About 96 million years ago in Utah, a seven year old Tyrannosaurid died and eventually fossilized. But according to the team from the North Carolina Museum of Natural Sciences that described the find, this Tyrannosaur wasn’t like the one you know best — it was roughly the size and weight of a male human.
Moros Intrepidus (named suavely for its globe trotting ways, as it appears closely related to Asian Tyrannosaurids) clears up a Tyrannosaur mystery — primitive Tyrannosaurs are known from the very early Cretaceous, where they lived in the shadows of the then-dominant Allosaurs. The larger kinds (like Albertosaurus, T-Rex, and Tarbosaurus) just seemed to start appearing in the fossil record 80 million years ago.
So a Tyrannosaur from 96 million years ago fills in a crucial gap: the earlier forms are small too, and it was long assumed that whatever Tyrannosaurs were up to, they were gradually getting bigger. Now it seems this is not so, and they grew to their gargantuan size (a 1000% larger) in no more than 16 million years!
(While small Tyrannosaurs were once thought to exist in T-Rex’s own time [Nanotyrannus] these are now thought to just be baby T-Rexes.)
From National Geographic:
“What Moros does for us is help us understand the who, what, why, where, and when of how tyrannosaurs ascended to top predator roles on the North American continent,” says paleontologist Lindsay Zanno of the North Carolina Museum of Natural Sciences, whose team reports the fossil find today in the journal Communications Biology.
Moros Intrepidus does look a lot like a T-Rex, but due to its light weight, it has gangly chicken legs. And the Utah of the time it lived in was quite unlike the Utah of today. A swampy floodplain, the other dinosaurs of the area were foragers, apex predators, and even burrowing dinosaurs. Zanno hopes to be able to describe the entire environment of mid-Cretaceous Utah.
“Hopefully,” she says, “we'll have a whole string of discoveries that are going to reveal this lost Cretaceous ecosystem.”