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1. • 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. Even though all modern cetaceans are obligate aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial artiodactyls, similar to small deer.
     evolution-outreach.biomedcentral.com › articles › 10

     From Land to Water: the Origin of Whales, Dolphins, and ...

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   How did marine mammals evolve?

   • The earliest representatives of each clade all show morphological features that indicate they were feeding while in the water, suggesting that feeding ecology is a key factor in the evolution of marine mammals. Abstract The fossil record demonstrates that mammals re-entered the marine realm on at least seven separate occasions.

   Evolution of marine mammals: Back to the sea after 300 million years

   anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.20545

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   When did mammalian evolution start?

   • This is no great surprise, because a great deal of mammalian evolution has been linked to changes in feeding ecology. It is also interesting to note that the clades of marine mammals seem to have originated at two discrete times, Cetacea and Sirenia during the early Eocene, and Desmostylia and Pinnipedia during the Oligocene.

   Evolution of marine mammals: Back to the sea after 300 million years

   anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.20545

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   Do marine mammals have evolutionary histories?

   • Before comparing the evolutionary histories of each of the clades of marine mammals, it is worth emphasizing that the evolutionary histories outlined here are only the most basic and superficial sketches of the morphological changes that these groups have undergone.

   Evolution of marine mammals: Back to the sea after 300 million years

   anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.20545

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   How long did it take a whale to become an aquatic animal?

   • That means that the transition from terrestrial animals to fully aquatic animals took about 12 million years. The key adaptations are mostly those that still characterize whales today: forelimbs modified into flippers, extra vertebrae in their trunk and back, and flukes on their tails for locomotion.

   Ocean Giants | Going Aquatic: Cetacean Evolution - PBS

   www.pbs.org/wnet/nature/ocean-giants-going-aquatic-cetacean-evolution/7577/

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3. evolution-outreach.biomedcentral.com › articles › 10From Land to Water: the Origin of Whales, Dolphins, and ...

   evolution-outreach.biomedcentral.com › articles › 10

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   Apr 16, 2009 · We focus on the evolution of cetacean organ systems, as these document the transition from land to water in detail. Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch.

   • Author: J. G. M. Thewissen, Lisa Noelle Cooper, Lisa Noelle Cooper, John C. George, Sunil Bajpai

   • Publish Year: 2009

4. anatomypubs.onlinelibrary.wiley.com › doi › fullEvolution of marine mammals: Back to the sea after 300 ...

   anatomypubs.onlinelibrary.wiley.com › doi › full

   May 21, 2007 · Evolution of marine mammals: Back to the sea after 300 million years. Mark D. Uhen. First published: 21 May 2007. https://doi.org/10.1002/ar.20545. Citations: 144. Sections. PDF. Tools. Share. Abstract. The fossil record demonstrates that mammals re-entered the marine realm on at least seven separate occasions.

   • Author: Mark D. Uhen
   • Cited By: 144

   • Publish Year: 2007
   • Published: 21 May 2007

5. www.nhm.ac.uk › discover › when-whales-walked-onWhen whales walked on four legs | Natural History Museum

   www.nhm.ac.uk › discover › when-whales-walked-on

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   680. Early ancestors of the ocean's biggest animals once walked on land. Follow their extraordinary journey from shore to sea. Although whales are expert swimmers and perfectly adapted to life underwater, these marine mammals once walked on four legs. Their land-dwelling ancestors lived about 50 million years ago.

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7. ocean.si.edu › through-time › ocean-through-timeOcean Through Time | Smithsonian Ocean

   ocean.si.edu › through-time › ocean-through-time

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   The first fully marine turtles emerged during the Cretaceous Period, a span of time lasting between 145 and 66 million years ago. By 120 million years ago, they resembled the sea turtles we are familiar with today.

8. www.smithsonianmag.com › smithsonian-institutionTake a Deep Dive Into The Reasons Land Animals Moved to the ...

   www.smithsonianmag.com › smithsonian-institution

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   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 ...

9. anatomypubs.onlinelibrary.wiley.com › doi › epdfEvolution of Marine Mammals: Back to the Sea After 300 ...

   anatomypubs.onlinelibrary.wiley.com › doi › epdf

   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.

10. www.pbs.org › wnet › natureOcean Giants | Going Aquatic: Cetacean Evolution - PBS

    www.pbs.org › wnet › nature

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    Mar 21, 2012 · When did scientists first propose that marine mammals evolved from land-living mammals? What findings led to this conclusion?