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A New and Ontogenetically Younger Specimen of Numataphocoena yamashitai from the Upper Part of the Horokaoshirarika Formation (Lower Pliocene), Numata, Hokkaido, Japan

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Title: A New and Ontogenetically Younger Specimen of Numataphocoena yamashitai from the Upper Part of the Horokaoshirarika Formation (Lower Pliocene), Numata, Hokkaido, Japan
Authors: Tanaka, Yoshihiro Browse this author →ORCID
Keywords: fossil
ontogeny
periotic
Phocoenidae
Issue Date: 1-Apr-2016
Publisher: 日本古生物学会
Journal Title: Paleontological Research
Volume: 20
Issue: 2
Start Page: 105
End Page: 115
Publisher DOI: 10.2517/2015PR026
Abstract: A new periotic of Numataphocoena yamashitai from the upper part of the Horokaoshirarika Formation (lower Pliocene), Numata, Hokkaido, Japan shows younger ontogenetic features in comparison to the matured holotype (NFL 7). The referred specimen of N. yamashitai is smaller (approximately 90% in size) than the physically and sexually matured holotype periotic. The holotype (NFL 7) and referred specimen (NFL 2617) show several differences owing to ontogenetic changes, such as: the holotype (NFL 7) has a more strongly swollen medial part of the anterior process, blunt anterior keel, rounded anterodorsal angle, deeper and clearer anterior incisure, more rounded pars cochlearis, deeper and narrower hiatus epitympanicus rather than a flat area, longer posterior process with an extra edge posterolaterally. N. yamashitai differs from other fossil phocoenids in having a narrower and sharper anterior part of the internal acoustic meatus and a robust anterior process. Haborophocoena toyoshimai similarly has a relatively narrow internal acoustic meatus and a robust anterior process, compared with other fossil phocoenids. Between N. yamashitai and H. toyoshimai, N. yamashitai has a narrower internal acoustic meatus and a more robust anterior process. These similarities imply a close relationship between Numataphocoena and Haborophocoena. The new specimen provides diagnostic features and insight into ontogenetic variation of N. yamashitai.
Type: article
URI: http://hdl.handle.net/2115/64951
Appears in Collections:総合博物館 (The Hokkaido University Museum) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 田中 嘉寛

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