| Archaeodobenus | |
|---|---|
 | |
| Partialholotype cranium shown from above, the left side, and below | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Parvorder: | Pinnipedia |
| Family: | Odobenidae |
| Genus: | †Archaeodobenus Tanaka & Kohno, 2015 |
| Species: | †A. akamatsui |
| Binomial name | |
| †Archaeodobenus akamatsui Tanaka & Kohno, 2015 | |
Archaeodobenus is an extinct genus ofpinniped that lived during theLate Miocene of what is now Japan. It belonged to theOdobenidae family, which is today only represented by thewalrus, but was much more diverse in the past, containing at least 16 genera.[1]
The first known specimen was collected in 1977 from theIchibangawa Formation inTobetsu Town on the island ofHokkaido. The specimen consists of a partial skull, vertebrae, and limb bones, and was made theholotype specimen of the new genus and speciesA. akamatsui by the Japanese palaeontologists Yoshihiro Tanaka and Naoki Kohno in 2015. Thegeneric name consists ofarchaio-, the Greek word for ancient, and the generic name of the walrus,Odobenus; in full, "ancient walrus". Thespecific name honors Morio Akamatsu, a curator of theHokkaido Museum.[1][2]
The diversity ofodobenids increased during the Late Miocene andPliocene (about 12.5 million to 10.5 million years ago), perhaps linked tomarine regression andtransgression, which could have geographically isolated their ancestors.Archaeodobenus was the contemporary of the odobenidPseudotaria 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 asImagotaria,Pontolis, the subfamilyOdobeninae, whereasPseudotaria seems to have been morebasal.[1]
Unlike the modern walrus,Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like asea lion.[2] The holotype specimen appears to have been a young adult male of about 3 metres (9.8 feet) in length, which would have weighed around 473 kg (1,043 lb). This is intermediate between the size of theSteller sea lion and theSouth American sea lion. Its canines were 86.3 mm (3.40 in) long, compared to modern walrus tusks, which can grow to up to 1 m (3 ft 3 in) long.Archaeodobenus can be distinguished fromPseudotaria by features such as the shape and size of theoccipital condyle (which connects with the first neck vertebra at the back of the skull), theforamen magnum (the opening through which thespinal cord passes into the cranium), themastoid process (where various muscles attach to the back of the skull), and some features in thepostcranial skeleton.[1][2][3]
