宮古島の上部中新統島尻層群大神島層より産出したナガスクジラ類化石 「シマジリクジラ」

Translated title of the contribution: A Late Miocene balaenopterid (“Shimajiri-kujira”) from the Ookamishima Formation, Shimajiri Group, Miyako Island, Okinawa, Japan

Toshiyuki Kimura, Akira Adaniya, Masayuki Oishi, Felix Marx, Naoki Kohno

Research output: Contribution to journalArticleResearch

Abstract

We report a new fossil mysticete, previously referred to as the "Shimajiri whale" (e.g., Adaniya, 1977), from the Upper Miocene of Miyako Island, Okinawa, Japan. The new material was recovered from the Ookamishima Formation (Shimajiri Group), which is correlative with foraminiferal Zone N17. Very little cetacean material has been described from the Ryukyu Islands and the wider area of Southeast Asia, making this an important find. The specimen consists of a fragmentary cranium including both periotics and the left tympanic bulla, but missing the rostrum and the left zygomatic and supraorbital processes. The surfaces of most of the bones are badly eroded and reveal little sutural detail. Nevertheless,the specimen can be confidently identified as a balaenopterid based on (1) its abruptly depressed supraorbital process, (2) cranially elongated pars cochlearis and (3) the overlap of the maxilla and parietal bones in lateral view. Potential generic assignments are more difficult to judge. The narrow vertex, slender ascending process of the maxilla, laterally oriented zygomatic process and distally expanded posterior process of the periotic may be primitive for Balaenopteridae, and argue against a referral to Balaenoptera or Diunatans. The specimen furthermore differs from Megaptera in having a much narrower nasal and ascending process of the premaxilla; from Archaebalaenoptera in lacking well-developed tuberosities on the supraoccipital; from Parabalaenoptera in having a distinctly concave anterior border of the supraorbital process of the frontal; from Plesiobalaenoptera in having a distally expanded posterior process of the periotic; from Protororqualusin having a blunt apex of the supraoccipital; from “Megaptera” hubachi in having narrower nasals and a cranially moreexpanded pars cochlearis; and from “M.” miocaena in having a less anteriorly projected supraoccipital. Pending further study, we therefore preliminarily refer the specimen to Balaenopteridae gen. et sp. indet.
Translated title of the contributionA Late Miocene balaenopterid (“Shimajiri-kujira”) from the Ookamishima Formation, Shimajiri Group, Miyako Island, Okinawa, Japan
Original languageJapanese
Pages (from-to)39-48
Number of pages10
JournalBulletin of the Gumna Museum of Natural History
Volume19
Publication statusPublished - 2015
Externally publishedYes

Keywords

  • Mysticeti
  • Balaenopteridae
  • Shimajiri Group
  • Late Miocene
  • Miyako Island
  • Okinawa Prefecture

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