''Desmostylus'' is an extinct genus of

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

mammal of the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Desmostylidae Desmostylidae is an extinct family (biology), family of herbivorous marine mammals belonging to the order of Desmostylia. They lived in the coastal waters of the northern Pacific Ocean from the Early Oligocene (Rupelian) through the Late Miocene ...

living from the Chattian stage of the

Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/ Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

subepoch through the Late Miocene subepoch (28.4 mya—7.250 Mya) and in existence for approximately .. Retrieved March 2013.

Description

''Desmostylus'' was a large,

hippopotamus The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...

-like creature, with the adult Keton specimen of ''D. hesperus'' measuring in length, in height and in body mass; the largest known humerus which is 1.3 times that of the Keton specimen in length probably belonged to an individual with a mass of . It had a short tail and powerful legs with four

hooves The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rumi ...

. Both the creature's jaws were elongated and sported forward-facing

tusks Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with pigs and walruses, or, in the case of elephants, elongated incisors. Tusks share ...

, which were elongated

canines Canine may refer to: Zoology and anatomy * a dog-like Canid animal in the subfamily Caninae ** ''Canis'', a genus including dogs, wolves, coyotes, and jackals ** Dog, the domestic dog * Canine tooth, in mammalian oral anatomy People with the surn ...

and

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s. Most likely fully aquatic, ''Desmostylus'' is thought to have lived in shallow water in coastal regions, usually less than 30 meters deep. Recent isotope work indicates that ''Desmostylus'' more likely lived (or spent a large amount of time) in freshwater or

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

ecosystems foraging for aquatic freshwater plants. Its less dense bone structure suggests that ''Desmostylus'' had a lifestyle of active swimming and possibly feeding at the surface, unlike other desmostylians that were primarily slow swimmers and/or bottom walkers and sea grass feeders.

Species

''Desmostylus hesperus'' (synonyms and invalid names: ''D. watasei'', ''D. cymatias'', ''D. californicus'', ''D. mirabilis'', ''D. minor'', ''Desmostylella typica''), ''D. coalingensis'' (syn. ''Vanderhoofius coalingensis''), and ''D. japonicus''. named the type specimen ''D. hesperus'' based on a set of isolated teeth that he had found near Mission San Jose, California (type locality: , paleocoordinates ). Marsh described his specimen as a

sirenia The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct ...

n and proposed affinities with ''

Metaxytherium ''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 inhabite ...

'' (a genus of extinct dugongs) and ''Halicore'' (an obsolete name for dugong). Several other species were later described based on minor differences in tooth morphology. Most or all of these species have been synonymized with ''D. hesperus'' since variation in tooth morphology between individuals assigned to one of these species has proven to be to greater than the differences between species. ''Desmostylus japonicus'' was described by based on a well-preserved partial skull and named by . It has been reproposed as distinct species based on cranial morphology.

Fossil distribution

Fossils have been discovered from along the northern Pacific Rim from Baja California Peninsula northward along the coast of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. T ...

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

and west to Sakhalin Island,

Hokkaido, Japan 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 la ...

, and south to the Shimane Prefecture, Japan.

Notes

References

* * * ** * * * * * * {{Authority control Desmostylians Miocene mammals Tortonian genus extinctions Extinct animals of Japan Extinct animals of North America Prehistoric placental genera Fossil taxa described in 1888 Taxa named by Othniel Charles Marsh Chattian genus first appearances Fossils of Japan Fossils of the United States Fossils of Mexico Fossils of Russia