Archaeodobenus

Last updated

Archaeodobenus
Temporal range: Late Miocene
Archaeodobenus.PNG
Partial holotype cranium shown from above, the left side, and below
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Odobenidae
Genus: Archaeodobenus
Tanaka & Kohno, 2015
Species:
A. akamatsui
Binomial name
Archaeodobenus akamatsui
Tanaka & Kohno, 2015

Archaeodobenus is an extinct genus of pinniped that lived during the Late Miocene of what is now Japan. It belonged to the Odobenidae family, which is today only represented by the walrus, but was much more diverse in the past, containing at least 16 genera. [1]

Contents

Taxonomy

The first known specimen was collected in 1977 from the Ichibangawa Formation in Tobetsu Town on the island of Hokkaido. 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 honors Morio Akamatsu, a curator of the Hokkaido Museum. [1] [2]

Evolution

The diversity of odobenids increased during the Late Miocene and Pliocene (about 12.5 million to 10.5 million years ago), perhaps linked to marine 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 , the subfamily Odobeninae, whereas Pseudotaria seems to have been more basal. [1]

Description

Life restoration of a pair Archaeodobenus restoration.PNG
Life restoration of a pair

Unlike the modern walrus, Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like a sea lion. [2] 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. 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 cord passes into the cranium), the mastoid process (where various muscles attach to the back of the skull), and some features in the postcranial skeleton. [1] [2] [3]

Related Research Articles

<span class="mw-page-title-main">Walrus</span> Species of marine mammal with tusks

The walrus is a large pinniped marine mammal with discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. It is the only extant species in the family Odobenidae and genus Odobenus. This species is subdivided into two subspecies: the Atlantic walrus, which lives in the Atlantic Ocean, and the Pacific walrus, which lives in the Pacific Ocean.

<span class="mw-page-title-main">Eared seal</span> Marine mammals in the family Otariidae

An eared seal, otariid, or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans, the southern Indian, and Atlantic Oceans. They are conspicuously absent in the north Atlantic.

<span class="mw-page-title-main">Pinniped</span> Infraorder of mammals

Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae, Otariidae, and Phocidae. There are 34 extant species of pinnipeds, and more than 50 extinct species have been described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage. Pinnipeds belong to the order Carnivora; their closest living relatives are musteloids, having diverged about 50 million years ago.

<span class="mw-page-title-main">Desmostylia</span> Extinct order of mammals

The Desmostylia are an extinct order of aquatic mammals that existed from the early Oligocene (Rupelian) to the late Miocene (Tortonian).

<i>Imagotaria</i> Extinct genus of carnivores

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.

<i>Desmostylus</i> Extinct family of mammals

Desmostylus is an extinct genus of herbivorous mammal of the family Desmostylidae living from the Chattian stage of the Late Oligocene subepoch through the Late Miocene subepoch and in existence for approximately 21.2 million years.

<i>Odobenocetops</i> Extinct genus of mammals

Odobenocetops is an extinct genus of small toothed whale known from Chile and Peru. Its fossils are found in Miocene-aged marine strata of the Bahía Inglesa Formation and Pisco Formation. Two species of Odobenocetops are currently recognized, O. peruvianus and the slightly younger O. leptodon.

<i>Gomphotaria</i> Extinct genus of carnivores

Gomphotaria is a genus of very large shellfish-eating dusignathine walrus found along the coast of what is now California, during the late Miocene.

Behemotops is an extinct genus of herbivorous marine mammal. It lived from the Early Oligocene (Rupelian) through the Late Oligocene, existing for approximately 10.9 million years. It is the most primitive known desmostylian, believed to be close to the ancestry of all other desmostylians.

<i>Ontocetus</i> Extinct genus of carnivores

Ontocetus is an extinct genus of walrus, an aquatic carnivoran of the family Odobenidae, endemic to coastal regions of the southern North Sea and the southeastern coastal regions of the U.S. during the Miocene-Pleistocene. It lived from 13.6 mya—300,000 years ago, existing for approximately 13.3 million years.

<i>Metaxytherium</i> Extinct genus of dugong

Metaxytherium is an extinct genus of dugong that lived from the Oligocene until the end of the Pliocene. Fossil remains have been found in Africa, Europe, North America and South America. Generally marine seagrass specialists, they inhabited the warm and shallow waters of the Paratethys, Mediterranean, Caribbean Sea and Pacific coastline. American species of Metaxytherium are considered to be ancestral to the North Pacific family Hydrodamalinae, which includes the giant Steller's Sea Cow.

<i>Brygmophyseter</i> Extinct genus of toothed whale (fossil)

Brygmophyseter, known as the biting sperm whale, is an extinct genus of toothed whale in the sperm whale family with one species, B. shigensis. When it was first described in 1994, the species was placed in the genus Scaldicetus based on tooth morphology, but this was later revised in 1995. In 2006, it was classified into the genus Naganocetus, which is considered to be a junior synonym. The only known specimen, a nearly complete skeleton, was dated to be around 15–14 million years old. Brygmophyseter is thought to have been 6.5–7 meters (21–23 ft) long, and it probably had 11 or 12 teeth in the upper and lower jaws. Brygmophyseter is part of a group of macroraptorial sperm whales which tended to be apex predators using their large teeth to catch struggling prey such as whales. It had a spermaceti organ which was probably used for biosonar like in the modern sperm whale. The whale has made an appearance on The History Channel's TV series Jurassic Fight Club.

<i>Scaldicetus</i> Extinct genus of mammals

Scaldicetus is an extinct genus of highly predatory macroraptorial sperm whale. Although widely used for a number of extinct physeterids with primitive dental morphology consisting of enameled teeth, Scaldicetus as generally recognized appears to be a wastebasket taxon filled with more-or-less unrelated primitive sperm whales.

<span class="mw-page-title-main">Capistrano Formation</span> Geologic formation in coastal southern Orange County, California

The Capistrano Formation is a geologic formation in coastal southern Orange County, California. It preserves fossils dating back to the late Miocene to early Pliocene, with the Oso Member representing a near-shore environment. Fifty-nine species and varieties of foraminifera are recognized from the Capistrano Formation alongside a diverse array of marine mammals including up to five species of walrus.

<i>Pontolis</i> Extinct genus of carnivores

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 North America along what is now the western coasts of California and Oregon between 11.608 and 5.332 million years ago, during the Miocene and Pliocene.

<i>Albicetus</i> Extinct genus of mammals

Albicetus is a genus of stem-sperm whales that lived during the Miocene Epoch, around 15 million years ago, and was discovered in Santa Barbara, California in 1909. It was categorized for decades as belonging to a group of extinct walruses erroneously thought to be sperm whales. It was named Albicetus, meaning "white whale", is a reference to the leviathan in Herman Melville's classic 1851 novel Moby-Dick.

<i>Prototaria</i> Extinct genus of pinniped

Prototaria is an extinct genus of pinniped that lived approximately 15.97 to 13.65 mya during the Middle Miocene in what is now Japan. It belonged to the family Odobenidae, the only extant species of which is the walrus. Members of the genus Prototaria are believed to be the most basal imagotariine pinnipeds.

<i>Proneotherium</i> Extinct genus of pinniped

Proneotherium is an extinct genus of pinniped that lived approximately 20.43 to 15.97 mya during the Early Miocene in what is now Oregon, U.S. It belonged to the family Odobenidae, the only extant species of which is the walrus.

Osodobenus is an extinct genus of walrus from the Miocene to Pliocene of California. Osodobenus may have been the first tusked walrus and shows several adaptations that suggest it was a suction feeder, possibly even a benthic feeder like modern species. Three skulls are known showing pronounced sexual dimorphism, with the female lacking the same tusks as the male. Only a single species, Osodobenus eodon, is currently recognized.

<i>Titanotaria</i> Genus of fossil mammals

Titanotaria is a genus of late, basal walrus from the Miocene of Orange County, California. Unlike much later odobenids, it lacked tusks. Titanotaria is known from an almost complete specimen which serves as the holotype for the only recognized species, Titanotaria orangensis, it is the best preserved fossil walrus currently known.

References

  1. 1 2 3 4 Tanaka, Y.; Kohno, N.; Mihlbachler, M. C. (2015). "A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids" (PDF). PLOS ONE. 10 (8): e0131856. Bibcode:2015PLoSO..1031856T. doi: 10.1371/journal.pone.0131856 . PMC   4526471 . PMID   26244784.
  2. 1 2 3 Geggel, Laura (2015). "No Tusks: Ancient Walrus Cousin Looked More Like a Sea Lion". Live Science. Retrieved 3 November 2018.
  3. Berta, A. & Sumich, J. L. (1999). Marine mammals: evolutionary biology. San Diego, CA: Academic Press. p. 494.