More than 20 years ago, paleontologists unearthed two partial skeletons of a mysterious dinosaur species in New Mexico. This creature, which lived about 92 million years ago, bore some resemblance to giant tyrannosaurs that reigned from about 80 million to 66 million years ago. One was even found with what could have been a partly digested lizard skull. But the dino was so tiny — only about a meter tall at the hip — it left scientists to wonder where it fit in.
“There was enough of a skeleton to be super intriguing, but not enough to nail it down,” says Sterling Nesbitt, a paleontologist at Virginia Tech in Blacksburg who dug up one of the fossils.
At the time, paleontologists didn’t have many other carnivores in the dinosaur’s size range to provide a point of comparison, Nesbitt says. Now, remnants of tyrannosaurs from Asia and North America have fleshed out the Tyrannosaurus rex’s family tree and allowed researchers to pin the new dinosaur as one of its kin.
Analyses of the newly identified dinosaur, named Suskityrannus hazelae, reveal that this small tyrannosaur boasted some of the signature skeletal features of its megapredator relatives, researchers report online May 6 in Nature Ecology and Evolution. This discovery helps illuminate how tiny hunters that emerged over 100 million years ago gave rise to such enormous, bone-crunching tyrannosaurs like T. rex (SN: 3/16/19, p. 11).
Like its later, apex-predator cousins, S. hazelae’s skull was built for a strong bite, and three bones in its feet called metatarsals were pinched together. This bundling of bones is thought to strengthen the ankle, which would have given dinosaurs like S. hazelae powerful hind feet for running and holding down prey, says coauthor Robert Denton, a geologist at the consulting engineering firm Terracon in Ashburn, Va.
These features were probably crucial for the supersize tyrannosaurs, which had such tiny front limbs that they “became extremely dependent on their hind feet and their enormous tooth-filled jaws to do all the business,” Denton says. Spotting these characteristics in S. hazelae reveals that tyrannosaurs developed these features while still relatively small.