Basilosaurus fossils were first discovered in Louisiana, USA in the 1830s. Believed to be giant reptilian sea monsters, they were named Basilosaurus, or 'king lizards'. Later, they were shown not to be reptilian but gigantic, ancient whales. They were more elongated than modern whales and had a pair of small legs, that could have been a hangover from their terrestrial ancestry. A large number of fossils of these marine predators has been found to date, leading to the conclusion that Basilosaurus were common in the warm shallow seas of the time.

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