Steller's sea cow
|Steller's sea cow|
|Drawing by Steller in 1743 on a dead female, thought to be the only first-hand illustration|
The Steller's sea cow, Hydrodamalis gigas, is an extinct herbivorous marine mammal. It is the largest member of the order Sirenia, which includes its closest living relative, the dugong (Dugong dugon), and the manatees (Trichechus spp.). They reached up to 9 metres (30 ft) in length, making the Steller's sea cow among the largest mammals other than whales to have existed in the holocene epoch. Steller's sea cow was first described by Georg Wilhelm Steller. Although the Steller's sea cow had formerly been abundant throughout the North Pacific, by the mid 1700s, its range had been limited to a single, isolated population surrounding the uninhabited Commander Islands. It was hunted for its meat, skin, and fat by fur traders, and was also hunted by aboriginals of the North Pacific coast. Within 27 years of discovery by Europeans, the slow-moving and easily captured Steller's sea cow was hunted to extinction.
Description and ecology
The sea cow grew to at least 26 to 30 ft (8 to 9 m) in length as an adult, much larger than the manatee or dugong; however, concerning their weight, Steller's work contains two contradictory estimates: 4.4 and 26.8 short tons (4 and 24.3 metric tons). The true value is estimated to lie between these figures, at around 9 to 11 short tons (8 to 10 metric tons). Their large size was probably to reduce their surface-area-to-volume ratio and conserve heat. The forelimbs, according to Steller, were used as sort of a holdfast to anchor themselves down to prevent being swept away by the strong nearshore waves around their habitat. Unlike other sirenians, the Steller's sea cow was positively buoyant, meaning they could not completely submerge. They had a thick epidermis to prevent injury from abrasions on sharp rocks and ice, and possibly to prevent the skin that is not submerged from drying out.
Its head was small and short compared to the huge body. The upper lip was large and broad, and extended so far beyond the mandible, that the mouth appeared to be located underneath the skull. Instead of teeth, Steller's sea cow had a dense array of white bristles, 1.5 inches (3.8 cm) long, which were used to pull out seaweed and hold food, and used keratinous plates for chewing. According to Steller, these plates, or "masticatory bones", were held together by papillae and had many small holes for nerves and arteries. The rostrum was pointed downwards, as in all sirenians, to better grasp kelp. Like other sirenians, the Steller's sea cow was an obligate herbivore, and kelp was most likely their main food source. They may have also fed on seagrasses, but they could not have been a main food source while supporting a viable population, because they did not occur in sufficient numbers. Since they floated, they most likely fed on canopy kelp. Kelp releases a chemical deterrent to prevent grazing, but canopy kelp release a lower concentration, allowing the sea cows to graze without developing resistance.
Whether or not Stellar's sea cows had any predators is unknown. They may have been hunted by killer whales and sharks, but their buoyancy may have made it difficult for killer whales to drown them, and the rocky kelp forests may have protected them from sharks. According to Steller, the young were kept into positions wherein the adults would guard them from predators.
Taxonomy and range
|Relations within Sirenia|
|Based on a 2004 study by Hitoshi Furusawa|
The Steller's sea cow was a direct descendant of the Cuesta sea cow, a tropical sea cow of California. It most likely went extinct due to the onset of the Ice Ages and the subsequent cooling of the oceans; individuals who were less than capable of adapting died out, and those that could started the lineage of the Steller's sea cow. The Steller's sea cow was a member of the genus Hydrodamalis, a group of large sirenians, whose sister taxon was Dusisiren. Much like the Steller's sea cow, the ancestors of the Dusisiren were tropical mangrove variety, who adapted to the cold climates of the North Pacific and to consuming kelp.
Steller's sea cow was discovered in the mid-18th century by Georg Wilhelm Steller, and subsequently named after him, who studied a relict population near Bering Island while he was shipwrecked there. His account was written in his posthumous publication De bestiis marinis, or "The Beasts of the Sea". In 1811, naturalist Johann Karl Wilhelm Illiger placed the Steller's sea cow under the genus Rhytina, which many writers at the time adopted. However, the animal had already been classified well before this. Zoologist Eberhard August Wilhelm von Zimmermann had described its specific name as gigas in 1780, and biologist Anders Jahan Retzius 17 years before Illiger had described the sea cow as Rhytina had placed it under the genus Hydrodamalis. He, however, described its specific name as stelleri, as Steller was the first person to describe it. It wasn't until the 1900s that Hydrodamalis gigas was used.
Their range at the time of their discovery was apparently restricted to the Commander Islands, though fossils discovered dating to the late Pleistocene were found in Monterey Bay, California. The first fossils discovered outside the Commander Islands were interglacial Pleistocene deposits in Amchitka. There is evidence that sea cows also inhabited the Near Islands during historic times.
The Steller's sea cow was quickly wiped out by the sailors, seal hunters, and fur traders who followed Vitus Bering's route past the islands to Alaska, who hunted it for its meat before sailing to nearby islands in search of sea otter pelts. 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 odor 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. It has been argued that the Steller's 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 is possible that the extinction of these remaining endangered populations of sea cow could have been affected solely by the hunting of the sea cow for meat by fur-trading mariners of the time, and no other factors (such as overpopulation of sea urchins) need contributed. Zoologist Leonhard Hess Stejneger estimated in 1887 that there had been fewer than 1,500 individuals remaining at the time of their discovery, and thus had been in immediate danger of extinction.
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 Bureaud found the film a "tongue in cheek and joyous but unsettling fable".
- List of extinct animals
- List of extinct animals of North America
- List of recently extinct mammals
- Evolution of sirenians
- Holocene extinction
- Domning, D.; Anderson, P.K.; Turvey, S. (2008). Hydrodamalis gigas. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 19 August 2016.
- Wilson, Don E.; Reeder, DeeAnn M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference. 1 (2 ed.). Baltimore: Johns Hopkins University Press. p. 92. ISBN 978-0-8018-8221-0.
- Palmer, Theodore S. (1895). "The Earliest Name for Steller's sea cow and Dugong". Science. 2 (40): 449–450. doi:10.1126/science.2.40.449-a. PMID 17759916.
- Helene 2011, p. 21.
- Scheffer, Victor B. (November 1972). "The Weight of the Steller Sea Cow". Journal of Mammalogy. 53 (4): 912–914. doi:10.2307/1379236. JSTOR 1379236.
- Helene 2011, p. 24.
- Steller, Georg W. (2011) . "The Manatee". In Royster, Paul. De Bestiis Marinis. Lincoln: University of Nebraska. pp. 13–43. ISBN 978-1-295-08525-5.
- Perrin, William F.; Wursig, Bernd; Thewissen, J. G. M. (2008). Encyclopedia of Marine Mammals (2 ed.). San Diego: Academic Press. p. 306. ISBN 978-0-12-373553-9.
- Whitmore, Jr., Frank C.; Gard, Jr., L. M. (1977). "Steller's Sea Cow (Hydrodamalis gigas) of Late Pleistocene Age from Amchitka, Aleutian Islands, Alaska" (PDF). Geological Survey Professional Paper. Washington D. C.: United States Government Printing Office. 1036: 9.
- Helene 2011, p. 32.
- Estes, James A.; Burdin, Alexander; Doak, Daniel F. (2016). "Sea otters, kelp forests, and the extinction of Steller's sea cow". Proceedings of the National Academy of Sciences of the United States of America. 113 (4): 880–885. doi:10.1073/pnas.1502552112. PMC .
- Helene 2011, p. 31.
- Furusawa, Hitoshi (2004). "A phylogeny of the North Pacific Sirenia (Dugongidae: Hydrodamalinae) based on a comparative study of endocranial casts". Paleontological Research. 8 (2): 91–98. doi:10.2517/prpsj.8.91.
- Helene 2011, p. 76.
- Domning, Daryl P. (1978). "An Ecological Model for Late Tertiary Sirenian Evolution in the North Pacific Ocean". Systematic Zoology. 25 (4): 352–362. JSTOR 2412510.
- Domning, D. P. (1978). Sirenian evolution in the North Pacific Ocean. 118. University of California Publications in Geological Sciences. pp. 1–176. ISBN 978-0-520-09581-6.
- Anderson, Paul K. (July 1995). "Competition, Predation, and the Evolution and Extinction of Steller's Sea Cow, Hydrodamalis gigas". Marine Mammal Science. Society for Marine Mammalogy. 11 (3): 391–394. doi:10.1111/j.1748-7692.1995.tb00294.x.
- MacDonald, Stephen O.; Cook, Joseph A. (2009). Recent Mammals of Alaska. University of Alaska Press. pp. 57–58. ISBN 978-1-60223-047-7.
- 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.
- Corbett, D. G.; Causey, D.; Clemente, M.; Koch, P. L.; Doroff, A.; Lefavre, C.; West, D. (2008). "Aleut Hunters, Sea Otters, and Sea Cows". Human Impacts on Ancient Marine Ecosystems. University of California Press. pp. 43–76. ISBN 978-0-520-93429-0. JSTOR 10.1525/j.ctt1pphh3.
- Haycox, Stephen W. (2002). Alaska: An American Colony. Seattle: University of Washington Press. pp. 55, 144. ISBN 978-0-295-98249-6.
- Jones, Ryan T. (September 2011). "A 'Havock Made among Them': Animals, Empire, and Extinction in the Russian North Pacific, 1741–1810". Environmental History. 16 (4): 585–609. doi:10.1093/envhis/emr091. JSTOR 23049853.
- Ellis, Richard (2004). No Turning Back: The Life and Death of Animal Species. New York City: Harper Perennial. p. 134. ISBN 978-0-06-055804-8.
- Turvey, ST; Risley, CL (March 22, 2006). "Modelling the extinction of Steller's sea cow". Biol Lett. 2 (1): 94–7. doi:10.1098/rsbl.2005.0415. PMC . PMID 17148336.
- "Tales of a Sea Cow (2012)". IMDb.
- "Etienne de France, "Tales of a Sea Cow" — Exhibition at Parco Arte Vivente, Torino, Italy". alan-shapiro.com.
- Bureaud, Annick. "Tales of a Sea Cow: A Fabulatory Science Story" (PDF). Retrieved August 19, 2016.
- 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: Cambridge University Press. pp. 18–35. ISBN 978-0-521-88828-8.
|Wikimedia Commons has media related to Hydrodamalis gigas.|
|Wikispecies has information related to: Hydrodamalis gigas|