Steller's sea cow
|Steller's sea cow|
|Drawing of a dead female published by Peter Simon Pallas in 1840, thought to be the only one drawn from an actual specimen|
|Map showing the position of the Commander Islands to the east of Kamchatka. The larger island to the west is Bering Island; the smaller island to the east is Copper Island.|
Steller's sea cow (Hydrodamalis gigas) is an extinct species of sirenian that was found exclusively around the Commander Islands, which is situated in the Bering Sea between Alaska and Russia. Its closest relative is the dugong (Dugong dugon), which is the sole surviving member of the Dugongidae of which Steller's sea cow was also a part of. They were among the largest mammals other than whales to have existed into the Holocene epoch, reaching weights of 8–10 metric tons (8.8–11.0 short tons) and lengths of 9 metres (30 ft).
Steller's sea cow was the largest of all sirenians, and had a much thicker epidermis in response to the cold waters of its environment. They were monogamous and gregarious, living in small family groups. They fed solely on kelp. They were slow swimmers. Like other sirenians, they probably cared for their young.
Georg Wilhelm Steller had discovered Steller's sea cow along with the Commander Islands in 1741 on Vitus Bering's Great Northern Expedition where they were shipwrecked, and much of what is known about the sea cow in life comes from Steller's account on the island documented in his posthumous publication "The Beasts of the Sea". Within 27 years of discovery by Europeans, the slow-moving and easily captured Steller's sea cow was hunted to extinction, though there were sightings proceeding 1768. They feature a role in various media, such as in Rudyard Kipling's The Jungle Book.
Steller's sea cow grew to be 8 to 9 m (26 to 30 ft) in length as an adult, much larger than the extant sirenians of today; however, concerning their weight, Georg Steller's work contains two contradictory estimates: 4 and 24.3 metric tons (4.4 and 26.8 short tons). The true value is estimated to lie between these figures, at about 8–10 metric tons (8.8–11.0 short tons), making it one of the largest mammals of the Holocene, besides whales. Their large size was probably to reduce their surface-area-to-volume ratio and conserve heat. The forelimbs, according to Steller, were used as a sort of holdfast to anchor themselves down to prevent being swept away by the strong nearshore waves around their habitat. In all collected skeletons, the manus is missing. Unlike other sirenians, 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 was 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.
The nostrils were 5.1 centimetres (2 in) long and wide, and located at the tip of the rostrum. The small eyes were parallel to the nostrils, halfway between them and the ears, and, like other sirenians, they used sphincters to close their eyes as opposed to eyelids. The irises were black, the eyeball was livid, and the canthi were not visible externally. Like other diving creatures, such as the sea otters, Steller's sea cow had a nictitating membrane which covered the eye to prevent injury while feeding. Their tongue was rough with short papillae; it was 30 centimetres (12 in) long and kept in the back of the mouth.
Whether or not Steller'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 guarded by the adults from predators. Steller described an ectoparasite on Steller's sea cow which was similar to the whale louse (Cyamus ovalis); however the parasite remains unidentified as the host has gone extinct and the original specimens he had collected are lost. Apparently, these parasites were picked off the sea cows by seagulls in a symbiotic relationship.
Like other sirenians, 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 this could not have been a main food source for supporting a viable population, because grasses did not occur in sufficient quantity. Since this animal floated, it 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. Steller noted that they get thin during the frigid winters, indicating a period of fasting.
Steller described the sea cows as being gregarious and highly social. He stated that they lived in small family groups and helped injured members. Steller's sea cow was apparently monogamous. Steller noted that, after a hunt wherein they had captured a female, her mate followed the boat to shore, even after she died. The group also attacked the boat while the female was being taken. Gestation took place in a little over a year, and calves, although they could have been born year-round, were delivered usually in autumn; females probably had one calf at a time. They may have exhibited childcare. To sleep, they went further out to sea to prevent beaching themselves when the tides recede.
|Relations within Sirenia|
|Based on a 2004 study by Hitoshi Furusawa|
Steller's sea cow was a direct descendant of the Cuesta sea cow, an extinct 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; lineages which could not adapt died out, and those that could started the lineage of Steller's sea cow. Steller's sea cow was a member of the genus Hydrodamalis, a group of large sirenians, whose sister taxon was Dusisiren. Much like Steller's sea cow, the ancestors of the Dusisiren were associated with tropical mangroves, and adapted to the cold climates of the North Pacific and to consuming kelp. Steller's sea cow is a member of the order Sirenia along with other sea cows, and of the family Dugongidae, whose sole surviving member, and thus closest living relative, is the dugong (Dugong dugon).
Steller's sea cow was discovered in the mid-18th century by Georg Wilhelm Steller, and subsequently named after him; Steller studied the local wildlife of Bering Island, including a relict population of sea cows, sea otters, Steller's sea lion, and the Northern fur seal, while he was shipwrecked there. His account was written in his posthumous publication De bestiis marinis, or "The Beasts of the Sea", which was published by the Russian Academy of Sciences in St. Petersburg, Russia in 1751. In 1811, naturalist Johann Karl Wilhelm Illiger placed Steller's sea cow under the genus Rhytina, which many writers at the time adopted. However, the animal had already been classified long 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, placed it under the genus Hydrodamalis. He, however, described its specific name as stelleri, as Steller was the first person to describe it. It was not until the 1900s that Hydrodamalis gigas was used.
For decades after their discovery, no osteological evidence, that is skeletal remains, of the existence of Steller's sea cow was discovered. The first Steller's sea cow bones were unearthed around 1840, over 70 years after they were presumed extinct. The first partial skull was discovered in 1844 by Ilya Voznesensky after spending two days in the Commander Islands, and the first skeleton in 1855 in northern Bering Island. It was sent to the Russian Academy of Sciences in St. Petersburg in 1857, and another nearly complete skeleton arrived in Moscow around 1860. Most of the skeletal remains were unearthed in the late 1800s; in the period between 1878 and 1883, 12 of the 22 skeletons (with a known time of collection) were discovered. Adolf Erik Nordenskiöld, Benedykt Dybowski, and Leonhard Hess Stejneger unearthed many large bones during this time period, from which complete skeletons were erected. Towards the end of the 1800s, Steller's sea cow specimens were valuable objects, and could be sold to museums for high prices. Collection died down in the 1900s, with many bones that were being sold commercially probably not actually belonging to a Steller's sea cow specimen. As of 2006, 27 nearly complete skeletons and 62 complete skulls exist.
Their range at the time of their discovery was apparently restricted to the Commander Islands, which consists mainly of Bering Island and Copper Island, and remained uninhabited until the Russian-American Company relocated Aleuts from namely Attu Island and Atka Island to hunt sea otters. The first fossils discovered outside the Commander Islands were interglacial Pleistocene deposits in Amchitka, and further fossils dating to the late Pleistocene that were found in Monterey Bay, California, Honshu, Japan, and Amchitka, Alaska suggest that their range was much more expansive in prehistoric times. According to Steller, they often resided in the shallow, sandy shorelines and in the mouths of freshwater rivers.
Bones fragments and accounts by native Aleut people indicate that sea cows also inhabited the Near Islands during historic times, possibly with viable populations in the western Aleutian Islands that were in contact with humans prior to their initial discovery by Steller. A sea cow rib discovered in 1998 on Kiska Island was dated to around 1,000 years old, and is now in the possession of the Burke Museum of Natural History and Culture in Seattle, Washington. The dating may be skewed due to the marine reservoir effect; the large reserves of C14 in the oceans cause radiocarbon dated marine creatures to appear much older than they actually are by several hundred years, so it is much more likely that the animal died between 1710 and 1785. One study in 2004 reported sea cow bones discovered in Adak Island and Buldir Island of the western Aleutian Islands found to be around 1,700 and 1,600 years old, respectively, however these bones may be from cetaceans. According to Lucien Turner, a late 1800s American ethnologist and naturalist, the sea cows of the Near Islands, based on interviews with the natives of Attu Island, survived into the 1800s, and were hunted from time to time by the natives. One sighting after 1768 includes one made by a passenger in the Nordenskiöld Archipelago whilst on board the Kruzenshtern's world voyage between 1803 and 1806.
Extinction and sightings
Steller's sea cow was quickly wiped out by the sailors, seal hunters, and maritime fur traders who followed Vitus Bering's route past the islands to Alaska, and hunted it for its meat before sailing to nearby islands in search of sea otter pelts. When the crew of the Great Northern Expedition were stranded om Bering Island, they hunted Steller's sea cow with relative ease; because of their large size, the challenge was hauling the animal back to shore. Their success inspired maritime fur traders on their North Pacific expeditions to stop by the Commander Islands and restock their food supply by hunting sea cows. 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 is possible that the extinction of these remaining endangered populations of sea cow could have been induced solely by the hunting of the sea cow for meat by fur-trading mariners of the time, and no other factors need have contributed.
It has been argued that 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. 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.
In 1963 the Russian magazine Priroda (Nature), official journal of the Academy of Sciences of the USSR, published an article reporting a possible sighting. In 1962 the whaling ship Buran had reported a group of large marine mammals in shallow water in Cape Navarin off Kamchatka, grazing on seaweed. The crew reported seeing a small group of six large animals ranging from 6 to 8 metres (20 to 26 ft), with trunks and split lips. There have also been reports from local fishermen in the northern Kuril Islands, and around the Kamchatka and Chukchi peninsulas. These possible sightings may be attributed to large arctic marine mammals, such as the narwhal (Monodon monoceros) and the Northern elephant seal (Mirounga angustirostris).
Portrayals in media
Kotick the rare white seal, on his journey to find a new home and escape hunters, consults Sea Cow in the story The White Seal contained in The Jungle Book by Rudyard Kipling, which takes place in the Bering Sea.
In Jules Verne's 1870 novel Twenty Thousand Leagues Under the Sea, the travelers in Captain Nemo's fictional submarine Nautilus encounter various sirenians during their journey. He describes them as being manatees, although he states that they weigh 5,000 kilograms (11,000 lb) each, which far exceeds the weight of the largest manatee, a West Indian manatee, on record at 1,655 kilograms (3,650 lb). Nemo also makes it a point that the sirenians are scarce due to hunting, yet harpoonist Ned Land kills the animal to eat it.
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 and 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".
Steller's sea cow appears in two books of poetry: Species Evanescens by Russian poet Andrei Bronnikov, and Nach der Natur by Winfried Georg Sebald. In Bronnikov's book, he depicts the events of the Great Northern Expedition in which Steller's sea cow was discovered through the eyes of Steller. Sebald's book looks at the conflict between man and nature as seen through the eyes of Steller and the extinction of Steller's sea cow, the German Renaissance painter Matthias Grünewald, and himself.
- Holocene extinction
- List of extinct animals of North America
- List of Asian animals extinct in the Holocene
- List of recently extinct mammals
- Evolution of sirenians
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