An extinct whale-like marine mammal from the Eocene epoch, about 35-50 million years ago, that combined features of whales and land mammals.
From Greek basileus (king) + saurus (lizard), named because early fossil finders thought it was a giant sea reptile or king of sea creatures.
Basilosaurus fossils sparked the 1840s sea serpent craze—people genuinely thought they'd found proof of Nessie-like monsters in rocks, until paleontologists explained these were just ancient proto-whales with weird body proportions.
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