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T. rex evolved from tiny dinosaurs

May 6, 2019

The mighty Tyrannosaurus rex used to be very small, and evolved over 20 million years into a massive super predator. Scientists say that newly discovered fossils provide a missing link showing how the dinosaur evolved.

A drawn image of a new relative of the Tyrannosaurus rex
Image: picture-alliance/AP/A. Atuchin

Paleontologists announced Monday in the scientific journal Nature Ecology & Evolution that the ferocious Tyrannosaurus rex (T. rex) evolved from dinosaurs no larger than a small child.

The study's lead author, Sterling Nesbitt, a paleontologist at Virginia Tech in the US, said that the fossils of the smaller T. rex cousin could provide one of the best examples yet as to how a smaller family of dinosaurs evolved into monstrous super predators.

Read more: T. rex was no Usain Bolt, say scientists

"The small group of dinosaurs would give rise to some of the biggest predators that we've ever seen," said Nesbitt.

The newly discovered dinosaur, called Suskityrannus hazelae, is estimated to have weighed anywhere between 45 to 90 pounds (20 to 40 kilograms). Its height would have only reached 3 feet (90 centimeters). T. rex weighed around 9 tons and measured about 40 feet (12 meters) in length.

Monday's report said that Suskityrannus hazelae provides an intermediate link between older, smaller tyrannosaurs and the gigantic, last-surviving members of the species.

Suskityrannus hazelae is thought to have existed 92 million years ago, about 20 million years before T. rex. 

Nesbitt says he first discovered an incomplete skeleton of Suskityrannus hazelae in New Mexico in 1997, and another, more complete, sample in 1998. But in the decades since, scientists weren't certain what it was until other fossils of smaller T. rex cousins were discovered.

Another tiny cousin of the T. rex, called Moros intrepidus, was discovered in February and is thought to have lived 96 million years ago. 

Tyrannosaurus rex couldn’t run says new research

A link in the evolutionary chain

"Suskityrannus gives us a glimpse into the evolution of tyrannosaurs just before they take over the planet," said Nesbitt.

The report points out that T. rex only roamed the earth for 15 million years before the species was wiped out. Smaller tyrannosaurs are thought to have existed up to 150 million years before the T. rex. Incomplete fossil records have made it difficult to determine how the dinosaur species evolved during that gap.

Read more: Dinosaurs are extinct because asteroid hit the wrong spot

Although the discovery helps with understanding how the T. rex evolved, paleontologists have said that it is still unclear as to why the smaller carnivorous dinosaurs evolved to become so large.

wmr/jm (AP, Reuters)

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