Steller's Sea Cow

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They were incredibly large animals, reported to have grown to 8 to 9 m (26 to 30 ft) long as adults. Based on recent skeletal findings, the estimated weight is around 8–10 t (8.8–11.0 short tons, or 17,600-22,000 lbs.). This size made the sea cow one of the largest mammals of the Holocene epoch, alongside baleen whales and some tooth whales. It was also most likely an adaptation to preserve body heat in the colder climates it lived in.

Unlike modern sirenians, the Steller's Sea Cow was completely buoyant, meaning it could not fully submerge itself. Their thick outer skin (around 1 in. thick) helped protect them from the cold as well as sharp rocks and ice. A dense layer of blubber, as thick as 3-4 inches, also helped protect them from the frigid waters of the Bering Sea. The skin was described as brownish-black, with white patches on some individuals. It was smooth along its back and rough on its sides. This rough texture lead to the nickname of "bark animal".

Unlike modern sirenians, the Steller's Sea Cow was completely buoyant, meaning it could not fully submerge itself. Their thick outer skin (around 1 in. thick) helped protect them from the cold as well as sharp rocks and ice. A dense layer of blubber, as thick as 3-4 inches, also helped protect them from the frigid waters of the Bering Sea. The skin was described as brownish-black, with white patches on some individuals. It was smooth along its back and rough on its sides. This rough texture lead to the nickname of "bark animal". The forelimbs were about 67 cm (26 in) long, and the tail's fluke was forked (similar to modern day Dugongs).

Georg Steller described the animal as being very social and gregarious, living in small family groups. They were noted to be monogamous and exhibited parental care toward the young. Mating season occurred in early spring, with gestation taking a little over a year. Since Steller observed a greater number of calves in autumn than at any other time of the year, it is likely calves were born in those months. Females had only one set of mammary glands, and as such, they likely had one calf at a time.

Steller also reported an incident where as one female was being captured, the rest of the group attacked the boat by ramming the sides with their heads. After the hunt, the mate of the captured female followed the boat to shore, even after she had passed.

[[File:Hydrodamalis gigas skeleton - Finnish Museum of Natural History - DSC04529.JPG|thumb|right|Skeleton of the Steller's Sea Cow at the Finnish Museum of Natural History. Photo by user Daderot.]]

The indigenous peoples of the Aleutian Islands and St. Lawrence Islands, namely the Aleut people and Siberian Yupik people respectively, heavily depended on the Steller's Sea Cow for food and hide. They frequently moved around to be able to hunt the animal. As such, many local populations were extirpated. By the time Europeans discovered them in the 1740's, it is estimated there may have been only 2,000 individuals left. Records conclude that by 1768, twenty-seven years after the discovery, the Steller's Sea Cow was extinct. However in 1887, zoologist Leonhard Hess Stejneger determined there had been fewer than 1,500 individuals remaining at the time of Steller's discovery, and argued there was already an immediate danger of the sea cow's extinction.

Evidence suggests Steller's sea cows, specifically ones around the Commander Islands, were the last of a much more spaced out population dispersed across the North Pacific coastal zones. During the recent glacial periods and reduction in sea levels and temperatures, suitable habitat substantially regressed, which fragmented the current population. By the time sea levels stabilized circa 5,000 years ago, the population as a whole had already plummeted. Both of these natural occurrences indicated that even without human influence, the Steller's sea cow would have still been a "dead clade walking", or an extinction caused by past events.

|trivia=[[File:Em - Hydrodamalis gigas model.jpg|thumb|left|Model in the Natural History Museum of London. Photo by Emőke Dénes.]]

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* The estimated weight of modern findings contradicts Steller's original writings: he guessed 4 and 24.3 t (4.4 and 26.8 short tons), which is equivalent to around 8800-53600 lbs.

* The sea cow's heart alone was estimated 16 kg (35 lb.) in weight

* Steller's sea cow's closest living relative is the [[Dugong]] (Dugong dugon)

* The first bones of a Steller's sea cow were unearthed around1840, more than 70 years after it was presumed to have become extinct.

|reference=* [[https://en.wikipedia.org/wiki/Steller%27s_sea_cow Wikipedia Page]]

* Scheffer, Victor B. (November 1972). "The Weight of the Steller Sea Cow". Journal of Mammalogy. 53 (4): 912–914.

* Mattioli, Stefano; Domning, Daryl P. (2006). "An Annotated List of Extant Skeletal Material of Steller's Sea Cow (Hydrodamalis gigas) (Sirenia: Dugongidae) from the Commander Islands". Aquatic Mammals. 32 (3): 273–288. doi:10.1578/AM.32.3.2006.273.

* Marsh, Helene; O'Shea, Thomas J.; Reynolds III, John E. (2011). "Steller's sea cow: discovery, biology and exploitation of a relict giant sirenian". Ecology and Conservation of the Sirenia: Dugongs and Manatees. New York, New York: Cambridge University Press. pp. 18–35.

* Forsten, Ann; Youngman, Phillip M. (1982). "Hydrodamalis gigas" (PDF). Mammalian Species (165): 1–3. doi:10.2307/3503855. JSTOR 3503855. Archived from the original (PDF) on 2016-10-20.

* Sharko, F. S.; Boulygina, E. S.; et al. (2021). "Steller's sea cow genome suggests this species began going extinct before the arrival of Paleolithic humans". Nature Communications. 12 (2215): 2215. Bibcode:2021NatCo..12.2215S. doi:10.1038/s41467-021-22567-5. PMC 8044168. PMID 33850161.

* Domning, Daryl P.; Thomason, James; Corbett, Debra G. (2007). "Steller's sea cow in the Aleutian Islands". Marine Mammal Science. 23 (4): 976–983. doi:10.1111/j.1748-7692.2007.00153.x.

* Domning, D. (2016). "Hydrodamalis gigas". IUCN Red List of Threatened Species. 2016: e.T10303A43792683. doi:10.2305/IUCN.UK.2016-2.RLTS.T10303A43792683.en. Retrieved 17 February 2022.

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