Haboroteuthis

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

Genus Haboroteuthis nov.

Type species: Haboroteuthis poseidon sp. nov., see below.

Etymology: After Haboro, a town near to the type species locality.

Diagnosis.—Large lower jaw characterised by long rostrum with sharply pointed tip (hook), dorsally convex shoul- der, relatively narrow hood weakly convex anteriorly with distinct radial notch on lateral side, long and anteriorly weakly curved crest, and long lateral wall that is parallelogram-shaped in lateral view and with relatively broad fold.

Discussion. —The lower jaw of the present new genus exhibits mosaic features of modern teuthids and sepiids, such as the modern teuthids Nototodarus of Ommastrephidae ( Clarke 1986: fig. 28) and Onychoteuthis of Onychoteuthidae ( Clarke 1986: fig. 32), in which the outer lamella is characterised by a long rostrum with a sharply pointed tip, a dorsally arched shoul- der, and a relatively short hood; however, the inner lamella of the present genus is more elongated posteroventrally than that of modern teuthids, which have an inner lamella with a short parallelogram- or rhomboidal-shaped lateral wall. The lower jaw of the present genus resembles that of modern sepiid and sepiolid genera in having a long parallelogram-shaped lateral wall in the inner lamella but is distinguished from the latter in the development of a lateral wall fold ( Clarke 1986; Clarke and Maddock 1988; Kubodera 2005).

Lower jaws comparable in size and overall shape to those of the present genus are thus far unknown in the fossil record. However, there is a possibility that the present genus is congeneric with Yezoteuthis Tanabe, Hikida, and Iba, 2006 , a monospecific teuthid genus represented by a single species, Y. giganteus ; this species was proposed based on a large upper jaw from the lower Campanian of the Nakagawa area, Hokkaido. This hypothesis might be verified from co-occurring upper and lower jaws that are comparable to the holotypes of the type species of the two genera. Such co-occurrence of upper and lower jaws would be confirmed in stomach and coprolite remains of their probable predators such as large Cretaceous marine reptiles.

Fossil records of coleoid shell remains are also important when considering taxonomic affinity with the present genus. Shell remains of the following Late Cretaceous coleoid genera other than Belemnoidea and Octobrachia have been described previously; Naefia Wetzel, 1930 , from the Maastrichtian of Chile ( Wetzel 1930) and possibly from the Campanian of Antarctica ( Wetzel 1930; Stilwell and Zinsmeister 1987) and California ( Hewitt et al. 1991); Cyrtobelus Fuchs, Keupp, Trask, and Tanabe, 2012 , from the upper Campanian to the upper Maastrichtian of Vancouver Island, British Columbia, Canada, and West Greenland ( Fuchs et al. 2012); Groenlandibelus Jeletzky, 1966 , from the upper Maastrichtian of Greenland Birkelund 1956; Fuchs et al. 2012, 2013a); and Longibelus Fuchs, Iba, Ifrim, Nishimura, Kennedy, Keupp, Stinnesbeck,

and Tanabe, 2013 from the Aptian of the Caucasus ( Doguzhaeva 1996), the Albian of South Africa and southern India, and the Cenomanian–Maastrichtian of Japan ( Hirano et al. 1991; Hewitt et al. 1991; Fuchs and Tanabe 2010), southern India ( Doyle 1986), Mexico ( Ifrim et al. 2004), and Alaska. Among these genera, the former three were included in either the order Sepiida ( Jeletzky 1966) or the order Spirulida ( Fuchs et al. 2012, 2013a), while Longibelus was assumed to be a taxon linking the Belemnoidea and the early Decabrachia ( Fuchs et al. 2013a). Although jaws and a complete proostracum are unknown, all these genera are represented by small phragmocones, usually less than 10 cm in length, suggesting their smaller body size than Haboroteuthis .

Stratigraphical and geographical range.—The genus Haboroteuthis is known to occur in the upper Santonian rocks of the Haboro area, Hokkaido, Japan (this paper).