Name: Hydrodamalis ‭(‬Water calf‭ ‬/‭ ‬Water tame calf‭)‬.‭
Phonetic: Hy-droe-dam-a-liss.
Named By: Anders Jahan Retzius‭ ‬-‭ ‬1794.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Sirenia,‭ ‬Dugongidae,‭ ‬Hydrodamalinae.
Species: H.‭ ‬gigas‭ (‬type‭)‬, H. cuestae, H. spissa.
Diet: Herbivore.
Size: Between‭ ‬8‭ ‬and‭ ‬9‭ ‬meters long depending upon species.
Known locations: Across the North Pacific.
Time period: Pliocene to Holocene.‭ ‬Went extinct around‭ ‬1768.
Fossil representation: Multiple remains.

       The story of Hydrodamalis is a sad one,‭ ‬as within twenty-seven years of the discovery of the last surviving population of Hydrodamalis around the uninhabited Commander Islands in‭ ‬1741,‭ ‬the remaining few were wiped out by sailors and hunters for its meat and fur.‭ ‬This was but the final nail in the coffin of this sea cow however as even before this time it is thought that‭ ‬hunting from‭ ‬indigenous peoples in other parts of the Pacific also contributed to their ultimate decline.‭ ‬Indirect hunting also seems to have affected them since sea otters are also thought to have been hunted and killed en masse.‭
       This all comes down to sea cows like Hydrodamalis feeding upon kelp which seemed to be their preferred food.‭ ‬Kelp can be threatened by sea urchins which eat the root stems of kelp causing the kelp to drift away and die,‭ ‬but normally the numbers of sea urchins are kept in check by predators like sea otters.‭ ‬When human hunters began slaughtering sea otters however,‭ ‬the population of sea urchins exploded causing devastation to kelp forests as the sea urchins munched their way through.‭ ‬With this and early human hunting combined,‭ ‬Hydrodamalis became restricted to the one untouched area they could find‭; ‬the Commander islands.‭ ‬Here they were at least safe until their rediscovery in the eighteenth century.
       Hydrodamalis gigas got the more common name of Steller’s sea cow from the explorer and naturalist Georg Wilhelm Steller who discovered the last population of Hydrodamalis when he took part in an expedition led by Vitus Bering.‭ ‬Although the Hydrodamalis is now extinct,‭ ‬Steller’s notes and description of the living animal still serve as teaching about this sea cow.‭ ‬Steller noted that Hydrodamalis had thick black skin‭ ‬like‭ ‬the bark of a tree.‭ ‬Also Hydrodamalis spent all of its time in the water,‭ ‬never venturing onto land.‭ ‬Again,‭ ‬kelp was observed as being the preferred food,‭ ‬with remnants of kelp being washed on the shores of the Commander islands after Hydrodamalis had been feeding.‭ ‬Hydrodamalis fed upon kelp by trapping it between two large dental plates in the top and bottom jaw that would snip off kelp when the mouth closed.‭
       Steller also noted two other things however,‭ ‬and these go quite some way to explaining why Hydrodamalis was such an easy target for hunters.‭ ‬One is that despite being an aquatic animal,‭ ‬Hydrodamalis was not a powerful swimmer,‭ ‬moving only very slowly and never actually submerging itself beneath the surface.‭ ‬The second is that the population around the‭ ‬Commander Islands was very tame and together these mean that not only Hydrodamalis couldn’t hide,‭ ‬but it didn’t even try to.
       There are at the time of writing three species of Hydrodamalis. These are H. gigas (Steller's sea cow), H. cuestae (Cuesta sea cow), and H. spissa (Takikawa sea cow).

Further reading
- Anmärkningar vid Genus Trichechi. Kongl. - Vetenskaps Academiens nya handlingar 2(15):286-300. - A. J. Retzius - 1794.
- A new species of hydrodamaline Sirenia from Hokkaido, Japan. - Takikawa Museum of Art and Natural History. pp. 1–73. - H. Furusawa - 1988.
- A phylogeny of the North Pacific Sirenia (Dugongidae: Hydrodamalinae) based on a comparative study of endocranial casts. - Paleontological Research. 8 (2): 91–98. - Hitoshi Furusawa - 2004.
- Steller's sea cow: discovery, biology and exploitation of a relict giant sirenian". Ecology and Conservation of the Sirenia: Dugongs and Manatees. - New York: Cambridge University Press. pp. 18–35. - Helene Marsh, Thomas J. O'Shea & John E. Reynolds III - 2011.


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