PARIS (AFP).- A tiny cousin of T-rex discovered in the United States could provide a key missing link in understanding how the apex predators evolved to top the food chain, scientists who unearthed the dinky dinosaur said Thursday.

The Moros intrepidus, standing just three feet (one metre) high at the hip and weighing as much as an adult human, roamed the plains of modern-day Utah around 96 million years ago, making it the earliest member of the Tyrannosaur family yet identified on the North American continent.

The team behind the discovery believes the new dinosaur -- whose name means "harbinger of doom" -- offers clues as to how its more famous cousin reached its epic size.

"Early in their evolution, Tyrannosaurs hunted in the shadows of (dinosaurs) such as Allosaurs that were already established at the top of the food chain," said Lindsay Zanno, paleontologist at North Carolina State University and lead author of the study detailing the findings.

By the time of the Cretaceous period -- around 80 million years ago -- Tyrannosaurs had evolved into the enormous, iconic predators so well known today.

But the discovery of Moros intrepidus shows they achieved such size and dominance in a relatively short time-scale of roughly 15 million years.

"When and how quickly Tyrannosaurs went from wallflower to prom king has been vexing paleontologists for a long time," said Zanno.

"Moros is key to understanding how quickly Tyrannosaurs ascended from minor players in the ecosystem to top of the food chain," she told AFP.

The specimen found by Zanno and the team would have weighed a shade less than 80 kilogrammes (175 pounds), making it extremely nimble.

"We know that Moros was lightning fast and likely hunted on smaller prey," she said.

"Although the earliest Cretaceous Tyrannosaurs were small, their predatory specialisations meant that they were primed to take advantage of new opportunities when warming temperatures, rising sea-level and shrinking ranges restructured ecosystems."

The study was published in the journal Communications Biology.


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