A recent discovery by a group of paleontologists headed by Dr. Mathieu Boisville (University of Tsukuba, Japan) revealed a new species of the extinct Ontocetus from the Lower Pleistocene deposits in the North Atlantic.
This species, Ontocetus posti, exhibits remarkable similarities in feeding adaptations to the modern walrus (Odobenus rosmarus), underscoring an intriguing case of convergent evolution. The findings are detailed in the open-access journal PeerJ Life & Environment.
The fossils of Ontocetus posti were found in Norwich, United Kingdom, and Antwerp, Belgium. Initially thought to belong to another species, Ontocetus emmonsi, a detailed analysis of the mandibles highlighted a unique combination of features that distinguish it as a new species.
These features include the presence of four post-canine teeth, a larger lower canine, and a fused and short mandibular symphysis. These anatomical characteristics suggest that Ontocetus posti was well adapted to suction-feeding, much like its modern relative, the walrus.
The Ontocetus genus originated in the North Pacific Ocean and later spread to the Atlantic during the Mio-Pliocene transition. This migration was likely made possible by the Central American Seaway, an important oceanic passage that existed before the closure of the Isthmus of Panama.
The subsequent global cooling in the Late Pliocene had a significant impact on marine life, leading to the extinction of Ontocetus posti during the Early Pleistocene and allowing the cold-adapted Odobenus rosmarus to emerge and eventually thrive.
This discovery provides valuable insights into the evolutionary history of walruses, highlighting how environmental changes have influenced the adaptations and survival of marine mammals. The convergence of feeding adaptations between Ontocetus posti and the modern walrus demonstrates the dynamic evolutionary processes that take place across different time periods and environments.
Journal reference:
- Mathieu Boisville, Narimane Chatar, Naoki Kohno. New species of Ontocetus (Pinnipedia: Odobenidae) from the Lower Pleistocene of the North Atlantic shows similar feeding adaptation independent to the extant walrus (Odobenus rosmarus). PeerJ, 2024; DOI: 10.7717/peerj.17666