Desmostylus

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 (28.4 mya—7.250 Mya) and in existence for approximately .
Description.
"Desmostylus" was a large, pig/hippopotamus-like creature of about long which weighed about . It had a short tail and powerful legs with four hooves. Both the creature's jaws were elongated and sported forward-facing tusks, which were elongated canines and incisors.
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 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 sirenian and proposed affinities with "Metaxytherium" (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, Oregon, Washington and west to Sakhalin Island, Hokkaido, Japan, and south to the Shimane Prefecture, Japan.