Tyrannosaur Fossil Shows Intelligence Came Before Brawn

Plenty of people know about the most famous tyrannosaur, Tyrannosaurus rex, even if their overall knowledge of dinosaurs is quite poor.

That’s because the huge predator was around 40 feet long and weighed a few tons, putting it at the top of the food chain. At the end of the dinosaur age, Tyrannosaurus rex was a dominant force. However a new fossil shows that the first tyrannosaurus was in fact about the size of a person.

New fossil could fill in evolutionary history of tyrannosaur

Until now scientists hadn’t properly understood what happened in the middle. A fossil found in Uzbekistan is providing researchers with more information on the evolutionary history of the Tyrannosaurus rex because it has the same characteristics as its huge successor without the size.

“It has long been thought that tyrannosaurs were such successful predators, in part, because of their large brains and ears well-attuned to low-frequency sound,” said Stephen L. Brusatte, a paleontologist at the University of Edinburgh in Scotland and lead author of a paper published Monday in the Proceedings of the National Academy of Sciences describing the new dinosaur. “The new Uzbek tyrannosaur has basically the same brain as T. rex — same shape, proportions, etc. — just smaller.”

Brusatte says that the fossils is evidence that the tyrannosaurus developed its intelligence before its size. “It is one of the closest cousins of T. rex and tells us that tyrannosaurs evolved sophisticated brains and senses before they became colossal apex predators,” Dr. Brusatte said.

Scientists excited by Uzbekistan find

The first tyrannosaurs were far smaller than contemporary meat-eaters like Allosaurus. Then there is a fossil gap which means that the only evidence of tyrannosaurs comes later, when they had evolved into huge predators.

Uzbekistan is one of few countries that has rocks from that fossil gap. In 2004 Hans-Dieter Sues, chairman of the paleobiology department at the Smithsonian’s National Museum of Natural History, and Alexander O. Averianov, a senior scientist at the Russian Academy of Sciences, found part of a tyrannosaur skull in the Kyzylkum Desert in northern Uzbekistan.

“The braincase proved to be the Rosetta stone for the whole thing,” Dr. Sues said. The new dinosaur was named Timurlengia euotica, and lived around 90 million years ago. Using other bones found in the area, scientists estimated that the dinosaur was about the size of a horse.

However a CT scan showed that the brain shape had more in common with later tyrannosaurs, and an ear structure that was good at picking up low frequencies. “We were very surprised it already had this sensory organization associated with T. rex and related animals,” Dr. Sues said.

Further research needed to paint a full picture

It is thought that the Allosaurus could not adapt to the warm climate on Earth at the time, and died out. This allowed the tyrannosaurs to grow in its place.

It is possible that other large tyrannosaurs had evolved in other places before Timurlengia, and one possible candidate is Xiongguanlong, found in China. It dates from around 100 million to 120 million years ago.

“At a glance, Xiangguanlong looks to my eye like an advanced tyrannosaur,” said Thomas Carr, a paleontologist at Carthage College in Kenosha, Wis., who has examined the brain case although he is not part of the research team.

Carr said that he thought Xiangguanlong and Timurlengia were closely related, but CT scans need to be performed on Xiangguanlong in order for detailed analysis to be published.

“This is what this work is all about, completing that evolutionary narrative,” Dr. Carr said. “At the end of the day, there’s much more to discover. It’s still a great leap from Timurlengia to T. rex.”