''Archaeodobenus'' is an extinct genus of

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammal, marine mammals. They comprise the extant taxon, extant family (biology ...

that lived during the Late Miocene of what is now Japan. It belonged to the

Odobenidae Odobenidae is a family of pinnipeds. The only living species is the walrus (''Odobenus rosmarus''). In the past, however, the group was much more diverse, and includes more than a dozen fossil genera. Taxonomy All genera, except ''Odobenus'', ...

family, which is today only represented by the

walrus The walrus (''Odobenus rosmarus'') is a large flippered marine mammal with a discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. The walrus is the only living species in the fami ...

, but was much more diverse in the past, containing at least 16 genera. Unlike the modern walrus, ''Archaeodobenus'' did not have tusks but instead had canines of moderate size, and looked more like a

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

Discovery

The first known specimen was collected in 1977 from the Ichibangawa Formation in Tobetsu Town on the island of

Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The lar ...

. The specimen consists of a partial skull, vertebrae, and limb bones, and was made the

holotype specimen A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

of the new genus and species ''A. akamatsui'' by the Japanese palaeontologists Yoshihiro Tanaka and Naoki Kohno in 2015. The generic name consists of ''archaio-'', the Greek word for ancient, and the generic name of the walrus, ''Odobenus''; in full, "ancient walrus." The specific name honors Morio Akamatsu, a curator of the

Hokkaido Museum opened in Sapporo, Hokkaidō, Japan in 2015. Located within Nopporo Shinrin Kōen Prefectural Natural Park, the permanent exhibition is dedicated to the nature, history, and culture of Hokkaido. Also known as , the museum integrates and replaces ...

. The holotype specimen appears to have been a young adult male of about 3 metres (10 ft) in length, which would have weighed around 473 kg (1,042 lb). This is intermediate between the size of the Steller sea lion and the

South American sea lion The South American sea lion (''Otaria flavescens'', formerly ''Otaria byronia''), also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the western and southeastern coasts of South America. It is the only member ...

. Its canines were 86.3 mm (3.4 in) long, compared to modern walrus tusks, which can grow to up to 1 m (3 ft 3 in) long. ''Archaeodobenus'' can be distinguished from ''Pseudotaria'' by features such as the shape and size of the

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...

(which connects with the first neck vertebra at the back of the skull), the foramen magnum (the opening through which the

spinal chord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

passes into the cranium), the

mastoid process The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, ...

(where various muscles attach to the back of the skull), and some features in the

postcranial Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated s ...

skeleton.

Classification

The diversity of odobenids increased during the Late Miocene and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58marine regression and transgression, which could have geographically isolated their ancestors. ''Archaeodobenus'' was the contemporary of the odobenid '' Pseudotaria'' from the same formation, which it may have diverged from in the western North Pacific during the Late Miocene. ''Archaeodobenus'' appears to have been closer related to later odobenids such as '' Imagotaria'', ''

Pontolis ''Pontolis'' is an extinct genus of large walrus. It contained three species, ''P. magnus, P. barroni,'' and ''P. kohnoi''. Like all pinnipeds, ''Pontolis'' was a heavily built amphibious carnivore. ''Pontolis'' lived along the Pacific coast of ...

'', the subfamily Odobeninae, whereas ''Pseudotaria'' seems to have been more basal.

References

{{Taxonbar, from=Q48557894, from2=Q25436860 Miocene pinnipeds Prehistoric carnivoran genera Fossils of Japan Extinct mammals of Asia Odobenids Fossil taxa described in 1931