Meet This Tiny Ancestor of the Fearsome T. Rex

Friday, February 22, 2019


Moros intrepidus is a distant relative that lived millions of years before the first T. rex was born, and tells scientists how Tyrannosaurs evolved.

Tyrannosaurus rex has become one of the most notorious predators that ever walked the earth, thanks to in part to movies like Jurassic Park. The T. rex you know and fear was a monster with teeth as long as a person’s forearm. But Tyrannosaurs haven’t always been so gigantic. According to a new fossil discovery, early Tyrannosaurs were much smaller.


Archaeologists working in Utah recently uncovered a fossilized member of a new Tyrannosaur species, called Moros intrepidus. It lived in the area around 100 million years ago, about 15 million years before the first giant Tyrannosaurs appeared.

Uniquely, Moros is significantly smaller than most of the well-known Tyrannosaurs, like the infamous Rex. While T. rex stood nearly 12 feet high, Moros would only come up to an adult human’s waist. It wouldn’t have been much bigger than a large dog.

Interestingly, scientists have found fossils of other Tyrannosaurs that are much older—about 150 million years old, to be exact—that are around the same size as Moros. According to these fossils, the vast majority of Tyrannosaurs were very small, and only started getting big toward the end of their history.

This discovery is a big deal because it fills what has been a blank spot in Tyrannosaurs' history. Prior to the discovery of Moros, we knew about Tyrannosaurs from 150 million years ago, and we knew about Tyrannosaurs from 80 million years ago, but we knew nothing about any of the Tyrannosaurs in between. That was a 70-million-year gap in the fossil record.

"When and how quickly tyrannosaurs went from wallflower to prom king has been vexing paleontologists for a long time,” said lead study author Lindsay Zanno in a press release. “The only way to attack this problem was to get out there and find more data on these rare animals."

Now, thanks to Moros, we have a clearer picture of how Tyrannosaurs evolved. We know that they spent most of their history not as gigantic fearsome predators, but as small and nimble hunters. Arguably, a smaller Tyrannosaur might be even scarier since it can fit through doorways.

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