Developmental Biology (2 of 2)

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Aetiocetus skull spacer Baleen whales have toothed ancestors
Toothed whales have full sets of teeth throughout their lives. Baleen whales, however, only possess teeth in the early fetal stage and lose them before birth. The possession of teeth in fetal baleen whales provides evidence of common ancestry with toothed whales and other mammals. In addition, fossil evidence indicates that the late Oligocene whale Aetiocetus (left), from Oregon, which is considered to be the earliest example of baleen whales, also bore a full set of teeth.

Again, these observations make most sense in an evolutionary framework where snakes have legged ancestors and whales have toothed ancestors.

Learn more about cetaceans at UCMP’s Introduction to Cetaceans page.

Read more about recognizing homologies.



Aetiocetus image courtesy of Tom Deméré, San Diego Natural History Museum.

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Cellular/Molecular Evidence

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