Bull. Tohoku Univ. Museum, No. 17, pp. 1–8, 2018
© by The Tohoku University Museum

Aulacocerid coleoids from the Triassic of the South
Kitakami Belt, Northeast Japan
Shuji Niko* and Masayuki Ehiro*** Department of Environmental Studies, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima
739-8521, Japan, ** The Tohoku University Museum, Sendai 980-8578, Japan
Abstract: Three species of aulacocerid coleoids from the South Kitakami Belt of Northeast Japan
deal herein. Miyagiteuthis gen. nov. is proposed for a Norian (Late Triassic) aulacoceratid species
Dictyoconites nipponicus Shimizu and Mabuti, 1941, by taxonomic revisions of the original
material and newly collected topotypes. The original two specimens of a Ladinian (Middle Triassic)
xiphoteuthidid species Atractites hatai Bando, 1963, are revised and assigned this species to
Choanoteuthis. A new xiphoteuthidid species Calliconites? shimizui is described from the Olenekian(Early Triassic) mudstones of the Osawa Formation in the Utatsu area.

Introduction
Aulacocerida is an order of coleoid cephalopods
characterized by the possession of aragonitic rostrum,
longiconic phragmocone with relatively low expansion
angle, long body chamber and prochoanitic (or achoanitic
in specialized taxa) in adult septal necks, and the absenceof proostracum and hyperbolar zone. It comprises threefamilies, namely Aulacoceratidae, Dictyoconitidae, andXiphoteuthididae (Jeletzky, 1966; Keupp and Fuchs, 2014).
Although aulacocerids occur widely in the Upper Permianto the Upper Jurassic strata in the Tethyan region (Doyle,1990), reports in Japan are scarce and restricted in the
Triassic of the South Kitakami Belt. Previously only two
species have been known. The first aulacocerid species
from the area described by Shimizu and Mabuti (1941),
who reported Dictyoconites nipponicus on the basis of
specimens collected from the early Norian (Late Triassic)
sandstones of the Chonomori Formation, Saragai Groupat the Niranohama locality (38° 41’ 26’’ N, 141° 30’ 11’’ E;
loc. A in Figure 1), western coast of Niranohama in the
Hosoura area, Minamisanriku Town, Miyagi Prefecture.
Subsequently, Bando (1963) described Atractites hatai fromthe early Ladinian (Middle Triassic) sandy mudstones of
the Rifu Formation. Collecting site of the type specimens of
A. hatai is a quarry (38° 21’ N, 141° 2’ E, the second timescales unknown because detailed documentations aboutcollecting site did not note in an original designation andthis quarry has a span of ca. 0.7 km; loc. B in Figure 1)
in the Rifu area, Rifu Town, Miyagi Prefecture. The main
objectives of this contribution are to revise their taxonomic

position. In addition, we describe Calliconites? shimizui sp.
nov. to further knowledge of the aulacocerid fauna of theSouth Kitakami Belt. The new species is recovered fromthe late Olenekian (Early Triassic) laminated mudstones of
the Osawa Formation at the Tatezaki locality (38° 42’ 50’’N, 141° 32’ 07’’ E; loc. C in Figure 1; see Ehiro et al., 2015,2016 for its stratigraphy and fauna) in the Utatsu area,
Minamisanriku Town, Miyagi Prefecture.
Abbreviation: IGPS (Institute of Geology and Paleontology,
Faculty of Science, Tohoku University, Sendai; kept in the
Tohoku University Museum).

Systematic Paleontology
Subclass Coleoidea Bather, 1888
Order Aulacocerida Stolley, 1919
Family Aulacoceratidae Mojsisovics, 1882
Genus Miyagiteuthis gen. nov.
Type species.─Dictyoconites nipponicus Shimizu and
Mabuti, 1941, by monotypy.
Diagnosis.─Aulacoceratid genus with cylindriconicalrostrum having strongly compressed panduriform to
sub-elliptical cross sections and well-developed pared
dorsolateral depressions in apical and stem regions; dorsal
part of rostrum forms protrusion having fan-shaped crosssection; surface ribs coarse.
Etymology.─The generic name is combination ofprefecture of the type locality, named Miyagi, and a suffix
teuthis meaning squid.
Discussion.─Miyagiteuthis gen. nov. resembles a Late

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Shuji Niko and Masayuki Ehiro

Figure 1. Map of southern part of the South Kitakami Belt from which aulacocerids were collected. Black areas represent
distributions of Triassic sedimentary rocks.
Triassic genus Aulacoceras Hauer (1860; type species, A.
sulcatum Hauer, 1860) that was an only representative of
the family. However, strongly compressed rostrum at theapical and stem regions with panduriform to sub-ellipticalcross sections of the new genus is the most distinctive
feature from Aulacoceras, whose cross sections of rostrum
are invaluably subcircular. Laterally compressed rostra
are common features in the more primitive genera (suchas Calliconites Gemmellaro, 1904, and Metabelemnites
Flower, 1944) belonging to the family Xiphoteuthididae.
Miyagiteuthis may be an ancestor of Aulacoceras.
Two dictyoconitid genera Prographularia Frech (1890;
type species, P. triadica Frech, 1890) and Dictyoconites
Mojsisovics (1902; type species, Orthoceras reticulatum
Hauer, 1847) are easily separated from Miyagiteuthis by
their significantly finer ribs. This difference warrants a familial
assignment of Miyagiteuthis.

Miyagiteuthis nipponica (Shimizu and Mabuti, 1941)
Figures 2.1‒2.12
Dictyoconites sp. nov., Shimizu and Mabuti, 1932, p. 314;
Inai, 1939, p. 237.
Dictyoconites nipponicus Shimizu and Mabuti, 1941, p.
923‒925, pl. 48, figs. 1, 2, 3a, b, 4a, b, 5a, b, 6, 7a‒c, 8, pl. 49, figs. 1‒7; Ichikawa, 1951, p. 19; Onuki andBando, 1958, p. 488; Bando, 1964, p. 12; Nakazawa,
1964a, p. 23; Nakazawa, 1964b, p. 524.
Dictyoconites japonicus [sic]. Ando, 1986, p. 41; Kamada,
1993, p. 36.
Prographularia nipponica. Doyle, 1990, p. 269.
Diagnosis.─As for the genus.
Description.─Rostrum cylindriconical, large, more than 132
mm in length and 25 mm in diameter; a distinct transverse
constriction may develop at alveolar region; in apical tostem regions cross sections of rostrum are panduriform to
sub-elliptical with strong lateral compression and a welldeveloped dorsolateral depression with bilateral distribution,

Triassic coleoids from South Kitakami Belt

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Figure 2. Miyagiteuthis nipponica (Shimizu and Mabuti, 1941). 1. Lectotype, IGPS coll. cat. no. 49600-1, longitudinal
section of rostrum, weathered surface. 2. Paralectotype, IGPS coll. cat. no. 49600-2, dorsoventral section of rostrum,
weathered surface, venter on left, arrow indicates dorsolateral depression. 3. Paralectotype, IGPS coll. cat. no. 4960034, cross section at apical region of rostrum, polished surface, venter down. 4. Topotype, IGPS coll. cat. no. 111755, crosssection at stem region of rostrum, polished surface, venter down. 5, 10. Paralectotype, IGPS coll. cat. no. 49600-41, alveolar
region of rostrum: 5, cross polished section at apical end, polished surface, venter down; 10, cross section at adoral end,
polished surface, venter down. 6. Topotype, IGPS coll. cat. no. 111753, cross section at alveolar region of rostrum, polishedsurface, venter down. 7. Paralectotype, IGPS coll. cat. no. 49600-18, cross section at stem region of rostrum, polishedsurface, venter down. 8, 9. Paralectotype, IGPS coll. cat. no. 49600-47, alveolar region of rostrum: 8, cross thin section,
venter down; 9, partial enlargement of Figure 2.8 to show details of siphuncle. 11. Paralectotype, IGPS coll. cat. no. 4960011, external view of rostrum, silicon rubber replica, coated by ammonium chloride. 12. Paralectotype, IGPS coll. cat. no.
49600-16, longitudinal section of phragmocone, weathered surface, coated by ammonium chloride. Scale bar is 30 mm in
Figures 2.1, 2.2; 10 mm in Figures 2.3‒2.8, 2.10, 2.11; 3 mm in Figure 2.9; 5 mm in Figure 2.12.

Shuji Niko and Masayuki Ehiro

4then they shift to subcircular and depressions become
diminished in their width and depth in alveolar region; dorsal
part defined by dorsolateral depressions forms protrusion
having fan-shaped cross section; surface of rostrum
marked by coarse longitudinal ribs and narrow furrows; noapex of rostrum and body chamber preserved. Alveolus
cylindrical with approximately 10° in dorsoventral section,
dorsoventrally depressed cross sections and dorsolateralgrooves; length of alveolus is less than half of total robustum
length. Phragmocone is not well preserved, but relatively
long camerae with deep and adapically concaved septa
and marginal siphuncle are discernible; wall of siphuncle
probably contact with ventral wall of phragmocone.
Material examined.─In the original description of thisspecies by Shimizu and Mabuti (1941), no holotype wasdesignated. Subsequent authors also have not designate alectotype. Therefore, we designate IGPS coll. no. 49600-1 as
the lectotype, and forty-six specimens 49600-2‒47 become
the paralectotypes. In addition, thirteen newly collected
specimens (topotypes), IGPS coll. cat. no. 111745‒111757,
from the type locality were also examined.
Occurrence.─Early Norian, the Chonomori Formation,
Northeast Japan.

Shimizu, in recognition of his early work of aulacocerids fromthe South Kitakami Belt.
Discussion.─Its general rostrum shape of this species
suggests affinity with Calliconites, but the presence ofa ventral groove deviates the diagnosis of the genus. In
addition, grooves on each flank of Calliconites occur at theventrolateral and dorsolateral positions forming a pair. A
lateral groove on each flank is also diagnostic character in
Atractites Gümbel (1861; type species, A. alpinus Gümbel,
1861), but the rostrum of the genus is extremely narrowwaisted and circular to subcircular in cross sections. The
generic assignment is indicated with question, because
no internal structure is preserved in the type specimens.
Calliconites? shimizui sp. nov. represents the first Early
Triassic and oldest records of aulacocerids in Japan.

Family Xiphoteuthididae Naef, 1922
Genus Calliconites Gemmellaro, 1904
Type species.─Calliconites dieneri Gemmellaro, 1904.

Description.─The original two specimens represent
imperfect stem and alveolar regions of rostrum that isnearly cylindrical with a shallow transverse constriction
near junction of these regions; no apical region preserved;
cross sections of rostra are elliptical indicating slight lateralcompression in stem region and nearly circular in alveolar
region; adoral end of alveolar region in a larger specimen(lectotype, see below, IGPS coll. cat. no. 79170-1) is 18 mm
in diameter; surface of rostrum is smooth lacking groove; noapical part of rostrum and body chamber preserved. Alveolus
very deep, more than 32 mm in depth. Phragmocone
orthoconic with expansion angle of approximately 10°
in dorsoventral section and nearly circular to slightly
compressed cross sections; septa deep, concave adapically;
septal spacing relatively wide; there are 2‒4 camerae incorresponding phragmocone diameter; siphuncular positionis close to ventral margin; ventral septal necks retrochoanitic
and straight (holoochoanitic?); dorsal septal necks bifurcate
into prochoanitic and retrochoanitic parts, the latter of whichrecurved (cyrtochoanitic); connecting rings thickened andcylindrical.
Material examined.─In Bando’s (1963) original descriptionof this species, he did not designated a holotype. Therefore,
we designate IGPS coll. cat. no. 79170-1 as the lectotype
and, a specimen 79170-2 becomes the paralectotype.
Occurrence.─Early Ladinian, the Rifu Formation,
Northeast Japan.
Discussion.─Although Bando (1963) assigned this species

Calliconites? shimizui sp. nov.
Figure 3.1‒3.7
Diagnosis.─Rostrum asymmetrical subhastate in profile,and cylindriconical in outline; cross sections of rostrum
laterally compressed elliptical; surface of rostrum marked by
ventral and lateral grooves.
Description.─Two external molds of imperfect rostra are
available for study; they relatively small, respectively 39
mm (holotype) and 33 mm (paratype) in length; profile ofrostrum asymmetrical subhastate and outline cylindriconical;
apex slightly displaced toward dorsum; cross sectionsof rostra are elliptical having lateral compression; form
ratios (lateral diameter/dorsoventral diameter) of rostrum
are approximately 0.7; the most inflated part of rostrum inthe holotype is 5 mm in dorsoventral diameter; surface ofrostrum is smooth, except for three grooves consisting ofa distinct median ventral groove and a very shallow lateralgroove on each flank. Internal structure unknown.
Material examined.─Holotype, IGPS coll. cat. no. 111759.
Paratype, IGPS coll. cat. no. 111758.
Occurrence.─Late Olenekian, the Osawa Formation,
Northeast Japan.
Etymology.─The specific name honors the late Dr. Saburo

Genus Choanoteuthis Fisher, 1951
Type species.─Choanoteuthis milleri Fisher, 1951.
Choanoteuthis hatai (Bando, 1963)
Figures 4.1‒4.9
Atractites hatai Bando, 1963, p. 48, 49, pl. 8, figs. 1‒6.

Triassic coleoids from South Kitakami Belt

5

Figure 3. Calliconites? shimizui sp. nov. 1, 2, 5. Paratype, IGPS coll. cat. no. 111758, silicon rubber replica of rostrum,
coated by ammonium chloride: 1, lateral view, venter on right; 2, dorsal view, arrow indicates position of Figure 3.5; 5, crosssection, venter down. 3, 4, 6, 7. Holotype, IGPS coll. cat. no. 111759, silicon rubber replica of rostrum, coated by ammonium
chloride: 3, lateral view, venter on left, upper and lower arrows indicate positions of respectively Figure 3.6 and 3.7; 4, ventral
view; 6, cross section, venter down, arrow indicates ventral groove; 7, cross section, venter down. Scale bar is 10 mm in
Figures 3.1‒3.3; 5 mm in Figures 3.4‒3.7.

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Shuji Niko and Masayuki Ehiro

Triassic coleoids from South Kitakami Belt
to Atractites, it is removed from the genus and placed in
Choanoteuthis from the following morphological respects:
nearly cylindrical shape in the stem and alveolar regionsof rostrum that does not exhibit extremely narrow-waist;
very deep rather than shallow alveolus; and the absence oflateral grooves. Choanoteuthis milleri Fisher (1951, p. 387,
388, 390, pl. 1, figs. 1-3, pl. 2, figs. 1, 2, text-fig. 1) from theNorian of Nevada differs from C. hatai by its more longer
camerae. Mariotti and Pignatti (1992) advocated a new
genus, Crassiatractites, based on Atractites crassirostris
Hauer, 1888, whose species occurs from the Anisian to
Ladinian of Bosnia, Albania and Austria, and has similarfeatures with C. hatai except for its conical stem region of
rostrum. There is a possibility that Crassiatractites is a juniorsubjective synonym of Choanoteuthis.

Acknowledgements
We are grateful to Dr. Jun Nemoto for assistance inexamining the original type series. We thank the Educational
Committee of Minamisanriku Town and Abei-Gumi Co.
Ltd. for permissions to excavate fossiliferous beds at the
Tatezaki locality. The manuscript has been improved by ananonymous reviewer for which we are also appreciative.

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Figure 4. Choanoteuthis hatai (Bando, 1963). 1, 7‒9. Paralectotype, IGPS coll. cat. no. 79170-2, stem and alveolar
regions of rostrum: 1, ventral view, arrow indicates position of Figures 4.7, 4.9, coated by ammonium chloride; 7, crosssection at alveolar region, fracture surface, venter down; 8, cross section near adoral end, polished surface, venter down; 9,partial enlargement of Figure 4.7 to show cross section of phragmocone. 2‒6. Lectotype, IGPS coll. cat. no. 79170-1, stem
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structure of siphuncle, venter on left; 6, cross thin section at alveolar region, venter down. Scale bar is 30 mm in Figures 4.1,
4.2; 15 mm in Figure 4.3; 6 mm in Figure 4.4; 3 mm in Figure 4.5; 10 mm in Figures 4.6‒4.8; 2 mm in Figure 4.9.

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