Before T-rex became humongous, it learned to hear footsteps

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Tyrannosaurus rex, the behemoth king of the late ages of the dinosaurs, grew its brain before its noteworthy body. That’s according to scientists at the Smithsonian’s National Museum of Natural History, who today unveiled the fossils for a new species in this family of apex predators: Timurlengia euotica.

Though this new species isn’t a direct ancestor of T.rex, it fills a mystifying hole in the evolutionary record of the Tyrannosaur superfamily. The oldest known members of this group of carnivorous dinosaurs were tiny, about the size of dogs, and roamed from 170 million to 100 million years ago. Fossils show that the 13-foot-tall T. rex and other large tyrannosaurs reigned supreme 80 million years ago, but until today, no one had found remains to bridge the 20-million-year gap.

Living 90 million years ago and being similar in size to a horse, Timurlengia euotica fills this evolutionary void, said Hans Sues, chair of the department of paleobiology at the Smithsonian’s National Museum of Natural History. Hues and his colleagues collected the fossils of the new species in the Kyzylkum Desert of Uzbekistan. Over the course of nine years — 1997 to 2006 — his team scraped away sand from an ancient river system to uncover the 15 bones that define this new specimen.

Reconstructed skeleton of Timurlengia euotica with discovered fossilized bones, highlighted in red, and other bones remaining to be discovered inferred from other related species of tyrannosaurs in white. Individual scale bars for the pictured fossilized bones each equal 2 cm. Photo courtesy of Brusatte et al., PNAS, 2016.

Reconstructed skeleton of Timurlengia euotica with discovered fossilized bones, highlighted in red, and other bones remaining to be discovered inferred from other related species of tyrannosaurs in white. Individual scale bars for the pictured fossilized bones each equal 2 centimeters. Photo courtesy of Brusatte et al., PNAS, 2016.

Life reconstruction of the new tyrannosaur Timurlengia euotica in its environment 90 million years ago. It is accompanied by two flying reptiles (Azhdarcho longicollis). The fossilized remains of a new horse-sized dinosaur, Timurlengia euotica, reveal how Tyrannosaurus rex and its close relatives became top predators, according to a new study published in the Proceedings of the National Academy of Sciences. Painting by Todd Marshall

Life reconstruction of the new tyrannosaur Timurlengia euotica in its environment 90 million years ago. It is accompanied by two flying reptiles (Azhdarcho longicollis). The fossilized remains of a new horse-sized dinosaur, Timurlengia euotica, reveal how Tyrannosaurus rex and its close relatives became top predators, according to a new study published in the Proceedings of the National Academy
of Sciences. Painting by Todd Marshall

Sues said the river bed’s loose gravel was crucial, because stiffer rocks, like those laden with iron, can impede fossil excavation. “The ground wasn’t enriched in iron, which makes it harder to remove rock from bone. We could have used mini jack hammers to brush away debris like iron, but then you might damage the fossil,” Sues told PBS NewsHour at today’s unveiling.

Field camp of the Uzbek-Russian-British-American-Canadian expedition at Dzharakuduk in the Kyzylkum Desert of Uzbekistan. The fossils of Timurlengia eutica were found about midway along the cliffs in the background. Photo courtesy of Brusatte et al., PNAS, 2016.

Field camp of the Uzbek-Russian-British-American-Canadian expedition at Dzharakuduk in the Kyzylkum Desert of Uzbekistan. The fossils of Timurlengia eutica were found about midway along the cliffs in the background. Photo courtesy of Brusatte et al., PNAS, 2016.

Hans Sues, a scientist at the Smithsonian’s National Museum of Natural History, excavating a dinosaur fossil at Dzharakuduk in the Kyzylkum Desert of Uzbekistan, September 2006. Photo by Hans Sues, Smithsonian.

Hans Sues, a scientist at the Smithsonian’s National Museum of Natural History, excavating a dinosaur fossil at Dzharakuduk in the Kyzylkum Desert of Uzbekistan, September 2006. Photo by Hans Sues, Smithsonian.

These gentle geologic conditions arguably yielded the top prize among the bones: a well-preserved braincase of Timurlengia euotica. A braincase is the part of the skull that encloses the squishy material of the brain, and its architecture can say a lot about how an animal perceives the world. For instance, Sues showed off two holes in the T. euotica braincase where nerves used to run from the brain to the creature’s eyes.

“Based on the size of these holds and the corresponding nerves, T. euotica had relatively large eyes,” Sues said, compared smaller predecessors.

Hans Sues, a paleobiologist at Smithsonian's National Museum of Natural History, holds up a 3D-printed version Timurlengia euotica's brain case. Sues is pointing to two openings in the brain case where cranial nerves led to the dinosaur's eyes. Photo by Nsikan Akpan

Hans Sues, a paleobiologist at Smithsonian’s National Museum of Natural History, holds up a 3D-printed version Timurlengia euotica’s brain case. Sues is pointing to two openings in the brain case where cranial nerves led to the dinosaur’s eyes. Photo by Nsikan Akpan

Tyrannosaurus Rex tooth (left) rests next to an actual tooth of the new tyrannosaur Timurlengia euotica from the Late Cretaceous Period that was found in the Kyzylkum Desert, Uzbekistan. Photo by Nsikan Akpan

Tyrannosaurus Rex tooth (left) rests next to an actual tooth of the new tyrannosaur Timurlengia euotica from the Late Cretaceous Period that was found in the Kyzylkum Desert, Uzbekistan. Photo by Nsikan Akpan

This Timurlengia euotica specimen also had a long cochlea, a part of the inner ear. This extra space may have allowed T. euotica to hear low-frequency sounds, such as the patter of its prey footsteps. Such a hunting advantage might mean more food, and eventually, a larger body size. Another theory is the long cochlea helped the dinosaurs decipher complex vocalizations from others.

Together, these cranial features resemble ones found in the larger Tyrannosaurs like T. rex, though the overall brain sizes between the two species differed significantly. T. rex had a basketball-size brain, while T. euotica’s was closer to a grapefruit.

“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,” paleontologist Steve Brusatte of the University of Edinburgh said in a statement. Brusatte’s team studied the fossils and identified the new species. Collectively, the investigations suggest that Tyrannosaurs didn’t gain their massive size until relatively late in their 70-million-year existence on Earth.

The findings were published today in the Proceedings of the National Academy of Sciences.

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