Octobrachia Fioroni, 1981

Tanabe, Kazushige, Misaki, Akihiro & Ubukata, Takao, 2015, Late Cretaceous record of large soft-bodied coleoids based on lower jaw remains from Hokkaido, Japan, Acta Palaeontologica Polonica 60 (1), pp. 27-38 : 32-33

Superorder Octobrachia Fioroni, 1981

Order Vampyromorpha Robson, 1929

Family uncertain

Genus Nanaimoteuthis Tanabe in Tanabe et al., 2008 Type species: Nanaimoteuthis jeletzkyi Tanabe in Tanabe et al., 2008; Lower Campanian (Upper Cretaceous) Pender Formation, about 10 km northwest of Courtenay, north-central Vancouver Island, Canada.

Species included: Nanaimoteuthis jeletzkyi Tanabe, 2008 , from the lower Campanian of Vancouver Island, Canada ( Tanabe et al. 2008), and the Haboro area, northwestern Hokkaido, Japan (AM unpublished data), and N. yokotai Tanabe and Hikida, 2010 , from the Turonian of the Tappu (Obira) and Nakagawa areas, Hokkaido ( Tanabe and Hikida 2010), and Nanaimoteuthis hikidai sp. nov.

Emended diagnosis.—Large lower jaw characterised by large outer lamella with very high wing fold, very broad hood that is prominently convex anteriorly without notch, weakly expanded wing, and short rostrum with pointed hook; short inner lamella with crest portion mostly covered by outer lamella, and lateral wall without fold or ridge.

Discussion.—Vampyromorphid coleoid lower jaws comparable in overall morphology and size to those of the present genus are hitherto unknown in the fossil record. However, large gladii of vampyromorphid genera Tusoteuthis Logan, 1898 ,of the suborder Mesoteuthina Naef, 1921 , and Actinosepia Whiteaves, 1897 , of the suborder Teudopseina Starobogatov, 1983 , have been reported from the Campanian strata of Vancouver Island ( Fuchs et al. 2007) in addition to the Campanian and Maastrichtian rocks in the Western Interi- or Province of North America ( Whiteaves 1897; Logan 1898; Waaage 1965; Nicholls and Isaak 1987; Larson 2010). The extremely large lower jaws of Nanaimoteuthis and gladii of Tusoteuthis and Actinosepia seem to suggest their taxonomic affinity, but this hypothesis should be verified from future discoveries of exceptionally well-preserved fossils showing a gladius-jaw apparatus association.

Stratigraphical and geographical range.—The genus Nanaimoteuthis has been reported from the Turonian to the Campanian rocks of Vancouver Island, Canada ( Tanabe et al. 2008), and Hokkaido, Japan ( Tanabe and Hikida 2010; Tanabe 2012; this paper).

Nanaimoteuthis hikidai sp. nov.

Fig. 6A–E .

2012 Nanaimoteuthis sp. nov.; Tanabe 2012: fig. 4-3a, b.

Etymology: Named for the palaeontologist Yoshinori Hikida (Nakagawa Museum of Natural History, Nakagawa, Hokkaido) in recognition of his significant contribution to the studies of Cretaceous molluscs from Hokkaido.

Holotype: KMNH IvP 902,001, a lower jaw, the only specimen available. Type locality: A riverside outcrop in the Detofutamata River , now un- der the Futamata Reservoir , about 200 m north-northeast from the Haboro-futamata Dam site, Haboro, northwestern Hokkaido, Japan ( Fig. 1 : Locality 1).

Type horizon: The Member Ui-j, the uppermost part of the Haborogawa Formation, lower Campanian, Upper Cretaceous.

Diagnosis.—Large lower jaw characterised by well-developed thick outer lamella with high wing fold, very obtuse jaw angle, long and gently arched hood with convex anterior margin, short rostrum with more or less pointed hook; relatively short inner lamella without ridge and fold, with crest portion mostly covered by outer lamella, and lateral wall lacking fold and ridge and instead sculptured by many fine radial striations.

Description. —Lower jaw extremely large, consisting of almost equally sized thick inner and outer lamellae, both of which are made of black, presumably originally chitinous material; rostrum short but sharply pointed with ridgeline-like hook. Outer lamella 3.1 mm thick in rostral region (much thicker than inner lamella), 1.2 mm thick in lateral wall portion, expanded laterally with large open angle of paired wings approximately 115°, with very high wing fold (see Fig. 6D ) and very long hood without notch; hood profile from lateral side gently arched anteriorly; wing shortly expanded posteriorly; jaw angle very obtuse (approximately 140°). Inner lamella weakly expanded posteroventrally, crest portion covered by outer lamella over 85% in profile from lateral side; crest narrowly rounded, and lateral wall lacking radial ridge and fold. Both outer and inner lamellae sculptured by many radial striations; those on inner lamella much stronger than those on outer lamella.

Measurements. —Crest length 90.4 mm, wing length 51.1

mm, hood length 78.4 mm, rostral length 13.0 mm, width of outer lamella ca. 87 mm.

Remarks. —The lower jaw of the present species is similar to that of N. jeletzkyi from the lower Campanian Pender Formation of the Nanaimo Group of Vancouver Island ( Tanabe et al. 2008: figs. 3, 4; Tanabe 2012: fig. 4-1) in overall shape and ornamentation but distinguished from the latter by having a less posteriorly expanded inner lamella and a broader, more anteriorly curved hood portion of the outer lamella. The low- er jaw of the present species resembles the lower jaws of N. yokotai Tanabe and Hikida, 2010 , from the Turonian in the Tappu (Obira) and Nakagawa areas of northern Hokkaido ( Tanabe and Hikida 2010: 146, fig. 1) in overall shape, but the latter have a much smaller open angle of paired wings and a shorter inner lamella in relation to the outer lamella.

In modern coleoids, the lower jaw size has a linear relationship with mantle length ( Clarke 1962, 1986). In Vampyroteuthis infernalis Chun, 1903 , the sole living species of the order Vampyromorpha , mature males have approximately 2 kg total body weight and 100 mm mantle length ( Pickford 1949), and the relationship between mantle length (ML, in mm) and hood length of the lower jaw (HL, in mm) is approximated by the following equation: ML = 9.02 HL – 5.8 ( Clarke 1986). When applying the relationship to the holotype of the present new species, its owner would have had a mantle length of approximately 700 mm.

Stratigraphical and geographical range. — Type locality and horizon only.

Figures

Fig. 6. Octobrachian coleoid Nanaimoteuthis hikidai sp. nov. KMNH IvP 902,001, holotype, a lower jaw; early Campanian, Late Cretaceous, Haboro area, Hokkaido, Japan. Right lateral (A), left lateral (C), dorsal (D), and frontal (E) views, and right lateral view after removing part of outer lamella (B).

Fig. 1. Map of Haboro area, northwest Hokkaido, Japan, showing the locations of the coleoid lower jaws examined.