Earth’s history is filled with incredible milestones, and the emergence of the first animals is one of the most captivating.

Rosie is a freelance writer living in London. She has covered everything from ancient Egyptian temples to exciting medical breakthroughs, but she particularly enjoys writing about wildlife ...

including rodent-size mammals and the first dinosaurs. By the start of the Triassic, all the Earth's landmasses had coalesced to form Pangaea, a supercontinent shaped like a giant C that straddled ...

Often called mammal-like reptiles—they looked like a cross between a dog and a lizard—the synapsids were Earth's first great dynasty of land vertebrates. "We've found fossils of many kinds of ...

Nobu Tamura/Wikimedia Commons The Triassic Period (252-201 million years ago) began after Earth's worst-ever extinction ... more gracile animals. It was around 240 million years ago that the first ...