https://orcid.org/0000-0001-5928-371X
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ABSTRACT
Kentriodontids are small- to medium-sized odontocetes with a wide geographic range that flourished during the Miocene. They are closely related to crown Delphinida. Seven fossil kentriodontid specimens have been recovered from the Haraichi Formation, Annaka Group (latest middle/earliest late Miocene, Serravallian/Tortonian), Gunma Prefecture, Japan. We describe and diagnose a new species of the genus Kentriodon. Kentriodon nakajimai, sp. nov., has a larger fossa for the hamular and preorbital lobes of the pterygoid sinuses, which suggests that the species was more highly adapted for diving than other Kentriodon species. Asymmetric development of left and right maxillary crests indicates asymmetric development of the facial muscles attached to the melon. If this is the case, it suggests that K. nakajimai possessed a more sophisticated echolocation system than other kentriodontids. Phylogenetic analysis suggests that K. nakajimai is most closely related to K. obscurus and the genus Kentriodon may have originated in the Pacific and then dispersed into the Atlantic several times.
ACKNOWLEDGMENTS
We gratefully acknowledge the efforts of H. Nakajima in discovering and preparing the holotype and referred specimens in this study. We also extend our thanks to M. Kitagawa in discovering the paratype specimen. We thank D. J. Bohaska, N. D. Pyenson, J. G. Mead, M. R. McGowen, J. J. Ososky, and D. P. Lunde of USNM; L. G. Barnes, S. A. McLeod, and J. Vélez-Juarbe of the Los Angeles County Museum; O. Lambert of the Institut royal des Sciences naturelles de Belgique; and H. Sawamura, T. Ando, and T. Shinmura of Ashoro Museum of Paleontology for facilitating access to the specimens in their care. Constructive comments from H. Ichishima, an anonymous reviewer, and editor O. Lambert considerably improved the quality of this work. We also thank Y. Takakuwa of GMNH, T. Mita formerly of GMNH, Mariko Kitagawa of volunteer staff of GMNH, M. Iijima of Hefei University of Technology, S. Maruyama of Natural History Museum and Institute, Chiba, and M. Murakami of Shumei University for their help. This work was supported by JSPS KAKENHI grant [JP18K01110] to T.K.
ORCID
Toshiyuki Kimura http://orcid.org/0000-0001-5928-371X