Altogether, the pieces reveal a slender tyrannosaur that roamed Cretaceous Mongolia about 86 million years ago and was about 13 feet long—or about the size of juvenile T. rex that would stalk North America 20 million years later.

Scientists announced the discovery of a new species of early tyrannosaur in a museum vault in Mongolia, an ancestor to notorious apex predators like T. rex.

Learn more about a newly discovered dinosaur species that is now the closest-known ancestor to the Tyrannosaurs.