The rules of life on Earth are always changing, but for the “thunder beast” during the first act of the Cenozoic, the mammalian game plan was simple—go big or go home. Darren Orf.

The fossil record is filled with with land animals who grew to impossibly large sizes. Brontotheres, the ancient North American ancestors of the horse, is a giantism outlier as—growing from ...

These crocodile-like beasts reached the Caribbean, outlasting mainland kin. Sebecids look straight out of the Age of Dinosaurs, but may have lived just 4 million years ago ...

This is What Earth Was Like During the Cenozoic Era. Posted: May 30, 2025 | Last updated: June 6, 2025. The curious minds at What If take a journey through the Earth during the Cenozoic era.

Starting out at around 40 pounds, scientists estimate that this “thunder beast” grew up to four or five tons in only 16 million years—a blink of an eye for a planet some 4.6 billion years old.

At the end of the Triassic period, small-sized dinosaurs roamed Earth alongside other groups of archosaurs—that is, until a widespread extinction event cleared the way for dinos to put on some serious ...