''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 The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene Epoch made up of two stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million years ago) to 5.333 Ma. The ...

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 f ...

, 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, Japan's Japanese archipelago, second largest island and comprises the largest and northernmost Prefectures of Japan, prefecture, making up its own List of regions of Japan, region. The Tsugaru Strait separates Hokkaidō from Honshu; th ...

. The specimen consists of a partial skull, vertebrae, and limb bones, and was made the holotype specimen 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 Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

honors Morio Akamatsu, a curator of the Hokkaido Museum. 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 The Steller sea lion (''Eumetopias jubatus''), also known as the Steller's sea lion and northern sea lion, is a near-threatened species of sea lion in the northern Pacific. It is the sole member of the genus ''Eumetopias'' and the largest of ...

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 (which connects with the first neck vertebra at the back of the skull), the foramen magnum (the opening through which the spinal chord passes into the cranium), the mastoid process (where various muscles attach to the back of the skull), and some features in the postcranial skeleton. Archaeodobenus restoration

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 A marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously-exposed land. Evidence of marin ...

and

transgression Transgression may refer to: Legal, religious and social *Sin, a violation of God's Ten Commandments or other elements of God's moral law *Crime, legal transgression, usually created by a violation of social or economic boundary **In civil law ju ...

, 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 ''Imagotaria'' is an extinct monotypic genus of walrus with the sole species ''Imagotaria downsi''. Fossils of ''Imagotaria'' are known from the early late Miocene of California (c. 10-12 million years ago). Description The long pinniped more ...

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

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

References

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