Steller's Sea Cow: Hydrodamalis gigas

Abstract

Two other common names for Steller's sea cow are the German “Borkentier,” referring to its rough bark-like hide, and the Russian “kapustnik” (cabbage eater), which Steller attributed to inhabitants of Kamchatka, where dead sea cows reportedly washed ashore after storms. There is no evidence for geographic variation. The northernmost Pacific was likely a marginal habitat as members of the Kommandorskiye population may have been stunted. Adults at Bering Island had a body length approximately 750 cm (25 ft) and a weight of 4500–5900 kg. Fossil material from farther south suggests maximum body lengths may have reached 9–10 m. Like other sirenians, Steller's sea cow had paired nostrils, abdominal testes, a pair of axillary mammae, no hindlimbs, horny plates on the occlusal surfaces of the rostrum and mandibular symphysis for macerating vegetation, and ribs and other bones that were swollen and completely compact. Historically, Steller's sea cow was known only from Bering and Medney (Copper) Islands at the western terminus of the Aleutians, 200 miles to the west of Attu Island and 150 miles east of the Kamchatka Peninsula. Mating apparently involved only a pair, with the male following or herding the female during prolonged “amorous preludes.” Copulation involved mutual clasping with the pectorals, the female in an inverted position and the male above. These magnificent animals would have been at least as vulnerable to healthy and skilled Pleistocene hunters along mainland shores. Steller's sea cows had no fear of humans. Feeding with the head submerged and half of the back above water they were easily approached and could be touched or speared from the rocks. Decimation of the otters in all probability triggered a sea urchin population explosion and the disappearance of chemically undefended shallow water kelps that were the sea cows' main food supply. Invasion of the shallow waters by chemically defended deep-water kelps left the hunted remnant of the sea cow population with kelp that was likely toxic.