Tiny T-Rex discovery shows how it became king of the dinosaurs

A newly discovered species of dinosaur was a tiny relative of Tyrannosaurus rex and has thrown light on how the reptile came to dominate the ancient North American food chain.

Named Moros intrepidus, the species is believed to have lived 96 million years ago in what is now Utah.

Back then, Utah was a lush delta, and Moros, while not the beast that the T-Rex would be, was already a fearsome predator, according to a paper published in the journal Communications Biology.

Tyrannosaurus dinosaurs were the most powerful animals on the planet for 15 million years.

They could bite with enough force to crush bone, had stereoscopic vision, and were able to grow rapidly to an enormous size.

"But it wasn't always that way," said Dr Lindsay Zanno, a palaeontologist at North Carolina State University, and the head of palaeontology at the North Carolina Museum of Sciences.

"Early in their evolution, tyrannosaurs hunted in the shadows of archaic lineages such as allosaurs that were already established at the top of the food chain," said the lead author of the research.

Moros was overshadowed by a much-larger dinosaur called Siats meekerorum.

"In short, the story of Moros and Siats is like an evolutionary David and Goliath in which small tyrannosaurs survive through dramatic changes in landscape, through mountain building and sea level rise, whereas the giant Siats and its relatives perish from existence," North Carolina State University palaeontologist Terry Gates said.

"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," he added.

Although medium-sized tyrannosaurs had been found in North America from eras as early as the Jurassic (around 150 million years ago), there is little between then and 81 million years ago when the giant T-Rex fossils date from.

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

"The only way to attack this problem was to get out there and find more data on these rare animals."

After a decade of hard search and analysis for dinosaur fossils within rocks, Dr Zanno finally found what she was looking for - a tiny relative of the T-Rex, standing only three or four feet tall at the hip.

Despite its diminutive size - in terms of its larger relative - the dinosaur named "harbinger of doom", because it heralded the coming of the T-Rex, was still a frightening predator.

"Moros was lightweight and exceptionally fast," Dr Zanno said.

"It could easily have run down prey, while avoiding confrontation with the top predators of the day.

"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 at the beginning of the Late Cretaceous.

"We now know it took them less than 15 million years to rise to power."