| Imagotaria | |
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Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Clade: | Pinnipedia |
| Family: | Odobenidae |
| Genus: | † Imagotaria |
| Species: | †I. downsi |
| Binomial name | |
| †Imagotaria downsi Mitchell, 1968 | |
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).
The 1.8 metres (6 ft) long pinniped more closely resembled in its overall shape a sea lion rather than a walrus. Unlike the extant walrus (Odobenus rosmarus), Imagotaria did not possess elongate, ever-growing tusks, but instead bore enlarged canines (with respect to other pinnipeds). [1]
Imagotaria is an example of a primitive walrus that does not grossly appear similar to a modern walrus. However, the walrus family (the Odobenidae) is a more inclusive group, that includes walruses without tusks (e.g. Imagotaria), walruses with upper and lower tusks (the subfamily Dusignathinae), and walruses with upper tusks like the extant walrus (subfamily Odobeninae, tribe Odobenini). It is possible to classify these pinnipeds as walruses because they share many other skull features (besides tusks) as well as many skeletal features, all of which indicate common ancestry.
The teeth of Imagotaria indicate that its feeding ecology was markedly different from that of modern walrus, and more similar to that of less specialized pinnipeds like seals, fur seals, and sea lions. Conical, unworn teeth and the lack of a vaulted palate indicate that Imagotaria did not feed on molluscs like modern walrus. Modern walruses do not use their teeth to chew molluscs like sea otters do. Instead, they hold a clam in their lips, and the vaulted palate allows them to use their tongue as a powerful piston to suck the soft parts right out of the clam shell. The shell is then dropped to the seafloor, never entering the oral cavity.
Additionally, fossils of Imagotaria (and the earlier Neotherium , c. 15 million years ago) demonstrate that early walruses had, by the middle and late Miocene, already developed extreme sexual dimorphism (males and females having different body sizes). It is unclear whether extreme sexual dimorphism is ancestral to all pinnipeds, or if it has been independently acquired in multiple pinniped lineages.
Carnivora is an order of placental mammals that have specialized in primarily eating flesh. Its members are formally referred to as carnivorans, though some species are omnivorous, such as raccoons and bears, and quite a few species such as pandas are specialized herbivores. The word carnivore is derived from Latin carō 'flesh' and vorāre 'to devour', and refers to any meat-eating organism. The order Carnivora is the fifth largest order of mammals and one of the more successful members of the group, as it comprises at least 279 species.
Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than true seals, and share with them external ears (pinnae), relatively long and muscular foreflippers, and the ability to walk on all fours. They are marked by their dense underfur, which made them a long-time object of commercial hunting. Eight species belong to the genera Arctocephalus and Arctophoca and are found primarily in the Southern Hemisphere, while a ninth species also sometimes called fur seal, the northern fur seal, belongs to a different genus and inhabits the North Pacific.
The walrus 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 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.
An eared seal or 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 and the southern Indian and Atlantic Oceans. They are conspicuously absent in the north Atlantic.
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 33 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 bears and the superfamily of musteloids, having diverged about 50 million years ago.
Caniformia is a suborder within the order Carnivora consisting of "dog-like" carnivorans. They include dogs, bears, wolves, foxes, raccoons, and mustelids. The Pinnipedia are also assigned to this group. The center of diversification for the Caniformia is North America and northern Eurasia. Caniformia stands in contrast to the other suborder of Carnivora, the Feliformia, the center of diversification of which was in Africa and southern Asia.
Potamotherium an extinct genus of caniform carnivoran from the Miocene epoch of France and Germany. It has been previously assigned to the mustelid family, but recent work suggests that it represents a primitive relative of pinnipeds.
Acrophoca longirostris, sometimes called the swan-necked seal, is an extinct genus of Late Miocene pinniped. It was thought to have been the ancestor of the modern leopard seal, however it is now thought to be a species of monk seal.
Enaliarctos is an extinct genus of pinniped, and may represent the ancestor to all pinnipeds. Prior to the discovery of Puijila, the five species in the genus Enaliarctos represented the oldest known pinniped fossils, having been recovered from late Oligocene and early Miocene strata of California and Oregon.
Desmatophoca is an extinct genus of early pinniped that lived during the Miocene, and is named from the Greek "phoca", meaning seal. A taxon of the family Desmatophocidae, it shares some morphological similarities with modern true seals. Two species are recognized: Desmatophoca oregonensis and Desmatophoca brachycephala. Little information exists regarding Desmatophoca, due to the small number of fossil samples obtained and identified.
Odobenocetops is an extinct genus of small toothed whale known from Peru and Chile. Its fossils are found in Neogene-aged marine strata dating from the Tortonian to the Zanclean. It had two tusks, and, in some fossils, one tusk was longer than the other.
A molluscivore is a carnivorous animal that specialises in feeding on molluscs such as gastropods, bivalves, brachiopods and cephalopods. Known molluscivores include numerous predatory molluscs,, arthropods such as crabs and firefly larvae, and, vertebrates such as fish, birds and mammals. Molluscivory is performed in a variety ways with some animals highly adapted to this method of feeding behaviour. A similar behaviour, durophagy, describes the feeding of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled molluscs, or crabs.
Gomphotaria pugnax was a species of very large shellfish-eating dusignathine walrus found along the coast of what is now California, during the late Miocene. It had four tusks, with one pair in the lower and upper jaws, and according to wear on the tusks, G. pugnax hammered shellfish open, rather than simply sucking them out of their shells as do modern walruses. In terms of the postcranial skeleton, Gomphotaria and other dusignathine walruses were built more like sea lions than modern walrus. Gomphotaria is a prime example of the extreme diversity that walruses once exhibited.
Kolponomos is an extinct genus of carnivoran mammal that existed in the Late Arikareean North American Land Mammal Age, early Miocene epoch, about 20 million years ago. It was likely a marine mammal. The genus was erected in 1960 by Ruben A. Stirton, a paleontologist at the University of California Museum of Paleontology, Berkeley, for the species K. clallamensis, on the basis of a partial skull and jaw found on the Olympic Peninsula. At the time, Stirton questionably assigned it to Procyonidae, its systematic position remained problematic until the discovery of more fossils including a nearly complete cranium from the original locality of K. clallamensis which helped identify it as part of the group from which pinnipeds evolved.
Allodesmus is an extinct genus of pinniped from the middle to late Miocene of California and Japan that belongs to the extinct pinniped family Desmatophocidae.
Puijila darwini is an extinct species of basal pinniped which lived during the Miocene epoch about 21 to 24 million years ago. Approximately a metre in length, the animal possessed only minimal physical adaptations for swimming. Unlike modern pinnipeds, it did not have flippers and its overall form was otter-like, albeit more specialized; its skull and teeth are the features that most clearly indicate that it is a seal.
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. Unlike the modern walrus, Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like a sea lion.
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.
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.A.. It belonged to the family Odobenidae, the only extant species of which is the walrus.
Nanodobenus is an extinct genus of pinniped that lived approximately 15.97 to 7.246 mya during the Miocene in what is now Baja California Sur, Mexico. It belonged to the family Odobenidae, the only extant species of which is the walrus.
Genera of pinnipeds and their stem-allies | |||||||||||||||||||||||||||||||||||
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