Desmostylus

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]

Desmostylus
Temporal range: Oligocene–Miocene
Desmostylus, Royal Ontario Museum
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: †Desmostylia
Family: †Desmostylidae
Genus: †Desmostylus
Marsh 1888
Species
Synonyms
  • †Vanderhoofius coalingensis

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

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 fully aquatic, Desmostylus is thought to have lived in shallow water in coastal regions, usually less than 30 meters deep.[4] 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.[5]

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.[6]

Species

Desmostylus hesperus (synonyms and invalid names: D. watasei, D. cymatias, D. californicus, D. mirabilis, D. minor, Desmostylella typica),[2] D. coalingensis (syn. Vanderhoofius coalingensis),[7][8] 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).[9] Marsh described his specimen as a sirenian and proposed affinities with Metaxytherium (a genus of extinct dugongs) and Halicore (an obsolete name for dugong).[10]

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.[11]

Desmostylus 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.[11]

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
  1. "bound pillar", from Greek δεσμός (desmos), bond, and στῦλος (stulos), pillar, referring to the shape of the molars.
  2. Desmostylus in the Paleobiology Database. Retrieved March 2013.
  3. Palmer 1999, p. 228
  4. Kumiko Matsui; Katsuo Sashida; Sachiko Agematsu; Naoki Kohno (2017). "Habitat preferences of the enigmatic Miocene tethythere Desmostylus and Paleoparadoxia (Desmostylia; Mammalia) inferred from the depositional depth of fossil occurrences in the Northwestern Pacific realm". Palaeogeography, Palaeoclimatology, Palaeoecology. 471: 254–265. doi:10.1016/j.palaeo.2017.02.005.
  5. Clementz, Hoppe & Koch 2003
  6. Hayashi, S.; Houssaye, A.; Nakajima, Y.; Chiba, K.; Ando, T.; Sawamura, H.; Inuzuka, N.; Kaneko, N.; Osaki, T. (2013). "Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria)". PLoS ONE. 8 (4): e59146. doi:10.1371/journal.pone.0059146. OCLC 837402105. PMC 3615000. PMID 23565143.
  7. Tomida & Ohta 2007, p. 60
  8. Inuzuka, Domning & Ray 1984
  9. "Mission San Jose, east (Miocene of the United States)". Fossilworks. Retrieved December 2013. Check date values in: |accessdate= (help)
  10. Marsh 1888, p. 96
  11. Uno & Kimura 2004, p. 1
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References
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