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1 day ago · Marine mammals are mammals that rely on marine (saltwater) ecosystems for their existence. They include animals such as cetaceans ( whales , dolphins and porpoises ), pinnipeds ( seals , sea lions and walruses ), sirenians ( manatees and dugongs ), sea otters and polar bears .
May 1, 2024 · Evolution of mammals - Wikipedia. Contents. hide. (Top) Definition of "mammal" The ancestry of mammals. Therapsids. Triassic takeover. From cynodonts to crown mammals. Earliest crown mammals. Expansion of ecological niches in the Mesozoic. Evolution of major groups of living mammals. Evolution of mammalian features. Sexual selection. See also.
13 hours ago · Background Marine mammals, which have evolved independently into three distinct lineages, share common physiological features that contribute to their adaptation to the marine environment. Objective To identify positively selected genes (PSGs) for adaptation to the marine environment using available genomic data from three taxonomic orders: cetaceans, pinnipeds, and sirenians. Methods Based on ...
Apr 15, 2024 · Nov. 2, 2021 — Pinnipeds -- a group including seals, sea lions and walruses -- are relatively recently derived marine mammals that evolved from terrestrial carnivorans and reentered the...
2 days ago · Evolution. The evolutionary record of the genus Orcinus is scanty. The earliest fossil identified as a killer whale is O. citonensis from the Pliocene Epoch (5.3 million to 2.6 million years ago) in Italy. This small mammal was about 4 metres long (13.1 feet) and had 14 teeth—more like a typical dolphin.
- The Editors of Encyclopaedia Britannica
Apr 21, 2024 · The Eocene is often divided into Early (56 million to 47.8 million years ago), Middle (47.8 million to 38 million years ago), and Late (38 million to 33.9 million years ago) epochs.
May 3, 2024 · In a process of convergent evolution, marine mammals, especially cetaceans such as dolphins and whales, redeveloped their body plan to parallel the streamlined fusiform body plan of pelagic fish. Front legs became flippers and back legs disappeared, a dorsal fin reappeared and the tail morphed into a powerful horizontal fluke .
