Hydrodamalis
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
- Anm�rkningar 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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