Bull. Tohoku Univ. Museum. No. 23, pp. 11‒15, 2024
© by The Tohoku University Museum

Late Devonian longiconic nautiloids from the TobigamoriFormation, Iwate Prefecture, 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: A geisonoceratid orthocerid, Geisonocerina? sp., and two pseudorthoceratid
pseudorthocerids, Spyroceras? sp. and Dolorthoceras sp., are described from the Famennian(latest Devonian) shale of the Tobigamori Formation from an abandoned quarry (“Nendoyama”) inthe Higashiyama area, Iwate Prefecture, Northeast Japan. They represent the first record of Late
Devonian longiconic nautiloids in East Asia.

Introduction
Our knowledge concerning Devonian longiconic nautiloids
in East Asia is very limited. Furthermore, previously
described occurrences are exclusively from the Lowerand Middle Devonian, including the Lochkovian parts of
the Kamianama and Fukuji formations, Central Japan(Niko, 1991, 1993, 1996, 2017; Kamiya and Niko, 1997),
the Emsian Daliancun and Liujing formations, Guangxi,South China (Lai and Zhang, 1988), the Eifelian rocks ofInner Mongolia, North China (Liang, 1981), the probably
Eifelian part of the Nakazato Formation (Niko, 1989), andthe Givetian Qiziqiao Formation, Hunan, South China (Laiand Zhang, 1988). The present Late Devonian specimensfrom the Tobigamori Formation in Northeast Japan are
therefore noteworthy even though their preservation is notalways satisfactory. The purpose of this paper is to describe
three species, Geisonocerina? sp., Spyroceras? sp. andDolorthoceras sp., based on the Tobigamori material forfurther taxonomic, biostratigraphic, and biogeographic
studies.
Abbreviations.–The following two abbreviations are used
to indicate the repositories of nautiloid specimens. IGPS:Tohoku University Museum, Sendai, Miyagi Prefecture.
MSK: Museum of Stones and Kenji Museum (Ishi to Kenji noMuseum), Ichinoseki, Iwate Prefecture.

Geologic setting and occurrence
The Tobigamori Formation is a thick sedimentary unit
(800–1800 m) composed of black shales with intercalationsof tuff, sandstone and conglomerate (Noda, 1934;Tachibana, 1952; Onuki, 1956). It unconformably overlies
ultramafic rocks probably associated with the Motai

metamorphic rocks (Sasaki et al., 1997). The relationshipbetween the formation and the overlying Karaumedate
Formation is inferred to be conformably (Okami et al., 1973;
Osawa et al., 1981; Kawamura and Kawamura, 1989).
Since the first discovery of the Late Devonian brachiopod
Spirifer verneuili by Yabe and Nada (1933), the diverse
fauna and flora ranging in age from the Famennian to theTournaisian (latest Devonian to earliest Carboniferous)
have been recorded from the Tobigamori Formation as
stated below. The main Famennian part is characterized byabundant occurrences of the index brachiopods Cyrtospiriferand Sinospirifer (Hayasaka and Minato, 1954; Noda andTachibana, 1959; Minato and Kato, 1979) and the vascularterrestrial plants Leptophloeum and Cyclostigma (Tachibana,1950, 1966). The exact age determinations of the upper touppermost parts ware done by Ehiro and Takaizumi (1992).
They confirm that the Devonian-Carboniferous boundary
situates within the Tobigamori Formation by findingsof the Famennian ammonoids, Costaclymenia sp. and
Platyclymenia (Platyclymenia) sp., from the 25–35 m below
of the top of the Tobigamori Formation and the Tournaisianammonoid Protocanites sp. from a float block derived fromthe 5–10 m below of ditto.
The examined specimens of longiconic nautiloids comefrom shale exposures of an abandoned quarry, which is called“Nendoyama”, at Minamiiwairi, Nagasaka in the Higashiyama
area, Ichinoseki City, Iwate Prefecture (see fig. 1 in Ehiro andTakaizumi, 1992, for its geographic position). Among them, aspecimen of Geisonocerina? sp. (IGPS coll. cat. no. 112841)
was collected from talus deposits, whose original horizon issituated approximately 35 m below the top of the formation.
Although the exact stratigraphic origin of the other specimens
MSK19921211, 19950501, 20230801-1, 2 (Geisonocerina?
sp.), MSK19950501 (Spyroceras? sp.) and MSK19950501

12Shuji Niko and Masayuki Ehiro

Late Devonian nautiloids from Iwate(Dolorthoceras sp.) are unknown, the lithologic characters of
their matrixes indicate that they derive from the upper part
indicating Famennian age.

Systematic paleontology
Subclass Orthoceratoidea Teichert, 1967
Order Orthocerida Kuhn, 1940Family Geisonoceratidae Zhuravleva, 1959
Genus Geisonocerina Foerste, 1935
Type species.–Orthoceras wauwatosense Whitfield, 1882.
Geisonocerina? sp.
Figures 1.A–1.C, 1.H
Description.–Three fragmentary specimens wereexamined; they are longiconic orthocones with very gradualexpansion and circular transverse sections; the largest
specimen is a phragmocone (IGPS coll. cat. no. 112841),
which measures 81 mm in length and approximately 9 mm inreconstructed diameter; conch surface ornamented by finetransverse lirae. Camerae relatively long with approximately
1.7 in form ratio (maximum reconstructed width per length).
Sutures directly transverse. No siphuncular structure
preserved.
Material examined.– MSK20230801-1, 2. IGPS coll. cat.
no. 112841.
Discussion.–Accurate generic identification of thespecimens is difficult because of their poor preservation, butthey are tentatively included in the geisonoceratid genus,
Geisonocerina, on the basis of the possessions of the very
gradually expanding conchs, the fine surface lirae, and therelatively long camerae.
Order Pseudorthocerida Barskov, 1963
Family Pseudorthoceratidae Flower and Caster, 1935
Subfamily Spyroceratinae Shimizu and Obata, 1935
Genus Spyroceras Hyatt, 1884
Type species.–Orthoceras crotalum Hall, 1861.
Spyroceras? sp.
Figures 1.D, 1.E

13Description.–A single fragment of deformed body chamber
was examined; it is an annulated orthocone with gradualexpansion and 69 mm in length; on the premise that thisbody chamber is conical, the reconstructed conch diameter
is approximately 25 mm near the adoral end; peristome
not preserved; annulations oblique at the present (by post
mortem deformation) with rounded crests; no distinct surface
ornamentation detected both on and between annulations.
Material examined.– MSK19950501.
Discussion.–This poorly preserved specimen is tentatively
placed in the pseudorthoceratid genus, Spyroceras,
because it is comparable in external morphology with thebody chamber of S. melolineatum Niko, 1996, describedfrom the Lower Devonian Takaharagawa Member, the Fukuji
Formation in Gifu Prefecture. Similar annulations also occur
in Cycloceras M’Coy, 1844, but its type species, Orthoceras
laevigatum M’Coy, 1844, has the much slenderer conch andoccurs exclusively in the Carboniferous.
Genus Dolorthoceras Miller, 1931
Type species.–Dolorthoceras circulare Miller, 1931.
Dolorthoceras sp.
Figures 1.F, 1.G, 1.I
Description.–A single specimen of imperfect phragmocone
was examined; it is a longiconic orthocone with moderate
expansion and 75 mm in length; assuming that the conchshape is conical, the reconstructed diameter is approximately
11 mm near adoral end; conch surface smooth lacking
distinct ornamentation. Camerae short indicating 3.2–3.7 inform ratio (maximum reconstructed width per length). Septa
relatively shallow. Sutures oblique because of post mortemdeformation. Siphuncle nearly central in position andconsists of suborthochoanitic(?) septal necks and weakly
inflated connecting rings.
Material examined.– MSK19921211.
Discussion.–Although the specimen is poorly preserved,
its gross conch shape, short camerae and connecting ring
shape warrant the generic assignment to Dolorthoceras.
This species may resemble some Late Devonian species,
such as D. elegans Flower, 1939, D. palmerae (Flower andCaster, 1935) and D. solitarium Flower, 1939, but it is not←Figure 1. A–C, H. Geisonocerina? sp. A, B, SKM20230801-1: A, side view of conch; B, partial enlargement of A toshow details of surface ornamentation: C, IGPS coll. cat. no. 112841, side view of phragmocone, silicone rubber cast: H,SKM20230801-2, side view of phragmocone, internal mold. D, E. Spyroceras? sp., body chamber, SKM19950501. D, sideview, silicone rubber cast; E, side view, internal mold. F, G, I. Dolorthoceras sp., phragmocone, SKM19921211. F, side view,silicone rubber cast; G, side view, internal mold; I, partial enlargement of G to show siphuncular structure, arrow indicatesconnecting ring. Scale bar is 10 mm in A; 6 mm in B, H; 15 mm in C, G; 20 mm in D–F; 4.3 mm in I.

Shuji Niko and Masayuki Ehiro

14
complete enough for confident comparisons.

Acknowledgements
The authors extend their thanks to the late Kiyoshi
Shichida, who collected most of the nautiloid specimens
examined herein. Because the present study could nothave been done without his private collection, we would
like to dedicate this paper to this excellent amateur fossil
researcher. We thank Jun Sugawara for providing usthe opportunity to examine the specimens owned by theMuseum of Stones and Kenji and Eiwa Kogyo Co., Ltd.
for allowing our field work in the property of the company.
Christian Klug made helpful comments on an earlier draft ofthe manuscript.

References
Barskov, I. S., 1963, System and phylogeny of pseudorthoceratids.
Biulleten Moskovskogo Obshchestva Ispytatelei Prirody, Otdel
Geologicheskii, vol. 38, p. 149–150. (in Russian)
Ehiro, M. and Takaizumi, Y., 1992, Late Devonian and Early
Carboniferous ammonoids from the Tobigamori Formationin the Southern Kitakami Massif, Northeast Japan and theirstratigraphic significance. The Journal of the Geological Societyof Japan, vol. 98, p. 197–204, pl. 1.
Flower, R. H., 1939, Study of the Pseudorthoceratidae.
Palaeontographica Americana, vol. 2, p. 1–214, pls. 1–9.
Flower, R. H. and Caster, K. E., 1935, The stratigraphy andpaleontology of northwestern Pennsylvania. Part II:Paleontology. Section A: The cephalopod fauna of theConewango Series of the Upper Devonian in New York andPennsylvania. Bulletins of American Paleontology, vol. 22, p.
199–271.
Foerste, A. F., 1935, Bighorn and related cephalopods. Journal ofthe Scientific Laboratories, Denison University, vol. 30, p. 1–96,pls. 1–22.
Hall, J., 1861, Report of the Superintendent of the GeologicalSurvey, Exhibiting the Progress of the Work. January 1, 1861,
52 p. L. A. Calkins & Co., Madison, Wisconsin.
Hayasaka, I. and Minato, M., 1954, A Sinospirifer-faunule fromthe Abukuma Plateau, Northeast Japan, in comparison withthe so-called Upper Devonian brachiopod faunule of theKitakami Mountains. Transactions and Proceedings of thePalaeontological Society of Japan, New Series, no. 16, p.
201–211, pl. 26.
Hyatt, A., 1883–1884, Genera of fossil cephalopods. Proceedings ofthe Boston Society of Natural History, vol. 22, p. 253–338.
Kamiya, T. and Niko, S., 1997, Devonian orthoconic cephalopods
from the Oise Valley in the uppermost reaches of theKuzuryu River, Fukui Prefecture. Chigaku Kenkyu (Journalof Geoscience), vol. 46, p. 83–86. (in Japanese with Englishabstract)
Kawamura, T. and Kawamura, M., 1989, The Carboniferous Systemof the South Kitakami Terrane, Northeast Japan, (part 1) –summary of the stratigraphy–. Chikyu Kagaku (Earth Science),
vol. 43, p. 84–97. (in Japanese with English abstract)Kuhn, O., 1940, Paläozoologie in Tabellen, 50 p. Fischer, Jena.

Lai, C. and Zhang, Z., 1988, Nautiloids from Early and Middle
Devonian of Hunan and Guangxi. Professional Papers ofStratigraphy and Palaeontology, vol. 21, p. 29–47, pls. 1–4. (inChinese with English abstract)
Liang, Z., 1981, Middle Devonian nautiloids from the central part ofDaxinganling. Bulletin of the Shenyang Institute of Geology andMineral Resources, Chinese Academy of Geological Sciences,vol. 2, p. 137‒145. (in Chinese with English abstract)
M’Coy, F., 1844, A Synopsis of the Characters of the Carboniferous
Limestone Fossils of Ireland, 274 p. Privately published.
(reissued by Williams and Norgate, London, 1862)
Miller, A. K., 1931, Two new genera of Late Paleozoic cephalopods
from Central Asia. American Journal of Science, Series 5, vol.
22, p. 417‒425.
Minato, M. and Kato, M., 1979, Chapter 2e, Upper Devonian, 2e3)
Palaeontology. In, Minato, M. et al., eds., Variscan Geohistoryof Northern Japan: The Abean Orogeny, p. 70‒71, Tokai
University Press, Tokyo.
Niko, S., 1989, A new Devonian cephalopod from the NakazatoFormation of the southern Kitakami Mountains. Transactions
and Proceedings of the Palaeontological Society of Japan,New Series, no. 156, p. 291‒295.
Niko, S., 1991, Plicatoceras, a new lamellorthoceratid cephalopod
genus from the Gedinnian (Early Devonian) of Central Japan.
Journal of Paleontology, vol. 65, p. 917–919.
Niko, S., 1993, Orthoceratid cephalopods from the Early Devonian
Fukuji Formation of Gifu Prefecture, Central Japan. Journal ofPaleontology, vol. 67, p. 210–216.
Niko, S., 1996, Pseudorthoceratid cephalopods from the Early
Devonian Fukuji Formation of Gifu Prefecture, Central Japan.
Transactions and Proceedings of the Palaeontological Societyof Japan, New Series, no. 181, p. 347‒360.
Niko, S., 2017, Early Devonian orthocerid cephalopods from theKamianama Formation, Fukui Prefecture, Central Japan.
Bulletin of the Tohoku University Museum, no. 16, p. 1–4.
Noda, M., 1934, Geology of the environs of Nagasaka, Kitakami
Mountainland. The Journal of the Geological Society of Tôkyô,vol. 41, p. 431–456. (in Japanese)
Noda, M. and Tachibana, K., 1959, Some Upper Devonian
cyrtospiriferids from the Nagasaka district, Kitakami
Mountainland. Science Reports of the Faculty of Arts andLiterature, Nagasaki University, no. 10, p. 15–21, pl. 1.
Okami, K., Kawakami, T. and Murata, M., 1973, Conglomerate ofthe Karaumedate Formation in the Kitakami Massif, Northeast
Japan. The Science Reports of the Tohoku University, SecondSeries, Special Volume, no. 6, p. 457–464.
Onuki, Y., 1956, Geology of the Kitakami Massif. In, Explanatory
Text of the Geology of Iwate Prefecture, II. Iwate Prefecture,
Morioka, p. 1–187. (in Japanese)
Osawa, M., Nagura, M., Tazawa, J. and Mori, K., 1981, Geologyof the Nagasaka district, Southern Kitakami Mountains,with special reference to the Devonian-Carboniferous andCarboniferous-Permian boundaries. Abstracts of the 88th
Annual Meeting of the Geological Society of Japan, p. 177. (inJapanese)
Sasaki, M., Tsukada, K. and Otoh, S., 1997, An outcrop ofunconformity at the base of the Upper Devonian Tobigamori
Formation, Southern Kitakami Mountains. The Journal of theGeological Society of Japan, vol. 103, p. 647–655, pls. 1, 2. (inJapanese with English abstract)
Shimizu, S. and Obata, T., 1935, New genera of Gotlandian andOrdovician nautiloids. The Journal of the Shanghai ScienceLate Devonian nautiloids from Iwate
Institute, Section 2, vol. 2, p. 1–10.
Tachibana, K., 1950, Devonian plants first discovered in Japan.
Proceedings of the Japan Academy, vol. 26, p. 54–60.
Tachibana, K., 1952, On the Tobigamori Group of the Nagasaka
district, Kitakami Mountainland. The Journal of the GeologicalSociety of Japan, vol. 58, p. 353–360. (in Japanese)
Tachibana, K. 1966, On the age and distribution of Leptophloeum
contained in the Tobigamori flora. The Annual Report of theFaculty of Education, University of Iwate, vol. 26, p. 9–22, 1pl.
(in Japanese with English abstract)
Teichert, C. 1967, Major features of cephalopod evolution. In,Teichert, C. and Yochelson, E. L. eds., Essays in Paleontology& Stratigraphy. R. C. Moore Commemorative Volume,

15

Department of Geology, University of Kansas Special
Publication 2, p. 162–210. The University Press of Kansas,Lawrence and London.
Whitfield, R. P., 1882, Paleontology. In, Geology of Wisconsin.
Survey of 1873-1879, Volume 4. State of Wisconsin,Commissioners of Public Printing, Madison, Wisconsin, p.
163–349, pls. 1–27.
Yabe, H. and Nada, M., 1933, Discovery of Spirifer verneuili
Murchison in Japan. Proceedings of the Imperial Academy, vol.
9, p. 521–523.
Zhuravleva, F. A., 1959, On the family Michelinoceratidae Flower,
1945. Materialy k Osnovam Paleontologii, vol. 3, p. 47–50 (inRussian)