Desmostylus

Name: Desmostylus ‭(‬Chain pillar‭)‬.
Phonetic: Dez-moe-sty-lus.
Named By: Othniel Charles Marsh‭ ‬-‭ ‬1888.
Synonyms: Desmostylella, Vanderhoofius coalingensis.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Paenungulata,‭ ‬Desmostylia,‭ ‬Desmostylidae.
Species: D.‭ ‬hesperus‭ (‬type‭), D. coalingensis, D. japonicus
Diet: Herbivore.
Size: 1.8‭ ‬meters long.
Known locations: Pacific coastlines of North America,‭ ‬Russia and Japan.
Time period: Chattian of the Oligocene through to Tortonian of the Miocene.
Fossil representation: Multiple specimens.

       Often described as hippopotamus-like because of its heavily built quadrupedal body,‭ ‬Desmostylus is a peculiar mammal.‭ ‬Palaeontologists are still unsure how Desmostylus is related to other mammals with theories covering a wide range of options from being related to elephants,‭ ‬to hippopotamuses to just being a separate side branch of mammals that left no modern descendants.
       Desmostylus is widely believed to have been a semi aquatic animal in that it regularly entered the water,‭ ‬but would return to land to rest.‭ ‬The remains of Desmostylus are known from across most of the northern Pacific Rim from Japan and Russia to the west coast of the United States.‭ ‬This pattern of fossils led to the idea that Desmostylus followed the coastlines to spread out into new territories,‭ ‬however a‭ ‬2003‭ ‬study has cast serious doubt upon this.‭ ‬The study in question conducted by Mark T.‭ ‬Clementz,‭ ‬Kathryn A.‭ ‬Hoppe and Paul L.‭ ‬Koch used isotope analysis‭ (‬of oxygen,‭ ‬carbon and strontium‭) ‬of tooth enamel from Desmostylus and concluded that it actually lived in freshwater systems.‭ ‬This reveals a picture of Desmostylus living around estuaries and the immediate freshwater‭ ‬systems,‭ ‬however it does not explain the fossil distribution as rivers tend to run into the ocean not run parallel to it.‭ ‬It is perhaps possible that early on Desmostylus was a marine creature that spent more time on the coast,‭ ‬but once a range was established and new mammals such as sirenians‭ (‬sea cows‭) ‬began to become more common during the Miocene,‭ ‬Desmostylus were outcompeted and pushed into freshwater ecosystems.
       Desmostylus is believed to have fed upon soft aquatic plants that it may have rooted up with its specialised teeth.‭ ‬The anterior lower jaw teeth were also enlarged into tusks and grew into a shovel-shaped arrangement similar to the prehistoric gomphothere elephants‭ (‬think Gomphotherium‭)‬.‭ ‬Two more tusk-like teeth grew down from the upper jaw.‭ ‬The back teeth have a cylindrical arrangement which was the inspiration for the name Desmostylus which means‭ ‘‬chain pillar‭’ ‬The lower foreleg was also adapted to work best in the water since the bones were fused together to make a rigid appendage.‭ ‬Although this would have been cumbersome on land,‭ ‬since the entire leg would have to be turned to turn the foot,‭ ‬this would have made it easier for Desmostylus to push itself along while in the water.

Further reading
- Notice of a new fossil sirenian, from California. - American Journal of Science 25 (8): 94–96. - O. C. Marsh - 1888.
- Notes on a New Fossil Mammal. - Journal of the College of Science, Imperial University, Tokyo, Japan 16. - S. Yoshiwara & J. Iwasaki - 1902.
- Notes on Desmostylus japonicus - S. Tokunaga & C. Iwasaki - 1914.
- A review of the Sirenia and Desmostylia. - University of California Publications in Geological Sciences 36 (1): 1–146. - Roy Herbert Reinhart - 1959.
- Summary of taxa and morphological adaptations of the Desmostylia. - Island Arc 3 (4): 522–537. - Norihisa Inuzuka, Daryl P. Domning & Clayton E. Ray - 1984.
- A paleoecological paradox: the habitat and dietary preferences of the extinct tethythere Desmostylus, inferred from stable isotope analysis. - Paleobiology 29 (4): 506–519. - Mark T. Clementz, Kathryn A. Hoppe, Paul L. Koch - 2003.
- Discovery of a desmostylian tooth from Kitami City, northeastern Hokkaido, Japan. - Memoir of the Fukui Prefectural Dinosaur Museum 6: 57–61. - Yukimitsu Tomida & Toshikazu Ohta - 2007.
- 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 - 2017.

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