In an excerpt from his new book, The Story of the Mammals in 25 Discoveries, Geology Professor Emeritus Donald R. Prothero explores how people interpreted fossils before vertebrate paleontology, when enormous bones were attributed to biblical giants and monsters and mammoth tusks from Siberia were believed to be unicorn horns or dragon tusks. He traces how religious beliefs and prevailing ideas about nature complicated early explanations of fossils until mounting evidence for vanished animals helped establish extinction as scientific fact.

This article was originally published by Live Science on October 2, 2026.