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A newly discovered species of living baleen whale


In the late 1970s eight Balaenoptera specimens of unknown identity were caught in the lower latitudinal Indo-Pacific waters by Japanese research whaling vessels1. The combination of the allozyme patterns and physical maturity of the eight specimens separated them from all acknowledged Balaenoptera species2. In September 1998 we collected a medium-sized baleen whale carcass on a coastal island in the Sea of Japan. This specimen and the previously collected eight specimens resembled Balaenoptera physalus (fin whale) in external appearance but were much smaller. Comparison of external morphology, osteology and mitochondrial DNA data grouped the nine specimens as a single species but separated them from all known baleen whale species. Therefore, here we describe a new species of Balaenoptera, which is characterized by its unique cranial morphology, its small number of baleen plates, and by its distant molecular relationships with all of its congeners. Our analyses also separated Balaenoptera brydei (Bryde's whale)3,4 and Balaenoptera edeni (Eden's whale)5 into two distinct species, raising the number of known living Balaenoptera species to eight.

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We thank C. Smeenk for comments, providing B. edeni tissue sample, paperwork for the CITES permit and critical reading of the manuscript; K. Ikemoto, S. Shimizu and T. Yokomachi for photographs of NSMT-M32505 and NRIFSF1; J. R. B. Alfred, S. Biswas, H. P. Castello, R. Chakravarti, S. K. Chakravarti, C. Dechsakulwatana, B. Fernholm, R. Harbord, P. D. Jenkins, Y. Musig, Y. Newi, S. K. Podder, C. W. Potter, P. Rudd, G. C. Ray, S. Said, A. K. Sanyal, R. Sabin and O. B. Vaccaro for permission to examine the specimens in their custody; Ú. Árnason, C. C. Kinze and J. G. Mead for comments and critical reading of the manuscript; L. B. Holthuis, K. Hosoya, Y. Masaki, M. C. Milinkovitch, N. Miyazaki and K. Numachi for comments; H. Hatanaka, S. Ohsumi and Y. Shimadzu for permission to use the data and materials from the research whaling; M. Etoh, S. Fujioka, M. Furuno, A. Tojima and T. Uchiyama for logistic support and help with preserving the holotype; T. Kakuda and T. Kobayashi for help with the phylogenetic analysis; T. Imamura for help with the research at Indian Museum; H. Ishikawa, T. Itoh, E. Jibiki, K. Kuramochi, K. Nakamura, T. Shimokawa and K. Tokutake for assistance in the field; and K. Arai, R. Imai, N. Kaneko, K. Maeda, M. Ogino, K. Shibayama, Y. Tajima, A. Umetani and Y. Watanabe for sample preparation and data collection.

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The authors declare that they have no competing financial interests.

Correspondence to Shiro Wada or Tadasu K. Yamada.

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Figure 1: The holotype skull of B. omurai sp. nov. (NSMT-M32505).
Figure 2: External morphology of B. omurai sp. nov.
Figure 3: Neighbour-joining tree22 of the complete mtDNA control region sequences of all eight species suggested to belong to Balaenoptera, constructed using Kimura's two-parameter model in MEGA23 with Balaena glacialis (right whale) as the outgroup.


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