A tiny tyrannosaur has finally found its place in the dinosaur family tree. Named Suskityrannus hazelae (Sus-kit-eye-RAN-us Hay-ze-lay), its bones are helping scientists chart the rise of giant dinos. Among those giants: Tyrannosaurus rex.
Sterling Nesbitt was part of a team of paleontologists who dug up this species in New Mexico. That was more than 20 years ago. The two partial skeletons they found looked a lot like those of towering tyrannosaurs. One skeleton was even found with what looked like a partly eaten lizard skull.
But S. hazelae is several million years older than the first titanic tyrannosaurs. It is also much smaller — only about a meter (3 feet) tall at the hip. The scientists wondered whether the species truly was a tyrannosaur. Perhaps it instead was some relative of small meat-eating dinos known as velociraptors.
“There was enough of a skeleton to be super intriguing, but not enough to nail it down,” recalls Nesbitt, who works at Virginia Tech in Blacksburg. Fossils of other meat-eaters around this dinosaur’s size would have helped ID it. But back then, those were hard to come by, he explains.
The tyrannosaur family tree has since filled out thanks to recent discoveries of small species in Asia and North America. That allowed Nesbitt and his colleagues to pin down S. hazelae as one of T. rex’s kin. The team reported its findings online May 6 in Nature Ecology and Evolution.
Like the king of the dinosaurs, S. hazelae’s skull was built for a strong bite. And three of its foot bones were pinched together. This bone bundle is thought to strengthen the ankle. That would have given this dino powerful hind feet for running and holding down prey, says Robert Denton. He is a geologist at Terracon, an engineering firm in Ashburn, Va.
These features were probably crucial for the supersize tyrannosaurs. With tiny front arms, the beasts depended “on their hind feet and their enormous tooth-filled jaws,” Denton says. Spotting these in S. hazelae suggests that tyrannosaurs gained the traits while still on the small side.