Evolution of cetaceans | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-05-10

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Evolution_of_cetaceans


00:01:44 1 Early evolution
00:05:13 1.1 iIndohyus/i
00:06:37 1.2 Pakicetidae
00:10:20 1.3 Ambulocetidae
00:13:48 1.4 Remingtonocetidae
00:16:05 1.5 Protocetidae
00:20:33 1.6 Basilosauridae
00:24:41 2 Evolution of modern cetaceans
00:24:52 2.1 Baleen whales
00:27:27 2.2 Toothed whales
00:31:45 3 Skeletal evolution
00:35:55 4 Ongoing evolution
00:36:05 4.1 Culture
00:39:26 4.1.1 Social structure
00:43:13 4.2 Environmental factors
00:47:10 5 See also



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SUMMARY
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The evolutionary history of cetaceans is thought to have occurred in the Indian subcontinent from even-toed ungulates 50 million years ago, over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla, and branched off from other artiodactyls around 50 mya (million years ago). Cetaceans are thought to have evolved during the Eocene or earlier, sharing a closest common ancestor with hippopotamuses. Being mammals, they surface to breathe air; they have 5 finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retained many skeletal features from their terrestrial ancestors. Discoveries starting in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.
The two modern parvorders of cetaceans – Mysticeti (baleen whales) and Odontoceti (toothed whales) – are thought to have separated from each other around 28-33 million years ago in a second cetacean radiation, the first occurring with the archaeocetes. The adaptation of animal echolocation in toothed whales distinguishes them from fully aquatic archaeocetes and early baleen whales. The presence of baleen in baleen whales occurred gradually, with earlier varieties having very little baleen, and their size is linked to baleen dependence (and subsequent increase in filter feeding).