Desmostylus

Desmostylus Temporal range:
Desmostylus, Royal Ontario Museum
Restoration of D. hesperus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
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 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.

Description

Skull of D. japonicus at the National Museum of Nature and Science, Tokyo, Japan. Holotype

Desmostylus was a large, hippopotamus-like creature, with the adult Keton specimen of D. hesperus measuring 275 cm (9.02 ft) in length, 105 cm (3.44 ft) in height and 1,283 kilograms (2,829 lb) 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 2.8 metric tons (3.1 short tons). It had a short tail and powerful legs with four hooves. The animal'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.

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: 37.6°N 121.9°W / 37.6; -121.9, paleocoordinates 36.8°N 117.6°W / 36.8; -117.6). 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 Yoshiwara & Iwasaki 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.

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, and south to the Shimane Prefecture.

References

• Clementz, Mark T.; Hoppe, Kathryn A.; Koch, Paul L. (2003). "A paleoecological paradox: the habitat and dietary preferences of the extinct tethythere Desmostylus, inferred from stable isotope analysis". Paleobiology. 29 (4): 506–519. Bibcode:2003Pbio...29..506C. doi:10.1666/0094-8373(2003)029<0506:APPTHA>2.0.CO;2. OCLC 211272891. S2CID 12567121.
• Inuzuka, Norihisa; Domning, Daryl P.; Ray, Clayton E. (1984). "Summary of taxa and morphological adaptations of the Desmostylia". Island Arc. 3 (4): 522–537. doi:10.1111/j.1440-1738.1994.tb00131.x.
• Marsh, O. C. (1888). "Notice of a new fossil sirenian, from California". American Journal of Science. 25 (8): 94–96. Bibcode:1888AmJS...35...94M. doi:10.2475/ajs.s3-35.205.94. OCLC 79838746. S2CID 129254943. Retrieved 17 December 2021.
  • "O. C. Marsh 1888". Fossilworks.
• Palmer, Douglas (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. ISBN 1-84028-152-9. OCLC 313633743.
• Reinhart, Roy Herbert (1959). "A review of the Sirenia and Desmostylia". University of California Publications in Geological Sciences. 36 (1): 1–146. OCLC 3474601.
• Tokunaga, Shigeyasu; Iwasaki, C. (1914). "Notes on Desmostylus japonicus". The Journal of the Geological Society of Japan. 21 (255): 33. doi:10.5575/geosoc.21.255_33.
• Tomida, Yukimitsu; Ohta, Toshikazu (2007). "Discovery of a desmostylian tooth from Kitami City, northeastern Hokkaido, Japan" (PDF). Memoir of the Fukui Prefectural Dinosaur Museum. 6: 57–61. Retrieved 1 December 2013.
• Uno, Hikaru; Kimura, Masaichi (2004). "Reinterpretation of some cranial structures of Desmostylia hesperus (Mammalia, Desmostylia): A new specimen from the Middle Miocene Tachikaraushinai Formation, Hokkaido, Japan" (PDF). Paleontological Research. 8 (1): 1–10. doi:10.2517/prpsj.8.1. Retrieved 1 December 2013.
• Yoshiwara, Shigeyasu; Iwasaki, Jūzō (1902). "Notes on a New Fossil Mammal" (PDF). Journal of the College of Science, Imperial University, Tokyo, Japan. 16. Retrieved 13 June 2023.