Scientists believe that many animals existed before dinosaurs. Of course, that has a lot to do with what animals we choose to call dinosaurs! We call certain animals that lived between the Triassic Period and the end of the Cretaceous Period dinosaurs.

The Triassic Period started about 250 million years ago. But we have studied fossils of animals that we think were alive 665 million years ago, during the Precambrian Eon. We have a good sense of how old these animals are thanks to carbon dating, an amazing scientific technique invented by Willard Libby in 1947. But it's much harder to tell exactly which animal came first, because we don't have fossil evidence, so scientists do not know for sure. Since we don't know, we haven't chosen a name for the first animal's species, but we did choose a name for the first animal: we named it the

urmetazoan.

Dinosaurs were not the first animals alive on Earth. We don't really know what the first animal was, because we don't have a fossil record of it: it would have been microscopic and soft-bodied, and thus unlikely to leave any fossil evidence. It probably lived between 650 and 600 million years ago.