A family of extinct cetaceans (whale relatives) from the Eocene epoch, formerly thought to be sea serpents or sea monsters before paleontology clarified their true nature.
From basilosaurus (Greek basileus, 'king' + saurus, 'lizard') plus Latin suffix '-idae' (family designation in taxonomy).
When first discovered, these whale ancestors seemed like actual sea serpents—the name 'basilosaurus' literally means 'king lizard'—until scientists realized they were cetaceans, showing how fossil discoveries can completely rewrite what we thought existed.
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