New Dino Reveals How T. rex Became Top Predator

Tyrannosaurus rex evolved from horse-sized scrappy dinos with relatively big brains and super sharp hearing.

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.

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."

This artistic rendering shows the tyrannosaur Timurlengia euotica, a predecessor of T. rex..

Paleontologists have just assembled the most comprehensive family tree of meat-eating dinosaurs. Published in the journal Current Biology, the family tree reveals how diverse carnivorous dinosaurs were and how birds eventually evolved from them. Tyrannosaurs, including

Tyrannosaurus rex

, are one key group on the meat-loving dino family tree. Lead author Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News, "The most iconic dinosaurs of all, tyrannosaurs were more than just the 13-meter-long (nearly 43 feet long), 5-ton monster predator

T. rex

." "Tyrannosaurs were an ancient group that originated more than 100 million years before

T. rex

, and for almost all of their evolutionary history they were small carnivores not much bigger than a human in size."

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"Some of the rarest theropods (two-legged carnivorous dinos) of all, compsognathids are represented by about half a dozen species," Brusatte said. "They were small, sleek meat-eaters which ate small prey like lizards." One of the more recent finds, Juravenator from Germany, is known from a nearly complete fossil.

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Ornithomimosaurs were theropods called "ostrich mimic" dinosaurs -- for a reason. "Like living ostriches, they could run fast on their long legs and used their sharp, toothless beaks to eat a varied diet of small prey, plants, and perhaps even small shrimps in the water just like living flamingos," Brusatte explained. "A recent find in Canada showed that not only were ornithomimosaurs feathered, but they also had complex feathers on their arms that would have formed something of a wing, although they couldn't fly."

Brusatte describes therizinosaurs as "perhaps the weirdest theropods of all." "These were big, bulky, cumbersome dinosaurs that ate plants. They had fat barrel-shaped chests, stocky legs, and big claws on their arms," Brusatte said. For many years paleontologists argued about which group this dinosaur belonged to, only recently settling on theropods. This means they were fairly closely related to birds, despite their weird anatomy.

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Alvarezsaurs were among the smallest dinosaurs of all, measuring just a few feet long and weighing less than 5 kilograms (10 pounds). "Some of them had only a single functional finger on their hand, which they probably used to prod deep into the nests of bugs, which were one of their main food sources," Brusatte said.

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Oviraptorosaurs, were a group of small omnivores that were lightweight, lacked teeth and had tall, hollow crests on their skulls. The recently discovered Anzu -- the so-called "

chicken from hell

" -- came by its nickname honestly. It towered more than five feet tall, weighed more than 400 pounds, and was covered in a coat of feathers.

"Troodontids were probably the smartest dinosaurs of all, as they had the largest brains relative to their body size of any dinosaur group," Brusatte said. "Most troodontids were small, fast-running dinosaurs that probably ate both meat and plants." Among the most recently discovered of this group are the small, feathered Anchiornis and Xiaotingia, which lived in China about 160 million years ago. "They look eerily similar to birds, so much so that some researchers think they could be primitive birds rather than troodontids with wings and feathers," Brusatte said.

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Dromaeosaurids were "raptor dinosaurs" that include Velociraptor from "Jurassic Park" fame. These dinosaurs were pack hunters who wielded a sharp, hyper-extendable "killer claw" on their second toe. "One of the most recently discovered dromaeosaurids is Balaur, a poodle-sized terror from Romania which had not one, but two 'killer claws' on each foot."

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"The oldest birds, like Archaeopteryx that lived 150 million years ago in Germany, are very hard to distinguish from their closest dinosaurian relatives," Brusatte said. "Unlike living birds, they had teeth, sharp claws on their wings, and long tails." "Over the past two decades," he continued, "over 50 new species of Mesozoic birds have been discovered in northeastern China, in the same rock units as the famous 'feathered dinosaurs.' So many birds are preserved here because entire ecosystems were buried by volcanic eruptions, turning animals to stone like a dinosaur version of Pompeii."

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"The 10,000 species of birds that live today -- from hummingbirds to ostriches -- are modern dinosaurs," Brusatte said. "They are dinosaurs in the same way that humans are mammals. The classic body plan of living birds -- feathers, wings, wishbones, air sacs extending into hollow bones -- did not evolve suddenly but was gradually assembled over tens of millions of years of evolution. But, when this body plan finally came together completely, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate." "They underwent a burst of evolution early in their history, which eventually led to the 10,000 species alive today -- more than twice the number of mammals."

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