Презентация на тему по английскому языку на тему Steller's sea cow (9 класс)

sirenian discovered by Europeans in 1741. At that time,

it was found only around the Commander Islands in the Bering Sea between Alaska and Russia; its range was more extensive during the Pleistocene epoch, and it is possible that the animal and humans previously interacted. Steller's sea cow was named after Georg Wilhelm Steller, a naturalist who discovered the species in 1741 on Vitus Bering's Great Northern Expedition when the crew became shipwrecked on Bering Island. Much of what is known about its behavior comes from Steller's observations on the island, documented in his posthumous publication On the Beasts of the Sea. Within 27 years of discovery by Europeans, the slow-moving and easily caught mammal was hunted into extinction for its meat, fat, and hide.

is unknown. It may have been hunted by killer

whales and sharks, though its buoyancy may have made it difficult for killer whales to drown, and the rocky kelp forests in which the sea cow lived may have deterred sharks. According to Steller, the adults guarded the young from predators. Like other sirenians, Steller's sea cow was an obligate herbivore and spent most of the day feeding, only lifting its head every 4–5 minutes for breathing. Kelp was its main food source, making it an algivore. Steller's sea cow only fed directly on the soft parts of the kelp, which caused the tougher stem and holdfast to wash up on the shore in heaps. The sea cow may have also fed on seagrass, but the plant was not common enough to support a viable population and could not have been the sea cow's primary food source. Further, the available seagrasses in the sea cow's range may have grown too deep underwater or been too tough for the animal to consume.

ECOLOGY

social. It lived in small family groups and helped

injured members, and was also apparently monogamous. Mating season occurred in early spring and gestation took a little over a year, with calves likely delivered in autumn, as Steller observed a greater number of calves in autumn than at any other time of the year. Since female sea cows had only one set of mammary glands, they likely had one calf at a time.
The sea cow used its fore limbs for swimming, feeding, walking in shallow water, defending itself, and holding on to its partner during copulation. According to Steller, the fore limbs were also used to anchor the sea cow down to prevent it from being swept away by the strong nearshore waves. While grazing, the sea cow progressed slowly by moving its tail from side to side; more rapid movement was achieved by strong vertical beating of the tail. They often slept on their backs after feeding. According to Steller, the sea cow was nearly mute and made only heavy breathing sounds, raspy snorting similar to a horse, and sighs.

time of its discovery was apparently restricted to the

shallow seas around the Commander Islands, which include Bering and Copper Islands. The Commander Islands remained uninhabited until 1825 when the Russian-American Company relocated Aleuts from Attu Island and Atka Island there. The first fossils discovered outside the Commander Islands were found in interglacial Pleistocene deposits in Amchitka, and further fossils dating to the late Pleistocene were found in Monterey Bay, California, and Honshu, Japan. This suggests that the sea cow had a far more extensive range in prehistoric times.