Meet T. Rex's Fierce, Fleet-Footed Relative

Scientists have discovered a nimble, meat-eating dinosaur with blade-like teeth that fills an important gap in Tyrannosaurus rex's family tree.

The newly named creature, Timurlengia euotica, sheds light on how a family of dinosaurs called tyrannosaurs advanced from being small predators to clever giants at the top of the food chain -- within the span of about 70 million years.

The long-legged, 600-pound T. euotica lived some 90 million years ago. It was around this time that tyrannosaurs developed impressive cognitive abilities and sharp senses, such as the ability to detect low-frequency sounds, according to a study published Monday in the Proceedings of the National Academy of Sciences .

Soon after, tyrannosaurs began to get bigger. By the late Cretaceous period, massive tyrannosaur species would emerge, such as T. rex, which lived around 66 to 68 million years ago, said Dr. Hans-Dieter Sues, the chairman of the paleobiology department at the Smithsonian’s National Museum of Natural History and a co-author of the study.

"Timurlengia has already evolved the sophisticated senses and many bone features of T. rex but was a much smaller animal," Sues said. "The new discovery fills in a multimillion-year gap in the evolution of one particularly successful group of dinosaurs."

Sues and Dr. Alexander Averianov, a senior scientist at the Russian Academy of Sciences, unearthed the T. euotica fossils in the Kyzylkum Desert of Uzbekistan during a series of expeditions between 1997 and 2006.

Sues and an international team of paleontologists reanalyzed the remains and found that they belonged to a previously unknown species, T. euotica, which they determined was a relative but perhaps not an ancestor of T. rex.

"As few dinosaur fossils are known from 90 million-year-old rocks, we hoped to find fossils that would tell us something about dinosaur evolution at this point in time," Sues said. "Still, Timurlengia showed unexpected features."

To learn more about the species and its cognitive abilities, the researchers took CT scans of T. euotica's fossilized brain case and used that data to build a model of its brain.

They concluded that, even though T. euotica's skull was much smaller than that of T. rex, its brain and senses were highly developed.

"The ancestors of T. rex would have looked a whole lot like Timurlengia, a horse-sized hunter with a big brain and keen hearing that would put us to shame," Dr. Steve Brusatte, a paleontologist at the University of Edinburgh in Scotland who led the new research, said in a statement. "Only after these ancestral tyrannosaurs evolved their clever brains and sharp senses did they grow into the colossal sizes of T. rex. Tyrannosaurs had to get smart before they got big."

This new research is not only noteworthy for what it teaches us about the tyrannosaurs' family tree, but also because it could provide clues about how dinosaurs evolved when faced with a changing environment, Sues said.

"Dinosaurs have been a huge evolutionary success since they first appeared about 230 millions year ago," he said. "Learning about their evolutionary history and how they coped with environmental changes holds important lessons for the many changes seen in today's world."