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Mammals Low‑importance

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Palaeontology Mid‑importance

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Unreferenced

The following content was unreferenced and have been removed. --Fama Clamosa (talk) 21:29, 16 February 2013 (UTC)[reply]

The archaeocetes were once thought to have evolved from the mesonychids, based on dental characteristics. However, recent studies in molecular genetics and non-dental morphology show that the first whales or the archaeoceti most likely evolved from artiodactyls; genetic evidence indicates that their closest living relatives are the family Hippopotamidae which includes the modern hippopotamus. The ancestors of archaeocetes probably diverged from the other artiodactyls around the time of the Cretaceous–Paleogene extinction event.

Most archaeocetes had hind limbs, suggesting that they were fully terrestrial. As the Eocene epoch progressed, the archaeocetes became less terrestrial and more aquatic. Before the Eocene epoch came to an end, one group of archaeocetes, the basilosaurids, gave rise to early modern cetaceans. The archaeocetes suffered a heavy loss of genera during the Eocene-Oligocene extinction event, but some species survived into the Oligocene. The last archaeocete, which was probably a basilosaurid, became extinct in the Oligocene. They may have become extinct from a combination of competition and climate change.

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