Steller's sea cow

Steller's sea cow
Drawing thought to be the only remaining illustration of a dead female examined by Steller, 1743. Many later depictions were based on it.
Conservation status
Extinct (1768) (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Sirenia
Family:	Dugongidae
Subfamily:	†Hydrodamalinae Palmer, 1895
Genus:	†Hydrodamalis Retzius, 1794
Species:	†H. gigas
Binomial name
Hydrodamalis gigas (Zimmermann, 1780)

The Steller's sea cow (Hydrodamalis gigas) is an extinct herbivorous marine mammal. It was the largest member of the order Sirenia, which includes its closest living relative, the dugong (Dugong dugon), and the manatees (Trichechus spp.). It reached up to 9 metres (30 ft) in length, making it among the largest mammals other than whales to have existed in the holocene epoch. Although the sea cow had formerly been abundant throughout the North Pacific, by 1741, when it was first described by Georg Wilhelm Steller, chief naturalist on an expedition led by explorer Vitus Bering, its range had been limited to a single, isolated population surrounding the uninhabited Commander Islands. Within 27 years of discovery by Europeans, the slow-moving and easily captured Steller's sea cow was hunted to extinction.

Description

Skeleton in Finland

The sea cow grew to at least 8 to 9 m (26 to 30 ft) in length as an adult, much larger than the manatee or dugong; however, concerning their weight, Steller's work contains two contradictory estimates: 4 and 24.3 metric tons. The true value is estimated to lie between these figures, at around 8 to 10 t. It looked somewhat like a large seal, but had two stout forelimbs and a whale-like fluke.

According to Steller, it "is not the sea cow of Aristotle, for it never comes upon dry land to feed", but it can use its fore limbs for a number of tasks: swimming, walking on the shallows of the shore, supporting himself on the rocks, digging for algae and seagrasses, fighting, and embracing each other.

"It is covered with a thick hide, more like unto the bark of an ancient oak than unto the skin of an animal; the manatee’s hide is black, mangy, wrinkled, rough, hard, and tough; it is void of hairs, and almost impervious to an ax or to the point of a hook."

Its head is small and short compared to the huge body. The upper lip is so large, so broad, and extends so far beyond the mandible, that the mouth appears to be located underneath the skull. The mouth is rather small, toothless, and equipped with double lips, both above and below. When it closes its mouth, the space between the lips is filled up with a dense array of very thick white bristles, 1.5 in (38 mm) long. These bristles take the place of teeth and are used to pull out seaweed and hold food. Mastication is performed by two white bones or solid tooth masses.

Behavior

Skull

It was completely tame, according to Steller. It fed on a variety of kelp. Wherever sea cows had been feeding, heaps of stalks and roots of kelp were washed ashore. The sea cow was also a slow swimmer and apparently was unable to submerge.

Habitat

Reconstruction

The number of sea cows was small and limited in range when Steller first described them; although he had said they were numerous and found in herds, zoologist Leonhard Hess Stejneger later estimated that at discovery there had been fewer than 1,500 remaining, and thus had been in immediate danger of extinction from overhunting. There is evidence that sea cows also inhabited the Near Islands during historic times. Oral tradition on Attu stated that sea cows were still hunted there after their extinction on the Commander Islands.

Fossils indicate Steller's sea cow was formerly widespread along the North Pacific coast, reaching south to Japan and California in the US. Given the rapidity with which its last population was eliminated, aboriginal hunting likely caused its extinction over the rest of its original range (aboriginal peoples apparently never inhabited the Commander Islands).

Population and extinction

The species was quickly wiped out by the sailors, seal hunters, and fur traders who followed Bering's route past the islands to Alaska, who hunted it both for food and for skins, which were used to make boats. It was also hunted for its valuable subcutaneous fat, which was not only used for food (usually as a butter substitute), but also for oil lamps because it did not give off any smoke or odour and could be kept for a long time in warm weather without spoiling. By 1768, 27 years after it had been discovered by Europeans, Steller's sea cow was extinct.

Hydrodamalis gigas skeleton with incorrectly restored hands, Muséum national d'histoire naturelle, Paris

It has been argued that the sea cow's decline may have also been an indirect response to the harvest of sea otters by aboriginal people from the inland areas. With the otters reduced, the population of sea urchins would have increased and reduced availability of kelp, the sea cow's primary source of food. Thus, aboriginal hunting of both species may have contributed to the sea cow's disappearance from continental shorelines. In historic times, though, aboriginal hunting had depleted sea otter populations only in localized areas. The sea cow would have been easy prey for aboriginal hunters, who would likely have exterminated accessible populations with or without simultaneous otter hunting. In any event, the sea cow was limited to coastal areas off islands without a human population by the time Bering arrived, and was already endangered. It has been demonstrated that the extinction of the sea cow could have been effected solely by the hunting of the sea cow for meat by fur-trading mariners of the time, and no other factors needed to have contributed.

Portrayals in media

Tales of a Sea Cow is a 2012 film by Icelandic-French artist Etienne de France "documenting" a fictional 2006 re-discovery by scientists of a population of Steller's sea cows off the coast of Greenland via sound recordings or their calls. This film has been exhibited in public institutions such as art museums and universities in Europe. Art critic Annick Buread found the film a "tongue in cheek and joyous but unsettling fable".

See also

• List of extinct animals
• List of extinct animals of North America
• Evolution of sirenians
• Holocene extinction

External links

• Animal Diversity Web
• Steller's sea cow information from the AMIQ Institute
• Hans Rothauscher's Die Stellersche Seekuh site (in German & English)
• Illustration of a sea cow skeleton and an extract from Steller's description