上總國君津郡湊町長濱の上部鮮新系基底層産化石逆叉の一新種 [in Japanese] A New Species of Orc from the Basal Calabrian at Naganuma, Minato Town, Province of Kazusa, Japan [in Japanese]
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The writer was kindly submitted by Mr. G. NATSUME of Minato Town, Kimitsu District, Province of Kazusa, a fragmental fossil tooth of orc from a gravel bed at Nagahama of the town for a study. This bed, corresponding to the writer's Parelephas protomammonteus typicus Zone, has hitherto yielded the remains of such vertebrates as Isurus hastalis (Agassiz), Carcharodon carcharias (Linne), Parelephas protomammonteus (MATSUMOTO) typicus, Giraffa (Orasius ?) nipponica Matsunoto and Cervus (cfr. Sika) kazusensis MATSUMOTO. The fossil orc in question is named here as follows. Orca paleorca, sp. nov. (Figs. 1 & 2) Type-specimen: Large fragment of abult tooth, which may likely be either a right upper one or a left lower. Horizon: Parelephas protomammonteus typicus Zone; gravel bed at base of the Sanuki Formation. Age: Basal Calabrian. The tooth is fairly large and stout. Its reference not to the Physeterids but to Orca is evident in lacking a thick coat of cement. The root is cylindrical, gently tapering apically, and is smoothly oval in transverse section. The pulp-cavity is rather large proximally. In living Orca orca (Linne), the root of tooth is compressedly oval in transverse section and its anterior and posterior sides show a tendency to be broadly and very shallowly grooved. Such a feature is entirely absent in the fossil tooth. It as preserved measures 50 mm in height, 29.5 mm in the greatest transverse diameter and 22.5 mm in the greatest longitudinal. The present tooth is much larger than that of Orca cylindrica LYDEKKER of British Pliocene, the former being distinctly closer to the teeth of Orca orca than the latter is to the same. It would be probable that the present species was actually ancestral to the living one.
動物学雑誌 49(5), 191-193, 1937