Haboroteuthis poseidon, Tanabe & Misaki & Ubukata, 2015

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 : 34-35

Haboroteuthis poseidon sp. nov.

Fig. 7A–D .

Etymology: Named for Poseidon, the god of the sea in Greek mythology.

Holotype: KMNH IvP 902,002, a lower jaw.

Type locality: Recovered as float in the Sankebetsu River, about 1.2 km east-northeast of the Haboro Dam site, Haboro, northwestern Hokkaido, Japan ( Fig. 1 : Locality 2).

Type horizon: Possibly derived from the upper part of the Member Uf-g in the upper part of the Haborogawa Formation, upper Santonian.

Diagnosis.—Same as for the genus, by monotypy.

Description. —Lower jaw large, consisting of moderately open outer lamella and posteriorly elongated inner lamella, both of which are fused together in the anterior portion, forming a sharply pointed rostral tip; they are made up of black, presumably originally chitinous material; outer lamella weakly expanded laterally with open angle of paired narrow wings, approximately 60°, with dorsally arched shoul- der and relatively narrow hood with distinct radial notch on lateral side; hood covers 35% of crest in profile from lateral side; hood line weakly convex anteriorly; wing prominently expanded posteriorly; jaw angle acute, approximately 80°. Inner lamella remarkably expanded posteroventrally with narrowly rounded anterior margin; crest line weakly convex anteriorly; lateral wall parallelogram-shaped in lateral view, ornamented with relatively broad fold.

Measurements. —Crest length 63.1 mm, wing length 31.1 mm, hood length 30.0 mm, rostral length 25.7 mm, width of outer lamella 49.0 mm.

Remarks. —The lower jaw of the present new species has a crest length of 63.1 mm, which is larger than the lower jaws of known modern coleoids. For example, in adult specimens of the giant squid Architeuthis kirki Robson, 1887 , of Architeuthidae , captured off Chatham Rise, New Zealand, with a total body length of approximately 7.7 m (AMNH 291938), and of the Humboldt squid Dosidicus gigas Orbigny, 1835 , of Ommastrephidae , captured off Baja California, Mexico, with a mantle length of 1.5 m (UMUT 31004), the lower jaws have crest lengths of 47.5 mm and 50.2 mm, respectively (see Tanabe 2012: fig. 3-1, 2). This rough comparison suggests that the present new species undoubtedly had an extremely large body size comparable to that of modern giant squids.

Figures

Fig. 7. Decabrachian coleoid Haboroteuthis poseidon gen. et sp. nov. KMNH IvP 902,002, holotype, a lower jaw; late Santonian, Late Cretaceous, Haboro area, Hokkaido, Japan. Frontal (A), left lateral (B), dorsal (C), and right lateral (D) views.

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