A big brain, keen hearing and a fortuitous extinction event all likely helped create the biggest, baddest carnivore that ever walked the earth, according to a study on a newly discovered ancestor of Tyrannosaurus rex.

The horse-sized dinosaur fills gaps in the fossil record of T. rex evolution, helping to solve many mysteries about the enormous carnivore that was at the top of the terrestrial food chain before it went extinct as the Age of Dinosaurs came to a close about 65 million years ago.

We now know that, long before T. rex emerged, "tyrannosaurs were already hardwired with the sensory arsenal of a top predator before they got to be super giants," project leader Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News.

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The findings are published in the journal Proceedings of the National Academy of Sciences.

Co-authors Alexander Averianov and Hans-Dieter Sues found the remains of the new tyrannosaur while conducting expeditions in the remote deserts of Uzbekistan, Central Asia. They named the tyrannosaur Timurlengia euotica after a central Asian warlord, Timur, and also with a word meaning "well eared." The word refers to the new dinosaur's incredible sense of hearing.

Brusatte explained that the 90-million-year-old dino had a very long spiral cavity of the inner ear (cochlea), which allowed it to hear low frequency sounds that would have been undetected by other dinosaurs.

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On top of this super sensory hearing, "Timurlengia was a nimble pursuit hunter with slender, blade-like teeth suitable for slicing through meat," Sues said, adding that "it probably preyed on the various large plant-eaters, especially early duck-billed dinosaurs, which shared its world."

The fast-running, long-legged Timurlengia was just a fraction of the size of T. rex, which could grow to be 40 feet long, 20 feet tall and weighed as much as 9 tons. The dichotomy in size strongly suggests that during the final 20 million years of the Cretaceous, tyrannosaurs evolved enormous bodies in a relatively short period of time.

As for why, Brusatte said "it is interesting that there was a mass extinction event about 94 million years ago, seemingly caused by extensive volcanism leading to global warming."

He suspects that the extinction of prior top carnivores left a void for "tyrannosaurs (to) opportunistically take over the apex predator role," but he said more fossils from the middle Cretaceous would be needed to test the theory.

T. rex, a top predator, is shown in this illustration.iStockPhoto

Vertebrate paleontologist Thomas Carr of Carthage College told Discovery News that the new study also lets us know where the impressive features of T. rex first evolved: Asia.

The ancestors of T. rex migrated out of that region, such that T. rex later dominated western North America. Carr agrees that Timurlengia helps to fill many gaps in the fossil record separating the earliest, most primitive tyrannosaurs from the giant, advanced species like T. rex.

Lindsay Zanno, head of the North Carolina Museum of Natural Sciences' Paleontology Research Lab and curator of paleontology, said about Timurlengia and other earlier, smaller tyrannosaurs, "We know these guys were understudies for other dinosaurian mega-predators on northern landmasses for some time before seizing the opportunity to be the starring act."

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"The size of the animal described here supports current ideas about tyrannosaur evolution, that is to say, they grew rapidly once top predator niches were vacated sometime between 80 and 90 million years ago in the Late Cretaceous, ultimately ballooning into the largest of all tyrannosaurs, the tyrant king T. rex."

In terms of T. rex's ultimate fate, Brusatte said that it was the last surviving tyrannosaur.

"It was there when the asteroid fell out of the sky on that random day 66 million years ago, knocking out all non-bird dinosaurs and ending the Cretaceous," he explained. "Pretty much everything went extinct. It was a really bad time to be a dinosaur."