Desmostylus

Desmostylus Temporal range: Oligocene–Miocene PreЄ Є O S D C P T J K Pg N
Skull of D. japonicus at the National Museum of Nature and Science, Tokyo, Japan. Holotype
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
(unranked):	Afrotheria
Order:	†Desmostylia
Family:	†Desmostylidae
Genus:	†Desmostylus Marsh 1888
Species
†D. hesperus (type) Marsh 1888 †D. coalingensis Reinhart 1959 †D. japonicus Tokunaga & Iwasaki 1914
Synonyms
†Vanderhoofius coalingensis

Desmostylus^[1] 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 21.2 million years.^[2]

Morphology

Restoration of D. hesperus

Illustration of the type specimen by Marsh 1888. Labial, ventral, and lingual view.

Desmostylus was a large, hippopotamus-like creature of about 1.8 metres (6 ft) long which weighed about 200 kilograms (440 lb). 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.^[3]

Most likely amphibious, Desmostylus is thought to have lived in shallow water in coastal regions. Some paleontologists have argued it may have fed on seaweed during low tide. However, 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.^[4]

Species

D. hesperus (synonyms and invalid names: D. watasei, D. cymatias, D. californicus, D. mirabilis, D. minor, Desmostylella typica),^[2] D. coalingensis (syn. Vanderhoofius coalingensis),^[5][6] and D. japonicus.

Marsh 1888 named the type specimen D. hesperus based on a set of isolated teeth that he had found near Mission San Jose, California (type locality: 37°36′N 121°54′W / 37.6°N 121.9°W / 37.6; -121.9, paleocoordinates 36°48′N 117°36′W / 36.8°N 117.6°W / 36.8; -117.6).^[7] Marsh described his specimen as a sirenian and proposed affinities with Metaxytherium (a genus of extinct dugongs) and Halicore (an obsolete name for dugong).^[8]

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.^[9]

D. japonicus was described by Yoshiwara & Iwasakai 1902 based on a well preserved partial skull and named by Tokunaga & Iwasaki 1914. It has been reproposed as distinct species based on cranial morphology.^[9]

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.^[2]

Notes

Wikimedia Commons has media related to Desmostylus.

References