"Harbinger of Doom" -Tiny Predecessor Paved Way for T-Rex Epoch

"Harbinger of Doom" -Tiny Predecessor Paved Way for T-Rex Epoch

"Moros was lightweight and exceptionally fast", Zanno says. "It could easily have run down prey, while avoiding confrontation with the top predators of the day", Zanno said.

Tyrannosaurus rex and its relatives ruled supreme in North America at the end of the age of dinosaurs-dominating the landscape as very big top predators. Moros was overshadowed in its warm, lush environment by a much-larger dinosaur called Siats meekerorum, which reached about 39 feet (12 meters) long, weighed four tons and was a member of a group called allosaurs that for tens of millions of years represented North America's dominant land meat-eaters.

Zanno - the head of paleontology at the North Carolina Museum of Natural Sciences - unveiled the dinosaur fossils at the museum Thursday afternoon. However, our knowledge has been limited by the lack of North American tyrannosauroid fossils dating from the 70-million-year "dark period", which begins just before the start of the Cretaceous Period.

Now, fossil evidence of a new tyrannosaur species closes that gap by about 15 million years. The fossil record between these time periods has been a blank slate, preventing scientists from piecing together the story behind the ascent of tyrannosaurs in North America.

So, as the allosaur declined, the tiny little tyrannosaur used its speed and size to its advantage, working its way up from zero to hero - or "wallflower to prom king", as Zanno put it. The unique shape of the foot and upper leg bone helped the team determine Moros was the oldest Cretaceous-era dinosaur discovered in North America.

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Zanno hopes they can eventually pinpoint exactly when allosaurs died out to help determine how tyrannosaurs made such a massive jump in size a relatively short period. Zanno estimates that the Moros was over seven years old when it died, and that it was almost full-grown.

"In true ironic fashion, once the giant predators were out of the way, the small tyrannosaurs, typified by Moros, evolved to become the largest predators in North America", Gates added.

Its name is delightful: Moros intrepidus. "T. rex and its famous contemporaries such as Triceratops may be among our most beloved cultural icons, but we owe their existence to their intrepid ancestors who migrated here from Asia at least 30 million years prior", Zanno says.

"What I find most interesting about what Moros can teach us about tyrannosaur evolution is that we often think about tyrannosaurs as being such incredible predators, that they were destined to rule the late Cretaceous ecosystems", Zanno tells Smithsonian.com.

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