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About 50 million years ago
- Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch.
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Did marine mammals evolve back to the sea after 300 million years?
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May 21, 2007 · 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 species of cetaceans have been described ...
- Mark D. Uhen
- 2007
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
Oct 18, 2012 · University of California Press, Berkeley, CA. 2012. 205 pp., $49.95 (cloth), $25.62 (Kindle). ISBN 9780520270572. Annalisa Berta leads readers through a vast range of topics regarding the evolution of marine mammals in Return to the Sea: The Life and Evolutionary Times of Marine Mammals. In this volume geared towards non-specialists (one might ...
- Mark D. Uhen
- muhen@gmu.edu
- 2013
Figure 1. Harbor seal, walrus, dugong, and right whale) The first mammals were certainly terrestrial. There is good evidence that mammals evolved from reptile-like ancestor. Therefore at some point there was a transition from terrestrial environment to an aquatic lifestyle in this group of species. How did that occur?
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Evolution of Marine Mammals: Back to the Sea After 300 Million Years MARK D. UHEN* Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC ABSTRACT The fossil record demonstrates that mammals re-entered the marine realm on at least seven separate occasions. Five of these clades are still
Nov 15, 2019 · What is noteworthy is that convergent morphological adaptations for an aquatic life (e.g., fusiform body shape, flukes, and flippers) evolved separately in the three taxonomic orders of extant marine mammals (Artiodactyla [infraorder Cetacea], Carnivora [clade Pinnipedia and sea otters], and Sirenia).
Between asteroid and comet bombardments, scientists believe enough time passed for vaporized water to condense and settle on the earth’s surface. According to the most recent scientific studies, an ancient ocean likely covered the entire planet 150 million years after the formation of Earth, about 4.4 billion years ago.
