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Paleontological Research
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Abstract
Abstract.
The family Eschrichtiidae is presently only represented by Eschrichtius robustus, a relict species from the North Pacific. Because of the scarcity of fossil records of the Eschrichtiidae, their evolutionary history is not well understood. A finely preserved mysticete skeleton was recovered from the Lower Pleistocene (1.77–1.95 Ma) of Tokyo, Japan, in 1961. The fossil consists of a cranium, mandibles, cervical, thoracic, lumbar and caudal vertebrae, chevrons, ribs, and forelimb bones, including scapula, humerus, radius, ulna and digit bones. Here, we describe and diagnose this fossil as a new species of the Eschrichtiidae, Eschrichtius akishimaensis sp. nov. This is the first fossil species of the genus Eschrichtius and suggests that at least two lineages represented by the modern species of Eschrichtius and the new species described here survived as late as the Early Pleistocene. This expands our knowledge of the paleodiversity of the eschrichtiids.
We gratefully acknowledge the efforts of Masato and Yoshio Tajima in discovering the holotype specimen. We would like to thank Hiroshi Ozaki and Shin Honda of the National Museum of Nature and Science, Tokyo (NMNS) and many others, including Yoshio Ito, Tetsuya Sato, Etsuo Omura and Hiromi Maruo, who contributed to the recovery, preparation and preservation of the holotype. Thanks are also extended to the Akishima City Government and the Akishima City Board of Education. We would like to thank Felix G. Marx of Monash University and the Royal Belgian Institute of Natural Sciences and Cheng-Hsiu Tsai of NMNS for their helpful and constructive review of the manuscript. For facilitating access to the specimens in their care, we would like to express our sincere thanks to Lawrence G. Barnes, Samuel A. McLeod, Jorge Velez-Juarbe, Vanessa R. Rhue, David S. Janiger, and Jim Dines of LACM; Nicholas D. Pyenson, David J. Bohaska, James G. Mead, and Charles Potter of NMNH (USNM); Tadasu K. Yamada and Yuko Tajima of NMNS; and Hajime Taru of KPM. We extend our thanks to Olivier Lambert of the Institut royal des Sciences naturelles de Belgique, Michelangelo Bisconti of the San Diego Natural History Museum, Klaas Post and Bram Langeveld of the Natuurhistorisch Museum Rotterdam, Cheng-Hsiu Tsai of NMNS, Yuji Takakuwa of GMNH, Toru Fukushima of Musashino Fossil School, and Mariko Kitagawa of the volunteer staff of GMNH for their help.
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