) the
latter two need to be separated from the species anddesignated as the types of a new species, T. sexlineatum
Tucker, 1976. Although his second opinion is reasonable,
we cannot agree with his first decision because the ventral
nodes of specimen no. 149 vanish in the adoral shell; thisdiagnosis is not known from any previously named speciesof Tainoceras. Thus, this specimen (Carnegie Museum cat.
no. 149) probably represents a new species. In addition,
Tucker (1976) synonymized T. murrayi Miller and Unklesbay,
1942b, with T. monilifer. This taxonomic treatment is also
unacceptable. Tainoceras murrayi is well differentiated fromT. monilifer by the absence of nodes at umbilical angles.

Pennsylvanian coiled nautiloids from Texas

3

Figure 2. Tainoceras monilifer Miller, Dunbar and Condra, 1933. A, G. AMNH 6023: A, lateral view; G, partial
enlargement of A to show embryonic to early juvenile shell morphologies. B, C. AMNH 6038: B, lateral view; C, ventralapertural view. D, E. AMNH 6068, shell wall mostly exfoliated: D, lateral view; E, ventral view. F, I. AMNH 6007: F, ventral
view; I, septal view, venter up. H. AMNH 6060, septal view, venter up. J. AMNH 6077, ventral view. Scale bar is 30 mm in A–F,
J; 6 mm in G; 20 mm in H, I.

4Shuji Niko, Royal H. Mapes and Barbara Seuss

Genus Metacoceras Hyatt, 1883
Type species.―Nautilus (Discus) sangamonensis Meek
and Worthen, 1860.
Metacoceras quadratum sp. nov.
Figure 3
Metacoceras sp., Mapes and Chaffin, 2003, fig. 4E;
McKinzie and McLeod, 2003, p. 88, fig. 4-31.
Diagnosis.―Small species of Metacoceras withwhorl sections of depressed subtrapezoidal in adoralphragmocones and depressed subquadrate shape in bodychamber; width/height ratios of whorls usually 1.4–1.9;
concavities of impressed area shallow to very shallow;
nodes strongly protruded, possess weak bulla-like extension.
Description.―Conchs small, discoidal and evolutewith gradual whorl expansion; umbilicus perforated; theholotype (largest specimen) represents an imperfect bodychamber with the last septum and is 40 mm in length,
24 mm in maximum whorl width and 16 mm in maximum
whorl height; reconstructed conch diameter from theholotype is approximately 60 mm; apex and peristome
are not preserved; whorl sections in juvenile shells facing
umbilical perforation are subcircular with a very shallow
median groove at venter, then their profiles shift towards
depressed subtrapezoidal shape with weakly inflated venter,rounded ventrolateral shoulders, nearly straight flanks that
acutely converse to dorsum, nearly straight umbilical zones
that obtusely converse to dorsum, and shallowly rounded
impressed area; furthermore, shapes of whorl sections inbody chamber shift to depressed subquadrate, where venter
becomes nearly flat, flanks weakly inflated, and concavity
of impressed area becomes very shallow; umbilical angles
rounded; median ventral groove disappears in adoralphragmocone and body chamber; width/height ratios ofwhorls are 1.4–1.9 in adoral phragmocone and 1.4–1.5
in body chamber. Juvenile shell surface ornamented by
distinct lirae that form V-shaped sinueses at venter, carinae
at ventrolateral shoulders and rounded sinueses at dorsum;
in more adoral shells, lirae become accentuated growthlines and strongly protruded and spine-like nodes developeon the position of ventrolateral shoulders; nodes possess
weak bulla-like extension on their dorsal side; peristome
shape can be reconstructed by growth lines as lingulate
ventral (hyponomic) and shallow lateral (ocular) sinuses.
Septa very shallow; sutures composed by broadly roundedventral lobes, rounded ventrolateral saddles, shallow laterallobes, and subtriangular dorsal lobes; siphuncle situatesnear halfway between conch center and ventral margin injuvenile, and subcentral position in more adoral shells; ratiosof distance between ventral shell surface and central axis ofsiphuncle per whorl height at dorsoventral plane are 0.31–
0.44.
Material examined.―Holotype, AMNH 6159. Paratypes,
AMNH 6102, 6108–6111, 6118, 6130, 6134, 6147–6149,
6472. In addition, 61 specimens (AMNH 6091–6101,
6103–6107, 6112, 6115–6117, 6119–6129, 6131–6133,
6135–6146, 6150–6158, 6160–6163, 6473) are assigned to
Metacoceras quadratum sp. nov.
Occurrence.―TXV-34 (AMNH 6092–6099), TXV-56(AMNH 6091, 6100–6112, 6473), TXV-120 (AMNH 6115),
TXV-200 (AMNH 6116–6163, 6472). All previous records ofthe new species as Metacoceras sp. by Mapes and Chaffin(2003) and McKinzie and McLeod (2003) are from the Finis
Shale Member in Texas.
Etymology.―The specific name is derived from the Latin,
quadratus (= quadrangular), referring to its whorl section
shapes in the body chamber.
Discussion.―In its gross conch form of the adoral shells
and ornament, Metacoceras quadratum sp. nov. is mostsimilar to M. cornutum Girty (1911, p. 145, 146; 1915,
p. 240–242, pl. 29, figs. 4, 4a, 4b, 5, 5a, 5b), which was
described from the Desmoinesian (Middle Pennsylvanian) of
Oklahoma. However, the impressed area of this new species
is shallower than that of M. cornutum and the subtrapezoidal
profiles developed in the phragmocones are not recognizedin M. cornutum. A Virgilian species, Metacoceras copei
Tucker (1976, p. 61, 62, pl. 1, fig. 6, pl. 3, figs. 1, 2, pl. 4.
fig. 3) from the Mattoon Formation of Illinois, also resembles
M. quadratum, but it possesses a median ventral groovein the adoral shells and the knob-like distal ends of nodes
exclude it from M. quadratum. Metacoceras clinocostatum
Sturgeon, Windle, Mapes and Hoare (1982, p. 1455, 1457,
1458, pl. 1, figs. 4, 8; 1997, p. 34, 35, pl. 1-8, figs. 4–9),
from the Desmoinesian Allegheny Group and the Missourian(Late Pennsylvanian) part of the Conemaugh Group of Ohio,
differs from M. quadratum by having strongly elongatednodes attaining the umbilical angles.
Family Koninckioceratidae Hyatt in Zittle, 1900
Genus Endolobus Meek and Worthen, 1865
Type species.―Nautilus spectabilis Meek and Worthen,
1860.
Endolobus sturgeoni sp. nov.
Figure 4
Diagnosis.―Species of Endolobus with 1.4–2.0 in
width/height ratios of adoral whorls; flanks narrowly
rounded; impressed area deeply concaved; nodes low anddorsoventrally elongated.
Description.―Conchs thick discoidal, evolute; whorl
expansion rapid in phragmocone, but it becomes gradual inPennsylvanian coiled nautiloids from Texas

5

Figure 3. Metacoceras quadratum sp. nov. A, B, E–G. paratype, AMNH 6118: A, lateral view of juvenile shell; B, septal viewof juvenile shell, venter up; E, ventral view; F, lateral view; G, septal view, venter up. C, D. paratype, AMNH 6472, juvenile shell: C,
ventral view; D, lateral view. H. paratype, AMNH 6130, septal view, venter up. I. paratype, AMNH 6134, dorsal view. J. paratype,
AMNH 6102, lateral view. K. paratype, AMNH 6147, septal view, venter up. L, M, P, Q. holotype, AMNH 6159: L, lateral view; M,
cross sectional view, venter up; P, ventral view; Q, dorsal view. N. paratype, AMNH 6110, ventral view, showing details of surface
ornamentation. O. paratype, AMNH 6111, lateral view. Scale bar is 6 mm in A–D; 12 mm in E–H, J, N; 15 mm in I, K–M, O–Q.

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Shuji Niko, Royal H. Mapes and Barbara Seuss

Figure 4. Endolobus sturgeoni sp. nov. A–C. paratype, AMNH 6081, shell wall mostly exfoliated: A, lateral view; B,
cross sectional view, venter up; C, partial enlargement of A to show details of juvenile shell. D. paratype, AMNH 6082, septal
view, venter up. E, F, L. paratype, AMNH 6085: E, lateral view; F, dorsal view; L, ventral view. G. paratype, AMNH 6087, shellwall mostly exfoliated, lateral view. H, J, M, N. holotype, AMNH 6086: H, lateral view; J, cross sectional view, venter up; M,
ventral view; N, dorsal view. I, K. paratype, AMNH 6084, shell wall mostly exfoliated: I, lateral view; K, cross sectional view,
venter up. Scale bar is 15 mm in A, B; 6 mm in C; 20 mm in D–N.

Pennsylvanian coiled nautiloids from Texas
body chamber; umbilicus perforated; the holotype represents
an imperfect body chamber with the last septum and is 47
mm in length, 34 mm in maximum whorl width, and 18 mm
in maximum whorl height; the largest specimen (paratype,
AMNH 6089) has 41 mm in whorl width and 21 mm(imperfect) in whorl height; reconstructed conch diameter ofthe holotype is approximately 60 mm; apex not preserved;
whorl sections are circular in juvenile shells facing umbilicalperforation, then they shift towards depressed subellipticalshapes, whose profiles consist of broadly rounded venterto ventrolateral shoulders, narrowly rounded flanks (=umbilical angles), weakly inflated umbilical zones androunded impressed area; width/height ratios of whorls are
1.4–1.6 in adoral phragmocone, these ratios increase to 2.0
in body chamber. Shell surface marked by dorsoventrally
elongated low nodes on flanks; except for nodes, surface
ornamentation absent; no peristome is preserved, but
presence of deep lingulate ventral (hyponomic) and very
shallow lateral (ocular) sinuses can be reconstructed by
growth line shapes. Septal curvature moderate; sutures
roughly straight, but some sutures have shallow laterallobes, directly transverse in juvenile shell and strongly incline
towards venter in adoral shell; siphuncle supracentral withweak to moderate dorsum wards shifting; ratios of distance
between ventral shell surface and central axis of siphuncle
per whorl height at dorsoventral plane are 0.54–0.72.
Material examined.―Holotype, AMNH 6086. Paratypes,
AMNH 6081–6085, 6087–6089.
Occurrence.―TXV-34 (AMNH 6081–6086), TXV-200(AMNH 6087–6089).
Etymology.―The specific name is in honor of the late
Myron T. Sturgeon in recognition of his contributions topaleontological studies of Pennsylvanian nautiloids andconodonts.
Discussion.―Endolobus schucherti Miller (1932, p.
64–66, pl. 12, figs. 12, 13) from the Upper Pennsylvaniansandstone of New Mexico has similar node shapes as E.
sturgeoni sp. nov., but it differs in its shallower impressed
area. In addition, a median longitudinal ridge on the venterof E. schucherti is not developed in the new species.
Superfamily Trigonoceratoidea Hyatt, 1884
Family Grypoceratidae Hyatt in Zittle, 1900
Genus Domatoceras Hyatt, 1891
Type species.―Domatoceras umbilicatum Hyatt, 1891.
Domatoceras tuckeri sp. nov.
Figure 5
Domatoceras sp., Mapes and Chaffin, 2003, figs. 4C, 4G, 4I;
McKinzie and McLeod, 2003, p. 88, fig. 4-29.

7

Diagnosis.―Species of Domatoceras having whorl
sections of compressed subtrapezoidal with concave venterin adoral phragmocone and compressed subrectangular inbody chamber; width/height ratios of whorls 0.8–1.1; weakly
waved carinae developed at ventral angles.
Description.―Conchs moderate in size, lenticular andevolute with relatively rapid whorl expansion; umbilicus
perforated; the holotype of fragmentary phragmocone
consisting of three volutions is 67 mm in maximum length,
37 mm in maximum whorl width, and 41 mm in maximum
whorl height; the largest specimen (paratype, AMNH 6227)
of imperfect body chamber attains 42 mm in whorl width(reconstructed from half width), 51 mm in whorl height andapproximately 160 mm in reconstructed conch diameter;
apex and peristome are not preserved; whorl sections are
subcircular in juvenile shell facing umbilical perforation,
subtrapezoidal to compressed subtrapezoidal in more adoralphragmocone, and compressed subrectangular in bodychamber; profiles of whorl sections in adoral phragmocones
consist of shallowly concave venter as ventral groove, nearlystraight ventrolateral shoulders that acutely converge toventer, straight flanks that very acutely converge to venter,straight umbilical zones that obtusely converge to dorsum,
and quadrate impressed area; in body chamber, venter
becomes flat, shoulders and flanks integrate; umbilicalangles bluntly pointed; width/height ratios of whorls are 0.9–
1.1 in adoral phragmocone and 0.8–0.9 in body chamber.
Surface of juvenile shell marked by sinuous lirae thatpersist in body chamber at ventral side, but are replacedby growth lines in other parts of more adoral shells; strong
carina having weakly waved margin and frill-like appearance
developed at ventral angle with bilateral symmetry in adoralshells; lirae and growth lines suggest peristome shapewith V-shaped ventral (hyponomic) and shallow lateral(ocular) sinuses. Septal curvatures are relatively weak;sutures indicate shallow ventral and broadly rounded laterallobes. Siphuncle is subcentral in position; ratios of distance
between ventral shell surface and central axis of siphuncle
per whorl height at dorsoventral plane are 0.48–0.52.
Material examined.―Holotype, AMNH 6278. Paratypes,
AMNH 6181, 6186, 6208, 6209, 6227–6230, 6255, 6256,
6279–6281. In addition, 95 specimens (AMNH 6173–6180,
6182–6185, 6187–6207, 6210–6226, 6231–6254, 6257–
6277) are assigned to Domatoceras tuckeri sp. nov.
Occurrence.―TXV-34 (AMNH 6173–6185), TXV55 (AMNH 6186), TXV-56 (AMNH 6187–6227), TXV200 (AMNH 6228–6281). All previous records of the new
species as Domatoceras sp. by Mapes and Chaffin (2003)
and McKinzie and McLeod (2003) are from the Finis Shale
Member in Texas.
Etymology.―The specific name is to honor the late John K.
Tucker in recognition of his contributions to paleontological8Shuji Niko, Royal H. Mapes and Barbara Seuss

Figure 5. Domatoceras tuckeri sp. nov. A–F. holotype, AMNH 6278: A, lateral view; B, cross sectional view, venterup; C, ventral view; D, dorsal view; E, lateral view of juvenile shell; F, partial enlargement of C to shew details of surface
ornamentation. H. paratype, AMNH 6281, lateral view. G, I. paratype, AMNH 6208, shell wall exfoliated: G, ventral view; I,lateral view. J, K. paratype, AMNH 6227: J, cross sectional view, venter up; K, lateral view. Scale bar is 30 mm in A–D, I–K; 6mm in E; 10 mm in F; 20 mm in G; 37.5 mm in H.

Pennsylvanian coiled nautiloids from Texas

9

Figure 6. Titanoceras sp., IGPS coll. cat. no. 112545. A. ventral view. B. lateral view. C. cross sectional view, venter up.
Scale bar is 100 mm in A, B; 75 mm in C.
studies of Pennsylvanian nautiloids.
Discussion.―This new species most closely resembles
Domatoceras oreskovichi Sturgeon, Windle, Mapes andHoare (1982, p. 1468, 1469, pl. 2, figs. 6, 7, 9, pl. 3, fig.
2; 1997, p. 60, 61, pl. 1-23, figs. 6, 7, pl. 1-24, figs. 2, 3,
pl. 1-26, figs. 1, 2, pl. 1-27, figs. 1–6, text-fig. 1-8A), fromthe Desmoinesian Allegheny Group of Ohio, by having
compressed subquadrate whorl sections with a concaved
venter. However, larger amplitude of the waved carinae
distinguishes it from Domatoceras tuckeri sp. nov. A
concaved venter is also developed in D. texanum Tucker
and Mapes (1978, p. 597, pl. 2, figs. 4, 5, pl. 3, fig. 6)
from the Missourian Wolf Mountain Shale of Texas. The
differences between D. texanum and D. tuckeri are its
subtrapezoidal whorl sections remain in the body chambers
and morphological shifting from carinae to nodes as shell
grows.
Genus Titanoceras Hyatt, 1884
Type species.―Nautilus ponderosus Meek, 1872.
Titanoceras sp.
Figure 6

Titanoceras sp., McKinzie and McLeod, 2003, p. 91, fig.
4-33.
Description.―A single very large specimen of fragmentarybody chamber is available for study; it is 352 mm in length,225–232 mm in whorl width and 137 mm in whorl height;
whorl sections are strongly depressed, subquadrate withwidth/height ratios of approximately 1.6 and consists ofbroadly concave venter and weakly inflated flanks; mostof umbilical zone is missing, but preserved part indicatesshallow concavity. Shell surface smooth; ventrolateral andumbilical angles are carinated; longitudinally elongatednodes occur on carina at ventrolateral angles.
Material examined.―IGPS coll. cat. no. 112545.
Occurrence.―TXV-200. Previous record of the species
by McKinzie and McLeod (2003) is from the Finis Shale
Member in Texas.
Discussion.―Its depressed subquadrate whorl sections
with a broadly concaved venter suggest the genericassignment of this specimen to Titanoceras rather than
Latitemnocheilus Sturgeon, Windle, Mapes and Hoare(1982; type species, Nautilus (Temnocheilus) latus Meek
and Worthen, 1870) and Temnocheilus M’Coy (1844; typespecies, Nautilus (Temnocheilus) coronatus M’Coy, 1844).

10

Shuji Niko, Royal H. Mapes and Barbara Seuss

General shape of the venter of Latitemnocheilus is weakly
convex and the whorl section of Temnocheilus indicatessubtrapezoidal profile.
The present Titanoceras sp. is well differentiated fromother species assigned to the genus by having a larger
width/height ratio of the whorl. However, erection of new
species is not possible due to lacking information about thephragmocone.
Superfamily Aipoceratoidea Hyatt, 1883
Family Solenochilidae Hyatt, 1893
Genus Solenochilus Meek and Worthen, 1870
Type species.―Nautilus (Cryptoceras) springeri Whiteand St. John, 1868.
Solenochilus jackense sp. nov.
Figure 7
Diagnosis.―Species of Solenochilus with subelliptical
whorl sections, whose width/height ratios are 1.4–1.5;
venter broadly rounded; ventrolateral shoulders rounded;flanks weakly inflated to straight; umbilical angles carinated;umbilical zones weakly concaved; impressed area
moderately concaved; camerae relatively long; except for
relatively deep ventral sinus, sutures roughly transverse.
Description.―Conchs large, subglobose with rapid whorl
expansion; inner whorls are narrowly evolute with narrowumbilical area, then coiling becomes loose in more adoralphragmocone; apex not observable; the holotype (largest
specimen) is fragmentary whorl of mature phragmocone
having 58 mm in whorl length, 52 mm in maximum whorl
width (reconstructed from half width, exfoliated lateral shallwall), and 36 mm in maximum whorl height (exfoliatedventral shall wall); a paratype (AMNH 6167) representing
immature phragmocone is 45 mm in diameter, 40 mm in
maximum whorl width (reconstructed from half width), 27
mm in maximum whorl height, and 0.2 in approximate ratioof umbilical diameter per conch diameter; whorl sections
are depressed and subelliptical; profiles of whorl sections in
immature phragmocone consist of broadly rounded venter,rounded ventrolateral shoulders, weakly inflated flanks,
weakly concaved umbilical zones and shallowly rounded
impressed area; in mature phragmocone, flanks becomestraight and acutely converge to venter; umbilical angles
carinated; width/height ratios of whorls are 1.4–1.5; nobody chamber preserved. Shell surface is mostly smooth
except for umbilical carinae that are marked by longitudinallirae; umbilical spine not preserved. Septa are shallowly
concaved; sutures are roughly transverse with narrow but
relatively deep ventral sinus, weak ventrolateral saddles,and nearly straight at lateral to dorsolateral portions;cameral lengths are relatively long for the genus, 17–20 mm

at ventral margin in the holotype. Siphuncle is at the ventral
margin; septal necks are suborthochoanitic in immature andorthochanitic in mature phragmocones.
Material examined.―Holotype, AMNH 6168. Paratypes,
AMNH 6166, 6167. In addition, two specimens (AMNH
6164, 6165) are assigned to Solenochilus jackense sp. nov.
Occurrence.―TXV-34 (AMNH 6164), TXV-200 (AMNH
6165–6168).
Etymology.―The specific name is derived from JackCounty, from which all examined specimens including thetype series were collected.
Discussion.―Solenochilus missouriensis Miller, Laneand Unklesbay (1947, p. 10, pl. 4, figs. 3, 4), from theMiddle Pennsylvanian Winterset Limestone of Missouri,
most closely resembles the new species, by its subelliptical
whorl sections with a width/height ratio of approximately
1.5 and relatively long camerae. However, this species
has more strongly fluted sutures especially at the lateral
to dorsolateral portions than those of S. jackense sp. nov.
Solenochilus greenensis Sturgeon (1946, p. 33–35, pl. 8,
fig. 6, pl. 9, fig. 3, text-fig. 3A; Sturgeon et al., 1997, p. 71,
72, pl. 1-31, figs. 1, 2, pl. 1-32, fig. 2, pl. 1-33, fig. 3, pl. 1-34,
figs. 1–3, text-fig. 1-11B), described from the Desmoinesian
Hamden Limestone, Ohio also resembles S. jackense, but
its dorsal part of the flanks is strongly concave. Solenochilus
mcfarlandi Sturgeon, Windle, Mapes and Hoare (1982,
p. 1469, 1471, 1472, pl. 5, figs. 3, 4; 1997, p. 73, 74, pl.
1-35, fig. 2, pl. 1-37, figs. 2, 3, text-fig. 1-12A) from theMissourian part of the Conemaugh Group of Ohio differsfrom S. jackense in having more depressed whorl sections
exceeding 1.8 in a width/height ratio and shorter camerae.
Other comparable species, including S. brammeri Miller,
Dunbar and Condra (1933, p. 234–236, pl. 22, figs. 6, 7,
pl. 23, fig. 1, pl. 24. fig. 1) from the Missourian Argentine
Limestone of Nebraska and S. springeri (White and St. John,
1868, p. 124, 125, fig. 10; Kummel, 1964, figs. 319, 320,1,
321; Mikesh and Glenister, 1966, p. 273–277, figs. 1A, 1B)
from the Middle Pennsylvanian of Iowa and Arkansas, arewell differentiated from S. jackense by the presence of a
mid-ventral groove in their mature phragmocones.
Superfamily Clydonautiloidea Hyatt in Zittel, 1900
Family Liroceratidae Miller and Youngquist, 1949
Genus Liroceras Teichert, 1940
Type species.―Coloceras liratum Girty, 1911.
Liroceras liratum (Girty, 1911)
Figure 8
Coloceras liratum Girty, 1911, p. 144, 145; 1915, p. 237,
238, pl. 28, figs. 2, 2a, b, 3, 3a, b, 4, 4a, 5, 6, 6a; Miller etal., 1933, p. 132–134, pl. 6, figs. 1–8.

Pennsylvanian coiled nautiloids from Texas

11

Figure 7. Solenochilus jackense sp. nov. A, B, E, F. paratype, AMNH 6167: A lateral view; B, ventral-apertural view;E, ventral view; F, ventral view, showing details of siphuncle. C, D, G. holotype, AMNH 6168, shell wall mostly exfoliated: C,
septal view, venter up; D, lateral view; G, ventral view, showing details of siphuncle. Scale bar is 20 mm in A–E; 6 mm in F, G.

Coloceras liratum obsoletum Girty, 1911, p. 145; 1915, p.
238, 239, pl. 29, figs. 1, 1a, b, 2, 2a, 3, 3a.
Coloceras obsoletum Girty. Miller et al., 1933, p. 134–136,
pl. 7, figs. 4–7.
Coloceras liratum? Girty. Miller and Cline, 1934, p. 173–175,
pl. 28, figs. 24–26.
Liroceras liratum (Girty). Teichert, 1940, p. 590; Young,
1942, p. 122; Sturgeon, 1946, p. 19–21, pl. 4, figs. 6–9;
Miller and Youngquist, 1949, pl. 53, figs. 3–6; Unklesbay
and Palmer, 1958, p. 1073, pl. 138, figs. 1–3; Unklesbay,
1962, p. 45–47, pl. 5, figs. 6–8, pl. 6, figs. 5, 6, text-fig. 1;
Kummel, 1964, figs. 324,3a, b; Murphy, 1970, p. 203, 204,

pl. 36, fig. 9; Tucker, 1976, p. 67, 68, pl. 3, fig. 4; Sturgeon
et al., 1997, p. 78, 79, pl. 1-44, figs. 1, 3–12; Seuß et al,
2009, p. 627.
Liroceras cf. liratum (Girty). Young, 1942, p. 122.
Liroceras sp., Miller and Unklesbay, 1942a, p. 137, 138, pl. 1,
fig. 13, text-fig. 1A; Sturgeon and Miller, 1948, p. 76, 77;
Mapes and Chaffin, 2003, fig. 4B; McKinzie and McLeod,
2003, p. 88, fig. 4-30.
Description.―Conchs small, having 70 mm inreconstructed diameter, subglobose, involute with moderate
whorl expansion; whorl sections are depressed and reniform12

Shuji Niko, Royal H. Mapes and Barbara Seuss

Figure 8. Liroceras liratum (Girty, 1911). A, B, F. AMNH 6305: A, lateral view; B, ventral-apertural view; F, lateral view,
showing details of surface ornamentation. C. AMNH 6348, shell wall mostly exfoliated, ventral view. D. AMNH 6310, septal
view, venter up. E. AMNH 6354, septal view, venter up. G. AMNH 6352, dorsal view. H. AMNH 6345, shell wall exfoliated,
lateral view. I. AMNH 6360, septal view, venter up. J. AMNH 6355, lateral view. K, L. AMNH 6357: K, dorsal view; L, ventral
view. Scale bar is 20 mm in A–E, G–L; 6 mm in F.

Pennsylvanian coiled nautiloids from Texas
consisting of rounded venter, ventrolateral shoulders toflanks, broadly rounded umbilical zones and rounded
impressed area; umbilical angles narrowly rounded; width/height ratios of whorls are 1.2–1.7. Shell surface is smooth,
except for portion of umbilical angles to umbilical zones in
inner volutions, where reticulate ornamentation is developed;
growth lines exhibit shallow ventral (hyponomic) and lateral(ocular) sinuses. Septa relatively deep; sutures are directlytransverse. Siphuncle is subcentral.
Material examined.―AMNH 6298–6471.
Occurrence.―The syntypes were collected from the
Desmoinesian Wewoka Formation of Oklahoma (Girty,
1911). Except for the type stratum, specimens of this species
are widely known from the Middle to Upper Pennsylvanianof the North American Midcontinent including the Allegheny
and Conemaugh Formations in Pennsylvania (Miller andUnklesbay, 1942a), the Pottsville, Allegheny and Conemaugh
Formations in Ohio (Sturgeon, 1946), the Mattoon Formationin Illinois (Tucker, 1976), the Burgner Formation in Missouri(Unklesbay and Palmer, 1958), the Weston Shale in Kansas(Miller et al., 1933), the Atoka, Pumpkin Creek, Boggy,
Stuart, Senora, Wetumka, Holdenville, Nellie Bly, Wann,
Vamoosa and Kanwaka Formations in Oklahoma (Miller etal., 1933), the Jacksboro Limestone and the Finis Shale
Member in Texas (Miller et al., 1933), and the Magdalena
Group in New Mexico (Young, 1942).
Localities of each examined specimen in this study are as
follows; TXV-34 (AMNH 6298–6302), TXV-36 (AMNH 6303),
TXV-54, (AMNH 6304), TXV-56 (AMNH 6305–6341), TXV120 (AMNH 6342–6347), TXV-200 (AMNH 6348–6471).
Discussion.―Unklesbay (1962) considered thatdifferences between Liroceras liratum and L. obsoletum,
especially in their surface ornamentations are intraspecificvariations and synonymized them. We agree with his
proposal. Liroceras liratum is the most abundant nautiloid
species in the Finis Shale Member.
Genus Peripetoceras Hyatt, 1894
Type species.―Nautilus freieslebeni Geinitz, 1843.
Peripetoceras bridgeportense Tucker and Mapes, 1978
Figure 9
Peripetoceras bridgeportense Tucker and Mapes, 1978, p.
598, 600, 603, pl. 1, figs. 1–3, pl. 2, figs. 1, 2, pl. 3, fig. 7.
Peripetoceras sp., Wani et al., 2012, fig. 3D.
Description.―Conchs small, having 50 mm inreconstructed diameter, subglobose, involute with rapid whorl
expansion; whorl sections depressed, reniform in apicaland subtrapezoidal in adoral shells; profiles of apical whorls
consist of rounded venter, ventrolateral shoulders to flanks,

13

narrowly rounded umbilical zones and rounded impressed
zone; in adoral whorls, subquadrate ventral angles appear
and following profiles indicate nearly flat venter, nearlyflat ventrolateral shoulders to flanks converging acutely
to venter, narrowly rounded umbilical zones, and deeply
rounded and wide impressed zone; umbilical angles broadly
rounded throughout; width/height rations of whorls range
from 1.5 to1.7. Shell surface is smooth; growth lines exhibit
narrowly rounded ventral (=hyponomic) sinus, broadly
rounded ventrolateral lobes, very shallow lateral (= ocular)
sinus; sutures are transverse and roughly straight; siphuncle
is supracentral in position and slightly off to dorsum.
Material examined.―AMNH 6282–6297.
Occurrence.―The holotype and all paratypes ofPeripetoceras bridgeportense were collected from theMissourian (early Late Pennsylvanian) Wolf Mountain Shale,
Texas (Tucker and Mapes, 1978).
Localities of each examined specimen in this study are as
follows; TXV-34 (AMNH 6282–6287), TXV-54 (AMNH 6288),
TXV-56 (AMNH 6289–6292), TXV-200 (AMNH 6293–6297).
Previous record of the species by Wani et al. (2012) is fromthe Finis Shale Member in Texas.
Discussion.―We assign the present specimens to
Peripetoceras bridgeportense on the basis of similarities
with the holotype in their whorl section shapes, ratios ofconch expansion, and siphuncular position. It is possible thatan unfigured species, Peripetoceras sp., recorded from theFinis Shale Member by McKinzie and McLeod (2003) also isconspecific with P. bridgeportense.
Family Ephippioceratidae Miller and Youngquist, 1949
Genus Ephippioceras Hyatt, 1884
Type species.―Nautilus ferratus Cox, 1858.
Ephippioceras ferratum (Cox, 1858)
Figure 10
Nautilus ferratus Cox, 1858, p. 574, 575, pl. 10, figs. 2, 2a.
Ephippioceras ferratum (Cox). Hyatt, 1884, p. 290; 1894,
p. 539, pl. 10, figs. 23–26; Miller et al., 1933, p. 114–118,
pl. 3, figs. 14–17; Miller and Owen, 1934, p. 209–211, pl.
12, figs. 3, 4, text-figs. 1A, B; Smith, 1938, p. 10, 11, pl.
1, fig. 17; Miller and Unklesbay, 1942a, p. 136, pl. 1, figs.
14, 15; Sturgeon, 1946, p. 18, 19, pl. 4, figs. 2–4; Miller
and Unklesbay, 1947, p. 320, pl. 1, figs. 7, 8; Miller et al.,1947, p. 6, pl. 2, figs. 7–10; Miller and Youngquist, 1949, p.
129, pl. 53, figs. 7, 8; Unklesbay, 1962, p. 50–52, pl. 4, fig.
3; Kummel, 1963, p. 357, pl. 15, figs. 4–7; 1964, fig. 326,
2; Sturgeon et al., 1997, p. 81, 82, pl. 1-46, figs. 1–5, 7, 9.
Ephippioceras (Nautilus) ferratum (Cox). Hyatt, 1891, p.
352.
[not] Ephippioceras ferratum (Cox). Gordon, 1964, p. 162,

14

Shuji Niko, Royal H. Mapes and Barbara Seuss

Figure 9. Peripetoceras bridgeportense Tucker and Mapes, 1978. A, B, F, K. AMNH 6289: A, septal view, venter up;
B, ventral view; F, lateral view; K, partial enlargement of B to show details of surface ornamentation. C, I, J. AMNH 6283:
C, ventral view; I, lateral view; J, septal view, venter up. D, G. AMNH 6292: D, ventral view; G, dorsal view. E. AMNH 6295,
septal view, venter up. H. AMNH 6297, lateral view. Scale bar is 20 mm in A–J; 12 mm in K.

Pennsylvanian coiled nautiloids from Texas

15

Figure 10. Ephippioceras ferratum (Cox, 1858). A–C. AMNH 6169, shell wall mostly exfoliated: A, ventral view; B, crosssectional view, venter up; C, lateral view. D–F. AMNH 6170, shell wall mostly exfoliated: D, ventral view; E, lateral view;
F, ventral-apertural view. G, H. AMNH 6171: G, septal view, venter up; H, ventral view. I, J. AMNH 6172, shell wall mostly
exfoliated: I, lateral view; J, ventral view. Scale bar is 15 mm.

163, pl. 16, figs. 1–3, text-fig. 31 [= E. sp. nov.].
Eohippioceras [sic.] ferratum (Cox). Seuß et al, 2009, p.
627.
Description.―Conchs small, subglobose and involutewith relatively rapid whorl expansion; a well-preserved
specimen (AMNH 6172) has 29 mm in conch diameter;whorl sections are strongly depressed, reniform consistingof rounded venter, ventrolateral shoulders to franks, weakly
inflated umbilical zones and deeply rounded impressed
area; umbilical angles bluntly pointed; width/height ratios ofwhorls are 1.6–1.8; mid-ventral conchal furrow developed.
Shell surface smooth. Cameral length short; sutures exhibit
distinct flutings indicating V-shaped and very prominent

16

Shuji Niko, Royal H. Mapes and Barbara Seuss

Figure 11. Paleogeographic reconstruction of the distribution of common Late Pennsylvanian coiled nautiloid species
with the Finis Shale assemblage (arrow). Map based on and modified from Algeo and Heckel (2008). 1, Liroceras liratumand Ephippioceras ferratum in the Conemaugh Formation, Pennsylvania; 2, L. liratum and E. ferratum in the Conemaugh
Formation, Ohio; 3, L. liratum in the Mattoon Formation, Illinois; 4, E. ferratum in the South Bend Formation, Nebraska; 5,
Tainoceras monilifer in the Iatan Limestone, Nebraska; 6, E. ferratum in the Dennis and Westerville limestones, Missouri;
7, L. liratum in the Weston Shale, Kansas;8, T. monilifer in the Lawrence Shale and Kereford and Burlingame Limestones,
Kansas; 9, T. monilifer in the Vamoosa Formation and L. liratum in the Nellie Bly, Wann, Vamoosa and Kanwaka Formations,Oklahoma; 10, Peripetoceras bridgeportense in the Wolf Mountain Shale, Texas; 11, L. liratum in the Magdalena Group, New
Mexico.
ventral saddle, broadly rounded lateral lobes and low
umbilical saddle. Siphuncle central to slightly supracentral in
position.
Material examined.―AMNH 6169–6172.
Occurrence.―The holotype of Ephippioceras ferratum
was collected from the Pennsylvanian (specific stratigraphic
setting unknown) of Kentucky (Cox, 1858). Specimensof this species are also known from the Middle toUpper Pennsylvanian of the Conemaugh Formation in
Pennsylvania (Miller and Unklesbay, 1942a), the Pottsville,
Allegheny and Conemaugh Formations in Ohio (Sturgeon,1946), the Cherokee Formation and the Dennis andWesterville Limestones in Missouri (Miller et al., 1933), theSouth Bend Formation in Nebraska (Miller et al., 1933), andthe Boggy Formation in Oklahoma (Smith, 1938).
Localities of each examined specimen in this study are as
follows; TXV-34 (AMNH 6169–6171), TXV-56 (AMNH 6172).
Discussion.―Gordon (1964) assigned a single Morrowan(Early Pennsylvanian) specimen from the Hale Formation,

Arkansas to Ephippioceras ferratum and stated that it is theearliest record of this species. However, we cannot agreewith his point of view because the ventral saddle in the
suture of this Morrowan specimen is much lower than that of
the typical ones of E. ferratum. We think that this specimen
probably represents a new species and the chronologicalrange of E. ferratum is, therefore, constrained exclusively in
Middle to Late Pennsylvanian time.

Coiled Nautiloid Assemblage
The Late Pennsylvanian coiled nautiloid assemblage fromthe Finis Shale Member is composed by Tainoceras monilifer
Miller, Dunbar and Condra, Metacoceras quadratum sp.
nov., Endolobus sturgeoni sp. nov., Domatoceras tuckeri
sp. nov., Titanoceras sp., Solenochilus jackense sp. nov.,
Liroceras liratum (Girty), Peripetoceras bridgeportense
Tucker and Mapes, and Ephippioceras ferratum (Cox).
In our previous studies concerning fossil cephalopods

17

Pennsylvanian coiled nautiloids from Texas
in the Midcontinent of North America, Niko et al. (2018)
examined the Middle Pennsylvanian orthoconic cephalopod
assemblage in the Buckhorn Asphalt Quarry, located ca.
150 km northeast of Jacksboro, and concluded that itdemonstrates provincialism. In contrast to this assemblage,
the Finis Shale assemblage indicates cosmopolitanism
and is characterized by the absence of endemic genera
and presence of common, widely occurring species to highdegree. Most of the area of Midcontinent North America,
situated in the low latitudes at this time, was flooded dueto the rise of the sea level forced by melting Gondwanan
ice sheets and submergence in the shelf sea (i.e., the Late
Pennsylvanian Midcontinent Sea (LPMS); Heckel, 1994).
The LPMS included the Appalachian Basin, the Illinois
Basin, the Midcontinent Shelf and the Willistone Basin,
and was connected to the Panthalassic Ocean through the
Marginal Sea (Algeo and Heckel, 2008; Algeo et al., 2008;
Algeo and Herrmann, 2017).
As obvious from the proceeding systematic part, Late
Pennsylvanian occurrences of the previously known four
species from outside the Finis Shale Member are as follows:
T. monilifer (Nebraska, Kansas, Oklahoma), L. liratum(Pennsylvania, Ohio, Illinois, Oklahoma, New Mexico), P.
bridgeportense (Texas), and E. ferratum (Pennsylvania,
Ohio, Missouri, Nebraska, Oklahoma). Among these, alllocalities in Texas (including the Finis Shale) and New
Mexico belong to the Marginal Sea while others are in the
LPMS; more particularly they belong to the Appalachian
Basin (Pennsylvania, Ohio), the Illinois Basin (Illinois)
and the Midcontinent Shelf (Missouri, Nebraska, Kansas,
Oklahoma), whose areas represent the southern partof the sea (Figure 11). Niko et al. (2018) suggested thatthe Buckhorn Asphalt was deposited in the restricted
epeiric sea during a cool episode. Differences of abovementioned composition between these two assemblages
can be referred to sea level change triggered by forming
and melting of ice sheets. We can conclude that the coiled
nautiloid assemblage from the Finis Shale inhabited the
Marginal Sea that was open to the Panthalassic Ocean
at that time and thus, had strong biotic linkage with thesouthern LPMS including the Appalachian Basin, the Illinois
Basin, and the Midcontinent Shelf.

Acknowledgements
We thank G. Mapes, A. Pradel and I. Kruta for theirsupports in our field trips. Many thanks also go to themembers of the Dallas Paleontological Society forassistance and collecting specimens during field work at
the TXV-200 section by BS (DFG-project SE 2283/2-1). The
helpful reviews by M. Ehiro improved this paper.

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Bull. Tohoku Univ. Museum. No. 21, pp. 21‒38, 2022
© by The Tohoku University Museum

Middle Permian cephalopods of the Takakurayama
Formation in the Yaguki area, the southwestern margin of
the South Kitakami Belt, Northeast Japan
Masayuki Ehiro
The Tohoku University Museum, Sendai 980-8578, Japan
Abstract: Middle Permian coiled nautiloids and ammonoids are described from two horizons
belonging to the upper part of the Takakurayama Formation distributed in the Yaguki area,
Northeast Japan. The nautiloids consist of nine species belonging to four genera, and include one
new species: Tainoceras cf. abukumaense Hayasaka, Tainoceras sp., Pleuronautilus chisatoi sp.
nov., Pleuronautilus cf. gregarius (Miller), Pleuronautilus sp., Pleuronautilus? sp., Endolobus? sp.
and Domatoceras sp. The ammonoid fauna is composed of eight species belonging to eight genera
and an indeterminable Kufengoceratinae: Agathiceras sp., Stacheoceras sp., Kufengoceratinae
gen. and sp. indet., Waagenoceras sp., Jilingites cf. bidentus Liang, Roadoceras cf. roadense(Böse), Neopopanoceras cf. scrobiculatum (Gemmellaro), Propinacoceras sp., Propinacoceras?
sp. and Paraceltites cf. elegans Girty. Reexaminations of some existing ammonoid species are also
given. Including the known ones, the ammonoid fauna of the formation clearly indicates that the
Takakurayama Formation is Wordian in age.

Introduction
The Permian mudstone-dominated strata, theTakakurayama Formation, is narrowly distributed in the
Yaguki area, Iwaki City, in the southeastern margin of the
Abukuma Massif, Northeast Japan. It belongs to the South
Kitakami Belt and situated at the southwestern margin of
the belt. Rather rich cephalopod fossils have been known
from its upper part (Hayasaka, 1965; Yanagisawa, 1967;
Tazawa et al., 2005; Ehiro, 2008; Fujikawa and Suzuki,2011). Based on the ammonoid fauna, Hayasaka (1965)
correlated the Takakurayama Formation with the Middle
Permian Sosio Stage. Yanagisawa (1967) considered that
the Takakurayama Formation ranges in age from Early to
Middle Permian. Tazawa et al. (2005) dated the ammonoid
fauna as Middle Permian Wordian in age, but regarded themas reworked fossils, without showing any sedimentologicalevidences. Ehiro (2008) described some ammonoids
from the formation. He also reviewed the taxonomy of thepreviously reported ammonoids and the mode of occurrenceof fossils from the formation, and concluded that the
Takakurayama Formation is correlated with the Wordian. On
the other hand, Fujikawa and Suzuki (2011) reported some
Early Permian ammonoids, including Artinskia, in addition to
the Wordian ones.
R e c e n t l y, m a n y c e p h a l o p o d s a m p l e s f r o m t h e

Takakurayama Formation, collected mainly in the 1960’s
to the early 1970’s by Chisato Suzuki, were donated to the
Tohoku University Museum. They are important for dating
the Takakurayama Formation. This paper describes themand discuss on the age of the formation.

Stratigraphy of the Takakurayama Formationand fossil horizons
The Takakurayama Formation is distributed in anarrow area, elongated from north to south, east of Mt.
Takakurayama in the Yaguki area, the southeastern marginof the Abukuma Massif (Fig. 1). It was originally named
as the Takakurayama Series (Iwao and Matsui, 1961) or
Takakurayama Group (Yanagisawa and Nemoto, 1961), andsubdivided into the Iriishikura, Motomura and Kashiwadaira
formations, in ascending order (Yanagisawa, 1967). Later,
Onuki (1966) treated the group as a formation rank and theformations as members (Fig. 2). The Iriishikura Member
is more than 100 m thick and consists mostly of laminatedmudstone. The Motomura Member is 60 to 7 m in thickness,thinning to the south, and is mainly composed of sandstone
and alternating beds of sandstone and mudstone. In thenorthern area, it includes conglomeratic sandstone withlimestone pebbles-boulders and lenses. The Kashiwadaira
Member is rather thick (more than 250 m) and consists of

22

Masayuki Ehiro

Figure 1. Geotectonic division
map of Northeast Japan showing
the study area (Yaguki Area) in
the South Kitakami Belt (A) andgeologic map of the Yaguki Area
(B). Longitude and latitude arefrom the International Terrestrial
Reference Frame.

laminated mudstone intercalated with thin sandstones andlenticular pebbly mudstones. Thickness of these sandstones
and pebbly mudstones are occasionally reaches 2 m, very
rarely 4 m, but usually less than 1 m. These strata trend
north-northeast and dip moderately to steeply west. Basedon the sedimentary structures such as cross beddings
and graded beddings in sandstone beds and laminas, nooverturned part exists.
Yanagisawa (1967) named small valleys in this area as
A-valley, B-valley, G2-valley, etc. for convenience (Figure 1).
He recognized eight fossil localities in the Takakurayama
Group (Formation) and named them as T1 to T8, and situatedT 1 Locality (B-valley) in the upper part of the Iriishikura
Formation, T3 (L2-valley), T4 (D3-valley) and T5 (F-valley) in
the Motomura Formation, and T2?, T6 (G1-valley), T7 (G2-valley) and T8 (H-valley) in the Kashiwadaira Formation.
Tazawa et al. (2005), Tazawa (2008) and Fujikawa andSuzuki (2011) used these Yanagisawa’s locality numbers (T1,
T7 and T8), and also positioned T1 in the Iriishikura Member
and T7 and T8 in the Kashiwadaira Member, but they did notshow any geologic map.
There is a large difference about the geologic map aroundA-, B- and L1-valleys between Yanagisawa (1967), and Ueno
(1992) and Ehiro (2008). In the geologic map of Yanagisawa(1967), the southern extension of the Motomura Member(Motomura Formation) is in the upper reaches of the L1and A-valleys, whereas Ueno (1992) and Ehiro (2008)
extended it to the middle reaches of the L1- and A-valleys.
According to my field survey, there is no thick sandstonedominated beds, correspond to the southern extension ofMiddle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan23

are in the middle part of the member. The exact stratigraphic
relationship between the last two is not clear, because twoareas including these two localities are separated by themetamorphic rocks and not continuous (Yanagisawa, 1967).
The present ammonoid specimens were collected from theT1 and T7 localities (Fig. 2).

Systematic description
Specimens described in this paper are housed in the
Tohoku University Museum (Institution abbreviation: IGPS
= Institute of Geology and Paleontology, Tohoku University,
Sendai). Morphological terminology basically follows Arkell
et al. (1957) and the classification of taxonomic ranks
higher than genus follows Teichert et al. (1964) for the order
Nautilida, Furnish et al. (2009) for the orders Goniatitida andProlecanitida, and Arkell et al. (1957) for the order Ceratitida.
The following abbreviations are used in the descriptions: D= diameter of whorl, H = height of whorl, W = width of whorl,
UD = diameter of umbilicus.
Subclass Nautiloidea Agasizz, 1847
Order Nautilida Agasizz, 1847
Superfamily Tainoceratoidea Hyatt, 1883
Family Tainoceratidae Hyatt, 1883
Genus Tainoceras Hyatt, 1883
Type species.—Nautilus quadrangulus McChesney, 1860
Tainoceras cf. abukumaense Hayasaka
Fig. 3.1

Figure 2. Generalized columnar section of the Takakurayama
Formation, showing the fossil horizons.

the Motomura Member, in the upper reaches of the L1- andA-valleys. Instead, thick sandstone-dominated beds (ca. 10
m in L1-valley and ca. 7 m in A-valley) expose in their middle
reaches, situated in the extended direction of the member
distributed in L2-valley, as shown in geological maps of Ueno
(1992) and Ehiro (2008). Although Yanagisawa (1967),
Tazawa et al. (2005), Tazawa (2008) and Fujikawa andSuzuki (2011) positioned the fossil locality T1 in the upper
part of the Iriishikura Member, according to Ueno (1992) andEhiro (2008), it is reasonable to consider that its stratigraphic
position is in the lower part of the Kashiwadaira Member.
The cephalopod specimens of the Takakurayama
Formation have been reported from three localities: T1, T7
and T8. As shown above, the first horizon is situated in thelower part of the Kashiwadaira Member, and the latter two

cf. Tainoceras abukumaense Hayasaka, 1957, p. 24, pl. 8,
figs. 1–3; Hayasaka, 1965, p. 13.
Tainoceras abukumense Hayasaka. Hayasaka, 1962, p.
137, pl. 11, figs. 1–3, text-fig. 1; Hayasaka, 1967, p. 1,
text-figs. A, B; Koizumi, 1975, p. 32, pl. 5, figs. 1–2.
Material examined.—One specimen, IGPS coll. cat. no.
112470.
Description.—An outer mold of left side is examined. The
sub-evolute shell attains more than 75 mm in diameter andthe ratio of UD/D is about 0.3. The flank is inclined to theumbilicus. The umbilical wall is moderately inclined. The
ventral shoulder is nearly perpendicular, although the venter
is not fully preserved. The shell surface is ornamented withsinuous growth lines. There are two rows of nodes on theflank, one along the ventral shoulder and the other along theumbilical shoulder. Both numbered 18–19 (partly estimated)
per volution. The former nodes are large and high, thecross section of which is circular to laterally elongated, andsometimes associated with short ribs diminishing their height
toward the umbilicus. The latter nodes are considerably

24

Masayuki Ehiro

Figure 3. Nautiloids (Tainoceras, Endolobus? and Domatoceras) from the Takakurayama Formation.
1, Tainoceras cf. abukumaense Hayasaka, IGPS coll. cat. no. 112470, lateral view; 2, Tainoceras sp., IGPS coll. cat. no.
112471, lateral (2a) and ventral (2b) views; 3, Endolobus? sp., IGPS coll. cat. no. 112480, lateral view (3a) and suture line (3b);4 and 5, Domatoceras sp.; 4, IGPS coll. cat. no. 112481, lateral view (4a) and suture line (4b); 5, IGPS coll. cat. no. 12482,
lateral view. Scale bars are 1 cm, unless otherwise stated.
smaller than the former ones. The suture is not preserved.
Comparison.—The shape of the flank and its
ornamentation, especially the shape of two rows of nodes ofthe present specimen is similar to the holotype of Tainoceras
abukumaense Hayasaka collected from the Takakurayama
Formation, but I refrain from identifying it at the specificlevel because its shell cross section and suture lines are
unknown.
Occurrence.—From the middle part of the Kashiwadaira
Member at G 2 -valley (T 7 Locality), Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Tainoceras sp.
Figs. 3.2a–b
Material examined.—One specimen, IGPS coll. cat. no.
112471.
Descriptive remarks.—A fragmental inner mold, obliquely

deformed, are examined. The evolute shell attains morethan 24 mm in shell diameter. At the preserved end, theheight is ca. 14 mm and the width is ca. 16 mm. The flanks
are flat and the venter is broadly rounded. There are sharpradial ribs, run from the umbilical shoulder and end at theventral shoulder forming small nodes. Two fine ridges run on
the venter forming the shallow central groove. The suture is
not preserved.
Based on the general shell morphology, it is highly
probable that the present specimen belongs to the genus
Tainoceras Hyatt, 1883, but the specific identification isdifficult due to the poor state of preservation.
Occurrence.—From the middle part of the Kashiwadaira
Member at G 2 -valley (T 7 Locality), Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Genus Pleuronautilus Mojsisovics, 1882
Type species.—Pleuronautilus trinodosus Mojsisovics, 1902

Middle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan
Pleuronautilus chisatoi sp. nov.
Figs. 4.1a–f
Etymology.—The species name is to honor Mr. Chisato
Suzuki, who collected the holotype and making it available
for study.
Material examined.—One specimen, IGPS coll. cat. no.
112472 (holotype).
Diagnosis.—A species of Pleuronautilus with thickly
discoidal and sub-evolute shell. The shell surface isornamented with prorsiradiate ribs on the flanks andlongitudinal lirae on both the flanks and venter.
Description.—The shell attains about 48 mm in maximum
diameter along the longest axis of the elliptically deformed
specimen, and the corresponding height and umbilical
diameter are 20.9 (H/D = 0.44) and 18.6 mm (UD/D = 0.39),
respectively. The shell width is apparently ca. 9.0 mm, but
this value is under tectonically flattened state and its exact
value is unknown. The flanks are slightly convex, with the
maximum shell width near the umbilical shoulder to umbilicalone-thirds of the flanks, and gently converge to the venter.
The umbilical wall is steep with acutely rounded umbilicalshoulder. The venter, with rounded ventrolateral shoulders,is nearly flat but its median part is slightly concave.
There are prominent lateral ribs on the flanks, numbered
24–25 per volution. The ribs are prorsiradiate and run fromthe umbilical shoulder, slightly strengthened ventrally, andend at the ventrolateral shoulder forming small nodes. Near
the umbilical shoulder, the ribs incline forward. In addition,
both the lateral and ventral shell surfaces are ornamented
with fine longitudinal lirae.
The external suture consists of very shallow? ventral lobe,
low ventrolateral saddle, and wide and shallow lateral lobe.
The dorsal suture seems to be nearly straight.
Comparison.—Pleuronautilus chisatoi sp. nov. is clearly
distinguished from all other species of Pleuronautilus inhaving longitudinal lirae on the shell surface.
Occurrence.—Lower part of the Kashiwadaira Memberof the Takakurayama Formation at B-valley (T1 Locality),eastern slope of Mt. Takakurayama, Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Pleuronautilus cf. gregarius (Miller)
Figs. 4.2–4.3
cf. Metacoceras gregarium Miller, 1945, p. 283, pl. 45, figs.
5–8.
Foordiceras gregarium (Miller). Miller and Youngquist,
1949, p. 98, pl. 36, fig. 5, pl. 38, figs. 5–8, pl. 39, figs. 1,
2, 6–9, pl. 40, figs. 1–4, pl. 41, figs. 5–9.
Pleuronautilus (P.) gregarium (Miller). Kummel, 1953, p.
36.

25

Pleuronautilus gregarius (Miller). Shimanskiy, 1967, p.
93.
Material examined.—Two specimens, IGPS coll. cat. no.
112473 and 112474.
Description.—The specimens are obliquely deformed.
One specimen (no. 112473), consisting of phragmocone anda part of the body chamber, attains 55.7 mm in maximum
diameter along the elliptically deformed specimen, andthe corresponding height and umbilical diameter are 26.1
(H/D = 0.47) and 16.9 mm (UD/D = 0.30), respectively. The
shell width is apparently ca. 15 mm, but this value is under
tectonically flattened state and its exact value is unknown.
Another one (no. 112474) is a phragmocone. It attains 64.0
mm in maximum diameter along the longest axis of theelliptically deformed specimen, and the corresponding height
and umbilical diameter are 26.0 (H/D = 0.41) and 22.2 mm(UD/D = 0.35), respectively.
The flanks of the specimens are nearly flat. The venter,with rounded ventrolateral shoulders, is nearly flat, but there
is a shallow groove? on the median part of no. 112473.
There are slightly prorsiradiate lateral ribs on the flanks,
running from the umbilical shoulder to the ventrolateralshoulder. They curve slightly backward and become wide
ventrally. The specimen no. 112473 have 19-20 ribs pervolution, adoral ones of which are slightly depressed at the
middle part. The ribs of another specimen (no. 112474)
numbers 11-12 per half volution, but they are indistinct near
the adoral end.
The external suture consists of shallow ventral lobe, lowventrolateral saddle, and wide and shallow lateral lobe. The
dorsal lobe is very shallow to nearly straight.
Comparison.—The present specimens from the
Takakurayama Formation are similar to Pleuronautilus
gregarius (Miller) from the Wordian strata of USA, but the
precise identification is difficult because of their poor stateof preservation. Foordiceras gregarium (Miller) described by
Yanagisawa (1967) from the Takakurayama Formation (Loc.
T7: G2-valley) is very poorly preserved and fragmental, andhence difficult to identify not only at the species level but
also at the genus level.
Occurrence.—Lower part of the Kashiwadaira Memberof the Takakurayama Formation at B-valley (T1 Locality),eastern slope of Mt. Takakurayama (no. 112473) and middle
part of the Kashiwadaira Member at G2-valley (T7 Locality)(no. 112474), Yaguki, Iwaki City, Fukushima Prefecture.
Middle Permian (Wordian).
Pleuronautilus sp.
Fig. 4.4
Material examined.—One specimen, IGPS coll. cat.

26

Masayuki Ehiro

Figure 4. Nautiloids (Pleuronautilus and Pleuronautilus?) from the Takakurayama Formation.
1, Pleuronautilus chisatoi sp. nov., IGPS coll. cat. no. 112472 (holotype); 1a and 1b, lateral (1a) and ventral (1b) views; 1c
and 1d, partial enlargements of lateral (1c) and ventral (1d) views showing longitudinal lirae; 1e and 1f, suture lines at H =10 mm (1e) and 17 mm (1f); 2 and 3, Pleuronautilus cf. gregarius (Miller); 2, IGPS coll. cat. no. 112473, lateral view (2a),ventral view (2b) and suture line (2c); 3, IGPS coll. cat. no. 112474; 3a, lateral view; 3b and 3c, suture lines at H = 15 mm(3b) and 22 mm (3c); 4, Pleuronautilus sp., IGPS coll. cat. no.112475, lateral view (4a), ventral view (4b) and suture line (4c);
5–8, Pleuronautilus? sp., all lateral views; 5, IGPS coll. cat. no. 112476; 6, IGPS coll. cat. no. 112477; 7, IGPS coll. cat. no.
112478; 8, IGPS coll. cat. no. 112479. Scale bars are 1 cm, unless otherwise stated.

no.112475.
Descriptive remarks.—A fragmental inner mold,tectonically compressed dorso-ventrally, is at hand. The shellis evolute and attains more than 55 mm in diameter. At thepreserved adoral end, the height and width are ca. 14 and
32 mm, respectively. The flat to slightly concave flanks, withacutely rounded umbilical and ventral shoulders, converge
toward the venter. The umbilical wall is nearly perpendicular.
The wide venter is flat to slightly concave. There are radialribs, curved backward, on the flanks. The venter is smooth.
The suture consists of a wide and shallow ventral lobe, small
and low ventrolateral saddle and a moderately deep laterallove. The dorsal suture is not well preserved.
Based on the shell outline, surface ornamentation andthe shape of the external suture, the present specimen isconsidered to belong to the genus Pleuronautilus, but the
specific identification is difficult because of its poor state ofpreservation.

Middle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan
Occurrence.—Middle part of the Kashiwadaira Member
at G 2-valley (T 7 Locality), Yaguki, Iwaki City, Fukushima
Prefecture. Middle Permian (Wordian).
Pleuronautilus? sp.
Figs. 4.5–4.8
Material examined.—Four specimens, IGPS coll. cat. no.
112476–112479.
Descriptive remarks.—Four fragmental outer molds,
obliquely deformed, are examined. They are evolute andthe flanks are nearly flat. The largest specimen (no. 112478)
attains more than 55 mm in diameter. The maximum
shell diameter of the second one is about 55 mm and its
corresponding umbilical diameter is ca. 23 mm (UD/D =0.42). The third one is 43 mm in maximum diameter with theratio of UD/D = ca. 0.35. The smallest specimen attains adiameter of 29 mm. There are prominent prorsiradiate lateralribs on the flanks. The ribs run from the umbilical shoulder,slightly strengthened ventrally, and end at the ventrolateralshoulder forming longitudinal nodes. Near the umbilicalshoulder, the ribs incline forward.
The shell outline and surface ornamentation of thepresent specimens resemble those of the species of thegenus Pleuronautilus, such as P. gregarius (Miller). But
there remains some doubt on the generic position of them,because they are fragmental and their shell cross sections
are unknown.
Occurrence.—All specimens are from the middle part of
the Kashiwadaira Member at G2-valley (T7 Locality), Yaguki,
Iwaki City, Fukushima Prefecture. Middle Permian (Wordian).
Family Koninckioceratidae Hyatt in Zittel, 1900
Genus Endolobus Meek and Worthen, 1865
Type species.—Nautilus spectabilis Meek and Worthen,
1860
Endolobus? sp.
Figs. 3.3a–3bMaterial examined.—One specimen, IGPS coll. cat. no.
112480.
Descriptive remarks.—The small specimen is tectonically
deformed obliquely, and precise original shell shape is notknown. It consists of inner mold and probable natural castof the outer mold, and shows semi-evolute and probably
thickly discoidal shell outline. The maximum shell diameterattains about 18 mm along the elliptically deformed longest
axis, and the corresponding height and umbilical diameterare both about 7 mm (H/D and UD/D = 0.39), respectively.
The shell width exceeds 5 mm. The flanks converge to theumbilicus. The venter is estimated to be broadly rounded27

with angular ventrolateral shoulders. The adapical partof shell surface is ornamented with fine radial striae or
growth lines. There are also rows of small nodes along theventrolateral shoulders. The external suture consists ofvery shallow (nearly straight) ventral and lateral lobes withindistinct ventrolateral saddle.
Based on the estimated shell outline, presence ofventrolateral nodes and the shape of the external sutureline, the present specimen is considered to belong to thegenus Endolobus, but some doubt remains on the generic
identification because of its severe tectonic deformation.
Occurrence.—Middle part of the Kashiwadaira Member
at G 2-valley (T 7 Locality), Yaguki, Iwaki City, Fukushima
Prefecture. Middle Permian (Wordian).
Superfamily Trigonoceratoidea Hyatt, 1884
Family Grypoceratidae Hyatt in Zittel, 1900
Genus Domatoceras Hyatt, 1891
Type species.—Domatoceras umbilicatum Miller, Dunberand Condra, 1933
Domatoceras sp.
Figs. 3.4–3.5
Material examined.—Two specimens, IGPS coll. cat. no.
112481 and112482.
Description.—Two fragmental specimens, both preserved
only one side, are examined. They are laterally compressed,
sub-evolute and flattened, and shell cross section is subrectangular. One specimen (no. 112481) attains about 64
mm in diameter, and its corresponding height and umbilical
diameter are ca. 25 (H/D = 0.39) and ca. 19 mm (UD/D= 0.30), respectively. The width exceeds 10 mm, but the
precise value is not known because of its ill preservation.
The flanks are nearly flat to very broadly convex, andparallel to very slightly converge to the venter. The umbilicalshoulder is rounded and the umbilical wall is steeply dipping.
The ventrolateral shoulder is acutely rounded. The shellsurface is almost smooth, but the specimen 112481 hassome laterally elongated nodes with short radial ribs on theventral shoulder of the phragmocone to the beginning of the
body chamber. Only the lateral suture, which consists of alarge love, is preserved in the specimen 112481.
C o m p a r i s o n . — T h e p r e s e n t s p e c i m e n 11 2 4 8 1 i scharacterized by having small elongated nodes of the ventral
shoulder. Domatoceras sp. from the Wordian of Mexico(Miller and Youngquist, 1949, p. 47, pl. 45, fig. 8) somewhat
resembles in shell outline and having ventrolateral nodes.
Domatoceras sculptile (Girty) (Metacoceras sculptile
Girty, 1911, p. 148; Girty, 1915, p. 245, pl. 31, figs. 1-2a;
Pseudometacoceras sculptile, Miller et al., 1933, p. 226, pl.
6, figs. 9-12; Domatoceras sculptile, Miller and Youngquist,

28

Masayuki Ehiro

1949, p. 41, text-fig. 5) from the Upper Carboniferous of
Oklahoma, Domatoceras williami Miller and Owen (Miller
and Owen, 1934, p. 246, pl. 16, fig. 4, pl. 17, figs. 1-4, pl. 18,
fig. 1, text-fig. 6) from the Upper Carboniferous of the MidContinent region, Domatoceras hayi (Hyatt) (Metacoceras
Hayi Hyatt, 1891, p. 339, text-figs. 38-39; Hay, 1893, p. 38,
text-figs. 8-9; Miller et al., 1933, p. 173, text-fig. 25) from theLower Permian (Carboniferous?) of the Mid-Continent region
also have ventrolateral nodes. It is, however, difficult to
identify the present specimens at the specific level, because
they are fragmental and poorly preserved.
Occurrence.—Both specimens are from the middle part of
the Kashiwadaira Member at G2-valley (T7 Locality), Yaguki,
Iwaki City, Fukushima Prefecture. Middle Permian (Wordian).
Subclass Ammonoidea Zittel, 1884
Order Goniatitida Hyatt, 1884
Suborder Goniatitina Hyatt, 1884
Superfamily Agathiceratoidea Arthaber, 1911
Family Agathiceratidae Arthaber, 1911
Genus Agathiceras Gemmellaro, 1887
Type species.—Agathiceras suessi Gemmellaro, 1887
Agathiceras sp.
Figs. 5.1–5.5
Material.—IGPS coll. cat. no. 112483–112496.
Descriptive remarks.—Fourteen specimens, ellipticallyand obliquely deformed, are examined. Specimens are
small, the diameter of which ranges from 17 to 23 mmalong the elliptically deformed longest axis. The umbilicus
is very small and almost closed. The sides are convex
with broadly rounded umbilical and ventral shoulders. The
venter is rounded. The shell surface is ornamented by manyfine spiral lirae. The suture is poorly preserved in somespecimens, and five saddles and four lobes are present on
the lateral side. The crests of the saddles are rounded. The
bases of the lobes are also rounded, but slightly pointed at
the center.
Based on the general shell shape, surface ornamentationand the outline of the suture line, the present specimens
are considered to belong to the genus Agathiceras, but thestrong tectonic deformation makes it difficult to identify themat the species level.
Occurrence.—Specimens no. 112483–112485 arefrom the lower part of the Kashiwadaira Member of the
Takakurayama Formation at B-valley (T1 Locality), eastern
slope of Mt. Takakurayama, and no. 112486–112496
are from the middle part of the Kashiwadaira Member
at G 2-valley (T 7 Locality), Yaguki, Iwaki City, Fukushima
Prefecture. Middle Permian (Wordian).

Superfamily Cycloloboidea Zittel, 1895
Family Vidrioceratidae Plummer and Scott, 1937
Genus Stacheoceras Gemmellaro, 1887
Type species.—Stacheoceras mediterraneum Gemmellaro,
1887
Stacheoceras sp.
Figs. 5.6–5.7
Material.—IGPS coll. cat. no. 112497 and 112498.
Descriptive remarks.—Two fragmental specimens are
examined. One specimen (no. 112497) consists of anouter mold with a small fragmental inner mold. The shell
diameter attains more than 30 mm. It is involute with closed
umbilicus. The conch has convex sides and acutely rounded
to carinate venter with a lenticular cross section, although
the lenticular shape may be due to the tectonic flattening.
The shell surface seems to be smooth. The external sutureis partly preserved. The ventral lobe is wide and deep, but
its basal part is not preserved. On the side, at least four setof lateral saddles and lobes are recognized, all diminishingin size toward the umbilicus. The crests of all saddles arerounded. The first lateral lobe is bifid at the base. The
second to fourth are bi- or trifid at the base. Another one (no.
112498) is a tectonically flattened, fragmental phragmocone.
The apparent cross section is lenticular. The shell surface
seems to be smooth. A part of the lateral suture, consistingat least four saddles and lobes are preserved on the side.
They gradually diminish in size toward the venter. All saddles
have rounded crest. The lateral lobes are trifid, the central
branches of them are deepest.
Based on the general shell shape and suture line, thepresent specimens are considered to belong to the genus
Stacheoceras, but the specific identification is difficult
because of its poor state of preservation.
Occurrence.—The middle part of the Kashiwadaira
Member at G 2 -valley (T 7 Locality), Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Family Cyclolobidae Zittel,1895
Subfamily Kufengoceratinae Zhao,1980
Kufengoceratinae gen. and sp. indet.
Figs. 5.8a–b
Material.—IGPS coll. cat. no. 112499.
Descriptive remarks.—A small, elliptically deformed andflattened specimen is examined. It is involute to sub-involuteand apparently discoidal. The diameter of the shell attains
30.2 mm along the longest axis of the elliptically deformed
specimen, and the corresponding height and umbilical
diameter are ca. 14.0 (H/D = 0.46) and 4.4 mm (UD/D

Middle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan

29

Figure 5. Ammonoids (Agathiceras, Stacheoceras and Kufengoceratinae gen. and sp. indet.) from the Takakurayama
Formation.
1–5, Agathiceras sp.; 1, IGPS coll. cat. no. 112483, ventro-lateral view; 2, IGPS coll. cat. no. 112484, lateral view; 3, IGPS
coll. cat. no. 112486, lateral view (3a) and suture line (3b); 4, IGPS coll. cat. no. 112487, lateral view; 5, IGPS coll. cat. no.
112488, lateral view; 6 and 7, Stacheoceras sp.; 6, IGPS coll. cat. no. 112497, lateral view of the outer mold and a part of theinner mold (6a) and suture line (6b); 7, IGPS coll. cat. no. 112498, lateral views of fragmental inner mold of the ventro-lateralpart (7a) and suture line (7b); 8, Kufengoceratinae gen. and sp. indet., IGPS coll. cat. no. 112499, lateral view (8a), ventral
view (8b) and suture line (8c). Scale bars are 1 cm, unless otherwise stated.

= 0.15), respectively. The sides of the shell are broadly
rounded. The umbilical wall is steep with sharply roundedumbilical shoulder. The venter is acutely rounded withbroadly rounded ventral shoulders. There are faint, rather
widely spaced, slightly prorsiradiate ribs or striations on theshell surface. There are some variations in the thickness,height and interspaces of the ribs. The fragmental lateral
suture consists of four saddles and three to four lobes.
The crests of saddles are all rounded. The lobes are rather
strongly serrated up to the upper part of the sides. The baseof the first lateral lobe has deep serrations, but bases of theother lobes are not well preserved.
Based on the general shape of the suture line, thepresent specimen is considered to belong to the subfamily
Kufengoceratinae, probably a species of the genus
Guiyangoceras Zhou, 1985, Liuzhouceras Zhao, 1980
or Paratongluceras Zhao and Zheng, 1977. The present
specimen has a discoidal conch shape and differs fromthose of these kufengoceratids, which have pachyconic
to globular conch. This is, however, due to the tectonic
deformation. It is difficult to identify it at the generic level

because of its poor state of preservation, especially ill
preserved suture line.
Occurrence.—From the middle part of the Kashiwadaira
Member at G 2 -valley (T 7 Locality), Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Subfamily Cyclolobinae Zittel,1895
Genus Waagenoceras Gemmellaro, 1887
Type species.—Waagenoceras mojsisovicsi Gemmellaro,
1887
Waagenoceras sp.
Figs. 6.1–6.4
Material.—IGPS coll. cat. no. 112500–112503.
Descriptive remarks.—Four specimens, elliptically
deformed, are examined. They are fragmental, except for thelargest specimen (no. 112500). The last specimen attains
a shell diameter about 120 mm in the obliquely deformed
state, and its corresponding height, width and umbilical
diameter are ca. 80, ca. 40 and ca. 15? mm, respectively.

30

Masayuki Ehiro

The shell flanks are broadly rounded with rounded umbilicaland ventral shoulders. The venter is also rounded. The shellsurface looks like smooth. The suture is partly preserved inall specimens. It is typical Waagenoceras-type as shown in
Figure 6.1b, 6.2b, 6.3b and 6.4b.
Based on the general shell shape and the suture line,
the present specimens undoubtedly belong to the genus
Waagenoceras, but the species level identification is difficult
because of its poor and severely deformed preservation.
Occurrence.—All specimens are from the middle part of
the Kashiwadaira Member at G2-valley (T7 Locality), Yaguki,
Iwaki City, Fukushima Prefecture. Middle Permian (Wordian).

The present species is similar to the type species Jilingites
bidentus in the shell shape and smooth shell surface, but the
specimens are rather poorly preserved and deformed, andsome doubt remains in the specific identification.
Occurrence.—Specimens no. 112504 and 112505 arefrom the lower part of the Kashiwadaira Member of the
Takakurayama Formation at B-valley (T1 Locality), eastern
slope of Mt. Takakurayama, and specimens no. 112506–
112510 are from the middle part of the Kashiwadaira
Member at G 2 -valley (T 7 Locality), Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).

Superfamily Marathonitoidea Ruzhentsev, 1938
Family Marathonitidae Ruzhentsev, 1938
Genus Jilingites Liang, 1982
Type species.—Jilingites bidentus Liang, 1982,

Superfamily Neoicoceratoidea Hyatt in Zittel, 1900
Family Paragastrioceratidae Ruzhentsev, 1951
Subfamily Pseudogastrioceratinae Furnish, 1966
Genus Roadoceras Zhou, 1985
Type species.—Gastrioceras roadense Böse, 1919

Jilingites cf. bidentus Liang
Figs. 6.5–6.8

Roadoceras cf. roadense (Böse)
Fig. 6.9

cf. Jilingites bidentus Liang, 1982, p. 651, pl. 1, figs. 10–13,
text-fig. 6.

cf. Gastrioceras roadense Böse, 1919, p. 85, pl. 2 figs. 28–
47.
Paragastrioceras roadense (Böse). Plummer and Scott,1937, p. 227, pl. 22, figs.15–17; Hayasaka, 1947, p.
27, pl. 1, fig. 4, pl. 2, fig. 3, text-fig. 4.
Pseudogastrioceras globulosissmum Plummer and Scott,1937 (parts), p. 279, pl. 18 fig. 10.
Pseudogastrioceras roadense (Böse). Miller and Furnish,
1940, p. 89, pl. 16, figs.1–7, pl. 17, fig. 5, pl. 18 fig. 10,
11, pl. 28 figs. 1–3; Miller in King et al., 1944, p. 89, fig.
8, pl. 24, figs. 2, 3, pl. 25, figs. 1–6; Miller, 1945, p. 16,
pl. 6, figs. 3–5, pl. 7, figs. 1–3; Clifton, 1946, p. 558,
pl. 85, figs. 1, 2; González-Arreola et al., 1994, p. 215,
pl.1, figs. i–k.
Altudoceras roadense (Böse). Ruzhentsev, 1960, fig.
34a; Liang, 1982, p. 649, pl. 2, figs. 3–4, pl. 3, figs.
3–6, text-figs. 4a, 4b.
Roadoceras roadense (Böse). Zhou, 1985, p. 196; Zhou,
1987, p. 327; Glenister et al. in Furnish et al., 2009, p.
172, text-figs. 106.6a–6c.
Pseudogastrioceras zittelli Gemmellaro. Tokai Fossil
Society, 1995, p. 50.

Material.—IGPS coll. cat. no. 112504–112510.
Description.—Seven elliptically deformed specimens are
examined. The shell is small and its maximum diameter
ranges from 20 to 45 mm, but the largest specimen attains
at least 60 mm. Six specimens are consists of phragmocone.
The living chamber, occupying more than three quartersof the last whorl, is only preserved in one specimen (no,112507). The conch has convex sides with a rounded
venter and a very small to closed, shallow? umbilicus.
The ventral and umbilical shoulders are broadly rounded.
Although the original shell shape is not precisely known due
to the tectonic deformation, its cross-section is presumably
thickly discoidal and the maximum shell width is near theumbilical two-thirds. The ornamentation of the shell surface
is not known, but the surfaces of inner molds are smooth.
The suture lines are partly preserved. The broad ventral
lobe is divided into two bifid prongs by rather high mediansaddle, which is about four-fifth of the ventrolateral saddle.
On the lateral sides, there are four to five bifid lateral lobes
and rounded saddles, but the suture near the umbilicus is
not preserved. The lateral lobes are all similar shape anddiminish in size towards the umbilicus.
Comparison.―Two species of Jilingites have beenreported: Jilingites bidentus Liang, 1982 from the Wordian of
Jiling, North China and J. kesennumensis Ehiro and Araki,
1997 from the Capitanian of South Kitakami Belt, Northeast
Japan. One questionable specimen of Jilingites was also
reported from the Takakurayama Formation (Ehiro, 2008).

Material.—IGPS coll. cat. no. 112511.
Description.—The shell is discoidal with rounded venter.
The sides are broadly convex, with acutely roundedumbilical shoulder and broadly rounded ventral shoulder.
The maximum shell width is about the center of the flank.
The umbilicus is small with steep umbilical wall. The shellattains about 30 mm in diameter with a ratio of UD/D = ca.
0.24. The shell surface is ornamented with fine spiral ribs. In

Middle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan

31

Figure 6. Ammonoids (Waagenoceras, Jilingites and Roadoceras) from the Takakurayama Formation.
1–4, Waagenoceras sp.; 1, IGPS coll. cat. no. 112500, lateral view (1a), ventral view (1b) and part of the suture line (1c);2, IGPS coll. cat. no. 112503, lateral view of the fragmental inner mold (2a) and suture line (2b); 3, IGPS coll. cat. no.
112501, cross section (3a) and ventral lobe (3b); 4, IGPS coll. cat. no. 112502, lateral view (4a) and suture line (4b); 5–8,
Jilingites cf. bidentus Liang; 5, IGPS coll. cat. no. 112505, ventral view (5a) and ventro-lateral suture line (5b); 6, IGPS coll.
cat. no. 112507, lateral view (6a) and suture line (6b); 7, IGPS coll. cat. no. 112508, lateral view (7a), ventral view (7b) andsuture line (7c); 8, IGPS coll. cat. no. 112504, lateral view of the outer mold and a part of the inner mold; 9, Roadoceras cf.
roadense (Böse), IGPS coll. cat. no. 112511, lateral view. Scale bars are 1 cm, unless otherwise stated.

addition, there are 16-17, fine and short, radial ribs per half
volution, along the umbilical shoulder. They are prorsiradiate
and extend to the inner one-thirds of the flank, but become
indistinct forward. The suture line is not preserved.
Discussion.—This specimen is probably the same
specimen reported as Pseudogastrioceras zittelli

Gemmellaro, 1887 by Tokai Fossil Society (1995, p. 50).
Based on the general shell shape and ornamentation, thepresent specimen is considered to belong to the genus
Roadoceras Zhou, 1985, and comparable with the typespecies Roadoceras roadense (Böse, 1919). However,I refrain from identifying it at the specific level precisely

32

Masayuki Ehiro

because of its ill state of preservation and lacking the sutureline.
Occurrence.—Lower part of the Kashiwadaira Memberof the Takakurayama Formation at B-valley (T1 Locality),eastern slope of Mt. Takakurayama, Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Genus Neopopanoceras Schindewolf, 1939
Type species.—Popanoceras scrobiculatum Gemmellaro,
1887
Tauroceras Tumanskaia, 1938, non Hope, 1840 (modern
insect)Neopopanoceras Schindewolf, 1939, non Spath, 1951
(Triassic ammonoid); Glenister et al., 2009
See “Nomenclatorial note” by Zhou and Glenister inFurnish et al., 2009, p. 218.
Neopopanoceras cf. scrobiculatum (Gemmellaro)Figs. 7.1–7.4
cf. Popanoceras scrobiculatum Gemmellaro, 1887, p. 25, pl.
3, figs. 22–26, pl. 8, fig. 26; Gemmellaro, 1888, p. 14,
pl. B, figs. 2–4, pl. C, figs. 9, 10; Frech, 1902, pl. 59a,
figs. 7a–7e; Ruzhentsev, 1951, text-fig. 56d; Miller etal., 1957, L. 52, text-fig. 2-8; Termier et al., 1972, p.
114, pl. 17, figs. 5–8
Tauroceras scrobiculatum (Gemmellaro). Tumanskaia,
1938, p. 145, text-figs. 1–4; Ruzhentsev, 1960, p. 111,
text-fig. 1g; Glenister and Furnish, 1988, p. 45, pl. 3,
fig. 8, pl. 4, fig.12–13, text-fig.1; Leonova, 2002, S 95,
text-fig. 59; Zhou and Yang, 2005, p. 387, text-figs. 5.1,
5.2, 11.
Neopopanoceras scrobiculatum (Gemmellaro). Glenister
et al. in Furnish et al., 2009, p. 181, text-figs. 115.1a–
1f.
Material.—IGPS coll. cat. no. 112512–112515.
Description.—Four small specimens, elliptically deformed,
are examined. They are mostly outer molds, but somefragmental inner molds are also preserved. The maximum
conch diameters range from ca. 12 to 35 mm.
The shell is narrowly discoidal and evolute, with amedium-sized umbilicus (the UD/D ratios are about onethirds). The flanks and venter are flattened with abruptly
rounded ventrolateral shoulders. Fine and dense radial ribs
are prominent on the umbilical wall to the venter, but are
rather inconspicuous on the flanks of the inner volution.
They are sinuous on the flanks and form a deep U-shaped
ventral sinus. At the midpoint of the flanks of the inner
volution, there are remarkable pits, which change in outline
from circular or longitudinally elongated to become radiallyelongated as they grow. The suture is not preserved.
Discussion.—From the shell shape and ornamentation,
the present specimens undoubtedly belong to the genus
Neopopanoceras Schindewolf, 1939, and most probably
identified as N. scrobiculatum (Gemmellaro). But the precise
identification at the specific level is difficult since they arepoorly preserved and lacking the suture line.
Occurrence.—Middle part of the Kashiwadaira Memberof the Takakurayama Formation at G2-valley (T7 Locality),eastern slope of Mt. Takakurayama, Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).
Order Prolecanitida Miller and Furnish, 1954
Superfamily Medlicottitoidea, Karpinsky, 1889
Family Medlicottidae Karpinsky, 1889
Subfamily Propinacoceratinae Plummer and Scott, 1937
Genus Propinacoceras Gemmellaro, 1887
Type species.—Propinacoceras Beyrichi Gemmellaro, 1887
Propinacoceras sp.
Figs. 7.5–7.8
Material.—IGPS coll. cat. no. 112516, 112519–112522.
Descriptive remarks.—Five fragmental specimens are athand. The conch is thinly discoidal and involute with almost
closed umbilicus. The sides are flat and almost parallel toeach other, but slightly converge toward the umbilicus. The
venter is also flat, but bears two rows of prominent nodes
or short ribs, which are separated by a median groove.
The umbilical and ventral shoulders are acutely rounded.
The suture is only poorly preserved in one specimen (no.
112516). The ventrolateral saddle seems to be low and widewith some serrations, but the precise shape is not known.
Lateral lobes are bifid or rounded at the base. All saddles
are rounded.
Based on the shell shape, shell ornamentation andgeneral shape of suture line, the present specimens seem tobelong to the genus Propinacoceras Gemmellaro, 1887. But
it is difficult to identify at the specific level, because of theirpoor state of preservation.
Occurrence.—Lower and middle part of the Kashiwadaira
Member of the Takakurayama Formation at B-valley (T 1
Locality: no. 112516) and G2-valley (T7 Locality: no. 112519–
112522), eastern slope of Mt. Takakurayama, Yaguki, Iwaki
City, Fukushima Prefecture. Middle Permian (Wordian).
Propinacoceras? sp.
Figs. 7.9–7.11
Material.—IGPS coll. cat. no. 112517, 112518, 112523–
112536.
Descriptive remarks.—Many fragmental specimens areMiddle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan

33

Figure 7. Ammonoids (Neopopanoceras, Propinacoceras, Propinacoceras? and Paraceltites) from the Takakurayama
Formation.
1–4, Neopopanoceras cf. scrobiculatum (Gemmellaro), all lateral views; 1, IGPS coll. cat. no. 112513; 2, IGPS coll. cat. no.
112512; 3, IGPS coll. cat. no. 112515; 4, IGPS coll. cat. no. 112514; 5–8, Propinacoceras sp.; 5, IGPS coll. cat. no. 112516,
lateral view (5a), ventral view (5b) and suture line (5c); 6, IGPS coll. cat. no. 112519, lateral (6a) and ventral (6b) views; 7,
IGPS coll. cat. no. 112520, lateral (7a) and ventral (7b) views; 8, IGPS coll. cat. no. 112521, lateral (8b) and ventral (8b)views; 9–11, Propinacoceras? sp.; 9, IGPS coll. cat. no. 112523, lateral (9a) and ventral (9b) views; 10, IGPS coll. cat. no.
112524, lateral view; 11, IGPS coll. cat. no. 112525, lateral (11a) and ventral (11b) views; 12–14, Paraceltites cf. elegans
Girty, all lateral views; 12, IGPS coll. cat. no. 112537; 13, IGPS coll. cat. no. 112538; 14, IGPS coll. cat. no. 112539 (14a)and 112540 (4b). Scale bars are 1 cm, unless otherwise stated.
at hand. Most specimens are small fragment of the ventral
part. The fragmentation is considered to be almost occurred
during the sampling process. The conch is thinly discoidal
with flat and parallel sides. The venter is also flat, with tworows of prominent nodes or short ribs, which are separated
by a median groove. The ventral shoulders are acutely
rounded.
The present specimens are likely to belong to the genus
Propinacoceras Gemmellaro, 1887, because they yieldedwith Propinacoceras specimens and having the same shell
shape and shell ornamentation with the genus. There is,however, another possibility that these species belong
to any genera of subfamily Propinacoceratinae, such as
Bamyaniceras Termier and Termier, 1970 and Difuntites
Glenister and Furnish, 1988 by their shell shape andornamentation.
Occurrence.—Lower and middle part of the Kashiwadaira
Member of the Takakurayama Formation at B-valley (T 134

Masayuki Ehiro

Locality: no. no. 112517, 112518) and G2-valley (T7 Locality:
no. 112523–112536), eastern slope of Mt. Takakurayama,
Yaguki, Iwaki City, Fukushima Prefecture. Middle Permian(Wordian).
Order Ceratitida Hyatt, 1884
Superfamily Xenodiscoidea Frech, 1902
Family Paraceltitidae Spath, 1930
Genus Paraceltites Gemmellaro, 1887
Type species.—Paraceltites elegans Girty, 1908
Paraceltites cf. elegans Girty
Figs. 7.12–7.14
cf. Paraceltites elegans Girty, 1908, p. 499, pl. 25, figs.
12–14; Plummer and Scott, 1937, p. 367, pl. 37, figs.
1–8; Miller and Furnish, 1940, p. 67, pl. 22, figs. 1–10,
text-fig. 17B; Yanagisawa, 1967, p. 103, pl. 3, fig. 11;
Spinosa et al., 1975, p. 249, pl. 1, pl. 2, figs. 1–7, pl.
3, figs. 1–9, text-figs. 3, 4, 5C, 10A, 11, 12; Zhao andZheng, 1977, p. 248, pl. 5, figs. 11, 12; Liang and Guo,
1982, p. 278, pl. 106, figs. 8, 9; Zheng, 1984, p. 191,
pl. 1, figs. 1–7, text-figs. 8a, 8b; Misaki and Ehiro,
2004, p. 136, fig. 8.3; Ehiro and Misaki, 2005, p. 11,
figs. 6.8–6.9.
Material.—IGPS coll. cat. no. 112537–112540.
Descriptive remarks.—Four elliptically deformed
specimens are examined. They are mostly outer mold andthe maximum shell diameter ranges from 14 to 29 mm. The
shells are evolute, with the ratios of UD/D about 0.5, andthinly discoidal with nearly flat to slightly convex sides. The
umbilicus is shallow and the umbilical shoulder is acutely
rounded. The venter seems to be rounded with roundedventral shoulders. The shell surface is ornamented by finesinuous ribs, which fade out near the ventral shoulder. The
suture is not preserved.
Based on the shell shape and the surface ornamentation,
the present specimens are comparable with Paraceltites
elegans Girty, 1908. The precise specific identification,
however, is difficult, because they are rather poorly
preserved and the suture is unknown.
Occurrence.—Middle part of the Kashiwadaira Memberof the Takakurayama Formation at G2-valley (T7 Locality),eastern slope of Mt. Takakurayama, Yaguki, Iwaki City,
Fukushima Prefecture. Middle Permian (Wordian).

Discussion
Faunal composition of cephalopods from the
Takakurayama Formation

As discussed in the stratigraphic section, cephalopod

fossils of the Takakurayama Formation came from threehorizons: the lower part (T1: B-valley) and middle part (T7:
G2-valley, and T8: H-valley) of the Kashiwadaira Member.
The T8 Locality is isolated and its exact stratigraphic relation
with T 7 Locality is unknown. In this paper, eight species
belonging to four genera of coiled nautiloids, including
some questionable ones, and nine species belonging
to eight genera of ammonoids and an indeterminable
Kufengoceratinae are described from the T 1 and T 7
localities. In the ammonoid fauna, Propinacoceras (including
questionable ones) is most abundant (more than twenty
specimens) and Agathiceras is the second (eleven). Others
are less than six specimens each. The faunal compositionsof the two horizons are as follows:
T1 Locality:
N a u t i l o i d s : P l e u r o n a u t i l u s c h i s a t o i s p . n o v. ,Pleuronautilus cf. gregarius (Miller)
Ammonoids: Agathiceras sp., Jilingites cf. bidentus
Liang, Roadoceras cf. roadense (Böse),Propinacoceras sp., Propinacoceras? sp.
T7 Locality:
Nautiloids: Tainoceras cf. abukumaense Hayasaka,
Tainoceras sp., Pleuronautilus cf. gregarius (Miller),
Pleuronautilus sp., Pleuronautilus? sp., Endolobus?
sp., Domatoceras sp.
Ammonoids: Agathiceras sp., Stacheocerassp., Kufengoceratinae gen. and sp. indet.,
Waagenoceras sp., Jilingites cf. bidentus Liang,
Neopopanoceras cf. scrobiculatum (Gemmellaro),
Propinacoceras sp., Propinacoceras? sp.,
Paraceltites cf. elegans Girty
In addition, some coiled nautiloid species have been
described from the Takakurayama Formation. Hayasaka(1957, 1965) described Tainoceras abukumaense Hayasaka,
T. aff. unklesbayi Miller and Youngquist and Tylonautilus
p e r m i c u s H a y a s a k a . Ya n a g i s a w a ( 1 9 6 7 ) r e p o r t e d
Foordiceras gregarium (Miller) (= Pleuronautilus gregarius).
The last specimen is, however, very poorly preserved, andfragmental, so its specific identification seems to be difficult.
These species are collected from the T7 Locality.
Ehiro (2008) described five genera of ammonoids fromthe T 7 Locality: Agathiceras, Jilingites?, Waagenoceras,
Popanoceras and Tauroceras (= Neopopanoceras). He also
reviewed and arranged the ammonoid fauna previously
reported from the Takakurayama Formation by Hayasaka(1965), Yanagisawa (1967), Koizumi (1975), Tokai Fossil
Society (1995) and Tazawa et al. (2005), and recognized
17 species belong to 13 genera and a questionable
Medlicottidae from the formation. They are:
T1 Locality: Roadoceras sp., Paraceltites aff. elegans
Girty
T 7 Locality: Agathiceras cf. suessi Gemmellaro,Middle Permian cephalopods of the Takakurayama Formation, South Kitakami Belt, Northeast Japan
Agathiceras sp., Popanoceras sp., Tauroceras sp.
(= Neopopanoceras), Stacheoceras aff. grunwaldti
Gemmellaro, Waagenoceras sp., Mexicoceras?
sp., Newellites richardsoni (Miller and Furnish),
Jilingites? sp., Altudoceras sp., Propinacoceras
aff. knighti Miller and Furnish, Propinacocerassp., Medlicottia cf. costellifera Miller and Furnish,
Medlicottidae? gen. and sp. indet., Paraceltites sp.
T8 Locality: Paraceltites elegans Girty
H o w e v e r, s o m e d o u b t r e m a i n s o n t h e s p e c i f i c
assignments of the genera Agathiceras, Stacheoceras andMedlicottia, because they are ill preserved and severely
deformed. And, moreover, the generic assignment ofMedlicottia by Yanagisawa (1967) is questionable, since it isfragmental, deformed specimens without suture line.
Later, Fujikawa and Suzuki (2011) reported someammonoids from the T1 Locality, such as Thalassoceras?
sp., Agathiceras sp., Paragastrioceras? sp. and Artinskia sp.
This generic identification has, however, some problems.
The specimens assigned to Thalassoceras? sp. andParagastrioceras? sp. are rather ill preserved to identify itat the generic level. Moreover, generic identification of their
Artinskia specimens is questionable. Because, according totheir figures, 1) these specimens have two rows of nodes
on the venter to ventral shoulder, and they do not extend to
the lateral part. 2) Although it is only partly preserved, theventrolateral saddle of the external suture is simple and low.
These features, especially the shape of the ventrolateralsaddle of the suture, completely differ from those of thegenus Artinskia, and, instead, indicate that these specimens
belong to any genera of subfamily Propinacoceratinae,
such as Bamyaniceras Termier and Termier, 1970,
Difuntites Glenister and Furnish, 1988 and Propinacoceras
Gemmellaro, 1887.
Therefore, the generic compositions of each cephalopod
locality in the Kashiwadaira Member of the Takakurayama
Formation are as follows:
T 1 Locality: Pleuronautilus, Agathiceras, Jilingites,
Roadoceras, Propinacoceras and Paraceltites.
T7 Locality: Tainoceras, Pleuronautilus, Endolobus?,
Domatoceras, Agathiceras, Stacheoceras,
Kufengoceratinae, Waagenoceras, Mexicoceras?,
Newellites, Jilingites, Popanoceras,
Neopopanoceras, Altudoceras, Propinacoceras,
Medlicottia? and Paraceltites.
T8 Locality: Paraceltites.
Of the cephalopod faunas from the Takakurayama
Formation, the fauna of the T7 Locality is rather diverse,
whereas the rest are less variety. Genera of the T1 and T8
localities are, except for Roadoceras, included in the faunaof the T7 Locality, and there is no remarkable difference ingeneric compositions in these faunas.

Age of the cephalopod fauna and Takakurayama
Formation

35

Of the nautiloid genera of the Kashiwadaira Member,including the previously described ones, Tainoceras,
Pleuronautilus and Domatoceras are long ranging from Late
Carboniferous to Permian or Triassic. Tylonautilus is rather
rare genus and only known from the Lower Carboniferous
and from the Takakurayama Formation. The stratigraphic
range of the genus Endolobus is generally considered tobe restricted in the Kungurian. Occurrences of Endolobus,
however, have also been reported from the Wuchiapingian ofSouth China (Zhao et al., 1978) and from the Changhsingianof South China and Iran (Korn et al., 2019). They were notdescribed, but their conch parameters were shown in table
S1 of Korn et al. (2019).
The present paper confirmed the occurrences ofeight genera of ammonoid (Agathiceras, Stacheoceras,
Waagenoceras, Jilingites, Neopopanoceras, Roadoceras,
Propinacoceras and Paraceltites) and added
Kufengoceratinae gen. and sp. indet. in the ammonoid
fauna of the Takakurayama Formation arranged by Ehiro(2008). In addition, five genera have also been known fromthe formation: Mexicoceras?, Newellites, Popanoceras,
Altudoceras and Medlicottia?
As discussed by Ehiro (2008), the ammonoid fauna fromthe Takakurayama Formation is Wordian in age. Additional
Kufengoceratinae does not conflict with this conclusion,
because it ranges from the Roadian to Capitanian(Lopingian?). Fujikawa and Suzuki (2011) reported someammonoids from the T1 Locality, including Artinskia sp.,and concluded that this fauna indicates an Early Permian(Sakmarian–Artinskian) age. As discussed above, however,their generic identification of their Artinskia specimens
is incorrect, and it belongs to any genera of subfamily
Propinacoceratinae, most probably Propinacoceras, whichranges up to the middle–upper Permian.
Among the Takakurayama ammonoids, Jilingites (ranges
from Wordian to Capitanian), Waagenoceras (Wordian to
Capitanian), Newellites (Wordian), Mexicoceras (Roadian to
Wordian), Altudoceras (Roadian to Capitanian), Roadoceras(Wordian to Wuchiapingian) and Neopopanoceras (Wordian)strongly support the Wordian age of the fauna.
On the other hand, Tazawa et al. (2005, 2015) regarded
almost all fossils from the Takakurayama Formation are
reworked, except for very few brachiopod specimens which
are considered to be Lopingian in age. As discussed by
Ehiro (2008), this interpretation has no sedimentologicalevidence. The Takakurayama Formation includes some
pebbly mudstone, but the fossil horizons are composed of
massive or sharply laminated mudstone. Almost all fossils,
such as trilobites, brachiopods, gastropods, bivalves,nautiloids and ammonoids, except for some fusulinoideans

36

Masayuki Ehiro

Figure 8. Stratigraphic ranges of
the cephalopod genera known fromthe Takakurayama Formation. Data
from Arkell et al. (1957), Furnish et al.
(2009), Kummel (1953), Miller et al.
(1957) and others.

and corals from the limestone pebbles and boulders in
the Motomura Member, have similar state of preservation.
They are usually well preserved, although suffered severe
tectonic deformation. Some specimens are fragmental,
but this is mainly due to the damage during the sampling
process. Therefore, the age of the Takakurayama Formation(Kashiwadaira Member) is Wordian as shown by theammonoid fauna. I think there is a large possibility that these“Lopingian” brachiopods actually range down into the Middle
Permian.
The Takakurayama fauna, comprising four genera ofnautiloid and fourteen genera of ammonoid, is the mostdiverse Wordian cephalopod fauna in Japan. It is far morethan a next diverse fauna from the uppermost part of the
Hosoo Formation, which is composed of six ammonoid
genera (Ehiro, 2010) with some nautiloids, distributed in thesouthern part of the Kitakami Massif, also belongs to theSouth Kitakami Belt.

Acknowledgments
I am greatly indebted to Mr. Chisato Suzuki for donating
cephalopod specimens from the Takakurayama Formationand help in the field. I also thank to the board of education,
Iwaki City for allowing to conduct a geological survey inthe area designated as a natural monument of Iwaki City
(Takakurayama Paleozoic Strata). Sincere thanks areextended to Tatyana B. Leonova for her careful review.

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Bull. Tohoku Univ. Museum. No. 21, pp. 39‒84, 2022
© by The Tohoku University Museum

Early Anisian (Aegean) ammonoids from the Fukkoshi
Formation (Inai Group) with special reference to the
Olenekian/Anisian boundary in the South Kitakami Belt,
Northeast Japan
Masayuki Ehiro
The Tohoku University Museum, Sendai 980-8578, Japan
Abstract: The Triassic Fukkoshi Formation is integral to clarifying the Olenekian/Anisian boundary
in the South Kitakami Belt, Northeast Japan, because it overlies conformably the Olenekian Osawa
Formation and one hand is covered by the Anisian Isatomae Formation. The middle and upperparts of the Fukkoshi Formation distributed in the Kamiwarizaki area yield abundant ammonoids
consisting of over 30 species belonging to 21 genera, including one new genus Psilokhvalynites
and four new species, Parapopanoceras involutum, Psilokhvalynites takaizumii, Paracrochordiceras
watanabei and Paradanubites ozashiense. The Fukkoshi ammonoid fauna is dominated in
the genera Leiophyllites (very abundant), Paradanubites, Danubites and Paracrochordiceras,
and, in addition, characterized common occurrences of those belonging to the families
Parapopanoceratidae, Japonitidae and Longobarditidae. Although it includes some Olenekian-type
genera, such as Hemilecanites, Pseudosageceras and Metadagnoceras, the majority of the fauna
are early Anisian (Aegean) genera and species. Therefore, the fauna is early Anisian in age, and theOlenekian/Anisian boundary is considered to locate somewhere in the lower part of the Fukkoshi
Formation. The generic composition of the Fukkoshi Aegean ammonoid fauna has similarities withthose of some localities located in the low-latitude regions of the Tethys and Panthalassa, especiallywith that of Qinghai, west China.

Introduction
The Triassic Fukkoshi Formation is the third formation of
the Lower–Middle Triassic Inai Group in the South Kitakami
Belt, Northeast Japan, which is distributed widely in thesouthern part of the Kitakami Massif (Figure 1). The groupis composed of a continuous, fossiliferous, shallow marine(partly alluvial to nearshore marine) clastic sediments, andtherefore, one of the most important reference sequencesof the Lower–Middle Triassic of Japan. It consists of theHiraiso, Osawa, Fukkoshi and Isatomae formations, inascending order (Onuki and Bando, 1959: Figure 2). The
Osawa and Isatomae formations are rich in ammonoids, andmany late Olenekian and Anisian–(Ladinian) ammonoids,
respectively, have been known. The Fukkoshi Formation
locates stratigraphically between them and, therefore,
is important to elucidate the stratigraphic position of theOlenekian/Anisian boundary (OAB) in the South Kitakami
Belt. The Fukkoshi Formation is, however, almost barenof ammonoid, since it is dominated in sandstone. Veryfew ammonoids have been described or reported from the
Fukkoshi Formation until now, but it still remains doubtful
about the stratigraphic position and taxonomy of these
specimens, as discussed below.
Recently, new ammonoid localities of the Fukkoshi
Formation were found in the Kamiwarizaki area, the borderarea of the north-side Minamisanriku Town and southside Kitakami-cho of Ishinomaki City, Miyagi Prefecture.
The ammonoid fauna is rather diverse and were collected
definitely from some horizons belong to the middle to upper
part of the formation. This paper describes these ammonoids
and discusses its biostratigraphical and biogeographicalsignificances.

Stratigraphy of the Fukkoshi Formation and its
biostratigraphic problems
The Fukkoshi Formation, 200 to 300 meters in total
thickness, consists mostly of sandstone and alternating
beds of sandstone and mudstone, with minor amount of

40

Masayuki Ehiro

Figure 1. Index map (A) and simplified geologic map of the Southern Kitakami Massif (South Kitakami Belt), Northeast
Japan, showing the distribution of the Lower-Middle Triassic Inai Group and study area (Fig. 2) (B). Longitude
and latitude are from the International Terrestrial Reference Frame. Thick solid and broken lines are faults.
NDB: Nedamo Belt, NKB: North Kitakami Belt, SKB: South Kitakami Belt. Localities 1–4 are related ammonoid
localities: see text.

mudstone. It overlies conformably the Osawa Formation,and in turn is covered conformably by the Isatomae
Formation.
The Osawa Formation is dominated in laminatedmudstone (250 to 350 m thick), and yields rich ammonoids.

Twenty-seven ammonoid genera have been described fromthe formation (e.g. Bando and Shimoyama, 1974; Ehiro etal., 2016; Ehiro, 2022 in press). The lower to middle partof the formation, the Subcolumbites Zone of Bando andShimoyama (1974), yields Columbites parisianus HyattEarly Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japanand Smith and Subcolumbites perrinismithi (Arthaber),associated with such genera as Hemilecanites, Albanites,
Pseudosageceras, Tardicolumbites, Yvesgalleticeras,
Hellenites, Metadagnoceras, Procarnites, Olenekoceras,
Nordophiceratoides, etc. The lower part of the upper part,the Arnautoceltites Zone of Bando and Shimoyama (1974),
contains Arnautoceltites, Nordophiceras, Prenkites, etc.
These two zones are correlated with the upper Olenekian(Bando and Shimoyama, 1974; Ehiro et al., 2016). Ehiro(2022 in press) proposed a new ammonoid zone, theEodanubites Zone, in the uppermost part of the formation,
based on the section at the south of Asadanuki (Loc. 1 inFigure 1). It consists of Olenekian genera Eodanubites,
Pseudosageceras, Ceccaisculitoides and Procarnites,
associated with Japonites and Procladiscites. The latter two
genera are common in the Anisian, but already appeared in
the latest Olenekian strata, and therefore, the Eodanubites
Zone is correlated with the uppermost Olenekian (Ehiro,
2022 in press).
Recently, Shigeta (2022 in press) re-examined someammonoid species reported from the lower to middle part
(Subcolumbites Zone) of the Osawa Formation by Bandoand Shimoyama (1974), and concluded that Columbites
parisianus, Subcolumbites perrinismithi and Eophyllites
cf. dieneri, collected from the Motoyoshi area, should be
attributed to Hellenites tchernyschewiensis Zakharov, H.
inopinatus Kiparisova, Neocolumbites grammi Zakharov, N.
insignis Zakharov, Procolumbites ussuriensis (Zakharov)and P. subquadratus Zakharov. Even in such case, thisfauna is compared with that of the N. insignis Zone of South
Primorye, Russian Far East, and correlated to the upper
Olenekian (Spathian) as a conventional one.
The Fukkoshi Formation is composed of thick sandstone
and alternating beds of sandstone and mudstone, with total
thickness of 200–300 m. According to Kamada (1984) thesesandstones of the Fukkoshi Formation were deposited
as a submarine fan complex. Because of its sandstone
dominated facies, the Fukkoshi Formation is almost barenof ammonoids. Only some Anisian species, Gymnites cf.
watanabei (Mojsisovics), Hollandites sp. and Balatonites
cf. kitakamicus (Diener), reported by Shimizu (1930), were
designated to come from the middle part of the Fukkoshi
Formation (Onuki and Bando, 1959). However, there aresome doubts about the stratigraphic position and localityof these ammonoids (Ishibashi, 2006) and reexaminationis needed. The locality of Shimizu (1930)’s ammonoids
was positioned by Onuki and Bando (1959) to the east of
Yanaizu (Loc. 3a in Figure 1), where the Fukkoshi Formation
is distributed. But, according to the attached label ofBalatonites cf. kitakamicus specimen (IGPS coll. cat. no.
36530) by Shimizu (1930), the locality is “Road side near
the southern end of Yanaizu Town”. The southern end of41

Yanaizu Town in 1930 is located about 4 km to the south of
Yanaizu (Fig. 1, loc. 3b), not to the east, and therefore exact
stratigraphic horizon of these ammonoids is unknown.
On the other hand, ammonoid specimens, Danubites aff.
ambica Diener, Danubites sp., Leiophyllites cf. pitamaha(Diener) and L. aff. pradyumna (Diener), described from a
locality at Konori (Konori-hama), Onagawa Town (Bando,
1970; Loc. 4 in Figure 1), which are considered to come fromthe Osawa Formation, may actually belong to the Fukkoshi
Formation. Bando (1970) stated that these ammonoids
were collected from the alternating beds of the uppermost
part of the Osawa Formation, but these alternating beds
may lithologically belong to the Fukkoshi Formation. In fact,
Working Group on the Permian-Triassic Systems (1975, p.
172), the members of which include Y. Bando, regarded thehorizon of these ammonoids as the Fukkoshi Formation.
The outcrop at Konori, however, was lost when thereconstruction work of “2011 off the Pacific coast of Tohoku
Earthquake” was extended, and the effective re-examination
is impossible.
Thus, the reliability of the ammonoid stratigraphy,
considered to come from the Fukkoshi Formation until now,
is insufficient.
The Isatomae Formation is more than 1,000 m thick andconsists of sandy laminated mudstone, often with thicksandstones or alternating beds of sandstone and mudstone.
Many Anisian ammonoids have been described from theformation by Mojsisovics (1888), Diener (1916a), Shimizu(1930) and others. The fauna comprises such genera
as Hollandites, Danubites, Gymnites, Japonites, Sturia,
Balatonites, Ussurites, Leiophyllites, etc. These ammonoids
are mostly from the middle part of the formation and thosefrom the lower part are rare. Ishibashi (2006) reported,
although not yet described, some species collected fromthe basal part of the formation at Kudanohama in Utatsu
area (Loc. 2 in Figure 1). He set two ammonoid zones
in the basal part: the Grambergia kitakamiensis Zone
below and the Lenotropites isatomaensis–Leiophyllites cf.
pseudopradyumna Zone above. The former zone yields
Grambergia kitakamiensis Ishibashi (MS), Grambergiasp., Tropigastrites cf. lahontanus Smith and Ussurites
sp. The latter consists of Lenotoropites isatomaensis
Ishibashi (MS), Leiophyllites pseudopradyumna (Welter)
and Paracrochordiceras sp. These Kudanohama ammonoid
zones probably corresponds to the Lenotropites–Japonites
Zone (Aegean: lowermost Anisian) of Qinghai, China(He et al., 1986), Japonites welteri beds to Lenotropites
caurus Zone (lower Anisian) of Nevada (Bucher, 1989),
Paracrochordiceras–Japonites beds (Aegean) of Deşli CairaHill, Romania (Grădinaru et al., 2007) and Chios (Assereto,
1974; Fantini Sestini, 1981).

42

Masayuki Ehiro

Figure 2. G eologic map of the Kamiwarizaki area (simplified from Kamada and Takizawa, 1992) (A) and columnar sectionsof the Fukkoshi Formation showing the ammonoid horizons (Fk-1–Fk-6) (B). Routes of the columnar sections (a–a’,
b–b’ and c–c’) are shown in figure A.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan

Materials and the stratigraphy of the newammonoid localities
Ammonoids specimens described here were collectedfrom the middle to upper part of the Fukkoshi Formation
distributed in the Kamiwarizaki area (Figure 1). In this area,
strata of the Inai Group, from the middle part of the Hiraiso
Formation to the lower part of the Isatomae Formation,
distribute parallel to the eastern coast of Kamiwarizaki(Figure 2A), striking nearly N-S and dipping 45˚-70˚ westerly.
Nearly continuous sections of the Fukkoshi Formation cropout along the southern and northern coasts, but the outcrops
are rather rare and imperfect in the inland area. Along thesouthern coast (a-a’ section in Figure 2B), the basal part of
the Fukkoshi Formation, consisting of the alternating beds ofsandstone and mudstone, conformably covers the laminatedmudstone of the underlying Osawa Formation. The lower
part of the formation (about 65 m thick) is dominated in
massive sandstone and sandstone dominated alternating
beds of sandstone and mudstone, but intercalating with thinalternating beds or mudstone dominated alternating beds ofsandstone and mudstone (about 22 m) in the lower part. The
middle part (about 34 m) is composed of laminated or poorly
laminated mudstones, intercalating with thin sandstone beds
(ca. 1.5 m thick, consisting of alternating beds of sandstone
and mudstone, and sandstone) in the uppermost part (fromca. 4.5 m to 3 m below the top). Ammonoid horizons Fk1a, Fk-1b and Fk-1c are in this mudstone beds (locatedat 38°36′18″N, 141°30′59″E). Horizon Fk-1c is situatedabout 7-8 m above the base of the mudstone. Fk-1a andFk-1b are in the uppermost part of the mudstone beds
and separated by the above-mentioned sandstone beds.
Fk-1a has an interval (1.5 m thick) from ca. 2 m to 0.5 m
below the intercalating sandstones, and Fk-1b has ca. 2
m interval immediately above the sandstone (Figure 2B).
The upper part of the formation is about 75 m in thickness
and dominated in sandstone. Thin (usually less than 3 m)
mudstone beds are often intercalated in the lower part, andabout 7 m mudstone dominated part are in the upper part.
The last mudstone beds are separated into the lower andupper parts by thin sandstone. The ammonoid horizon Fk2a and Fk-2b (located at 38°36′19″N, 141°30′56″E) aresituated in the lower and upper parts of this mudstone beds,
respectively (Figure 2B).
Along the old forest road (b-b’ section in Figure 2B) to
the northwest of Ozashi, rather thick mudstone beds (20m+ thick) are sporadically cropped out, dipping steeply
to the west. This mudstone beds are situated above thesporadically distributed sandstone beds and are correlatedwith the mudstone dominated part (middle part) of the a-a’section. From the upper part of this beds, two ammonoids
were collected (Horizon Fk-3a and 3b: 38°36′53″N,

43141°31′8″E).
Nearly continuous section of the Fukkoshi Formation
can also be observed along the northern coast, east of
Terahama (c-c’ section in Figure 2B). Although some parts
are missing or hardly accessible, the total thickness of theformation is estimated to be about 240 m, which is slightly
thicker than that along the southern coast. In this section,
the lower (about 110 m) and upper (ca. 90 m) parts of the
Fukkoshi Formation are composed mainly of sandstone
and alternating beds of sandstone and mudstone, withminor amount of mudstone intercalations. The middle
part (ca. 35 m thick) consists of laminated mudstone. This
mudstone dominated part is stratigraphically correlated withthe middle mudstone dominated part along the southerncoast, although no ammonoid fossil has been collected
here. Some mudstone intercalations in the upper part yieldammonoids: Fk-4 and Fk-5 (38°38′9″N, 141°31′26″E), andFk-6 (38°38′10″N, 141°31′25″E) (Figure 2B). Fk-4 yields only
one poorly preserved, undeterminable specimen, so it will
not be covered here.
The precise correlation of thin mudstone intercalationsin the upper part of the formation between those distributealong the southern and northern coasts is difficult, becauseof lateral facies change and thickness change of each bed.
But, considering their relative stratigraphic positions, thehorizon Fk-2a and Fk-2b seem to be roughly correlated with
Fk-6.
Ammonoid specimens studied in this paper were buried
in mudstone beds with their plane of symmetry lying
mostly parallel to the bedding plane. Many specimens
are preserved only their lower half due to probably
the synsedimentary erosion. Some specimens having
extremely narrow shell, such as ones belong to the genera
Pseudosageceras, Psilokhvalynites, Arctohungarites andLeiophyllites, sometimes hold both sides of the shell, but it isdifficult to measure their exact shell width, because they had
suffered from severe tectonic flattening. Thin film-like pyrite
crystals are sometimes formed on the outer or inner shellsurfaces.

Systematic description
The specimens described here are all kept in the Tohoku
University Museum (Institution abbreviation: IGPS = Instituteof Geology and Paleontology, Tohoku University, Sendai).
Systematic descriptions basically follow the classification
established by Tozer (1981, 1994) and terminology of conchshape (umbilical width) follows Korn (2010). The following
abbreviations are used in the descriptions: D = diameterof whorl, H = height of whorl, W = width of whorl, UD =diameter of umbilicus.

44

Masayuki Ehiro
Order Ceratitida Hyatt, 1884
Superfamily Xenodiscoidea Frech, 1902
Family Hemilecanitidae Guex et al., 2010
Genus Hemilecanites Spath, 1934
Type species.—Lecanites discus Arthaber, 1908.
Hemilecanites discus (Arthaber, 1908)
Figures 3.1, 3.2

Lecanites discus Arthaber, 1908, p. 268, pl. 11, figs. 5a–c;
Renz and Renz, 1948, p. 55.
Hemilecanites discus (Arthaber), Spath, 1934, p. 135, pl.
13, figs. 7a–7d; Kummel in Arkell et al., 1957, p. L136, fig.
169-3; Chao, 1959, p. 41, pl. 3, figs. 1, 2; Kummel, 1969,
p. 374, pl. 25, figs. 9, 10, text-fig. 4-E; Ehiro et al., 2016, p.
93, figs. 2.1–2.3.
Material examined.—Two specimens, IGPS coll. cat. nos.
112546 and 112547.
Descriptive remarks.—The conch is evolute andcompressed, with lenticular cross section. They attain morethan 23 (no. 112547) and 27 mm (no. 112546) in maximum
diameter, but the last volution of each conch is not wellpreserved. It consists of phragmocone and living chamber,the latter occupies about one volution. In specimen no.
112547, at a diameter of ca. 20 mm, the correspondingheight and umbilical diameter are ca. 6.0 and 8.8 mm(UD/D = 0.44), respectively. In specimen no. 112546, theheight and umbilical diameter at D = ca. 27 mm are ca. 7.5
and 13.3 mm (UD/D = 0.49), respectively.
The flanks are broadly convex to nearly flat, with broadly
rounded umbilical and ventral shoulders. The maximum
width is at about the center of the flank. The venter is notwell preserved. The umbilicus is shallow. The shell surface
seems to be smooth. The external lateral suture is partly
preserved. It is goniatitic and consists of three roundedsaddles and three probably rounded lobes. Sides of lobes
are nearly parallel. The saddles and lobes diminish in size
slightly towards the umbilicus.
Although the sutural trace differs slightly from that of thetype specimen of Hemilecanites discus (Lecanites discus
Arthaber, 1908), the general shell shape and dimensionsof the present specimens are similar to those of the typespecimen from the late Olenekian of Albania (Arthaber,
1908, p. 268, pl. 11, figs. 5a–c). The species of the genus
Hemilecanites have mostly been known from the late
Olenekian strata, but H. cf. paradiscus Kummel were
described from the Lower Anisian Japonites welteri beds,
NW. Nevada (Bucher, 1989, p. 961, pl.6, figs. 7-8, text fig. 3).
Occurrence.—Both specimens are from the middle
part (Fk-1b) of the Fukkoshi Formation at the south of

Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Superfamily Sageceratoidea Hyatt, 1884
Family Sageceratidae Hyatt 1884
Genus Parasageceras Welter, 1915
Type species.—Parasageceras discoidale Welter, 1915.
Parasageceras aff. discoidale Welter
Figures 3.3, 3.4
aff. Parasagecers discoidale Welter, 1915, p. 113, pl. 89, fig.
4; Kutassy, 1932, p. 608; Spath, 1934, p. 62, text-figs.
9a–9c.
Parasagecers aff. discoidale Welter, Spath, 1934, p. 62.
Material examined.—Two specimens, IGPS coll. cat. nos.
112548 and 112549.
Description.—The specimen no. 112548 consists
largely of a phragmocone with a part of body chamber.
The conch diameter attains about 25 mm in the obliquely
deformed state. The umbilicus is not well preserved, butvery small. Another specimen (no. 112549) is composedof phragmocone and body chamber, the latter of which
occupies about three-fourth of the last whorl. It attains adiameter of ca. 21.5 mm, and corresponding height andumbilical diameter are 12.2 and 2.2 mm (UD/D = 0.10),
respectively. The sides of both specimens are nearly flat,with broadly rounded umbilical shoulder and acute ventral
shoulder. The venter seems to be flat. Faint, slightly
sigmoidal fine ribs, projected and most distinct near theventral shoulder, are on the sides.
The ventral lobe is shallow and divided into two, simple,
pointed prongs by a low, rounded, median saddle. The firstlateral lobe is widest and has four irregular denticulations
at the base. A denticulation situated on the ventral side ismost remarkable. The second to sixth lateral lobes are bifid,
and the followings (more than three, probably eight or more)
have rounded base. The second lobe has nearly the same
width as the first, but slightly small and shallow. The second
lateral saddle is as large as the first and highest. The othersaddles and lobes diminish in size toward the umbilicus.
Almost lateral saddles have rounded crest, except for thesixth, which is slightly wider than the surrounding ones anddivided into two parts by a shallow depression.
Comparison.—The shell shape and surface ornamentationof the present species are similar to those of Parasagecers discoidale Welter, 1915 from the Anisian of Timor. But
the present species differs from the Timor species in having
more flexosus ribs, and in having complex first lateral lobe.
Occurrence.—Middle part (Fk-1a: no. 112548 and Fk-

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan

45

Figure 3. H emilecanites, Parasageceras, Pseudosageceras and Megaphyllites from the Fukkoshi Formation in the
Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1 and 2, Hemilecanites discus (Arthaber); 1, IGPS coll. cat. no. 112546; 1a, lateral view; 1b, suture line; 2,
IGPS coll. cat. no. 112547; 2a, lateral view; 2b, suture line; 3 and 4, Parasageceras aff. discoidale Welter; 3,
IGPS coll. cat. no. 112548; 3a, lateral view; 3b, suture line; 4, IGPS coll. cat. no. 112549, lateral view; 5–7,
Pseudosageceras multilobatum Noetling; 5, IGPS coll. cat. no. 112550; 5a, lateral view; 5b, suture line; 6, IGPS
coll. cat. no. 112551; 6a, lateral view; 6b, suture line; 7, IGPS coll. cat. no. 112552, lateral view; 8, Megaphyllites
sp., IGPS coll. cat. no. 112664; 8a, lateral view; 8b, suture line. Scale bars are 1 cm unless otherwise stated.

1b: no. 112549) of the Fukkoshi Formation at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Family Hedenstroemiidae Waagen, 1895
Genus Pseudosageceras Diener, 1895aType species.— Pseudosageceras sp., Diener, 1895a.
Pseudosageceras multilobatum Noetling
Figures 3.5–3.7
Pseudosageceras sp., Diener, 1895 a, p. 28, pl. 1, fig. 8.

46

Masayuki Ehiro

Pseudosageceras multilobatum Noetling, 1905a, p. 181,
pls. 19–27; Noetling, 1905b, pl. 23, fig. 4, pl. 25, fig. 1,
pl. 26, fig. 3; Arthaber, 1908, p. 279, pl. 12, fig. 3; Krafft
and Diener, 1909, p. 145, pl. 21, fig. 5; Wanner, 1911, p.
181, pl. 7, fig. 4; Welter, 1922, p. 94, text-fig. 3; Diener,
1925, p. 96, fig. 26 ; Smith, 1932, p. 87, pl. 4, figs. 1–3, pl.
5, figs. 1–6, pl. 25, figs. 7–16, pl. 60, fig. 32, pl. 63, figs.
1–6; Collignon, 1933, p. 56, pl. 11, fig 2; Spath, 1934, p.
54, text-fig. 6a; Kiparisova, 1947, p. 127, pl. 25, figs. 3–4;
Chao, 1959, p. 31, 183, pl. 1, figs., 9, 12; Jeannet, 1959,
p. 30, pl. 6, fig. 1; Tozer, 1961, p. 44, pl. 13, figs. 8, 9;Chao et al., 1965, p. 135, pl. 35, fig. 5; Kummel, 1966, p.
388, pl. 1, figs. 11, 12; Hada, 1966, pl. 4, fig. 6; Kummel
and Erben, 1968, p. 112, pl. 19, fig. 9; Shevyrev, 1968,
p. 79, pl. 1, figs. 1, 2; Kummel, 1969, p. 361, pl. 34, fig.
6, text-fig. 2; Collignon, 1973, p. 5, pl. 1, fig. 1; Weitschat
and Lehmann, 1978, p. 75, pl. 10, fig. 2; Vu Khuc, 1984, p.
26, pl. 1, fig. 1, text-fig. 1; Pakistani-Japanese ResearchGroup, 1985, pl. 12, figs. 5–7, pl. 14, fig. 3; Vu Khuc,1991, p. 119, pl. 45, figs. 5, 6, text-fig. 2.2; Tozer, 1994, p.
83, pl. 18, fig. 1, text-fig. 17; Brayard and Bucher, 2008,
p. 70, pl. 37, figs. 1–5, text-fig. 61; Shigeta and Zakharov,in Shigeta et al., 2009, p. 140, figs. 129, 130; Brühwiler
et al., 2010, p. 429, fig. 16.14; Brühwiler and Bucher in
Brühwiler et al., 2012a, p. 47, pl. 26, fig. 4; Brühwiler andBucher, in Brühwiler et al., 2012b, p. 109, figs. 95A–95N;
Brayard et al., 2013, p. 208, figs. 77a–77f; Shigeta andNguyen, in Shigeta et al., 2014, p. 137, figs. 98, 99; Ehiro,
2016, p. 2, fig. 2.1; Ehiro, 2022 in press, figs. 5.2, 5.3.
Pseudosageceras intermontanum Hyatt and Smith, 1905,
p. 99, pl. 4, figs. 1–3, pl. 5, figs. 1–6, pl. 63, figs. 1, 2.;
Mathews, 1929, p. 3, pl. 1, figs. 18–22; Renz and Renz,
1948, p. 90, pl. 16, figs. 4, 7.
Pseudosageceras drinense Arthaber, 1911, p. 201, pl. 17,
figs. 6, 7; Spath, 1934, p. 55, text-fig. 6c; Renz and Renz,
1948, p. 92, pl. 16, fig. 6.
Pseudosageceras clavisellatum Diener, 1913, p. 28, pl. 4,
figs. 5, 6.
Pseudosageceras paomochungenense Tien, 1933, p. 24, pl.
3, fig. 7; Chao et al., 1965, p. 137, pl. 35, figs. 12, 13.
Pseudosageceras cf. clavisellatum Diener, Renz and Renz,
1948, p. 90, pl. 16, fig. 3.
Pseudosageceras longilobatum Kiparisova, in Kiparisova
and Krishtofovich, 1954, p. 20, pl. 11, fig. 3; Kiparisova,
1961, p. 29, pl. 6, fig. 1, 2, text-fig. 2; Popov, 1961, p. 12,
pl. 10, fig. 1, text-fig. 2.
Pseudosageceras cf. longilobatum Kiparisova, 1961, p. 30,
pl. 5, fig. 3, text-fig. 3.
Pseudosageceras longilobatum var. kwangsiense Chao,
1959, p. 32, 186, pl. 1, figs. 5, 6, pl. 8, figs. 10, 11, text-fig.
5c; Chao et al., 1965, p. 136, pl. 35, figs. 14–16.
Pseudosageceras tsotengense Chao, 1959, p. 32, 184, pl.

1, figs. 7, 8, text-fig. 5b; Chao et al., 1965, p. 136, pl. 35,
figs. 9–11.
Pseudosageceras schamarense Kiparisova, 1961, p. 31, pl.
7, figs. 3a, 3b.
Material examined.—Three specimens, IGPS coll. cat.
nos. 112550–112552.
Description.—Three specimens, strongly compressed
and involute with almost closed umbilicus, are at hand.
The specimen no. 112552 is about 80 mm in diameterand consists of phragmocone and body chamber, thelatter occupies about three-fourth of the last whorl. The
diameter of the fragmental specimens nos. 112550 and
112551, both consists of phragmocone, exceed 60 and 40
mm, respectively. The sides are almost flat except for theslightly depressed umbilical margin. The venter is not wellpreserved, but estimated to be acutely rounded. The shellsurface appears to be smooth. The suture is ceratitic withnumerous adventitious elements. The lateral lobes are
essentially bifid, but some of which are again bifid or, rarely,
trifid.
Discussion.—Although the present specimens ofPseudosageceras are not so well preserved, their generalshell morphologies and especially the shape of the suturelines allow to identify it with Pseudosageceras multilobatum
Noetling.
Occurrence.—Middle part (Fk-1a: no. 112551; Fk-1b:
nos. 112550 and 112552) of the Fukkoshi Formation at thesouth of Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City,
Miyagi Prefecture.
Superfamily Megaphyllitoidea Mojsisovics, 1896
Family Parapopanoceratidae Tozer, 1971
Genus Parapopanoceras Haug, 1894
Type species.— Popanoceras verneuili Mojsisovics, 1886.
Remarks.—When Popov (1961) proposed a new genus
Stenopopanoceras, the fundamental difference between
the genera Parapopanoceras and Stenopopanoceras isin the shell shape. However, Dagys and Ermakova (1981)
clarified that the shell shape of the genus Parapopanoceras
is variable not only between species but also in the stepsof ontogeny, and shell shape in some of them is similar tothat of Stenopopanoceras. They considered, instead, thatthe distinctive feature of the genus Parapopanoceras is in
the suture line: the species of the genus Parapopanoceras
have at least four external lateral lobes, which are serrated
not only the bases but also their sides, even in their early
ontogenetic stage.
Parapopanoceras involutum sp. nov.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
Figures 4.1–4.7
Material examined.—Eight specimens, IGPS coll. cat. nos.
112553 (holotype) and 112554–112560 (paratypes).
Etymology.―The species name is from its involute shellform.
Diagnosis.—Parapopanoceras having very smallumbilicus (UD/D < 0.11) even in the large specimen (D up
to 120 mm). The number of lateral lobes, which are strongly
denticulate, is four in all ontogenetic stages (D from 20 to
120 mm).
Description.—The specimen no. 112554 is a small
fragment of the ventral part of the phragmocone. The widthof it reaches at least 20 mm. The venter is broadly rounded,
but its broadness may partly be caused by the tectonic
flattening. The ventral shoulder is rounded. The specimen
no. 112557 is a small fragmental phragmocone, and about
a half of a volution is preserved. The shell diameter is ca. 20
mm with a small umbilicus, the ratio of UD/D is estimatedto be 0.21-0.25. The flank is broadly convex and continues
smoothly with broadly rounded venter. The umbilicalshoulder is rounded. Other specimens, including theholotype (no. 112553), consist of phragmocone and bodychamber, the latter of which occupies about two-thirds ofa volution. The maximum preserved shell diameter ranges
from ca. 48 to 124 mm, and the ratios of H/D and UD/D atthe last whorls range 0.42-0.54 and 0.07-0.11 (mostly 0.100.11), respectively. Although the umbilical edge of the bodychamber of the largest specimen (no. 112558) is broken
off and precise ratio of UD/D is unknown, the adoral endof the phragmocone is well preserved and the ratio of UD/
D there (D = ca. 120 mm) is ca. 0.10. The side is convex
with rounded umbilical and ventral shoulders. The maximum
shell width is near the center of the flank. In two specimens(holotype and no. 112559), there are faint, slightly sigmoidal
growth lines on the shell surface, but the shell surfaces of
the rest seem to be smooth.
The ventral lobe is divided into two prongs by a low andnarrow median saddle, and the base to lower one-third of
the sides of the prong is denticulate. The median saddle
is about a half height to the ventrolateral saddles. The firstlateral love has nearly the same width and depth as theventral lobe. There are four lateral lobes in all specimens. Alllobes are strongly denticulate in their base to lower one-thirdof their sides. The first lobe is the largest and they diminish
in size toward the umbilicus. There are some auxiliary
lobes, except for the smallest specimen, at the umbilicalmargin. The crests of lateral saddles are all rounded, andthe saddles also gradually diminish in size towards theumbilicus.
Discussion.—Based on the general shell shape, having
rounded venter and small umbilicus, and the trace of

47

external suture lines, the present specimens are considered
to belong to the genus Parapopanoceras Haug, 1894. The
present species differs from the known species of the genus
in having small ratio of UD/D (0.10 to 0.11) even in thelarge specimens (D = ca. 50 to 120 mm). Small specimens(D < 40 mm) of P. plicatum Bytschkov have rather smallumbilicus (UD/D = 0.12–0.16), but larger specimens of thespecies (D > 40 mm) have rather large umbilicus (UD/D =0.15–0.34) (Bytschkov in Bytschkov et al., 1976, p. 138, pl.
23, figs. 2–4, text-fig. 13; Dagys and Ermakova, 1981, p. 61,
pl. 11, figs. 1–7, text-figs. 38–41).
Occurrence.—Middle part of the Fukkoshi Formation at thesouth of Ozashi (Fk-1c: nos. 112558, 112560; Fk-1a: nos.
112554, 112557; Fk-1b: nos. 112553, 112556, 112559) andat the northwest of Ozashi (Fk-3b: no. 112555) , Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Family Megaphyllitidae Mojsisovics, 1896
Genus Megaphyllites Mojsisovics, 1879
Type species.—Ceratites Jarbas Münster, 1841.
Megaphyllites sp.
Figures 3.8a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112664.
Descriptive remarks.—A small, discoidal and involute
to sub-involute specimen is examined. It consists of thephragmocone and body chamber, the latter attains about
one-thirds of the preserved last whorl. The shell diameterattains 30.4 mm in the elliptically deformed state, and its
corresponding height and umbilical diameter are 7.2 and ca.
5.0 mm (UD/D = 0.16), respectively. The umbilical margin issomewhat indistinct. The side of the phragmocone is broadly
convex and the maximum width is at about the center ofthe side, whereas the side of the body chamber is nearlyflat. The ventral shoulder is rounded. The small umbilicus
is rather deep and funnel-shaped. The shell surface issmooth without any ornamentation and constriction. The
external suture line is imperfectly preserved, but typical forthe genus Megaphyllites. There are at least seven saddles
and six lobes. The crests of saddles are all rounded. The
second saddle is highest and saddles gradually diminish
in size towards the umbilicus. The deep first lateral lobe
is denticulate not only at the base but also on the sides.
The basal denticulations are strong. The second lobe isnearly equal in depth with the first and have the same
denticulations, the basal two denticulation of which arevery long. The third lobe has nearly the same outline as thesecond, but the depth is about two-thirds of the second.
Following lobes gradually diminish in size towards the

48

Masayuki Ehiro

Figure 4. P arapopanoceras involutum sp. nov. from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt,
Northeast Japan.
	1, IGPS coll. cat. no. 112553 (holotype); 1a, lateral view; 1b, suture line; 2, IGPS coll. cat. no. 112554; 2a, ventral
view; 2b, suture line; 3, IGPS coll. cat. no. 112555; 3a, lateral view; 3b, suture line; 4, IGPS coll. cat. no. 112556,
lateral view; 5, IGPS coll. cat. no. 112559, lateral view; 6, IGPS coll. cat. no. 112557; 6a, lateral view; 6b, sutureline; 7, IGPS coll. cat. no. 112558; 7a, lateral view; 7b, suture line. Scale bars are 1 cm unless otherwise stated.

umbilicus.
The general shell shape of the present specimen, withbroadly convex to flat sides and small but distinct umbilicus,
is similar to those of Megaphyllites compressus Shevyrev
from Caucasus (Shevyrev, 1995, p. 123, pl. 22, fig. 4, textfig. 73), Megaphyllites evolutus Welter from Timor (Welter,
1915, p. 114, pl. 7, figs. 2a–2c) and from Qinghai (Heet al., 1986, p. 207, pl. 17, figs. 5–7, text-fig. 14c), andMegaphyllites tenuis Chen in He et al. from Qinghai (He etal., 1986, p. 207, pl. 17, figs. 14–16, text-fig. 14d). But it issomewhat difficult to identify it at the specific level becauseof its small size and poor state of preservation.
Occurrence.—Middle part (Fk-1b) of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Superfamily Dinaritoidea Mojsisovics, 1882

Family Khvalynitidae Shevyrev, 1968
Genus Metadagnoceras Tozer, 1965
Type species.—Metadagnoceras pulchrum Tozer, 1965.
Metadagnoceras sp. A
Figures 5.2a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112561.
Descriptive remarks.—A small specimen is discoidal andinvolute to sub-involute. The maximum shell diameter may
exceed 40 mm, but exact diameter is unclear because its
ventral part of the preserved end is missing. The umbilicus
is small and the ratio of UD/D is estimated to be 0. 15 or so.
The side is broadly convex to nearly flat with the maximum
width at about the center of it. The umbilicus is shallow, but

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japanthe umbilical wall is steep with rounded umbilical shoulder.
The venter seems to be convex to flat with sharp ventral
shoulder. The shell surface looks like smooth, but finesinuous ribs are preserved near the apertural end. The
external suture consists of shallow ventral lobe, narrow
first lateral saddle, very large and deep first lateral lobe,
large and rounded second lateral saddle and auxiliaries
near the umbilical margin. One of the prongs of the ventral
lobe is visible and its base has irregular denticulations.
The first lateral saddle is rounded, but its crest is incised.
The first lateral lobe occupies the center of the side and isdenticulate deeply at the base. The denticulations extend
up to the ventral side to nearly the top of the first lateralsaddle, whereas the umbilical side is almost smooth. The
wide rounded second lateral saddle is asymmetric having
long ventral side and short umbilical side. The auxiliaries areshallow and pointed.
The present specimen is rather small and not wellpreserved, so the specific identification is difficult. It
somewhat resembles Metadagnoceras pulchrum Tozer, 1965
from the upper Olenekian (Spathian) of British Columbia in
the general shell shape and outline of the suture, but theshape of the first lateral saddle is different; M. pulchrum has
a symmetric, equally incised first lateral saddle, whereas thethat of the present specimen has irregularly incised ventral
side.
Occurrence.—Middle part (Fk-1a) of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Metadagnoceras sp. B
Figures 5.1a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112562.
Descriptive remarks.—A fragmental phragmocone is athand. Its height attains more than 30 mm. The venter is
not preserved. The side is nearly flat with acutely roundedumbilical shoulder. The umbilicus probably deep with steep
wall, but not well preserved. The shell surface seems to besmooth. The external lobe is partly preserved, although theventral lobe is missing. The probable first lateral saddle ishighly denticulate, but may be not well individualized. The
large and deep first lateral lobe occupies the central part ofthe side and strongly denticulate. The denticulations extend
up to the ventral side to nearly the top of the first lateralsaddle, whereas the umbilical side is almost smooth. The
second lateral saddle is large and rounded, and its outline
is asymmetrical, having long ventral side and short umbilicalside. Near the umbilical edge, there are some pointed
auxiliary lobes.
Based on the general shell shape and the outline of the49

suture, the present specimen is considered to belong to thegenus Metadagnoceras Tozer, 1965. Its sutural pattern issomewhat similar to that of M. youngi Bucher from the lower
Anisian of Nevada (Bucher, 1989, p. 963, pl. 1, figs. 2–5,
text-fig. 5), but the specific designation is difficult becauseof the fragmental state of preservation of the present
specimen.
Occurrence.—Middle part (Fk-1b) of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Genus Psilokhvalynites gen. nov.
Type species.—Psilokhvalynites takaizumii gen. and sp.
nov.
Etymology.—The generic name refers to it smooth (Greek,
Psilo-) shell surface, and a genus name Khvalynites, thegeneral shell shape and sutural trace of which resemble
those of the present new genus.
Diagnosis.—The shell is involute and extremely discoidal
with almost smooth surfaces. The sides are broadly
convex and converge slightly to the flat to convex venter.
The external suture line is similar to that of the genus
Khvalynites, consisting a large and deeply denticulate laterallobe and two rounded lateral saddles. The ventral side of thefirst lateral saddle is smooth.
Discussion.— Psilokhvalynites gen. nov. resembles an
Olenekian (Early Triassic) genus Khvalynites Shevyrev,
1968 in its general shell shape and sutural traces. However,smooth shell surface of the new genus is the most distinctive
character from Khvalynites, which has remarkable radialribs. The smooth ventral side of the first lateral saddle of the
new genus is also unique in the family Khvalynitidae. Some
species of Anisian genus Alanites Shevyrev, 1968, such as
Alanites visendus Shevyrev 1968 and A. laevis Tozer, 1994
have smooth surface, but is easily distinguished from thepresent new genus in having thickly trapezoidal shell crosssection and having serrated saddles.
Psilokhvalynites takaizumii gen. and sp. nov.
Figures 5.3–5.7
Material examined.—Seven specimens, IGPS coll. cat.
no. 112563 (holotype) and nos. 112564–112569 (paratypes).
Etymology.—The specific epithet is dedicated to Yukihiro
Takaizumi, who donated many ammonoid specimens,
including the present new species, from the Fukkoshi
Formation.
Diagnosis.―As for the genus.
Description.—The shell is involute and extremely
discoidal. The holotype is the largest and its maximum

50

Masayuki Ehiro

Figure 5. M etadagnoceras, Psilokhvalynites, Aegeiceras?, Eogymnites and Buddhaites? from the Fukkoshi Formation in
the Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1, Metadagnoceras sp. B, IGPS coll. cat. no. 112562; 1a, lateral view (U: umbilicus); 1b, suture line; 2,Metadagnoceras sp. A, IGPS coll. cat. no. 112561; 2a, ventral view; 2b, suture line; 3–7, Psilokhvalynites
takaizumii gen. and sp. nov.; 3, IGPS coll. cat. no. 112565; 3a, lateral view; 3b, suture line; 4, IGPS coll. cat. no.
112564, lateral view; 5, IGPS coll. cat. no. 112569, lateral view; 6, IGPS coll. cat. no. 112566; 6a, lateral view; 6b,
suture line; 7, IGPS coll. cat. no. 112563 (holotype); 7a, lateral view; 7b, suture line; 8, Aegeiceras? sp., IGPS
coll. cat. no. 112583; 8a, lateral view; 8b, suture line; 9, Eogymnites sp., IGPS coll. cat. no. 112584; 9a, lateralview; 9b, suture line; 10, Buddhaites? sp., IGPS coll. cat. no. 112588; 10a, lateral view; 10b, suture line. Scalebars are 1 cm unless otherwise stated.

diameter may attain to 90 mm, but it lacks part of shell
margins. The preserved shell diameters of other specimens
range from ca. 30 mm to over 80 mm. The ratio of UD/D
ranges from 0.12 to 0.17, the majority of which is 0.12 to
0.13. The sides are broadly convex to nearly flat with broadly

rounded umbilical shoulder. The maximum shell width isat or near the umbilical shoulder and the sides slightly
converge to the venter. The venter is not well preserved, but,in the holotype, seems to be nearly flat with acute ventral
shoulders. The umbilicus is shallow with low umbilical wall.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast JapanThe shell surface is almost smooth, except for faint sinuous
growth lines.
The general outline of the external suture line is similar
to that of the genus Khvalynites. The ventral lobe is not wellpreserved, and only probably a part of its prong is visible.
It is shallow and denticulate, with smooth side. A wide anddeep, U-shaped lateral lobe occupies the central part of theflank, with two rounded saddles on each side. The base of
the lobe is deeply denticulate and some small denticulations
are up to the middle part of the ventral side. Crests of two
saddles are rounded. The first lateral saddle is symmetrical,
whereas the wide second saddle is asymmetrical withshort umbilical side, which continue to some pointed small
auxiliary lobes on the umbilical shoulder.
Occurrence.—Middle part (Fk-1a: no. 112564; Fk-1b: nos.
112563, 112565–112568) of the Fukkoshi Formation at thesouth of Ozashi, Jusanhama, Kitakami-cho, Ishinomaki Cityand from the upper part (Fk-5: no. 1112569) at the eastern
coast of Terahama, Togura, Minamisanriku Town, Miyagi
Prefecture.
Superfamily Ceratitoidea Mojsisovics, 1879
Family Acrochordiceratidae Arthaber, 1911
Genus Paracrochordiceras Spath, 1934
Type species.—Acrochordiceras anodosum Welter, 1915.
Paracrochordiceras cf. denseplicatum Fantini Sestini
Figures 6.1–6.3
cf. Acrochordiceras ex aff. anodosum Welter, Bender, 1970,
p. 439, pl. 2, fig. 9.
Paracrochordiceras denseplicatum Fantini Sestini, 1981,
p. 49, pl. 4, figs. 2, 3.
Material examined.—Three specimens, IGPS coll. cat.
nos. 112570–112572.
Descriptive remarks.—Specimens are discoidal and subevolute. The flanks are nearly flat with acutely roundedumbilical shoulder. The umbilicus is shallow. The venter is
not well preserved. Sample no. 112570 attains a maximum
diameter of ca. 42.0 mm, and its corresponding height andumbilical diameter are ca.16.0 and 14.0 mm (UD/D = 0.33),
respectively. There are 39–40 ribs on the shell surface. The
ribs are rectiradiate and run from the umbilical shoulder tothe ventral shoulder, slightly strengthened to the venter,but slightly curve forward at the ventral shoulder. Theyreach to the venter, but whether they cross the venter or
not is unclear because the venter is not well preserved.
Very few ribs bifurcate near the ventral shoulder. The
maximum shell diameter of sample no. 112571 is 43.5 mm,with corresponding height and umbilical diameter of ca.

51

13.5 and 15.5 mm (UD/D = 0.36), respectively. There are
34–35 rectiradiate ribs on the last whorl. The ribs run fromthe umbilical shoulder, slightly strengthened to the venterand probably cross the venter. About one-thirds of ribs
bifurcate or associated with short secondary ribs near theventral shoulder. No. 112572 is a fragmental and deformed
specimen having fine ribs resemble to no. 112571.
The external suture is partly preserved in specimen no.
112570. Three lateral saddles and two lateral lobes areobservable, although the first saddle is only preserved onits umbilical side. The saddles are rounded. The lobes arestrongly denticulate at the base and small denticulations
reach to the middle part of their sides.
The general shell outline and surface ornamentation,
especially their flat sides, closely resemble
Paracrochordiceras denseplicatum Fantini Sestini, 1981,
described from the Lower Anisian (Aegean) of Chios Island,
Greece. But I refrain from identifying the present specimens
definitely at the specific level, because the present
specimens are not well preserved and Chios specimen lacks
suture line. Proacrochordiceras kiparisovae Korchinskayadescribed from Spitsbergen (Korchinskaya, 1983, p. 110,
figs 1a–h, 2a–b) is somewhat similar to the present species
in its shell form, surface ornamentation and outline of thesuture line. But the former differs from the latter in having
umbilical tubercles on the inner whorls and in having coarser
ribs.
Occurrence.—Upper part of the Fukkoshi Formation at thesouthern coast of Ozashi (Fk-2b: no. 112570), Jusanhama,
Kitakami-cho, Ishinomaki City, and at the eastern coastof Terahama (Fk-5: nos. 112571, 112572), Togura,
Minamisanriku Town, Miyagi Prefecture.
Paracrochordiceras watanabei sp. nov.
Figures 6.4–6.7
Material examined.—Six specimens: IGPS coll. cat. nos.
112573 (holotype) and 112574–112578 (paratypes).
Etymology.―The species name is to honor Yuta
Watanabe, who collected important specimens including theholotype, and making them available for this study.
Diagnosis.—Paracrochordiceras having coarse radialribs which are largely rursiradiate. The shell is moderately
evolute with oval cross section.
Description.—The shell is discoidal and sub-evolute. It
consists of a phragmocone and body chamber, the latter ofwhich occupies about half part of the preserved last volution.
The maximum diameter ranges from ca. 30 mm to 52.5 mm.
The ratio of UD/D is in the range of 0.38–0.43 (Table 1). The
flanks are nearly flat to broadly convex with acutely roundedumbilical shoulder. The umbilicus is shallow. The venter
is not fully preserved, but probably rounded with broadly

52

Masayuki Ehiro

Figure 6. P aracrochordiceras from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1–3, Paracrochordiceras cf. denseplicatum Fantini Sestini; 1, IGPS coll. cat. no. 112570; 1a, lateral view;
1b, suture line; 2, IGPS coll. cat. no. 112571, lateral view; 3, IGPS coll. cat. no. 112572, lateral view; 4–7,
Paracrochordiceras watanabei sp. nov.; 4, IGPS coll. cat. no. 112574, 4a, lateral view; 4b, suture line; 5, IGPS
coll. cat. no. 112573 (holotype); 5a, lateral view; 5b, suture line; 6, IGPS coll. cat. no. 112575; 6a, lateral view; 6b,
suture line; 7, IGPS coll. cat. no. 112576, lateral view; 8, Paracrochordiceras sp. A, IGPS coll. cat. no. 112579;
8a, lateral view; 8b, suture line; 9-11, Paracrochordiceras sp. B; 9, IGPS coll. cat. no. 112580, lateral view; 10,
IGPS coll. cat. no. 112581; 10a, lateral view; 10b, suture line; 11, IGPS coll. cat. no. 112582, lateral view. Scalebars are 1 cm unless otherwise stated.

rounded ventral shoulder, which continued from the roundedmargin of the side. The maximum shell width is at the centerto ventral two-thirds of the flank, and the flanks slightly
converge to the umbilicus. There are rursiradiate ribs on theflanks. They are convex and sometimes slightly sigmoidal.
They run from the umbilical wall, slightly strengthened andwidened to the venter, and probably cross the venter. They
seem to be simple on the inner whorls, but, on the last whorl,
sometimes bifurcate near the ventral shoulder or associatedby intercalary ribs. There are 28 to 32 (rarely 24) primaryribs on the last whorl.
The external lateral suture consists of three roundedEarly Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
Table 1. D imensions (in mm) and ratios of Paracrochordiceras watanabei sp. nov. from the Fukkoshi Formation. α: the angular position adapical from thepreserved end; D: diameter of whorl; H, height ofwhorl; W: width of whorl; UD: diameter of umbilicus.

saddles and two serrated lobes. The ventral lobe is notpreserved. The second saddle is widest and the third issmall. The first lateral lobe is deep, with smooth sides which
are subparallel each other to slightly widened toward thebase. The base has four to five strong denticulations. The
small and shallow second lobe bifurcates, rarely trifurcatesat the base. The auxiliary robe is simple and pointed.
Discussion.—The general shell outline and surface
ornamentation, especially their nearly flat sides, of thepresent species somewhat resembles Paracrochordiceras
denseplicatum (Fantini Sestini, 1981, p. 49, pl. 4, figs. 2, 3)
described from the Lower Anisian (Aegean) of Chios Island,
Greece. The present species, however, clearly distinguishedfrom P. denseplicatum and other previously known speciesof Paracrochordiceras in having coarser, rursiradiate ribs.
Occurrence.—Middle part (Fk-1a: nos. 112577, 112578;
Fk-1b: nos. 112573–112576) of the Fukkoshi Formation at
the southern coast of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Paracrochordiceras sp. A
Figures 6.8a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112579.
Descriptive remarks.—A specimen collected from a float
near the locality Fk-1a and Fk-1b is examined. About twothirds of the conch is preserved. It is discoidal and subevolute. The maximum diameter is about 35 mm, andits corresponding height and umbilical diameter are ca.
12 and 12-13 mm (UD/D = 0.34-0.37), respectively. The
broadly rounded flanks continue to the umbilical wall and53

venter without well-defined umbilical and ventral shoulders.
The maximum shell width is at about the center of theflanks. Exact shell width is not known, but, based on thepreserved shell thickness, the width at least reaches 10mm, and probably larger than the corresponding height.
The umbilicus is deep and umbilical wall is steep. The shellsurface is ornamented with strong radial ribs, which run
from the umbilical shoulder, broadened to the venter andprobably cross the venter. They are rursiradiate on the inner
whorls, but partly falcoid on the last whorl. Although thelarge part of the shell surface of the last whorl is worn out
and not well preserved, many of the ribs on the preserved
last whorl seem to bifurcate at the center of the flank or near
the ventral shoulder. There are 15-16 primary ribs per half
volution.
The external suture is partly preserved, but the ventral
lobe and auxiliary ones near the umbilicus are notpreserved. The crests of three saddles are all rounded. The
first saddle is highest, but narrow, and the second is wide.
The first lateral lobe is wide and deep, showing somewhat
circular outline. Its base is strongly denticulate and shallow
denticulations are up to the middle part of the ventral side.
The small second lateral lobe is also denticulate.
Based on its general shell shape and shape of sutureline, the present specimen very likely belongs to the genus
Paracrochordiceras. Although its coarse ribbing and uniquerib pattern suggests that the present species is a new
species, I refrain from proposing it because of their poor
state of preservation.
Occurrence.—From a float at the middle part (Fk1) of the Fukkoshi Formation at the southern coast of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Paracrochordiceras sp. B
Figures 6.9–6.11
Material examined.—Three specimens, IGPS coll. cat.
nos. 112580–112582.
Descriptive remarks.—The specimens are discoidal
and sub-involute to sub-evolute. The maximum diametersof them are ca. 45 mm, and the ratios of UD/D are 0.30
(specimen no. 112580), 0.38 (no. 112581) and 0.44 (no.
112582). The flanks are nearly flat to broadly convex withacutely rounded umbilical and ventral shoulders. The
venter is not well preserved, but seems to be rounded.
The umbilicus is shallow. The maximum width is near theventral shoulder to the center of the flank. The shell surface
is ornamented with slightly sigmoidal to slightly concave,rectiradiate to slightly rursiradiate, fine radial ribs. They
run from the umbilical shoulder, slightly broadened to theventer, and fade out short before the venter or probably

54

Masayuki Ehiro

cross the venter. Very fine ribs or growth lines, parallel tothe primary ribs, are also present in specimen no. 112580.
There are about 50 primary ribs per volution. The suture is
only preserved in specimen no. 112581. It is rather simple
and consists of deep ventral lobe, high and large, rounded
first lateral saddle, moderately deep first lateral lobe, small
second rounded saddle and small second lobe. Although all
lobes are not well preserved, the lower part of the first laterallobe is pointed at three or four parts.
The general shell shape and rib pattern, and the outline of
the suture line of the present specimen resemble with thoseof the species of the genus Paracrochordiceras. The ribsof the present specimens are remarkably finer than thoseof the known species. However, I refrain from identifying
it at the specific level, because they are in poor state ofpreservation.
Occurrence.—From the middle part (Fk-1a) of the
Fukkoshi Formation at the southern coast of Ozashi,
Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Superfamily Pinacoceratoidea Mojsisovics, 1879
Family Gymnitidae Waagen, 1895
Subfamily Japonitinae Tozer, 1971
Genus Aegeiceras Fantini Sestini, 1981
Type species.—Gymnites ugra Diener, 1895b.
Aegeiceras? sp.
Figures 5.8a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112583.
Descriptive remarks.—A small specimen is discoidal andsub-evolute. It consists of phragmocone and body chamber,the latter occupies about a half of the last whorl. The shellattains 24.4 mm in diameter and its corresponding height
and umbilical diameter are 10.0 and 8.0 mm (UD/D = 0.33),
respectively. The side is broadly convex with maximum
width at the center of it. The apparent width is very small
and about 2 mm, but this is partly tectonic flattening. The
venter is carinate, without remarkable ventral shoulder. The
umbilicus is shallow with rounded umbilical shoulder. The
shell cross section is lenticular. The shell surface seems tobe smooth on the phragmocone, but on the body chamber,there are faint, fine radial ribs, running from just above theumbilical shoulder to near the venter. They are rectiradiateon the inner side of the whorl, but slightly curve adorally on
the outer side. There are also seen three, indistinct spiralridges on the body chamber: at the ventral one-fourth, centerand ventral three-fourth. They slightly expand on the radialribs.

The external lateral suture line is ammonitic and similar tothat of Aegeiceras, although the ventral lobe is only partly
preserved and its details sometimes in distinct because of
its small size and ill preservation. The all saddles and lobes
are finely frilled. The ventral lobe is shallow than the firstlateral lobe. There are three saddles on the lateral side, thesecond is highest and the third is low. The first lateral lobe
is deepest. The second lobe is slightly shallow than the first.
Near the umbilical edge, there are some auxiliaries.
The general shell shape and sutural outline are similar
to those of the genus Aegeiceras Fantini Sestini, 1981,
although the ratio of UD/D of the present species is little
smaller than the known species of Aegeiceras. The speciesof Aegeiceras have only one spiral ornament constituted
by clavi. The present species has three faint spiral ridges
on the body chamber. Some specimens of Aegeiceras ugra
also have additional spiral ornament, although they are very
indistinct ridge (Diener, 1895b, pl. 30, fig 5a; Bender, 1970,
pl. 3, fig. 6; Fantini Sestini, 1981, pl. 5, fig. 2). The spiralornaments of the present species are ridge, instead of clavi,
but they expand on the radial ribs as nodes. Thus, the present
species is thought to belong to the genus Aegeiceras, butthere remain some questions about the generic assignment
due to its small size and poor state of preservation.
Occurrence.—Middle part (Fk-1a) of the Fukkoshi
Formation at the southern coast of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Genus Eogymnites Spath, 1951
Type species.—Japonites arthaberi Diener, 1915.
Eogymnites sp.
Figures 5.9a, bMaterial examined.—One specimen, IGPS coll. cat.
no.112584.
Descriptive remarks.—A small specimen, consisting ofphragmocone and body chamber, is at hand. The bodychamber occupies more than two-thirds of the preserved
last whorl. The shell is extremely discoidal and sub-evolute.
It attains 32.8 mm in diameter and its corresponding height
and umbilical diameter are ca. 12.0 and 14.5 mm (UD/D =0.44), respectively. The apparent width is 1.8 mm, but its
discoidal form may be partly due to the synsedimentarycompaction and tectonic flattening. The sides are broadly
convex with broadly rounded umbilical and ventral
shoulders. The umbilicus is shallow and the venter isprobably acutely rounded. The maximum shell width is at thecenter of the flank, and the shell cross section is lenticular.
The shell surface is almost smooth, but with faint, slightly
sinuous, radial ribs.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast JapanThe external lateral suture consists of large and deep
first lateral lobe, high second lateral saddle, deep second
lateral lobe and small third lateral saddle on the umbilicalshoulder. Ventral lobe is not seen and the first lateral saddle
is only preserved on its umbilical side. At maturity all parts ofsaddles and lobes are serrated, but on the inner whorls thecrests of saddles are rounded. The serration of the base of
the lobes are rather deep. Sides of lateral lobes are parallel
to each other.
Based on the general shell shape and sutural traces,
especially in having parallel lobe sides, the present
specimen belongs to the genus Eogymnites Spath, 1951.
But the precise specific identification is difficult, because it israther small and ill preserved.
Occurrence.—Middle part (Fk-1a) of the Fukkoshi
Formation at the southern coast of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Genus Japonites Mojsisovics, 1893
Type species.—Ceratites planiplicatus Mojsisovics, 1888.
Japonites cf. meridianus Welter
Figures 7.5a, b
cf. Japonites meridianus Welter, 1915, p. 122, pl. 93. figs.
2a–2c, text-fig. 21; Wang and He, 1976, p. 414, pl. 42,
figs. 3–4, pl. 43, figs. 10–11; He et al., 1986, p. 240, pl. 9,
figs. 7–14, text-figs. 33c–33d.
Material examined.—One specimen, IGPS coll. cat. no.
112585.
Descriptive remarks.—A fragmental specimen, about ahalf volution, is at hand. Inner whorls are missing. It largely
consists of body chamber, but a part of the phragmocone isalso preserved. The shell attains about 54 mm in diameter,
and its corresponding height and umbilical diameter areca. 15.5 and 23.3 mm, respectively. The ratio of UD/D is0.43. The shell is compressed and the side is nearly flat tobroadly convex. The ventral and umbilical shoulders are
not well preserved, but seem to be acutely rounded. The
shell surface bears faint fine ribs, which are rursiradiate andpartly slightly sinuous. They run from the umbilical shoulder
to near the ventral shoulder. The external suture line israther well preserved, except for ventral lobe and auxiliaries
near the umbilical shoulder. It is typical Japonites-type. The
ventral lobe is probably bifurcated by the median saddle andthe serrated prong is moderately deep. There remains threelateral saddles and two lateral lobes, all are fully serrated.
The first and second saddles are nearly the same height
and the third is low. The first lateral lobe is deeper than thesecond.

55

Based on the general shell shape, shell ornamentationand outline of the suture line, the present specimen closely
resembles Japonites meridianus Welter, but the exact
specific identification is difficult, because the present
specimen is fragmental and not well preserved. J. cf.
meridianus collected from the underlying Osawa Formation(Ehiro, 2022 in press) has smaller umbilicus.
Occurrence.—Middle part (Fk-1a) of the Fukkoshi
Formation at the southern coast of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Japonites raphaelizoyae (Tommasi)
Figures 7.7a, b
Gymnites Raphaelis Zoja Tommasi, 1899, p. 41, pl. 6, figs. 5,
6; Renz, 1910, p. 41, pl. 2, figs. 10, 12 (non 2), text-fig. 4.
Japonites Raphaelis Zojae (Tommasi), Welter, 1915, p. 123,
pl. 10, figs. 1–4, text-figs. 22–24.
Japonites raphaelis-zojae (Tommasi), Bender, 1970, p. 448,
pl. 4, fig. 1.
Japonites raphaelis zojae (Tommasi), He et al., 1986, p.
240, pl. 9, figs. 15–19, text-fig. 33g.
Japonites raphaelis zojae (Tommasi), Wang et al., 1979, p.
46, pl. 11, figs. 11–14, text-fig. 25b–c.
Material examined.—One specimen, IGPS coll. cat. no.
112586.
Description.—The shell is discoidal and evolute. It consistsof phragmocone and body chamber, the latter occupies
about three-fourth of the last whorl. The shell diameter at
the preserved end is 73.5 mm, with corresponding height
and umbilical diameter of 25.0 and 34.3 mm (UD/D = 0.47),
respectively. The sides are broadly rounded connecting to
the rounded venter and rounded umbilical slope without
distinct shoulders. The maximum shell width is near thecenter of the flank, and it is more than 10 mm. The shellcross section is approximately elliptical. The umbilicus isshallow. There are strong, slightly sigmoidal radial ribs,
26–27 per volution, on the shell surface. They run from theumbilical wall, widening to the venter, to the ventral shoulder
and fade out. Fine ribs or growth lines, parallel to the ribs,
are also present.
The external suture is preserved except for the ventral
lobe. It consists of high, rather narrow first lateral saddle,
deep and wide first lateral lobe, wide second lateral saddle,
shallow second lateral lobe, small third lateral saddle andsome auxiliary lobes on the umbilical shoulder to umbilicalwall. All saddles and lobes are serrated irregularly. The firstlateral lobe has nearly parallel sides and its base is strongly
serrated. The second lateral lobe narrows toward the base.
Comparison.—The general shell shape, especiallyin having elliptical shell cross section and rather wide

56

Masayuki Ehiro

Figure 7. J aponites from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1, 3, 4, Japonites sp. B; 1, IGPS coll. cat. no. 112667; 1a, lateral view; 1b, suture line; 3, IGPS coll. cat. no.
112665; 3a, lateral view; 3b, suture line; 4, IGPS coll. cat. no. 112666; 4a, lateral view; 4b, suture line; 2,
Japonites sp. C, IGPS coll. cat. no. 112668; 2a, lateral view (rubber cast); 2b, suture line; 5, Japonites cf.
meridianus Welter, IGPS coll. cat. no. 112585; 5a, lateral view; 5b, suture line; 6, Japonites sp. A, IGPS coll. cat.
no. 112587; 6a, lateral view; 6b, suture line; 7, Japonites raphaelizoyae (Tommasi), IGPS coll. cat. no. 112586;
7a, lateral view; 7b, suture line. Scale bars are 1 cm unless otherwise stated.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japanumbilicus, the present specimen is identified with Japonites
Raphaelis Zojae (Tommasi), especially very similar to thespecimen J. Raphaelis Zojae form 2 described by Welter(1915, p. 123, pl. 10, fig. 2, text-fig. 23) from Timor.
Occurrence.—Upper part (Fk-6) of the Fukkoshi Formation
at the eastern coast of Terahama, Togura, Minamisanriku
Towny, Miyagi Prefecture.
Japonites sp. A
Figures 7.6a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112587.
Descriptive remarks—A fragmental specimen, about
a quarter of one-volution, consists of phragmocone andbody chamber. It is evolute and discoidal, and its maximum
diameter is considered to exceeds 100 mm. The side isbroadly convex with rounded umbilical shoulder. The venter
is not well preserved. The maximum shell width is near theumbilical shoulder, and sides converge to the venter. The
shell surface is ornamented with low, but wide, radial ribs,
which run from the umbilical wall, bifurcate at the umbilicalshoulder, and run to the ventral shoulder. There are four
primary ribs per quarter whorl. The external suture ispreserved except for the ventral lobe. Three lateral saddles
are all serrated from lower to top. The first and second
saddles are nearly the same height. The first is narrow,
whereas the second is wide. The height of the third is about
a half of the second. The first lateral lobe is large and deep
with strong denticulations at the base. The lower part of itis slightly expanded. The depth of the second lobe, which
is denticulate as with the first, is about two-thirds of thefirst. There may be some auxiliary lobes near the umbilicalshoulder, but only a part is visible.
Based on the general shell shape and outline of thesuture line, the present specimen is considered to belong
to the genus Japonites. Bifurcate rib pattern of the present
specimen is unique for the genus Japonites, but it is not wellpreserved enough to propose a new species.
Occurrence.—Middle part (Fk-1b) of the Fukkoshi
Formation at the southern coast of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Japonites sp. B
Figures 7.1, 7.3, 7.4
Material examined.—Three specimens, IGPS coll. cat.
nos. 112665–112667.
Descriptive remarks—Three fragmental specimens areat hand. They are discoidal and sub-evolute. The maximum
shell diameter of the specimen no. 112665 exceeds 60 mm.
At the estimated diameter is ca. 65.0 mm, its corresponding

57

height and umbilical diameter are ca. 20, and ca. 28 mm(UD/D = 0.43), respectively, and at D = ca. 50.5 (about 180°
adapical from the preserved end) the height and umbilical
diameter are 17.2 and 19.3 mm (UD/D = 0.38), respectively.
Another specimen (no. 112666) is a fragment of about onethird of a whorl, the height of which is ca. 22 mm. They havenearly flat to very slightly convex side with acutely roundedumbilical and ventral shoulders. The venter probably
rounded, but not well preserved. The umbilicus is shallow.
There are low but prominent ribs on the shell surface. They
are substantially rectiradiate, but slightly rursiradiate andconvex, and run from umbilical shoulder to ventral shoulder,slightly strengthened to the venter. On the outer molds
there are also fine striae parallel to the ribs, although they
are rather obscure. There are nine to ten ribs per quartervolution (ca. 40 ribs per volution) of the whorl.
Specimen no. 112667 moderately large specimen,
about a half of outer volution and a part of inner volution ispreserved. It is discoidal and sub-evolute. The maximum
shell diameter probably attains about 80 mm, with thecorresponding height (estimated) and umbilical diameterare 30 and 31.0 mm (UD/D = 0.39), respectively. The sides
are nearly flat to very broadly convex with acutely roundedumbilical shoulder. The umbilical wall is steep. The venteris probably rounded with broadly rounded shoulder. The
maximum shell width is near the ventral shoulder and thesides slightly converge toward the umbilicus. On the shellsurface, there are 22–23 rectiradiate ribs per half volution.
They run from umbilical wall to the venter, strengthened to
the ventral shoulder.
The suture lines are only partly preserved and obscure in
all specimens. Preserved parts are the ventral side region of
the inner whorl in specimen no. 112665, the umbilical side
region in specimen no. 112666 and the ventral two-thirds
in specimen no. 112667. They are composed of the fully
serrated deep lobes and/or high saddles.
The present specimen is considered to belong to thegenus Japonites, based on the general shape of the suturelines and discoidal and sub-evolute shell shape. The surface
ornamentation is somewhat similar to that of Japonites
meridianus, but the specific identification is difficult becauseof their poor state of preservation.
Occurrence.—Two specimens (nos. 112665, 112666)
come from the middle part (Fk-1c) and one specimen(no. 112667) from the upper part (Fk-2a) of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Japonites sp. C
Figures 7.2a, bMaterial examined.—IGPS coll. cat. no. 112668.

58

Masayuki Ehiro

Descriptive remarks—A fragmental phragmocone, about
one-third to one-fourth of a volution, is at hand. It is discoidal
and sub-evolute. The diameter near the preserved end isestimated to be 80–85 mm, and its corresponding height
and umbilical diameter are ca. 30 and 28 mm (UD/D =0.33–0.35), respectively. The side is nearly flat with broadly
rounded ventral shoulder and acutely rounded umbilicalshoulder. The venter and umbilicus are not well preserved.
The maximum shell width is at the ventral shoulder and thesides slightly converge to the umbilicus. On the flanks there
are 13 to 15 fine ribs per quarter. They are rectiradiate andslightly concave, and run from the umbilical shoulder to theventral shoulder. Few ribs bifurcate at about ventral onethird. Fine striae parallel to the ribs are also seen.
The suture lines are obscure and only parts of narrowand high saddles are visible, although some parts are little
unreliable. They are fully serrated.
The present specimen is considered to belong to thegenus Japonites, based on the general shape of the suturelines and discoidal and sub-evolute shell shape. The
specific identification is difficult because of the poor state ofpreservation. It has finer and closely spaced ribs than theabove-described Japonites sp. B.
Occurrence.—From the middle part (Fk-1a) of the
Fukkoshi Formation at the south of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Subfamily Gymnitinae Waagen, 1895
Genus Buddhaites Diener, 1895bType species.—Gymnites (Buddhaites) rama Diener,
1895b.
Buddhaites? sp.
Figures 5.10a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112588.
Descriptive remarks.—Specimen attains a maximum
diameter of ca. 26.5 mm. It is discoidal and involute. The
umbilicus is not well preserved but its diameter is probably
less than 2 mm. The side is broadly convex with maximum
width at the center of the side. The umbilicus is shallow.
The venter, with broadly rounded ventral shoulder is notwell preserved but seems to be acutely rounded. The shellsurface seems to be smooth. The partly preserved external
suture line is ammonitic and resembles that of the family
Gymnitidae. The first lateral saddle (ventro-lateral saddle)
is wide and asymmetrical. Its ventral side, the enveloping
surface of which is gently inclined ventrally, has rather deep
secondary lobes.
Based on the shell morphology and the sutural outline,

the present specimen is considered to belong to the genus
Buddhaites Diener, 1895b, but there remains a question
about the generic assignment due to the poor state of thepreservation of the suture line.
Occurrence.—Middle part (Fk-1a) of the Fukkoshi
Formation at the southern coast of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Superfamily Danubitoidea Spath, 1951
Family Danubitidae Spath, 1951
Genus Danubites Mojsisovics, 1893
Type species.—Ceratites Floriani Mojsisovics, 1882.
Danubites cf. ambika Diener
Figures 8.1, 8.2
cf. D anubites ambika Diener, 1895b, p. 104, Pl. 29, figs.
2a–2c.
Danubites aff. ambika Diener, Bando, 1970, p. 347, pl.
38, fig. 1.
Material examined.—Three specimens, IGPS coll. cat.
nos. 112589, 112590, 112669.
Descriptive remarks.—Specimens are discoidal andevolute. Conch is slowly increasing in height and shallowly
embracing the preceding whorls. The maximum shell
diameter of specimen no. 112589 exceeds 35 mm, and at
the diameter of 34.9 mm, the corresponding height andumbilical diameter are 10.7 (H/D = 0.29) and 16.2 mm(UD/D = 0.46), respectively. The maximum diameter of thespecimen no. 112590 exceeds 45 mm, and at a diameterof 44.9 mm the ratios of H/D and UD/D are 0.32 and 0.43,
respectively. The maximum diameter of the specimen no.
112669 is 47.8 mm, with the corresponding height andumbilical diameter are 17.2 (H/D = 0.36) and 18.2 mm (UD/D = 0.38), respectively. The sides are broadly convex tonearly flat and sometimes slightly concave in the outer part.
The umbilical and ventral shoulders are acutely rounded.
The venter is not well preserved, but seems to be flat toslightly convex. The umbilicus is shallow. The shell surface
is ornamented with strong, rectiradiate ribs, which run fromumbilical shoulder to near the ventral shoulder and fade out.
They become widened forward. There are 28-29 (specimen
no. 112589) or about 34 (no. 112590, 112669) ribs on thelast whorl. The suture is only preserved in specimen no.
112669. Three lateral saddles and two lateral lobes areobserved. The crests of saddles are all rounded. The second
is highest and the third is small. The first lateral lobe is wideand deep, with parallel sides and denticulate base. The
second lobe has similar shape as the first, but small in size.
The present specimens resemble Danubites ambika

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan

59

Figure 8. D anubites and Paradanubites from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt,
Northeast Japan.
	1–2, Danubites cf. ambika Diener; 1, IGPS coll. cat. no. 112669 ; 1a, lateral view, 1b, suture line; 2, IGPS coll.
cat. no. 112590, lateral view; 3–6, Danubites floriani (Mojsisovics); 3, IGPS coll. cat. no. 112591; 3a, lateral view;
3b, suture line; 4, IGPS coll. cat. no. 112592, lateral view; 5, IGPS coll. cat. no. 112593, lateral view; 6, IGPS coll.
cat. no. 112594; 6a, lateral view; 6b, suture line; 7–9, Danubites cf. tozeri Korchinskaya; 7, IGPS coll. cat. no.
112595; 7a, lateral view; 7b, suture line; 8, IGPS coll. cat. no. 112596; 8a, lateral view; 8b, suture line; 9, IGPS
coll. cat. no. 112597, lateral view; 10–12, Paradanubites ozashiense sp. nov.; 10, IGPS coll. cat. no. 112605; 10a,lateral view; 10b, suture line; 11, IGPS coll. cat. no. 112604; 11a, lateral view; 11b, suture line; 12, IGPS coll. cat.
no. 112603 (holotype); 12a, lateral view; 12b, suture line. Scale bars are 1 cm unless otherwise stated.

Diener from the lower Anisian of Himalayas (Diener, 1985b)
and Danubites aff. ambika Diener from the late Olenekian
Osawa Formation (Bando, 1970), especially the latter, inhaving evolute shell with rather flat sides and rather coarse
ribbing. But its precise comparison is difficult, because
present specimens are poorly preserved. As stated in thepreceding chapter, there is some doubt on the stratigraphic
position of Bando’s specimen. The present author considers
that it may come from the Fukkoshi Formation.
Occurrence.—All specimens from the middle part (Fk1a) of the Fukkoshi Formation at the southern coast of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi

60

Masayuki Ehiro

Prefecture.
Danubites floriani (Mojsisovics)
Figures 8.3–8.6

Table 2. D imensions (in mm) and ratios of Danubites
floriani (Mojsisovics) from the Fukkoshi Formation.
Abbreviations see Table 1.

Celtites Floriani Mojsisovics, 1882, p. 145, pl. 28, figs. 5–7,
pl. 31, fig. 4.
Danubites Floriani Mojsisovics, 1893, p. 398; Spath, 1951, p.
13.
Florianites floriani Hyatt, 1900, p. 553.
Material examined.—Four specimens, IGPS coll. cat. nos.
112591–112594.
Description.—Specimens are slightly deformed obliquely
and flattened laterally. The shell is composed of thephragmocone and body chamber, the latter occupies about
a half of the last whorl. The specimens are moderately
evolute. The maximum shell diameter ranges from 24.5 to
39.0 mm, with the ratios of H/D and UD/D are 0.31–0.40 and
ca. 0.37, respectively (Table 2). The exact shell width is notknown, but, judging by the preserved half part, the maximum
width of specimen no. 112591 is ca. 8 mm. The sides andventer are both broadly rounded and the umbilicus is rather
deep with steep umbilical wall. Both umbilical and ventral
shoulders are gradual. The maximum shell width is at thecenter of the side, and therefore, the shell cross section
is nearly circular, although it is suffered from tectonic
flattening. The shell surface is ornamented with simple,
rectiradiate to slightly rursiradiate ribs, which are slightly
strengthened to the venter and fade out before the venter.
On the last whorl there are 26 to 30 ribs
The ventral lobe is not preserved. The large first laterallobe is deep with nearly parallel sides and the base of it
has many denticulations. The second lateral lobe is smaller
remarkably than the first and trifurcates at the base, themiddle branch of which is the deepest. There are threerounded saddles on the side and the second is the widest.
Comparison.—The present specimens from the Fukkoshi
Formation closely resemble Danubites floriani (Mojsisovics,
1882) (originally described as Celtites Floriani) from theMiddle Triassic of Austria in the shell shape, surface
ornamentation and sutural trace. The ratio of UD/D of theAustrian specimens ranges from 0.32 to 0.45, increasing as
the diameter increase, and those of the present specimens
are in this range. The number of ribs of the former is slightly
larger than those of the latter, but almost the same. The
lateral suture line of the Mojsisovics (1882)’s specimen(figured in pl. 31, fig. 4 ; at about 39 mm in shell diameter)is almost similar to that of the present specimen. The both
specimens have the large and deep first lateral lobe withdenticulate base and trifurcated small second lateral lobe.
Both second saddles are wider than the first.

Occurrence.—Middle part (Fk-1a: nos. 112591, 112592;
Fk-1b: nos. 112593, 112594) of the Fukkoshi Formation at
the southern coast of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Danubites cf. tozeri Korchinskaya
Figures 8.7–8.9
cf. D anubites tozeri Korchinskaya, 1982, p. 60, pl. 16, figs.
7–9, text-figs. в, г; Vavilov and Arkadiev, 1986, p. 41, pl. 3,
fig. 3, text-fig. 3a.
Material examined.—Three specimens, IGPS coll. cat.
nos. 112595–112597.
Descriptive remarks—The specimens are compressed andsub-evolute. It consists largely of phragmocone with a partof the living chamber. The shell diameter of the preserved
end of no. 112595 is 36.4 mm with the correspondingheight and umbilical diameter of 13.2 and 15.0 mm(UD/D = 0.41), respectively. At the diameter of ca. 32 mm,
the height and umbilical diameter are 11.4 and 14.2 mm(UD/D = 0.44), respectively. The shell diameter of no. 112596
exceeds 35 mm in the deformed state. At the diameter ofca. 28.5 mm, about 60° adapical from the preserved end,
the corresponding height and umbilical diameter are ca. 9.0(H/D = 0.32) and 12.7 mm (UD/D = 0.45), respectively. At
about 180° adapical from the preserved end (D = ca. 29mm), height and umbilical diameter are 11.8 and 11.5 mm(UD/D = 0.40), respectively. No. 112597 exceeds 35 mm indiameter and the ratio of UD/D is ca. 0.41.
The side are broadly convex and the maximum width isabout the center of the side. The steeply dipping umbilicalwall is low but distinct with rounded umbilical shoulder.
The ventral shoulder is rounded but the venter is not wellpreserved. The shell surface is ornamented with slightly
rursiradiate, straight, coarse ribs, running from the umbilicalwall to the ventral shoulder. The ribs are slightly broadened
to the ventral shoulder, but seem to not cross the venter.
There are 24 to 26 ribs per volution.
The ventral lobe is not preserved. There are three

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
rounded saddles on the lateral side. The second saddle iswidest and the third is small. The first lateral lobe, having
subparallel smooth sides, is wide and deep, and the basehas four denticulations. The second lobe is small and bi- or
tri-furcate. The auxiliary lobe is not seen.
The general shell shape, coarse ribbing and outline of
the suture line of the present species resembles to thoseof Danubites tozeri Korchinskaya reported from the lower
Anisian of Svalbard (Korchinskaya, 1982) and eastern
Taimyr (Vavilov and Arkadiev, 1986). But the present forms
differ from the latter two in having oval cross section insteadof sub-square to sub-rectangular, and in having slightly
rursiradiate ribs.
Occurrence.—Middle part (Fk-1a: no. 112595, 112597;
Fk-1b: no. 112596) of the Fukkoshi Formation at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Genus Paradanubites Shevyrev, 1968
Type species.—Ceratites (Danubites) kansa Diener, 1895b.
Paradanubites kansa (Diener)
Figures 9.1–9.3
Ceratites (Danubites) kansa Diener, 1895b, p. 103, pl. 29,
fig. 1.
Ceratites (Florianites) kansa (Diener), Diener, 1907, p. 70,
pl. 5, fig. 5.
Danubites kansa Diener, Diener, 1915, p. 116 ; Arkell et al.,1957 , p. 154, fig. 186.6.
Paradanubites kansa (Diener), Shevyrev, 1968, p. 123 ; Heet al., 1986, p. 228, pl. 5, figs. 22–30, text-figs. 26c, 26f.
Material examined.—Three specimens, IGPS coll. cat.
nos. 112598–112600.
Description.—The compressed shell of no. 112598 ismoderately evolute. It consists of phragmocone and bodychamber, and the latter occupies the about 3/4 of thepreserved last whorl. The maximum shell diameter is about
77 mm and corresponding height and umbilical diameterare ca. 32.0 (H/D = 0.42) and 28. 2 mm (UD/D = 0.37),
respectively. The ratios of UD/D of the inner volutions areslightly small (0.35–0.34). The cross section of the shellis elongated oval with convex sides and acutely rounded
venter. The umbilical wall is steep with rounded umbilicalshoulder. The ventral shoulders are broadly rounded. The
maximum shell width is near the center of the flanks, but
at the preserved end it is near the center, but a little to theventer. The shell surface is ornamented with strong radialribs. They run from the umbilical wall, become thickening
slightly, to the ventral shoulder and fade out. There are 34

61(inner whorl) to 39 (last whorl) ribs per volution. The venteris smooth.
Other two specimens are fragmental. Specimen no.
112599 is a phragmocone, the diameter of which attains 48.8mm and the ratio of UD/D is 0.42. On the last whorl, there
are 34-35 radial ribs per volution. Specimen no. 112600
consists probably phragmocone and body chamber and its
maximum diameter attains 40 mm, but it is ill preserved. It
has 17-18 ribs per half volution.
The external lateral suture of no. 112598 consists of threerounded saddles and serrated lobes. The ventral lobe is
not preserved. The first lateral lobe is very large and deep
with sides slightly widened toward the base. The base of itis strongly serrated with deep denticulations and the lower
half of the sides are also serrated. The second lobe is small
and its base tri-furcate remarkably. The small auxiliary lobe
has two denticulations. The first lateral saddle is narrow, thesecond is high and wide and the third is small. The externallateral suture of no. 112599 has deep and denticulate firstlateral lobe, narrow second lateral saddle, small second lobe
with four denticulations and small auxiliary lobe having two
small denticulations.
Comparison .—The general shell shape, surface
ornamentation and suture line of the present specimen are
all very similar to those of the holotype of Paradanubites
kansa (Diener).
Occurrence.—Middle part (Fk-1a: nos. 112598, 112599;
Fk-1b: no. 112600) of the Fukkoshi Formation at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Paradanubites cf. kansa (Diener)
Figures 9.4, 9.5
Synonym list compared see above.
Material examined.—Two specimens, IGPS coll. cat. nos.
112601, 112602.
Description.—Two large, discoidal and subevolute
specimens are at hand. One specimen, no. 112601, consistsof about two-thirds of inner volutions and a fragmental outerone. Its maximum diameter probably exceeds 120 mm.
The body chamber occupies over one volution. The ratio of
UD/D is estimated to be about 0.40. Sides are nearly flatto broadly convex with maximum width at the center of theside. The umbilical shoulder is broadly rounded and low wallis steeply dipping. The venter is probably acutely rounded,though it is not well preserved, with rounded shoulder. The
shell surface is ornamented with radial ribs, which run fromthe umbilical wall to ventral shoulder. There are 15–16 ribs
per half volution on the inner whorl. The ribs rarely bifurcate
near the umbilical shoulder.

62

Masayuki Ehiro

Figure 9. Paradanubites from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1–3, Paradanubites kansa (Diener); 1, IGPS coll. cat. no. 112598; 1a, lateral view; 1b, suture line; 2, IGPS
coll. cat. no. 112599; 2a, lateral view; 2b, suture line; 3, IGPS coll. cat. no. 112600, lateral view; 4 and 5;
Paradanubites cf. kansa (Diener); 4, IGPS coll. cat. no. 112601; 4a, lateral view; 4b, suture line; 5, IGPS coll. cat.
no. 112602; 5a, lateral view; 5b, suture line; 6–8, Paradanubites phyllus He; 6, IGPS coll. cat. no. 112606; 6a,lateral view; 6b, suture line; 7, IGPS coll. cat. no. 112607; 7a, lateral view; 7b, suture line; 8, IGPS coll. cat. no.
112608; 8a, lateral view; 8b, suture line; 9–11, Paradanubites sp.; 9, IGPS coll. cat. no. 112610, lateral view; 10,
IGPS coll. cat. no. 112611, lateral view; 11, IGPS coll. cat. no. 112612, lateral view. Scale bars are 1 cm unlessotherwise stated.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
Another specimen, no. 112602, is fragmental and aquarter of the shell is preserved. Its diameter probably
reaches 80 mm. The side is nearly flat with acutely roundedumbilical and ventral shoulders. The umbilicus is shallow.
On the shell surface there are rectiradiate ribs, about 12 perquarter (about 40 per volution) on the outer whorl.
The external suture lines are both partly preserved,
although somewhat deformed. They consist of three narrowsaddles, having rounded crests, and large and wide firstlobe, small and shallow second lobe, and small auxiliaries
near the umbilical margin. The base of the first lateral lobe
has three deep denticulations and short denticulations
extend up to the both sides, gradually diminishing in size.
The second lobe also deeply denticulate at the base, but the
number of denticulations is rather small: three to five? in no.
112601 and three in no. 112602.
Comparison .—The general shell shape, surface
ornamentation and suture line of the present specimen
are similar to those of Paradanubites kansa (Diener). But
their shell sizes are larger than the known specimens of P.
kansa and the details of the suture line somewhat differ fromeach other. Then, it is difficult to identify them with P. kansa
definitely.
Occurrence.—Middle part (Fk-1b) of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Paradanubites ozashiense sp. nov.
Figures 8.10–8.12
Material examined.—Three specimens, IGPS coll. cat.
nos. 112603 (holotype), 112604 and 112605 (paratypes).
Etymology.―The species name is from the geographic
name “Ozashi” near the fossil locality.
Diagnosis.—Paranubites having rursiradiate, convex,
coarse ribs, the width and interspaces of them are somewhat
irregular. The shell is moderately evolute with oval crosssection. The umbilical side of the second lateral lobe issmooth.
Description.—Three specimens, slightly deformed
obliquely and flattened laterally, are at hand. They consistof the phragmocone and body chamber, the latter occupies
at least a half volution. The specimens are compressedand sub-evolute. The sides are broadly convex with acutely
rounded umbilical shoulder and broadly rounded ventral
shoulder. The maximum shell width is at about the centerof the flank. The venter is probably rounded. The umbilicus
is shallow, but with steep wall. The shell cross section iselongated oval. In holotype specimen, the maximum shell
diameter attains ca. 51.0 mm, and corresponding height
and umbilical diameter are 16.7 (H/D = 0.35) and 18.5 mm(UD/D = 0.39), respectively. In specimen no. 112604, the63

maximum shell diameter is ca. 48 mm, with ratios of H/Dand UD/D are 0.35 and 0.39, respectively. Specimen no.
112605 attains a diameter of 33.5 mm and ratios of H/D and
UD/D are 0.37 and 0.31, respectively. The shell surface isornamented with slightly rursiradiate, convex ribs. They aresimple and run from the umbilical wall, slightly strengthening
to the venter, and reach to the venter. It is uncertain whether
they cross the venter or not, because the venter is not fully
preserved. The width of ribs and the width of interspaces
are rather irregular and partly associated with very fine ribs.
On the last whorl there are 39–40 (no. 112603) or 34–35 (no.
112604, 112605) primary ribs.
The ventral lobe is not fully preserved and only a part of
one denticulate prong is visible. The depth is about twothirds of that of the first lateral lobe. The first lateral lobe is
deep with laterally expand sides and the outline of the lobe
is ellipse. There are numerous strong denticulations on
the base of it and shallow denticulations extend upwards,
reducing in size, to two-thirds of the sides. The second
lateral lobe is small and asymmetrical. The ventral side
is long and serrated from the base to near the top, but
the umbilical one is short and smooth. The auxiliary lobe
is simple. All saddles have rounded crest. The second is
widest and the first is rather elongated vertically.
Comparison.—The present new species is easily
distinguished from other species of the genus Paradanubitesin having small number of ribs, which are rursiradiate andhave rather irregular widths and interspaces, and in having
asymmetrical second lateral lobe.
Occurrence.—Middle part (Fk-1b) of the Fukkoshi
Formation at the southern coast of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Paradanubites phyllus He
Figures 9.6–9.8
Paradanubites phyllus He in He et al., 1986, p. 231, pl. 6,
figs. 22–29, text-figs. 26d, 26e.
Material examined.—Four specimens, IGPS coll. cat. nos.
112606–112609.
Description.—The shell is compressed and sub-evolute.
The shell dimeter ranges from 42 to 55 mm, and the ratioof UD/D ranges 0.37 to 0.42. The flanks are broadly convex
with rounded umbilical and ventral shoulders. The crosssection of the shell is elongated oval and the maximum
shell width is at the center to ventral one-thirds of the flanks.
The venter is not well preserved. The umbilicus is shallow.
The shell surface is ornamented with sharp ribs, which arerectiradiate and straight, but sometimes slightly concave.
They run from the umbilical wall, become thickening slightly,
to the ventral shoulder and fade out. There are 40 to 46 ribs

64

Masayuki Ehiro

per volution.
The external lateral suture consists of three roundedsaddles and serrated lobes. The ventral lobe is notpreserved. The first lateral lobe is very large. Its sides
expand laterally and the outline of the lobe is sub-circular.
The base of it is strongly denticulate and the denticulations
extend up to the two-thirds of sides. The outline of thesecond and probably third lateral lobes are similar to thefirst, but small and shallow. All lateral saddles have small,
sub-circular crest.
Comparison .—The general shell shape, surface
ornamentation and suture line, especially the external lateral
suture line of the present specimens are very similar to
those of Paradanubites phyllus He in He et al., 1986.
Occurrence.—Middle part (Fk-1a: of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Paradanubites sp.
Figures 9.9–9.11
Material examined.—Three specimens, IGPS coll. cat.
nos. 112610–112612.
Descriptive remarks.—The shell is compressed and subevolute. The shell dimeter exceeds 50 mm. The ratio of
UD/D is 0.40-0.42 in specimen no. 112611 at D = ca. 40
mm, and ca. 0.32 in specimen no. 112610 at D = ca. 70
mm. The flanks are broadly convex with rounded umbilicaland ventral shoulders. The maximum shell width is near thecenter of the flank. The venter is not well preserved. The
umbilicus is shallow. The shell surface is ornamented withstrong rectiradiate ribs. They run from the umbilical wall,
become thickening slightly, to the ventral shoulder and fadeout. In specimen no. 112610, faint striae or growth lines also
run parallel to the ribs. There are 40 to 45 ribs per volution.
The suture is not preserved.
Based on the general shell shape and surface
ornamentation, the specimens are considered to belong to
the genus Paradanubites, and they somewhat resemble
Paradanubites phyllus He. But I refrain from identifying themat the specific level since no suture line is preserved.
Occurrence.—Middle part (Fk-1a) of the Fukkoshi
Formation at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Family Longobarditidae Spath, 1951
Subfamily Groenlanditinae Assereto, 1966
Genus Groenlandites Kummel, 1953
Type species.—Groenlandites nielseni Kummel, 1953.
Groenlandites sp.

Figures 9.1a, bMaterial examined.—A specimen, IGPS coll. cat. no.
112613.
Descriptive Remarks.—A fragmental conch, about a halfof a volution, is compressed and involute. The maximum
shell diameter is ca. 23.0 mm and corresponding height andumbilical diameter are ca. 11.0 (H/D = 0.48) and ca. 2.0 mm(UD/D = 0.09), respectively. The maximum shell width is at
the umbilical third to the central part of the side. The shell islaterally flattened tectonically and, in the deformed state, themaximum width is estimated larger than 6 mm. The sides
are slightly convex with rounded ventral shoulder and theventer is rounded. The shell surface seems to be almost
smooth.
The external lateral suture consists of five saddles andlobes. The ventral lobe is not preserved. The first lateral lobe
is widest and deepest with strongly denticulate base. The
second and third lobes, become narrower and shallower
than the first, also have denticulate bases. The bases of the
fourth and fifth lobes seem to be smooth. All saddles haverounded crests and become smaller to the umbilicus.
Based on the general shell outline and the shape of thesuture, the present specimen is considered to belong to thegenus Groenlandites Kummel, but the specific identification
is difficult due to their poor state of preservation.
Occurrence.—Middle part of the Fukkoshi Formation(Fk-1a) at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Genus Lenotropites Popov, 1961
Type species.—Lenotropites solitarius Popov, 1961.
Lenotropites spp.
Figures 9.2, 9.3
Material examined.—Two specimens, IGPS coll. cat. nos.
112614, 112615.
Descriptive Remarks.—Two small specimens, the conchof which are compressed and involute to sub-involute,
are at hand. The smaller one (no. 112614) consists ofphragmocone and body chamber, the latter occupies
more than a half volution. It attains a maximum diameterof ca. 18.5 mm (at -60° from the preserved end) in theelliptically deformed state. Its corresponding height andumbilical diameter are ca. 9.0 and ca. 3.5 mm (UD/D =0.19), respectively. The sides are broadly convex with the
maximum width near the center of the side. The shell crosssection is oval with broadly rounded umbilical shoulder
and rounded ventral shoulder. The venter may be rounded.
The umbilicus is shallow. Shell surface is ornamented with

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
sigmoidal faint ribs or growth lines.
The other specimen (no. 1126105) is also elliptically
deformed and composed of phragmocone and bodychamber. The body chamber reaches more than a volution.
The maximum shell diameter is 25.8 mm (at -30° from thepreserved end), and its corresponding height is 14.9 mm.
The umbilicus is almost closed. The sides are broadly
convex with rounded umbilical and broadly rounded ventral
shoulders. The maximum width is near the umbilicalshoulder to a little on the outer part, and the sides converge
to the venter. The venter is probably rounded. Shell surface
is ornamented with sigmoidal, low, faint ribs and/or growthlines.
In the both specimens the ventral suture are notpreserved. In specimen no. 112614 the lateral suture
consists probably of five set of saddle and lobe. The
rounded saddles diminish in size towards the umbilicus.
The first and second lateral lobes are deep with parallelsides and serrated base. The rest are small and shallow,
and their bases are probably rounded. The lateral suture of
the specimen no. 112615 consists of four saddles and at
least three, probably four lobes. The crests of saddles are
all rounded. The first one is the highest and the second to
fourth are gradually diminish in their size. The first laterallobe is large and deep with parallel sides. Its base is strongly
denticulate. The second has a similar shape to the first but
smaller in size. The third is small and simple.
Although two specimens slightly differ from each other inshell morphology and sutural traces, based on their generalshell morphology and the shape of the suture line, they
are considered to belong to the genus Lenotropites Popov,
1961. But it is difficult to identify them at the specific level
because of their poor state of preservation.
Occurrence.—Both from the middle part of the Fukkoshi
Formation (Fk-1b) at the south of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Subfamily Longobarditinae Spath, 1951
Genus Grambergia Popov 1961
Type species.—Grambergia taimyrensis Popov, 1961.
Grambergia cf. tetsaensis McLearn
Figures 9.4–9.8
cf. G rambergia tetsaensis McLearn, 1969, p. 36, p1. 7, figs.
1–5, text-fig. 15; He et al., 1986, p. 210, pl. 11, figs. 23–
25, 31–33, text-fig. 15a; Tozer, 1994, p. 101, pl. 43, figs.
3, 4, pl. 44, figs. 3, 4, 10, text-figs. 31c, d.
Material examined.—Five specimens, IGPS coll. cat. nos.
112616–112620.

65

Description.—The specimens are small, ranging theirmaximum shell diameters from ca. 21 mm to ca. 32 mm.
They are compressed with almost flat sides and very
involute with the ratios of UD/D = 0.08–0.13. The specimen
no. 112617 and 112619 have acutely rounded to acuteventral shoulder. In the specimen no. 112618, there is a faintspiral ridge near the venter on the flank, which probably
corresponds to the ventral shoulder. The surface of the shellis almost smooth, but in the specimen no. 112618, somefaint sigmoidal growth lines are present.
The external suture lines consist of shallow ventral lobe,
deep and wide first lateral lobe and following 3–4 lobes androunded saddles, but they vary in detail among specimens.
The ventral lobe of the specimen no. 112616 is shallow anddivided into serrated prongs by low, rounded median saddle.
The first lateral lobe is widest and deepest with remarkabledenticulation at the base. The second to fourth lateral lobes
are also denticulate, but become considerably shallower andsmaller than the first. The small fifth lobe is V-shaped andthere is probably an additional lobe at the umbilical shoulder.
All lateral saddles are rounded. The ventral lobes of otherspecimens are also shallow and divided into two prongs, but
their precise shapes are not seen. The second lateral lobesof the specimens no. 112617 and 112618 bear denticulations
at the base, whereas that of specimen no.112619 seems tobe smooth, and the following lobes have smooth bases.
Discussion.—Based on their general shell shapes, havingvery compressed, nearly flat, smooth sides, and suture lines
with shallow ventral lobe, considerably deep first laterallobe and following 4–5 lobes, the present specimens are
considered to belong to the genus Grambergia Popov 1961.
They closely resemble Grambergia tetsaensis McLearn,1969 in having deep first lateral lobe and high second
saddle, but the precise identification is difficult due to thepoor state of preservation and small size.
Occurrence.—Middle part of the Fukkoshi Formation (Fk1a: nos. 112616–112618; Fk-1b: no. 112619; Fk-1c: no.
112620) at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Subfamily Czekanowskitinae Tozer, 1994
Genus Arctohungarites Diener, 1916 b
Type species.—Hungarites triformis Mojsisovics, 1886.
Arctohungarites sp.
Figures 11.1–11.3
Material examined.—Three specimens, IGPS coll. cat.
nos. 112621–112623.
Descriptive remarks.—Three more or less fragmental,
imperfect specimens are at hand. The shell is compressed

66

Masayuki Ehiro

and involute. Specimen no. 112621 consists of phragmocone
and body chamber, but their boundary is not well known.
The shell diameter exceeds 55 mm and estimated ratio of
UD/D is ca 0.16. Specimen no. 112622 is a fragment of ashell having small umbilicus. Specimen no. 112623 attains
a maximum diameter of ca. 59.0 mm, and its correspondingheight and umbilical diameter are ca. 25.0 and 19.0 mm(UD/D = 0.32), respectively. The sides of the specimens arebroadly convex, the maximum width of which is at about thecenter of the side. The venter is probably acutely roundedwith rounded ventral shoulder. The umbilicus is shallow
and its shoulder is acutely rounded. The shell cross sectionis thin lenticular, although its compressed shell shape ispartly due to the tectonic deformation. The shell surface isornamented with widely spaced, low and slightly sinuous
ribs, which run from the umbilical shoulder to near theventral shoulder. There are 12-13 ribs per half volution.
The poorly preserved external suture line consists of large
and rounded first lateral saddle, large and deep first laterallobe, the base of which is denticulate, second roundedsaddle, medium-sized, serrated second lateral lobe, smallrounded third saddle, small third lateral lobe and small
fourth lateral saddle. The base of the third lobe is not wellobserved.
Based on the general shell shape, surface ornamentationand outline of external suture line, the present specimens
are considered to belong to the genus Arctohungarites
Diener, 1916b with high probability. But it is difficult to
identify them at the specific level because of their poor stateof preservation.
Occurrence.—All from the middle part of the Fukkoshi
Formation (Fk-1b) at the south of Ozashi, Jusanhama,
Kitakami-cho, Ishinomaki City, Miyagi Prefecture.
Longobarditidae? gen. and sp. indet.
Figure 9.10
Material examined.—One specimen, IGPS coll. cat. no.
112624.
Descriptive Remarks.—A small specimen is at hand. It
is compressed and involute. The conch attains about 14.0mm in diameter and the corresponding umbilical diameteris 2.8 mm (UD/D = ca. 0.20). The sides are convex andthe venter is probably carinate or acutely rounded without
remarkable ventral shoulder. The shell surface has rather
strong, sinuous ribs. They run from the umbilical shoulder tothe ventral one-fourth, with maximum height at the center ofthe side, and fade out. There are 25 ribs per volution. The
suture is not preserved.
The general shell outline and its rib pattern of the present
specimen are somewhat similar to those of Groenlandites
silberlingi Tozer, 1994. But the present specimen is so smallin size, poor state of preservation and lacks suture line.
Moreover, some species belong to the longobarditid genera,such as Lenotropites Popov, 1961 and Intornites Assereto,
1966, have similar shell shape and ornamentation in theirearly ontogenetic stages.
Occurrence.—Middle part of the Fukkoshi Formation(Fk-1b) at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Superfamily Arcestoidea Mojsisovics, 1875
Family Cladiscitidae Zittel, 1884
Subfamily Procladiscitinae Gamsjäger, 1982
Procladiscites Mojsisovics, 1882
Type species.—Procladiscites broncoi Mojsisovics, 1882.
Procladiscites brancoi Mojsisovics
Figures 11.4–11.6
Procladiscites broncoi Mojsisovics, 1882, p. 114, pl. 48, figs.
1–2 ; Arthaber, 1896, p. 85; 1915, p.175, pl. 5, fig. 8; He etal., 1986, p. 233, pl. 18, figs. 6–16, 20–22, text-figs. 28a–b; Germani, 1997, p. 288, pl. 3, figs. 2a–b, text-fig. 11.
Procladiscites brancoi Mojsisovics var., Salopek, 1911, p.
24, pl. 2, figs. 3a–b.
Procladiscites cf. yasoda Diener, Welter, 1915, p. 112, pl. 9,
fig. 4.
Material examined.—Three specimens, IGPS coll. cat.
nos. 112625–112627.
Description.—Two specimens (specimens no. 112625 andno. 112627) are side of the conch and the rest (no. 112626)
is a fragment of the venter. The conch is compressed andinvolute with almost closed umbilicus. The sides are slightly
convex with maximum width at half height of the whorl.
The umbilical shoulder is rounded. The venter is not wellpreserved, but seems to be acutely rounded to rounded. The
shell surface is ornamented with numerous spiral striae.
The lateral suture consists of phylloid and terminatedlateral saddles and denticulate ptychitid lateral lobes. The
ventral lobe, only preserved in the fragmental specimen(no. 112626), is divided into two prongs by a moderately
high median saddle. The base of the prong has two deep
denticulations. The crests of first three lateral saddles aresemi-triangular. The second lateral saddle is the highest andthen saddles are become smaller to the umbilicus. There areat least six, probably eight to nine, lateral lobes. The basesof these lobes are deeply denticulate. The second laterallobe is the largest and deepest, and the third has about ahalf depth of the second and following ones become smaller
to the umbilicus.
Discussion.—Based on the general shell shape andEarly Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan

67

Figure 10. Groenlandites, Lenotropites, Grambergia and Longobarditidae? gen. and sp. indet. from the Fukkoshi Formationin the Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1, Groenlandites sp., IGPS coll. cat. no. 112613; 1a, lateral view; 1b, suture line; 2 and 3, Lenotropites sp.; 2,
IGPS coll. cat. no. 112614; 2a, lateral view; 2b, suture line; 3, IGPS coll. cat. no. 112615; 3a, lateral view; 3b,
suture line; 4–8, Grambergia cf. tetsaensis McLearn; 4, IGPS coll. cat. no. 112616; 4a, lateral view; 4b, sutureline; 5, IGPS coll. cat. no. 112617; 5a, lateral view; 5b, suture line; 6, IGPS coll. cat. no. 112618; 6a, lateral view;
6b, suture line; 7, IGPS coll. cat. no. 112619; 7a, lateral view; 7b, suture line; 8, IGPS coll. cat. no. 112620,
lateral view; 9, Longobarditidae? gen. and sp. indet., IGPS coll. cat. no. 112624. Scale bars are 1 cm unlessotherwise stated.
surface ornamentation, the present species is well identified
with Procladiscites broncoi Mojsisovics, 1882. They differ
only in details of the median saddle of the ventral lobe:
The sides of it is simple in the holotype, but serrated in the
Fukkoshi specimen. Welter’s (1915) specimen from Timor
has similar serrated median saddles. P. towaensis (Bandoand Ehiro) (originally described as Eosturia towaensis
Bando and Ehiro, 1982) from the uppermostpart of theunderlying Osawa Formation is somewhat similar to thepresent species in the general shape of the suture line, but
clearly distingished by having lateral ribs along the ventral
margin.
Occurrence.—Middle part of the Fukkoshi Formation (Fk1a: nos. 112625, 112626; Fk-1b: no. 112627) at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.

68

Masayuki Ehiro
Procladiscites sp.
Figure 11.7

Material examined.—IGPS coll. cat. no. 112628.
Descriptive remarks.—Two fragments of lateral part and
one fragment of ventral part, yield adjoining each other, areat hand. It is unclear whether they are parts of the same
individual or not. The largest fragment consists of flat flankwith the umbilical margin, which is slightly depressed gently.
It attains more than 70 mm in height, and the umbilicus
is rather small, probably less than 15 mm. Another small
fragment of a part of a flank is also flat and more than 30
mm in height. The ventral fragment has broadly rounded
venter and apparent shell width attains more than 27
mm. The shell surface of both the venter and flank areornamented with numerous spiral striae. The suture is notpreserved.
Although the specimens are fragmental, based on theestimated shell shape and surface ornamentation thepresent species is considered to belong to the genus
Procladiscites. The specific identification, however, is difficult
because of the poor state of preservation.
Occurrence.—Middle part of the Fukkoshi Formation(Fk-1b) at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Order Phylloceratida Zittel, 1884
Superfamily Ussuritoidea Hyatt, 1900
Family Palaeophyllitidae Popov, in Luppov and Drushchits,
1958
Genus Leiophyllites Diener, 1915
Type species.—Monophyllites suessi Mojsisovics, 1882.
Leiophyllites cf. confucii (Diener)
Figure 12.1
cf. M onophyllites Confucii Diener, 1895b, p. 107, pl. 30, fig.
7, pl. 31, figs. 1, 2; Diener. 1907, p. 107, pl. 13, fig. 10;
Arthaber, 1915, p. 151, pl. 13, fig. 6.
Monophyllites cf. suessi Toula, 1896, p. 171, pl. 20, fig. 7.
Monophyllites (Leiophyllites) confucii (Diener), Frech,
1903, p. 17, fig. 4; Diener, 1915, p. 205.
Monophyllites (Monophyllites) confucii Diener, Diener,
1907, p. 103, pl. 13, fig. 10.
Leiophyllites confucii (Diener), Wang et al., 1979, p. 53,
pl. 14, figs, 9, 10, text-fig. 30a.
Leiophyllites visendus Shevyrev, 1968, p. 113, pl. 6, fig. 2,
text-fig. 26.
Leiophyllites taramelti (Martelli), 1906, p. 135, pl. 6, figs.
3-4.

Material examined.—One specimen, IGPS coll. cat. no.
112529.
Descriptive remarks.—Small specimen is extremely
discoidal and evolute to very evolute, with slowly increasing
whorls. Specimen attains a diameter of ca. 17.0 mm, andits corresponding height and umbilical diameter are ca. 4.0(H/D = 0.24) and 10.0-10.5 mm (UD/D = ca. 0.60),
respectively. The sides are broadly convex and the
maximum shell width is at the center of the flanks. The
umbilical and ventral shoulders are rounded. The umbilicus
is very shallow. The venter is not well preserved. Suture is
not preserved.
Based on in its shell shape, especially having large
umbilicus and slowly increasing height, the present species
resemble to Leiophyllites confucii (Diener) describedfrom Himalayas and eastern Europe. But, the precise
identification at the specific level is difficult because it lacks
suture line.
Occurrence.—Upper part (Fk-5) of the Fukkoshi Formation
at the eastern coast of Terahama, Togura, Minamisanriku
Towny, Miyagi Prefecture, Miyagi Prefecture.
Leiophyllites pitamaha (Diener)
Figures 11.2–11.7
Monophyllites pitamaha Diener, 1895b, p. 107, pl. 31, figs. 5,
7, 8.
Xenodiscus middlemissi Diener, 1895b, p. 110, pl. 30, fig. 6.
Monophyllites (Leiophyllites) pitamaha (Diener), Diener,
1915, p. 205; Kutassy, 1932, p. 595; Mitrova and
Nestorovsky, 1960, p. 105, pl. 1, fig. 2.
Xenodiscus indo-australica Welter, 1915, p. 129, pl. 93, fig.
4.
Leiophyllites pitamaha (Diener), Spath, 1934, p. 297;
Shevyrev, 1968, p. 112, pl. 6, fig. 3, text-fig. 25; Wang etal., 1979, p. 54, pl. 15, fig.4; Fantini Sestini, 1981, p. 57;
He et al., 1986, p. 252, pl. 16, figs. 4–12, 16–22, text-fig.
29.
Leiophyllites? middlemissi (Diener). Spath, 1934, p. 308.
Xenaspis laevis Welter. Bender, 1970, p. 429, pl. 2, fig. 8.
Leiophyllites stoecklini Tozer, 1972, p. 37, pl. 5, fig. 5, textfig. 2B.
Leiophyllites cf. middlemissi (Diener). Wang and He, 1976, p.
429, pl. 47, figs. 6–8, text-fig. 73c.
Leiophyllites cf. pitamaha (Diener). Wang and He, 1976, p.
430, pl. 47, figs. 14, 15, pl. 48, figs. 8, 9, text-fig. 73e.
Leiophyllites aff. pitamaha (Diener). Fantini Sestini, 1988, p.
69, pl.14, fig. 5.
Material examined.—Seven specimens, IGPS coll. cat.
nos. 112630–112636.
Description.—The shell is discoidal and evolute. The

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan

69

Figure 11. A rctohungarites and Procladiscites from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt,
Northeast Japan.
	1–3, Arctohungarites sp.; 1, IGPS coll. cat. no. 112621; 1a, lateral view; 1b, suture line; 2, IGPS coll. cat.
no. 112622, lateral view; 3, IGPS coll. cat. no. 112623; 3a, lateral view; 3b, suture line; 4–6, Procladiscites
brancoi Mojsisovics; 4, IGPS coll. cat. no. 112625; 4a, lateral view; 4b, suture line; 5, IGPS coll. cat. no. 112626;
5a, ventral view; 5b, suture line; 6, IGPS coll. cat. no. 112627, lateral view; 7, Procladiscites sp., IGPS coll. cat.
no. 112628, lateral (7a and 7b) and ventral (7c) views. Scale bars are 1 cm unless otherwise stated.

maximum diameter ranges from 28 mm to more than 75
mm. The larger specimens (D > 40 mm) are composed ofphragmocone and body chamber, the latter occupies overa half volution. The ratio of H/D ranges from 0.26 to 0.39,
but mostly about 0.30. The ratio of UD/D ranges from 0.44
to 0.53, but mostly 0.48 to 0.53 (Table 3). The sides arenearly flat to slightly convex. The umbilicus is shallow withmoderately inclined wall and rounded umbilical shoulder.
The venter is acutely rounded with broadly roundedumbilical shoulder which continued to the flanks without
clear boundary. The cross section is compressed oval. Inner
whorls are sometimes ornamented by faint and low, radial toconcave ribs or fold. The surface of outer whorls is almost

smooth, but often have faint sigmoidal ribs or growth lines.
Constrictions parallel to the ribs or growth lines are rarely
visible on the last whorl.
The ventral lobe is not well preserved, but shallow. The
first lateral lobe is wide and its base has irregular, strong
denticulations, seven to eight in number. The second lobe
is small, but it also has four to five strong denticulations.
Auxiliary lobe is simple and pointed. There are threesaddles on the lateral side. The saddles are all rounded andnarrowed toward the base. The second saddle is highest
and the third is small.
Discussion.—The present specimens are very similar to
Leiophyllites pitamaha Diener reported from the Anisian

70

Masayuki Ehiro

Figure 12. L eiophyllites from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt, Northeast Japan.
	1, Leiophyllites cf. confucii (Diener), IGPS coll. cat. no. 112629, lateral view; 2–7, Leiophyllites pitamaha(Diener); 2, IGPS coll. cat. no. 112632, lateral view; 3, IGPS coll. cat. no. 112633, lateral view; 4, IGPS coll.
cat. no. 112630; 4a, lateral view; 4b, suture line; 5, IGPS coll. cat. no. 112631; 5a, lateral view; 5b, suture line;
6, IGPS coll. cat. no. 112635, lateral view; 7, IGPS coll. cat. no. 112636, lateral view; 8 and 9, Leiophyllites
cf. praematurus Kiparisova; 8, IGPS coll. cat. no. 112637; 8a, lateral view; 8b, suture line; 9, IGPS coll. cat.
no. 112638; 9a, lateral view; 9b, suture line; 10, Leiophyllites sp. A; 10a, lateral view; 10b, suture line; 11–13,
Leiophyllites sp. B; 11, IGPS coll. cat. no. 112657, lateral view; 12, IGPS coll. cat. no. 112658, lateral view;13,
IGPS coll. cat. no. 112661, lateral view. Scale bars are 1 cm unless otherwise stated.

strata of Himalayas, Qinghai and east Europe, in the generalshell shape, surface ornamentation, although the umbilicusof the present specimens is slightly larger than that of theholotype (UD/D = 0.44).
Occurrence.—Middle part of the Fukkoshi Formation (Fk-

1c: no. 112635; Fk-1a: nos. 112630–112634) at the southof Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City,and upper part (Fk-6: no. 112636) at the eastern coast of
Terahama, Togura, Minamisanriku Town, Miyagi Prefecture.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
Table 3. D imensions (in mm) and ratios of Leiophyllites
pitamaha (Diener) from the Fukkoshi Formation.
Abbreviations see Table 1.

Leiophyllites cf. praematurus Kiparisova, 1958
Figures 11.8, 11.9
cf. Leiophyllites praematurus Kiparisova, in Kiparisova andPopov, 1958, p. 32, pl. 7, fig. 13, text-fig. 17б; Kiparisova,
1961, p. 134, pl. 28, figs. 5, 6, text-figs. 101, 102.
Leiophyllites pitamaha Diener. Kummel, 1969, p. 531,
text-fig. 49B.
Material examined.—Two specimens, IGPS coll. cat. nos.
112637, 112638.
D e s c r i p t i v e r e m a r k s . — Tw o s p e c i m e n s a r e b o t hphragmocone, and the shell is discoidal and sub-evolute toevolute. The maximum shell diameter of the small specimen(no. 112636) is 19.6 mm and the corresponding height andumbilical diameter are 5.6 (H/D = 0.29) and 9.0 mm (UD/D =0.46), respectively. The larger specimen (no. 112637) attains
a maximum diameter of ca. 25 mm and its correspondingheight and umbilical diameter are ca. 9.5 (H/D = 0.38)
and 10.2 mm (UD/D = 0.41), respectively. The sides arerounded in the smaller specimen and broadly convex in thelarger one, with the maximum width near the center of theflank. The venter of the small specimen is rounded with akeel. That of the larger specimen is not well preserved. The
umbilicus is shallow. Both the ventral and umbilical shoulder
are indistinct and rounded to convex side continue to theventer and umbilical wall. The conch section is compressed
oval, and that of the larger one is more compressed. There
are short, low but wide ribs, slightly curved backward, on the
inner side of the flanks of the smaller specimen. The shellsurface of the larger specimen is nearly smooth, but similar
short ribs are on the inner whorls.
The ventral lobe is not seen. The external lateral suture
consists of three saddles, two lobes and auxiliary ones.
All saddles have rounded crests and nearly parallel sides.

71

The first and second saddles have nearly the same height,
but the third is considerably small. The first lateral lobe is
deep with subparallel sides. The base of it has six strong
denticulations and the lower part of the sides are also
denticulate, though very weak. The second lobe is shallow
and its base has three short or indistinct denticules. The
auxiliary lobe is simple and pointed.
Although there are some differences in the ratio of
H/D and UD/D and surface ornamentation between thetwo materials described, their general shell form andsutural shape resemble those of Leiophyllites praematurus
Kiparisova (1958, 1968). But the present species differsfrom the latter in having a ventral keel. The present species
also somewhat resembles L. laevis (Welter) form 1 (originallyas Xenaspis laevis) from the Anisian of Timor (Welter, 1915,
p. 130, pl. 10, figs. 7a–7b). The Timor specimen differs from
L. praematurus in having larger umbilicus and in having
downwardly narrowed saddles.
Occurrence.—Middle part of the Fukkoshi Formation(Fk-1a: no. 112637; Fk-1b: 112638) at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.
Leiophyllites suessi (Mojsisovics)
Figures 13.1–13.7
Monophyllites Suessi Mojsisovics, 1882, p. 205, pl. 79, fig.4;
Hauer, 1887, p. 33; Patte, 1926, p. 185, pl. 12, figs. 6, 7.
Monophyllites (Mojsvarites) Suessi Mojsisovics, Kraus,
1916, p. 289.
Monophyllites (Leiophyllites) Suessi (Mojsisovics), Renz,
1931, p. 57; Kutassy, 1932, p. 595.
Leiophyllites suessi (Mojsisovics), Spath, 1934, p. 303, textfig. 104b; Wiedmann, 1970, p. 969, pl. 1, figs. 1, 2, textfig. 3.
Leiophyllites pradyumna (Diener), Zakharov, 1968, p. 124,
pl. 23, figs. 2, 3, text-fig. 29h.
Leiophyllites suessi (Mojsisovics), Krystyn and Tatzreiter,
1991, p. 142, pl. 2, fig. 7.
Material examined.—Ten specimens, IGPS coll. cat. nos.
112639–112648.
Description.—The shell is discoidal and sub-evolute toevolute. The maximum diameter ranges from 24 mm tomore than 70 mm. They are composed of phragmocone
and body chamber, the latter occupies over three-fourth ofthe last whorl. The ratio of H/D ranges from 0.29 to 0.35
(mostly 0.31-0.35) and that of UD/D ranges from 0.41 to 0.53
(mostly 0.45-0.48) (Table 4). The sides are broadly convex
to rounded with maximum width near the umbilical shoulder
to the center of the flank. The venter is acutely rounded withrounded ventral shoulder. The umbilicus is shallow. There

72

Masayuki Ehiro

Table 4. D imensions (in mm) and ratios of Leiophyllites
suessi (Mojsisovics) from the Fukkoshi Formation.
Abbreviations see Table 1.

City, Miyagi Prefecture.
Leiophyllites wakoi Ehiro, Sasaki and Kano
Figures 14.1–14.6
Leiophyllites wakoi Ehiro, Sasaki and Kano, 2016, p. 99,
figs. 4.4a–d.

is no remarkable umbilical shoulder and the sides gradually
down into the umbilical seam. The cross section of the conch
is elongated oval. The shell surface is almost smooth, but on
the last whorl there are faint, slightly convex to falcoid ribs or
growth lines. Many strong and wide constrictions, which arealso convex to falcoid, are also visible on the outer whorl.
They number four to eight, mostly six to seven per volution.
The external suture consists of three saddles, twolobes and auxiliary ones. The ventral lobe is not wellpreserved and only a part of the prong, having at least three
denticulations at the base, is visible. The crests of saddles
are all rounded. The saddles are vertically elongated andbecome narrower downward. The second one is the highest.
The first lateral lobe is deep and wide, and expandedbase has five to seven (mostly five) strong denticulations.
The second lobe has a similar shape to the first, including
the denticulation, but smaller in size, The auxiliary one iscomposed of a small, pointed lobe, and low and wide saddle
on the umbilical shoulder.
Discussion.—The present specimens from the Fukkoshi
Formation are very similar to Leiophyllites suessi(Mojsisovics) reported from the Anisian strata of east Europe
in the general shell shape, surface ornamentation and theoutline of the suture line. A slight deference between themis a number of constrictions. The Fukkoshi specimens
have more constrictions than the European specimens.
Leiophyllites pradyumna (Diener) resembles to Leiophyllites
suessi (Mojsisovics) in the general shell shape and shapeof the suture. But it differs from the latter in having bulges(ribs) instead of constrictions on the shell surface. L.
pseudopradyumna Welter, 1915 is also distinguished fromthe present species in having bulges.
Occurrence.—Middle part of the Fukkoshi Formation (Fk1c: nos. 112645–112648; Fk-1a: nos. 112639–112644) atthe south of Ozashi, Jusanhama, Kitakami-cho, Ishinomaki

Material examined.—Seven specimens, IGPS coll. cat.
nos. 112649–112655.
Descriptive remarks.—Small- to medium-sized shells
are discoidal and evolute. They consist of phragmocone
and a part of the body chamber. The shell diameter ranges
from ca. 25 to 58 mm. The ratio of H/D ranges from 0.27
to 0.31 and that of UD/D varies from 0.47 to 0.53 (mostly
around 0.50) (Table 5). The sides are broadly convex toflat at maturity, with broadly rounded umbilical and ventral
shoulders. The maximum conch width is near the centerof the flank. The cross section is flattened oval. The shellsurface of the inner whorls seems to be smooth, whereas
fine but distinct, biconcave ribs are on the outer whorl. Someshallow constrictions parallel to the ribs are also present.
The ventral lobe is not well preserved and only a part of its
prong is visible, which has denticulate base. The first laterallobe is large and its rounded base has five to seven, slightly
irregular denticulations. The second lobe is about half depthof the first and asymmetrical. It has four to six denticulations.
Main deep denticulations are at the base. Small, one or two
denticulations are up to the lower part of the ventral side,
whereas the umbilical side is smooth. The auxiliary lobe is
simple and pointed. There are three rounded saddles on thelateral side. The second is largest and highest, and the thirdis small.
The general shell shape and especially the biconcave ribson the last volution of the present specimens are closely
similar to those of Leiophyllites wakoi described by Ehiro
Table 5. D imensions (in mm) and ratios of Leiophyllites
wakoi Ehiro, Sasaki and Kano from the Fukkoshi
Formation. Abbreviations see Table 1.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan

73

Figure 13. L eiophyllites suessi (Mojsisovics) from the Fukkoshi Formation in the Kamiwarizaki area, South Kitakami Belt,
Northeast Japan.
	1, IGPS coll. cat. no. 112639; 1a, lateral view; 1b, suture line; 2, IGPS coll. cat. no. 112640; 2a, lateral view; 2b,
suture line; 3, IGPS coll. cat. no. 112641, lateral view; 4, IGPS coll. cat. no. 112642, lateral view; 5, IGPS coll.
cat. no. 112643, lateral view; 6, IGPS coll. cat. no. 112644; 6a, lateral view; 6b, suture line; 7, IGPS coll. cat. no.
112645; 7a, lateral view; 7b, suture line. Scale bars are 1 cm unless otherwise stated.

et al. (2016) from the underlying late Olenekian Osawa
Formation. The ratio of UD/D of the latter is rather small (0.40
at D = 65-90 mm), but it is 0.45–0.46 at D = 43 mm, andalmost the same as the present specimens.
Occurrence.—Middle part of the Fukkoshi Formation(Fk-1a: nos. 112649, 112651–112654; Fk-1b: nos. 112650,
112655) at the south of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.
Leiophyllites sp. A
Figure 12.10a, bMaterial examined.—One specimen, IGPS coll. cat. no.
112656.
Descriptive remarks.—An outer mold of moderately
large specimen with impressions of suture lines are athand. It consists of phragmocone and body chamber, thelatter occupies about a half part of the last volution. The
shell is probably extremely discoidal and sub-evolute. The
maximum shell dimeter attains more than 97 mm, and at D
= ca. 81 mm, corresponding height and umbilical diameterare ca. 25.0 and 35. 5 mm (UD/D = 0.44), respectively. The
side is broadly convex with broadly rounded umbilical andventral shoulders. The maximum shell width is near theumbilical shoulder and the sides slightly converge to theventer. The venter is not well preserved. The shell surface
is almost smooth. The external lateral suture, preserved
as impressions on the outer mold, consists of the first andsecond lateral saddles and first and second lateral lobes.
The crests of saddles are both rounded and the second
lateral saddle is higher than the first. The first lateral lobe is
deep and wide, and its base has many denticulations. The

74

Masayuki Ehiro

Figure 14. L eiophyllites wakoi and Ussuriphyllites amurensis from the Fukkoshi Formation in the Kamiwarizaki area, South
Kitakami Belt, Northeast Japan.
	1–6, Leiophyllites wakoi Ehiro, Sasaki and Kano; 1, IGPS coll. cat. no. 112649; 1a, lateral view; 1b, suture line; 2,
IGPS coll. cat. no. 112650, lateral view; 3, IGPS coll. cat. no. 112651; 3a, lateral view; 3b, suture line; 4, IGPS
coll. cat. no. 112652, lateral view; 5, IGPS coll. cat. no. 112653, lateral view; 6, IGPS coll. cat. no. 112654; 6a,lateral view; 6b, suture line; 7 and 8; Ussuriphyllites amurensis (Kiparisova); 7, IGPS coll. cat. no. 112663; 7a,lateral view; 7b, suture line; 8, IGPS coll. cat. no. 112662; 8a, lateral view; 8b, suture line. Scale bars are 1 cm
unless otherwise stated.
second lobe is shallow and small, and its base is probably
tri-denticulate. The ventral lobe is not preserved and there
is some space between the third saddle and the umbilicaledge.
Based on the general shell form and suture line, thepresent specimen is considered to belong certainly
the genus Leiophyllites Diener, 1915, but the specificidentification is difficult because of its poor state ofpreservation. This specimen is clearly larger than the other
Leiophyllites species collected from nearly the same horizon
at the south of Ozashi (Fk-1a–1c).
Occurrence.—Middle part of the Fukkoshi Formation(Fk-3a) at the west of Ozashi, Jusanhama, Kitakami-cho,Ishinomaki City, Miyagi Prefecture.

Leiophyllites sp. B
Figures 12.11–12.13
Material examined.—Five specimens, IGPS coll. cat. nos.
112657–112661.
Descriptive remarks.—Small shells are discoidal andevolute. The maximum shell diameter ranges from ca. 20 to
40 mm. The ratio of H/D ranges from 0.20 to 0.32, but mostly
around 0.30. The ratio of UD/D varies from 0.47 to 0.60.
They have five to six volutions at D = 20 mm. The sides arebroadly convex to flat, with broadly rounded umbilical andventral shoulders. The maximum conch width is near thecenter of the flank. The umbilicus is very shallow. The crosssection is flattened oval. The shell surface is almost smooth.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan75

The suture is not preserved.
Based on the general shell form, the present specimen
is considered to belong certainly the genus Leiophyllites
Diener, 1915 and somewhat similar to the juvenile shell of L.
pitamaha, but the specific identification is difficult because
they lack of suture line and are poor state of preservation.
Occurrence.—Middle part of the Fukkoshi Formation (Fk1c: nos. 112657–112660; Fk-1a: no. 112661) at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.

Discussion.—The shell shape, surface ornamentationand outline of the suture line of the present specimensfrom the Fukkoshi Formation are identical with those of
Ussuriphyllites amurensis (Kiparisova) reported from theTriassic strata of South Primorye, Far East Russia, although
the umbilicus is rather small in the small specimen.
Occurrence.—Middle part of the Fukkoshi Formation(Fk-1a: no. 112662; Fk-1b: no. 112663) at the south of
Ozashi, Jusanhama, Kitakami-cho, Ishinomaki City, Miyagi
Prefecture.

Genus Ussuriphyllites Zakharov, 1967

Discussion

Type species.—Eophyllites amurensis Kiparisova, 1961.

Ammonoid fauna of the Fukkoshi Formation and its
geologic age
Fukkoshi ammonoid fauna comprises 13 families, 21
genera and about 40 species listed below:
Family Hemilecanitidae
Hemilecanites discus (Arthaber)
Family Sageceratidae
Parasageceras aff. discoidale Welter
Family Hedenstroemiidae
Pseudosageceras multilobatum Noetling
Family Parapopanoceratidae
Parapopanoceras involutum sp. nov.
Family Megaphyllitidae
Megaphyllites sp.
Family Khvalynitidae
Metadagnoceras spp.
Psilokhvalynites takaizumii gen. and sp. nov.
Family Acrochordiceratidae
Paracrochordiceras cf. denseplicatum Fantini Sestini
Paracrochordiceras watanabei sp. nov.
Paracrochordiceras spp.
Family Japonitidae
Aegeiceras? sp.
Eogymnites sp.
Japonites cf. meridianus Welter
Japonites raphaelizoyae (Tommasi)
Japonites spp.
Family Gymnitidae
Buddhaites? sp.
Family Danubitidae
Danubites cf. ambika Diener
Danubites floriani (Mojsisovics)
Danubites cf. tozeri Korchinskaya
Paradanubites kansa (Diener)
Paradanubites cf. kansa (Diener)
Paradanubites ozashiense sp. nov.
Paradanubites phyllus He
Paradanubites sp.
Family Longobarditidae

Ussuriphyllites amurensis (Kiparisova)
Figures 14.7, 14.8
Eophyllites amurensis Kiparisova, 1961, p. 137, pl. 28, figs.
7, 8, text-fig. 104.
Ussuriphyllites amurensis (Kiparisova), Zakharov, 1967, p.
50, pl. 4, figs. 8–10, text-figs. 1g, 1h, 2; Zakharov, 1968,
p. 123, pl. 22, figs. 12, 13, pl. 23, fig. 1; Zakharov et al.,2005a, fig. 3; Zakharov et al., 2005b, fig. 8; Shigeta andKumagae, 2016, p. 54, figs. 6A, 6B.
Material examined.—Two specimens, IGPS coll. cat. nos.
112662, 112663.
Description.—Two specimens are discoidal and subinvolute, and consists of phragmocone and body chamber,the latter of which occupies about three-fourth of the lastwhorl. The sides are broadly convex. The maximum width
is at about the center of the flank, from where the flankconverges to both the venter and umbilicus. The umbilicus
is very shallow without distinct umbilical wall. The venter is
not well preserved, but seems to be acute or carinated. The
shell cross section is lenticular. The maximum shell dimeterof specimen no. 112662 attains more than 60 mm, and at D
= ca. 58 mm, corresponding height and umbilical diameterare 23.8 and 15.5 mm (UD/D = 0.28), respectively. Anothersmaller specimen (no. 112663: max. D > 45 mm) has
rather small umbilicus (UD/D < 0.08). The shell surface isornamented with faint, slightly sigmoidal, fine radial ribs andfine, sparse, concentric ribs. There are four to five concentricribs between the umbilical shoulder to the ventral shoulder.
The ventral lobe is partly preserved and its base isserrated. Three lateral saddles have rounded crest. The
second is largest and the third is small. The first andsecond lateral lobes are denticulate at the base and thedenticulations are up to the one-third of the sides in thespecimen no. 112662. The auxiliary loves are irregular inshape and size.

76

Masayuki Ehiro

Figure 15. S
 tratigraphic distribution of ammonoid species from the Fukkoshi Formation in the Kamiwarizaki area, South
Kitakami Belt, Northeast Japan. Ammonoids from the uppermost part of the Osawa Formation at the south of
Asadanuki and from the lowermost part of the Isatomae Formation at Kudanohama are also shown.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
Groenlandites sp.
Lenotropites spp.
Grambergia cf. tetsaensis McLearn
Arctohungarites sp.
Longobarditidae? gen. and sp. indet.
Family Cladiscitidae
Procladiscites brancoi Mojsisovics
Procladiscites sp.
Family Palaeophyllitidae
Leiophyllites cf. confucii (Diener)
Leiophyllites pitamaha (Diener)
Leiophyllites cf. praematurus Kiparisova
Leiophyllites suessi (Mojsisovics)
Leiophyllites wakoi Ehiro, Sasaki and Kano
Leiophyllites spp.
Ussuriphyllites amurensis (Kiparisova)
These ammonoids were collected from the nine localities(horizons) belonging to the middle to upper part of the
Fukkoshi Formation (Figure 15), but these are largely
classified into three horizons: the mudstone dominatedmiddle part (FkM: including the horizons Fk-1c, Fk-3a, Fk3b, Fk-1a and Fk-1b: about 30 m total stratigraphic interval),
mudstone beds of the lower part of the upper part (FkU1: horizon Fk-5) and upper mudstone dominated beds inthe upper part (FkU-2: including the horizons Fk-2a, Fk2b
and Fk-6: less than 10 m interval). FkM has rather wide
stratigraphic range of ca. 30 m, but there is no remarkabledifference between the generic compositions of Fk-1a andFk-1b, and genera from the Fk-1c, Fk-3a and Fk-3b are also
yield from Fk-1a and Fk-1b. The ammonoid specimens are
few in number in both FkU-1 and FkU-2 and it makes precise
comparison with FkM difficult, but their faunas are poor in
number of specimens belong to the family Palaeophyllitidae
and Danubitidae, which are predominated in the FkM.
Among the fauna of FkM, specimens belong to the genera
Leiophyllites are most dominated and hold more than half ofthe collection, including those ill preserved and undescribed
ones. Those belong to the genera Paradanubites is thenext, and those of Parapopanoceras, Psilokhvalynites,
Paracrochordiceras and Danubites are also common.
More than half of the genera (13 genera) among the fauna(20 genera: excluding the new genus Psilokhvalynites), are
known from the Anisian strata (rarely from also Ladinianor late Triassic strata), and mostly restricted in the lower
Anisian (Aegean): Parasageceras, Parapopanoceras,
Megaphyllites, Paracrochordiceras, Aegeiceras, Buddhaites,
Danubites, Paradanubites, Groenlandites, Lenotropites,
Grambergia, Arctohungarites and Ussuriphyllites. The
last genus has been only known from the lower AnisianUssuriphyllites amurensis Zone of South Primorye(Zakharov, 1967, 1968; Zakharov et al., 2005a, 2005b).
Shigeta and Kumagae (2016) stressed that the genus

77

Ussuriphyllites is late Olenekian (late Spathian) in age,
because it is associated with Keyserlingites sp. However,U. amurensis is accompanied with typical Anisian genera,such as Parasageceras, Megaphyllites, Paracrochordiceras,
Prohungarites, Arctohungarites, Tropigastrites and Ussurites
in the U. amurensis Zone of the Atlasov Cape section,
South Primorye (Zakharov et al., 2005a, 2005b). Moreover,genus Keyserlingites is not restricted in the Olenekian. Many
species of Keyserlingites (= Durgaites) have been reported
from the lower Anisian strata in the Tethys region, such as
Qinghai (e.g. Wang, 1985; He et al., 1986) and Spiti (Krystin
et al., 2004). Therefore, the genus Ussuriphyllites is early
Anisian in age.
Two genera, Japonites and Procladiscites, are also
typical for the Anisian of Tethys province, although they
already appeared in the latest Olenekian as reported fromthe uppermost part of the underlying Osawa Formation(Ehiro, 2022 in press). The genus Leiophyllites ranges from
Olenekian to Anisian.
Few exceptions are the genera Hemilecanites,
Pseudosageceras, Metadagnoceras and Eogymnites.
They are typical Olenekian or Induan to Olenekian genera.
However, the first three have been also described from thelower Anisian strata, although very few in number. Bucher(1989) described Hemilecanites cf. paradiscus Kummel,
Metadagnoceras youngi Bucher and Metadagnoceras sp.
from the Lower Anisian of Nevada. Pseudosageceras? sp.
described from the Anisian strata of Primorye, Far East
Russia (Kiparisova, 1961) is ill preserved, but it has involuteconch with multi-lobed suture line and its generic assignment
is highly probable. The present discovery of these three
genera from the Fukkoshi Formation in association withmany Anisian genera clarified that they range up to the lower
Anisian, although these genera are generally thought to be
restricted in pre-Anisian strata. The species of the genus
Eogymnites have been reported from the upper Olenekian,but Eogymnites is closely related with Japonites and someauthors consider that it is synonymous with the genus
Japonites.
Among the Fukkoshi ammonoid fauna from FkM, twogenera, Parapopanoceras and Buddhaites, are generally
considered to be middle Anisian (to late Anisian) genera, but
the majority of the genera of the fauna are stratigraphically
restricted to or range down into the lower Anisian. Therefore,
the ammonoid fauna from FkM is definitely early Anisian(Aegean) in age.
Fauna from FkU-1 and FkU-2 are not diverse,
a n d c o m p r i s e o n l y P s i l o k h v a l y n i t e s ( g e n . n o v. ) ,Paracrochordiceras, Japonites and Leiophyllites. They
are also considered to be early Anisian in age, because of
the occurrence of Paracrochordiceras. The early Anisiangenera, such as Grambergia, Lenotropites, Tropigastrites

78

Masayuki Ehiro

and Ussurites, are also known from the lowermost part ofthe overlying Isatomae Formation (Ishibashi, 2006).
Olenekian/Anisian boundary in the South Kitakami Belt,
Northeast Japan
Although some candidate sections have been proposedas the global boundary stratotype section and point (GSSP)
for the base of the Anisian, it is yet to be ratified. There are
two dominant biostratigraphic markers for the base of theAnisian: ammonoid and conodont. When Grădinaru et al.
(2007) proposed the base of ammonoid Paracrochordiceras–
Japonites Beds in the Deşli Caira Hill, Dobrogea, Romania
as the GSSP, this level was considered to coincide alsowith the FAD of conodont Chiosella timorensis (Orchard
et al., 2007). Goudemand et al. (2012), however, clarified
that this conodont FAD datum is actually in the underlying
Deslicairites Beds, which characterized by Olenekianammonoids.
Gaetani et al. (1992) had proposed that the base of the
Aegeiceras–Japonites beds, that is correlated with the
Paracrochordiceras–Japonites Beds of Dobrogea, at the
Marathovouno section in Chios Island, Greece as the baseof the Anisian. It coincides with the base of the Aegean
Substage proposed by Assereto (1974). Also in Chios,
the FAD of C. timorensis is slightly below the base of the
Aegeiceras–Japonites beds and located in the late Spathian
bed with Procarnites and Hellenites (Assereto et al., 1980;
Gaetani et al., 1992). The same stratigraphic relationshipbetween the ammonoids and conodonts are also known fromNevada, North America. The occurrence of C. timorensis
from the upper part of the Olenekian Neopopanoceras haugi
Zone was reported by Goudemand et al. (2012).
Based mainly on the FAD of C. timorensis, some OAB
boundary sections in the Nanpanjiang Basin, Guangxi,
South China have been introduced for the candidate GSSP
for the base of the Anisian (e.g. Ovtcharova et al., 2006;
Galfetti et al., 2007, 2008; Chen et al., 2020). In these
sections, unfortunately, the ammonoid fossils are very poor.
Recently, Golding (2021) proposed a new criterion of
conodont-based definition for the base of the Anisian. He
suggests that Neogondolella curva and associated species
is suitable for the index of the base of the Anisian. The FADsof these species are slightly above that of C. timorensis
and nearly the same as those of Anisian ammonoids,that characterize the Paracrochordiceras–Japonites
Beds or its correlatives. Grădinaru (2022) investigatedthe biostratigraphy of some OAB boundary sections andthe stratigraphic position of FAD of C. timorensis withproblems on its taxonomy and definition, and stressed thatC. timorensis is ineligible for the stratigraphic index for the
OAB and the OAB boundary should be defined basically on
ammonoids.

By adopting the ammonoid-based (traditional) criteria or
Golding’s (2021) proposal, the base of the Anisian in theSouth Kitakami Belt is considered to be located below the
middle part of the Fukkoshi Formation, because it yields rich
early Anisian (Aegean) ammonoids, which correlate with
Paracrochordiceras–Japonites Beds and its correlatives.
Since the uppermost part of the underlying Osawa
Formation is characterized by the Olenekian ammonoids(Ehiro, 2022 in press), the Olenekian/Anisian boundary is
considered to locate somewhere in the lower part of the
Fukkoshi Formation.
Comparison with the early Anisian ammonoid faunas in
the Tethys and Panthalassa regions
The ammonoid fauna of the Fukkoshi Formation is very
diverse (consisting of 21 genera and 38 species) among
the early Anisian (Aegean) ammonoid fauna, being equal
to those of Qinghai, China (He et al., 1986) and Nevada,North America (Bucher, 1989). It is most dominated in
the genera of the Family Palaeophyllitidae, mostly of
Leiophyllites, and characterized common occurrences ofthe families Danubitidae (Danubites and Paradanubites),Acrochordiceratidae (Paracrochordiceras) andLongobarditidae (Groenlandites, Lenotropites, Grambergia
and Arctohungarites). The fauna also includes quite a few
specimens belong to the families Parapopanoceratidae(Parapopanoceras) and Khvalynitidae (Metadagnoceras,
Psilokhvalynites). The Fukkoshi ammonoid fauna has someresemblance in the generic and species compositions tothose known from southern Tethys (Himalayas: Diener,
1895b; Timor: Welter, 1915), western and central Tethys(Chios: Fantini Sestini, 1981 and Gaetani et al., 1992;
Caucasus: Shevyrev, 1968, 1995; Qinghai, western China:
He et al., 1986), western Panthalassa (South Primorye:
Zakharov et al., 2005a, 2005b) and eastern Panthalassa
provinces (Nevada: Bucher, 1989).
Qinghai, west China: The ammonoid fauna reported
from Qinghai, west China (He et al., 1986) is one of themost diverse Aegean faunas, which comprises 47 species
belonging to 18 genera of ammonoids. According to He et al.
(1986), the majority of this fauna are specimens belonging
to the genera Groenlandites, Pearylandites, Lenotropites,
Grambergia and Arctohungarites (family Longobarditidae)
and those of the genera Keyserlingites, Japonites,
Procladiscites, Leiophyllites, Ussurites, Paradanubites andMegaphyllites are also common. Among the genera known
from Qinghai, ten genera are also known in the Fukkoshi
fauna, and dominant and common genera in the Qinghai
fauna are also included in the Fukkoshi fauna, except
for the genus Ussurites. The main difference between
these two faunas is the absence of the genera of family
Acrochordiceratidae in the Qinghai fauna.

Early Anisian (Aegean) ammonoids from the Fukkoshi Formation, South Kitakami Belt, Northeast Japan
Nevada, USA: Lower Anisian beds in the northern
Humboldt Range, Nevada, USA are classified into the
Japonites welteri beds, Pseudokeyserlingites guexi beds,
Mulleri Zone and Caurus Zone, in ascending order (Bucher,1989). The lower Anisian ammonoid fauna of Nevada isanother diverse one and comprises 28 species of 17 genera.
Ten genera are common in both Nevada and Fukkoshi
faunas. It is worthy of attention that both faunas include
two “relict” genera Hemilecanites and Metadagnoceras.
However, there are some faunal differences between them:Silberlingites and Caucasites, both common elements in
the Nevada fauna are absent in the Fukkoshi fauna and, on
the other hand, the genera of the family Danubitidae andPalaeophyllitidae, dominated or common in the latter, arerare in the former.
Timor: From the Anisian limestone (2 m in thickness)in Nifoekoko, Timor, Welter (1915) described 12 genera(23 species) of ammonoids. Based on the re-examinationof these genera by Shevyrev (1968, 1995), Spath (1954),
Fantini Sestini (1981), etc., this fauna is considered tobe composed of 13 genera (22 species). Among these,eight genera are common to the Fukkoshi fauna. Generaof the family Longobarditidae are missing and those of
Acrochordiceratidae are rare in the Timor fauna.
Chitichun, Himalayas: The Chitichun limestone in
Himalayas is classical Aegean ammonoid locality. Chitichun
ammonoids originally described by Diener (1895b) havebeen reexamined by Diener (1915), Spath (1934), Shevyrev(1968), Wang and Chen (1979) and Fantini Sestini (1981,1988), and are now classified into 13 species belonging
to eight genera: Paracrochordiceras pandya (Diener),
Danubites ambika Diener, Paradanubites kansa (Diener),
Aegeiceras ugra (Diener), Psilosturia mongolica (Diener),
Procladiscites yasoda Diener, Leiophyllites confucii(Diener), L.? middlemissi (Diener), L. pitamaha (Diener),L. pradyumna (Diener), L. pseudopradyumna (Welter),
Ussurites hara (Diener) and U. kingi (Diener). Among theseeight genera, six of them are common to the Fukkoshi
fauna, and three species (P. kansa, L. confucii, L. pitamaha)from the Fukkoshi Formation are identified or compared to
the Chitichun ones. According to Diener (1895b), specimensof Leiophyllites have, as with the Fukkoshi fauna, thelargest number (35 specimens) among the fauna, followedby those of Procladiscites (10 specimens). On the other
hand, the Chitichun fauna lacks the genera of the family
Longobarditidae.
South Primorye: The Lower Anisian strata of the Atlasov
Cape section, South Primorye, Far East Russia yield 15
species belonging to 12 genera of ammonoids (Zakharov
et al., 2005a, 2005b). Among them seven genera arecommon to the Fukkoshi fauna. The fauna dominated in
Ussuriphyllites amurensis (Kiparisova), which is endemic

79

to South Primorye but now known from the Fukkoshi
Formation. The Atlasov Cape fauna, however, differ fromthe Fukkoshi fauna in lacking the genera belonging to thefamilies Japonitidae and Longobarditidae, and in small
number of specimens of family Danubitidae and genus
Leiophyllites.
Chios Island, Greece: The Marathovouno section in
Chios Island, Greece includes the proposed candidate
GSSP (the base of the Aegeiceras–Japonites beds: the baseof the Aegean Substage proposed by Assereto, 1974) forthe base of the Anisian (Gaetani et al., 1992). The Aegeanammonoid fauna was studied by Bender (1970), Assereto(1974), Fantini Sestini (1981) and Gaetani et al. (1992). Thisfauna comprises 17 species in 10 genera, of which seven
genera are common to the Fukkoshi fauna. Former faunadiffers from the latter in lacking the genera of the family
Longobarditidae.
Caucasus: According to Shevyrev (1995), the lower
Anisian Malotkhach Formation of Caucasus yields
Stenopopanoceras transiens Tozer, Megaphyllites
compressus Shevyrev, Megaphyllites sp., Groenlandites?
glaber Shevyrev, Longobardites caucasius Shevyrev,
Laboceras gracile Shevyrev, Leiophyllites pitamaha (Diener).
Three genera of them are also known in the Fukkoshi fauna,but the Caucasus fauna lacks in the genera belonging to
the families Danubitidae and Acrochordiceratidae, which arecommon in the Fukkoshi fauna.

Conclusions
1. Ammonoid fauna from the middle to upper part of
the Fukkoshi Formation in the Kamiwarizaki area, South
Kitakami Belt, Northeast Japan is diverse, consisting 21
genera. Among them, the genus Leiophyllites is mostdominated and specimens belonging to the genera
Paradanubites, Parapopanoceras, Psilokhvalynites,
Paracrochordiceras and Danubites are also abundant.
The majority of the genera are stratigraphically restricted
to or range down into the lower Anisian, and therefore, theammonoid fauna is considered definitely to be early Anisian(Aegean) in age.
2. Since the uppermost part of the underlying Osawa
Formation yields late Olenekian ammonoids, the Olenekian/Anisian boundary in the South Kitakami Belt is located to be
somewhere in the lower part of the Fukkoshi Formation.
3. The Fukkoshi ammonoid fauna exhibits somesimilarities in the generic composition with those of somelocalities exhibited in low-latitude regions in the Tethys andPanthalassa, especially with that of Qinghai, west China.

80

Masayuki Ehiro

Acknowledgements
The author wishes to express his sincere gratitude
to Yukihiro Takaizumi, Yuta Watanabe and Harumasa
Kano for their assistance in the field survey and donating
ammonoid specimens for study. Deep appreciation is also
due to the Tohoku Regional Environment Office, Ministryof the Environment Government of Japan for allowing thegeological survey and sample collection in the area of theSanriku Fukko (reconstruction) National Park. I also thankto Yuri D. Zakharov for his help with the literature and forproviding valuable comments that improved the manuscript.

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Paleontologischeskii Zhurnal, 1967, p. 44–51, p1. 4–5. (inRussian; original title translated)
Zakharov, Yu. D., 1968, Biostratigraphy and Ammonoids of theLower Triassic of Southern Primorye, 175 p., 31 pls. Nauka,
Moskva. (in Russian; original title translated).
Zakharov, Yu. D., Popov, A. M. and Buryi, G. I., 2005a, Uniquemarine Olenekian–Anisian boundary section from South
Primorye, Russian Far East. Journal of China University ofGeoscience, vol. 16, p. 219–230.
Zakharov, Yu. D., Popov, A. M. and Buryi, G. I., 2005b, Triassic
Ammonoid Succession in South Primorye: 4. Late Olenekian– Early Anisian zones of the Atlasov Cape Section. Albertiana,
no. 32, p. 36–39.
Zittel, K. A., 1884, Cephalopoda. In, Zittel, K. A. ed., Handbuch
der Paläontologie, Band 1, Abt. 2, p. 329–522. Oldenbourg,
München and Leipzig.

Bull. Tohoku Univ. Museum. No. 21, pp. 85‒91, 2022
© by The Tohoku University Museum

マイクロフォーカス X 線 CT を用いた大型底生有孔虫研究木下峻一 1)
1)

独立行政法人国立科学博物館

Studies of large benthic foraminifers using microfocus X-ray CT
Shunichi Kinoshita1)
1)

National Museum of Nature and Science
Abstract: The method of microfocus X-ray computed tomography (CT) is one of novel visualizing
and measuring techniques in the micropaleontology. Especially, larger benthic foraminifers havecomplex inner structures, and the inside morphological research of the shell has been generally
used in thin section or broken individuals. The X-ray CT method enables the measurement of theseinside structures with non-destruction. However, this method still remains many technical andpractical problems for actual researches. Here, I reviewed the instructions of microfocus X-ray CT
three-dimensional visualizing and measurement method, focusing on the microfossils’ utility suchas large foraminifers. I also presented examples of ecological studies of large foraminifers using
microfocus X-ray CT research, and finally propose future prospects of X-ray CT methods.

1．はじめに有孔虫は，熱帯から極域，また海洋表層から深海底に至るまで広く分布し、主に炭酸塩の殻をつくる原生動物である．この生物は大きく底生種と浮遊性種とに分類される．
この底生種のうち，一般に 1mm 以上のサイズに成長し，共生藻を持つという共通の特徴を示すグループが大型底生有孔虫（Large Benthic Foraminifer）と呼ばれる．大型底生有孔虫は，サンゴ礁海域に生息し，多くの有孔虫と同様に炭酸カルシウムの房室を付加することで殻全体の容積を徐々に増加させて成長していく．殻形成による炭酸塩生産力は，サンゴ礁海域の生態系において，造礁サンゴや石灰藻に次ぐ大きさであり（Hallock, 1981），その生態の解明は，サンゴ礁の生態系や，今後の環境変動による炭素循環システム
への影響予測において非常に重要な意味をもつ．また，殻の成長速度や成長量は光量（Hallock et al., 1986; Fujita andFujimura, 2008） や 水 温（Uthicke et al., 2012; Kinoshita etal., 2021），pH（Kuroyanagi et al., 2009）などの様々な環境条件の影響を受けることが明らかになっており，有孔虫殻に記録される情報は生息水域の海水環境の指標ともなりうる．
房室の付加を繰り返して成長する大型底生有孔虫において，もっとも基本となる成長量のひとつが房室数である．

しかし，その数を外形から計測することは多くの種で困難であり，房室数の正確な計測には標本の破壊を伴ってしまう．このように房室数の計測には，標本の保存の問題，正確な断面を出す技術的な難易度や手間などの問題があり，従来，物理的な成長パラメータとしては，殻サイズや重量が多く用いられてきた．特に標本の破壊は，化石種の同定においては避けたい問題であり，標本の内部情報の取得と非破壊保存は，大型底生有孔虫の研究にとって常に非常に重要な課題であった．
この「大型底生有孔虫の非破壊での形態解析」を実現させたのが，X 線 CT 手法の活用である．産業用に開発された
X 線 CT 装置は，近年の性能向上が著しく，マイクロメート
ル単位の解像度を持つマイクロフォーカス X 線 CT が現在では広く利用されるようになった．しかし，大型底生有孔虫をはじめとして，有孔虫類，あるいは微化石への X 線 CT の応用は未だに不安定な状況が続いている．本来，産業用 X
線 CT 装置の撮影に関しては，対象として微化石などの微小な（古）生物サンプルは考慮されていなかった．期待する画質の CT 像を得るためには，撮影者が標本に合わせた撮影用のステージ制作をしたり，さらに撮影条件を工夫したりするなど，適宜調整することが求められた．
本論では，最初にマイクロフォーカス X 線 CT による撮影，3 次元計測手法について，大型底生有孔虫などの微化石撮影

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時における留意点を中心に概説する．また，実際に 3 次元
計測手法を用いた研究例を紹介し，マイクロフォーカス X
線 CT 研究が有孔虫の生態の理解や環境解析にどのように貢献しているか，今後の展望等についても考察する．

2．マイクロフォーカス X 線 CT 手法の基礎
2.1）マイクロフォーカス X 線 CT 撮影の基本的な流れ
CT とは Computed Tomography ＝コンピュータ断層撮影の略称であり，X 線による走査によって断層撮影を行うことを X 線 CT 撮影と呼ぶ．この手法で得られる生データは，投影像であり，再構成処理などを加えて断層像（断面）や 3
次元データが取得できる．図 1 に，撮影準備から 3 次元化
までの基本的な流れを示す．現在，微化石標本の撮影に利用されているマイクロフォーカス X 線 CT 装置は，その多くが産業用として開発された撮影装置である．このような撮影装置は対向する X 線管と X 線検出器，その間に配置された標本ステージから構成され，一般に標本ステージを回転させ，標本の 360°あらゆる方向からの X 線走査を行い，X
線投影像群を得る（図 1D）．したがって，標本ステージの回転角を r 度として走査を行うと，360/r 枚の投影像群が得られる．投影像の拡大率 M は，以下の式に従う．

M=D/d
ここで，d は X 線管と標本ステージ，D は X 線管と X 線検出器，それぞれの距離である．これは，X 線が放射状に発生する（コーンビーム）ためで，標本ステージを X 線管
図 1．マイクロフォーカス X 線 CT による，サンプリングかに接近させることで M は大きくなり，解像度（空間分解能）ら 3 次元モデル化までの基本的な作業工程．D ～ F のも高くなる．多くの装置では，得られた投影像群を断層像
図は，同一標本の投影像（D），断層像（E），3 次元モデル像（F）をそれぞれ表す．
群に再構成するソフトウェアが付属しており，再構成処理を経て断層像が得られ（図 1E），一連の撮影が完了する．断
層像は，撮影時における標本ステージ上での標本上部から下部にかけての連続断面像であり，再構成する範囲は一般なる．そのため，断層像のコントラスト低下が起こり，微に任意に決定できる，注目部位のみ断層像に再構成するこ化石標本を撮影する時のように比較的低エネルギーの X 線とも可能である．再構成された断層像からは，フェルドカ
を用いて撮影する場合には注意して，設定する必要がある．
ンプ再構成法（Feldkamp et al., 1984）などによる 3 次元像 n の設定項目は装置によって異なるが，ビニングモード，への再構成が可能になる（図 1F）． 3 次元再構成や 3 次元
あるいは画像サイズとされていることが多い．
表示，計測が可能なソフトウェアも多様化しており，研究
一方，画像コントラストは強くすることでより精密に密目的に応じて選択して利用できる．
度差を表現することにつながるため，密度方向の解像度（密度分解能）と解釈できる．この密度分解能は，主に X 線の2.2）撮影条件について量に強く影響される．元来，X 線 CT は原理的には検出器へ
断層像の空間分解能は，それぞれ独立する条件である， 到達した X 線の量を観測しており，検出された X 線の量の差，
投影像の拡大率 M と，投影像 1 ピクセルあたりの X 線検出
理想的には入射 X 線量からサンプルの X 線吸収量を減算し器の素子数 n によって決まる．上述のように，M が大きい
た値が画像のコントラストとして再現される．したがって，ほど高解像度になるが，n を小さくすることでも空間分解能
一般的には高出力にして入射 X 線量を増やし，より吸収量を高めることができる．ただし n を小さくすると，投影像の幅を取ることによってコントラストの向上を実現させる
1 ピクセルあたりの X 線検出量が小さくなり投影像が暗くことができる．しかし，高出力の X 線は透過力も向上するマイクロフォーカス X 線 CT を用いた大型底生有孔虫研究87

を 勘 案 し た． こ の 方 法 は，“Natural laboratory approach”
ことや，大型底生有孔虫を含む微化石のような微小な標本や比較的低密度な標本では，潜在的に X 線が透過しやすい （N-lab 手法）とよばれ，潮間帯に分布する大型底生有孔虫の生態を解明する研究に用いられている．
ことにより，高出力条件下ではサンプルの X 線吸収量が極
大型底生有孔虫の成長に関しては，これまではサイズ（長端に減少するため，結果的にコントラストが低くなりやす
径）や重量が主な指標となっていた．一方，有孔虫はそのい．そのため，このような微小・低密度な標本（低コント
細胞の成長に伴って房室を付加しながら成長するため，本ラスト標本）においては，測定標本に最適な X 線出力の条
来は房室の付加率も成長の基礎的な指標である．しかし，件設定が求められる．
多くの種では外部形態から房室数を正確に把握することはこれらの分解能の設定は相互に干渉しあい，撮影時間にできず，切片化して薄片を作成するなど，標本の破壊や多も影響する．上述のように，より高解像度を実現するために X 線検出器の素子数 n を小さくすると投影像が暗くなる． くの手間を必要とした．ところが，マイクロフォーカス X
線 CT を使うと，非破壊で内部を観察でき，房室数など内
そこで，明るさを確保するためにもより高出力の X 線を利部構造の把握が簡便となった．そのため N-lab 手法では，用したいが，密度差を詳細に測定したい場合などには，コ
この測定方法が殻構造の計測手段として一般的になった
ントラスト面から出力に制限がかかるため，十分な明るさ．
が確保できない状況が生じやすい．結果的に，高解像度・ （Kinoshita et al., 2017; Eder et al., 2019）
Kinoshita et al.（2017）は，水深 50m の深度で 15 ヶ月に高コントラストを実現し十分な明るさを確保するためには，渡って定期的なサンプリングを毎月行い，N-lab 手法とマイ露光時間を長くすることになり，1 標本あたりの撮影時間がクロフォーカス X 線 CT を組み合わせて，Palaeonummulites
長くなりやすい．したがって，研究の目的に合わせて，空間分解能・密度分解能・撮影時間や標本数について，優先 venosus の成長様式を検討した．収集された各個体の房室数
すべき要素や最低限求められる水準を明確にすることが撮と殻サイズを統計学的に検討すると，平均値の分布から研
影条件決定の基盤となる．
究期間の群集は４つの世代から構成されることが明らかとなった（図 2）． N-lab 手法では測定データから各標本個体
3．マイクロフォーカス X 線 CT を利用した研究例 の房室数やサイズと生息日との関係を検討することができる（例えば，第２世代では，５月９日～１月 16 日の期間で約 29 室が付加されている）．そこで Kinoshita et al.（2017）
マイクロフォーカス X 線 CT を用いた大型底生有孔虫の研では，連続的に記録を追跡できる第２世代と第３世代に焦究には，3 次元画像上で単純な形態計測を行ったものや，セグメンテーション（領域分割，領域抽出）などにより空間， 点をあて，殻の成長率（房室形成率とサイズ増加率）を求めた（図３）．この研究は，P. venosus の房室形成率を自然
あるいは物体の物理的なパラメータの測定を行ったものなどがある．以下に それら実際の研究例をいくつか紹介する． 環境下のデータから明らかにした初めての結果となった．
また，同時にサイズ増加率も得られており，いずれの成長
3.1）大型底生有孔虫のライフサイクル
率もこれまでの飼育実験での報告（Krüger, 1994）よりも速
野外（自然環境下）での大型底生有孔虫の成長や寿命にく，自然環境下での成長では飼育環境下での 5 か月分の成関する研究は，サンゴ礁の礁縁部などの潮間帯（eulittoral
長量（房室数 40，サイズ 1.45mm）に 2 か月で到達している．
zone） に 生 息 す る 種 や（e.g. Sakai and Nishihira, 1981;
前述のように，N-lab 手法により，以下の房室形成率が得
Hohenegger, 2006）比較的サンプリングが容易な数 m 程られた．
度 の 亜 潮 間 帯 の 水 深（the shallowest sublittoral zone） の種に偏っている（e.g. Zochary et al., 1980; Fujita et al., 2000;
m = 81.3 × t / (67.2 + t )Hikami et al., 2011）．これより深い深度（deeper sublittoralzone）に生息する種の成長や生殖に関する研究は，主に室ここで，m は房室数，t は発生からの日数（生育日数）で内の飼育実験で行われている．しかし，飼育実験の生育個ある．これを t に関する式に変換すると，体では，外形が正常に成長したように見えても，X 線 CT で観察すると房室内を分ける隔壁（septula）の不足や空洞のt = m × 67.2 / (81.3 - m )形成など，内部構造に不規則な形態がみられることがわかってきた（Hohenegger et al., 2014）．また，天然海水を利用となる．この式により，各個体の生息日数を推定できるするなど，可能な限り自然環境の再現を試みた場合であっので，採集日より生育日数をさかのぼることで，個体毎のても，飼育実験では成長が阻害されることも報告されてい生殖時期を推定することもできる（Kinoshita et al.，2017）．
る（Hohenegger et al., 2014）． そ の た め，Hohenegger et
研究地域の P. venosus は，これまでの同地域の他の大型底al.（2014）は，野外の定点で定期的なサンプリングを行い， 生 有 孔 虫 の 報 告 例（Sakai and Nishihira 1981; Fujita et al.,
統計学的な手法を用いて個体群の動態を明らかにする方法
2000; Hohenegger 2006） と 同 様 に，6 月 お よ び 11 月 に

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図 2．各 サンプルに含まれる P. venosus 個体の平均房室数と平均サイズの分布．各プロットは，各々のサンプリ
ング試料に含まれる個体の房室数およびサイズを測定し，頻度分布の値を有意な正規分布の成分に分解して得られた平均値である．各時期には優位な２〜３の平均値がみとめられる．房室数でもサイズでも同様の結果を示すことから，同時期に複数世代の個体群の存在が示唆され，最終的に試料中に含まれる世
代は，４世代にわたると推定される（Kinoshita et al.，2017）．

図 3．連 続的にデータが取れる P. venosus の第２および３世代における房室数とサイズの測定から求めた房室形成率およびサイズ増加率．N-Lab 法により図２の分布図から各サンプリング群集の生息日時を推定することができる（Kinoshita et al.，2017）．そこで，房室数とサイズ分布と生息日数との関係からそれぞれの成長率をもとめることができる．各世代間では有意差は検出されなかったので，両世代でほぼ差はないと思われる．

生殖のピークがみられる．一方，年間を通して常に一定以上の生殖頻度も保たれており，これまでの熱帯赤道域での報告とも類似する（Fujita et al., 2016）．ただし，熱帯赤道域では生殖に顕著なピークがみられていない．すなわち，
Kinoshita et al.（2017）の結果は，これまで地域ごとに報告されていた季節性と恒常性が同時にみられる事例となった．
同様に，N-lab 手法とマイクロフォーカス X 線 CT 計測を利用した Eder et al.（2019）では，水深 20m，50m の異なる地点における Heterostegina depressa の房室形成率とサイズ増加率を明らかにした．異なる水深におけるサイズ増加率は，環境に応じて差が生じるのに対して房室の形成率はほぼ一致し，房室形成率が水深によらない普遍的な成長因子である可能性を示唆した．このように，マイクロフォー
カス X 線 CT による形態計測は，形態の記載や定量化に留まらず，生態学的な研究にも大きく貢献している．
3.2）大型底生有孔虫の環境応答
X 線 CT の断層像は，空間部分（黒色系）と物体部分（白色系）の 2 系統に大別して見分けることができるので，閾値処理や二値化処理，画像解析ソフトによるセグメンテーションを行うことで空間の容積，あるいは物体の体積を計測することができる．大型底生有孔虫では，房室の空間部分は細胞質で満たされており，それぞれの房室容積は成長量，総容積は総細胞質量と解釈される．Hohenegger et al.（2019）
は，Kinoshita et al.（2017）の研究を発展させ，CT 撮影によって得た 3D 画像から各個体の全房室の容積を算出した．前述のように Kinoshita et al.（2017）の研究から生息日時を推定することが可能となったので，生息日時と房室容積の関係を検討し，各々の成長日時における房室容積の理論値を

マイクロフォーカス X 線 CT を用いた大型底生有孔虫研究

89

図 5．房 室容積の標準化残差と正午の潮位との関係．点プ
ロットは実測値，緑色の破線曲線は残差の周期回帰曲線を示す．赤色の破線の曲線は理論的な 14 日周期成分で，青い周期曲線は正午の潮位の周期を表す．
房室容積の変化は約 14 日変動を示し，潮位の変動と負の相関関係をもつ．

図 4．A は P. venosus の房室容積（実測値）と生息日数の関係とその回帰曲線（理論値）．Ｂは A の実測値と理論値の差（残差）の割合を示した．残差の変動の回帰曲線（残差理論値）は周期解析によって得られた（Hohenegger et al.，2019）．

計算した（図 4A）．さらに，実際の房室容積の値（実測値）と理論値との差（残差として表現）の割合も計算した（図4B）．この地域の P. venosus の各房室は，図４が示すように理論値に対して，より成長したり，十分な成長をしなかったりを繰り返している（成長振動という）．さらに．その周期を解析すると約 14 日が主要な値として検出された．一方，サンプリング地域の海面水位の変動も約 14 日間の周期をもっており，この成長振動とは負の相関関係をもつ（図 5）．
採 集 地 点 の 光 合 成 有 効 放 射 量（Photosynthetically Active
Radiation, PAR）は，平均 22.5µmol m-2 s-1 であり，干潮時と 満 潮時 で 約 5 ～ 20 µmol m-2 s-1 程 度 の 差 が 生じている（Hohenegger et al., 2019）．Nobes et al.（2008）や Ziegler
and Uthicke（2011）によると，この範囲の PAR の変化は共生藻（珪藻）の活性度を大きく左右する．したがって，P.
venosus の成長振動は，潮の干満差による僅かな水深の差がもたらす光強度の差によって生じていると思われる．
一方，CT 画像の物体部分は有孔虫においては基本的に殻にあたる．有孔虫の殻は環境と密接な関係があり，大型底生有孔虫においても，これまでに重量やサイズが環境によって変動することが明らかになっている（e.g. Hikami et al.,2011）．ところが，天然の複雑な環境条件下では有孔虫殻の３次元的なパラメータ（体積や密度）の変動を引き起こす
環境要因を特定することは困難であるため，環境因子との因果関係は主に飼育実験によって解明されている．例えば，
高すぎる水温（約 29℃以上）は，サイズや重量からみた有孔虫の成長を阻害したり（Schmidt et al., 2016; Maeda et al.,2017, 2018），生理機能に悪影響を及ぼしていることが知られている（Uthicke et al., 2012）．また Prazeres et al.（2017）
は，高温条件下での飼育では，大型底生有孔虫の白化現象と死亡率が増加することを報告している．
これらの研究でも，マイクロフォーカス X 線 CT の活用によって新しい知見が得られている．Kinoshita et al.
（2021）は，６段階で水温を制御（19，21，23，25，27，29℃）した大型底生有孔虫 Sorites orbiculus の飼育個体をマイクロフォー
カス X 線 CT を用いて測定し，殻重量やサイズに加え，房室数や殻体積についても水温による成長量の差を検討した（図6A）．その結果，S. orbiculus 種は，殻の重量，サイズ，体積はいずれも互いに類似した傾向を示し，約 25℃で成長率が最大となり，より高温条件・低温条件のいずれの場合も成長が抑制されていることが示された．一方，殻重量およ
び殻体積を用いて算出された殻密度では，各温度条件下でほぼ一定の値となっている（図 6B）．これまで殻重量の変動の仕組みに関しては，殻の体積（主に厚さ）の変動，あるいは殻の密度の変動のいずれが主要因であるか明確に解明されていなかったが，この研究から S. orbiculus の水温変化に対応した殻重量変動は，殻体積の変動が主要因であることが明らかにされた．さらに，Kuroyanagi et al.（2021）
では，酸性度（pH）について Amphisorus kudakajimensis
種を用いて同様の飼育実験を行い，低 pH 条件下（pH ＝ 7.7）

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木下峻一

4．まとめ

図 6．飼育実験で得られた大型底生有孔虫の殻体積（A）および殻密度（B）と水温との関係．殻体積は約 25℃で成長率が最大となるが，殻密度は，各温度条件下でほぼ一定の値となっている．このことから，殻重量変動
は，殻体積の変動が主要因であることがわかる．

では，殻の重量や体積，密度のいずれも高 pH 条件下（pH＝ 8.3）に比べて低い値になることが示された．この結果は，海洋酸性化が進行すると大型底生有孔虫の殻生成を量的に阻害するだけでなく，生成される殻の質的な劣化も引き起こすことを示唆している．これらの詳細な殻パラメータ変動の解明は，マイクロフォーカス X 線 CT による３次元物体の体積の定量化によってもたらされた結果であり，本手法の利点が非常によく活かされている．
殻密度の変化については，近年の海洋酸性化への懸念の高まりとともに関心が集まっており，浮遊性有孔虫でも検討が行われている．Iwasaki et al.（2015）では，方解石の標準物質を用いて CT 画像における相対画素値を calcite CT
number と定義し，殻密度に相当する指標として使用した．
すなわち，画像の画素数の違いを用いて密度の指標とするのである（Iwasaki et al., 2015）．この研究では，画素数の濃淡から浮遊性有孔虫の殻溶解が１次形成層で選択的に起こることが示唆されている．

マイクロフォーカス X 線 CT 撮影の最も重要な特徴は，標本を破壊することなく，切断面を含めたあらゆる角度からの観察を可能にする点である．実際に，化石種の大型底生有孔虫では，初室を通る水平断面，あるいは同様の垂直断面に基づいて分類するので，標本を失わずに，かつ任意の断面を描くことができるこの手法は，今後も分類や記載において非常に大きな貢献をすることは疑いない．また，非破壊計測，3 次元計測も本手法の大きな利点である．例えば，殻の体積や密度は，マイクロフォーカス X 線 CT の登場で定量性と精密性が飛躍的に向上したパラメータであり，有孔虫の成長や環境応答への定量的な解析に有力な指標としてさらに使われていくことが期待される．
微化石の撮影に利用するような産業用の CT 撮影装置の機
械的な性能は 2010 年代において急速に向上しており，今後もハード・ソフト両面でさらに向上することが予測される．
低コントラスト問題を中心とした微化石の CT 撮影上の問題
も，撮影環境とともに改善されていくことは想像に難くない．加えて，今日の海洋の環境において温暖化と酸性化は主要な課題であり，それらの環境変動に対する石灰化生物の量的（体積）あるいは質的（密度）な変化への関心も引き続き高まることが予測される．今後は，これまで行われてきた現地モニタリングや飼育実験などによって得られた知見をさらに拡大するために，より精密な形態解析のためのツールとしてマイクロフォーカス X 線 CT がさらに広く活用されていくことが見込まれる．

謝辞

東北大学総合学術博物館の高嶋礼詩教授，黒柳あずみ助
教には本論文をまとめる機会をいただくとともに，様々なご指導をいただいた．また，福井県立大学の西弘嗣教授，東北大学の佐々木理准教授，鹿納晴尚博士，ウィーン大学の Johann Hohenegger 教授，東京大学の川幡穂高教授，琉球大学の藤田和彦教授，国立科学博物館の齋藤めぐみ博士，久保田好美博士，産業技術総合研究所の鈴木淳博士，
JAMSTEC の木元克典博士の各位からは貴重なご意見，ご教示をいただいた．ここに深く感謝いたします．

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93

東北大学総合学術博物館紀要（Bulletin of the Tohoku University Museum）
編集委員会規定2004 年 1 月 31 日


( 設置 )
第１条

東北大学総合学術博物館 ( 以下「博物館」という。) に東北大学総合学術博物館紀要編集委員会 ( 以下「委員会」という。) を置く。
( 任務 )
第２条

委員会は，館長の求めに応じ，『東北大学総合学術博物館紀要』( 以下「紀要」という。) に掲載する論文等の審査及び編集に当たるとともに，これに関する事項について審議する。
( 組織 )
第３条

委員会は，次に掲げる者をもって組織する。

一．博物館の教官で館長が指名した者。
二．博物館の運営委員及び兼任教官で館長が委託した者。
三．その他，特に館長が必要と認めた者。
( 委員長 )
第４条

委員会に，委員長を置く。

一．委員長は，第３条第１項，及び第２項の委員の互選によって定める。
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この規定は，2004 年 1 月 31 日から施行する。

94

東北大学総合学術博物館『紀要』寄稿要項
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２

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①

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Bulletin of the Tohoku University Museum