Since the early 1980s, the story of how whales walked into the sea has become one of the most celebrated of all evolutionary transitions. Pakicetus, Ambulocetus, Rodhocetus, and many, many more—these fossil whales with legs have beautifully demonstrated how land-dwelling mammals became adapted to life at sea. But between 50 million and 40 million years or so ago, whales were just going through a transition that many other vertebrate groups had gone through before. They were not the first vertebrates to return to the sea, nor were they the last, and a paper recently published in Paleobiology by paleontologists Johan Lindgren, Michael Polcyn, and Bruce Young has traced the history of how a very different group of animals got their sea legs.
Mosasaurs were formidable oceanic predators. Take a Komodo Dragon, put flippers on it, and, in some cases, blow it up until it’s over 40 feet long and you’ll have some idea of what these Cretaceous marine lizards were like. Their fossil record—stretching over 27 million years—is also relatively well known, and so the mosasaurs provided Lindgren and colleagues with a good opportunity to see how these peculiar animals evolved.
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