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Apr 16, 2009 · Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Even though all modern cetaceans are obligate aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial artiodactyls, similar to small deer. The transition from land to water is documented by a series of intermediate fossils, many of ...
- J. G. M. Thewissen, Lisa Noelle Cooper, Lisa Noelle Cooper, John C. George, Sunil Bajpai
- 2009
May 21, 2007 · The fossil record demonstrates that mammals re-entered the marine realm on at least seven separate occasions. Five of these clades are still extant, whereas two are extinct. This review presents a brief introduction to the phylogeny of each group of marine mammals, based on the latest studies using both morphological and molecular data.
- Mark D. Uhen
- 144
- 2007
- 21 May 2007
Meet Pakicetus, a goat-sized, four-legged creature that scientists recognise as one of the first cetaceans (the group of marine animals that includes dolphins and whales). How Pakicetus ' descendants evolved into whales is one of the most intriguing evolutionary journeys known to science.
Apr 16, 2015 · April 16, 2015. The oceans are teeming with tetrapods—“four-legged” birds, reptiles, mammals and amphibians—that have repeatedly transitioned from the land to the sea, adapting their legs ...
Sep 24, 2014 · If I understand evolutionary biology correctly, mammals first evolved on land as small, rodent-like creatures, in a time when reptiles were dominant on land. Eventually, they diversified into the species we know today.
Marine Mammal Diversity. Living groups of marine mammals vary greatly in their diversity. Rice (1998; Table 1 therein) reports that living Cetacea include 83 species in 39 genera; living Pinnipedia include 36 species in 21 genera; and Recent Sirenia include 5 species in 3 genera. Since then, several new spe-cies of cetaceans have been described ...
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How did mammals evolve?
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Nov 15, 2019 · However, another hypothesis is that Odobenidae first evolved in the North Pacific and then dispersed into the Arctic Ocean and North Atlantic during an interglacial event in the Pliocene or Pleistocene.
