text: The discovery of remains belonging to a new species of horse-sized dinosaur is shedding light on how Tyrannosaurus Rex (T. Rex) became one of Earth's top predators, according to scientists. 
   
   The remains were unearthed in northern Uzbekistan and are now said to be providing insights into how a family of small-bodied dinosaurs evolved over millions of years to become fearsome giants. 
   
   The study shows the dinosaurs - known as tyrannosaurs - developed huge body sizes rapidly towards the end of the age of dinosaurs, and that their keen senses, which evolved earlier in much smaller species, enabled them to climb to the top of the prehistoric food chain. 
   
   Little has been known about how tyrannosaurs became the giant, intelligent predators that dominated the landscape about 66 million years ago. 
   
   A team of palaeontologists, led by researchers at the University of Edinburgh, studied a collection of tyrannosaur fossils found in the Kyzylkum desert. 
   
   Photo: Todd Marshall/University of Edinburgh/PA 
   
   Scientists said the newly-discovered species, named Timurlengia euotica, lived about 90 million years ago and the remains fill a 20-million-year gap in the fossil record of tyrannosaurs. 
   
   The species' skull was much smaller than that of T. Rex, suggesting it did not grow to the same enormous size. 
   
   But key features of Timurlengia's skull reveal its brain and senses were already highly developed, the team said. 
   
   "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 
   
   Timurlengia was about the size of a horse and could weigh up to 250kg. It had long legs and a skull studded with sharp teeth, and was likely a fast runner, researchers added. 
   
   The first tyrannosaurs lived around 170 million years ago and were only slightly larger than a human. 
   
   But by the late Cretaceous period - around 100 million years later - tyrannosaurs had evolved into animals like T. Rex and Albertosaurus, which could weigh more than seven tonnes. 
   
   Photo: Todd Marshall/University of Edinburgh/PA 
   
   The fact the new species was still small some 80 million years after tyrannosaurs first appeared indicates that huge size developed only at the very end of the group's evolutionary history, researchers concluded. 
   
   Dr Steve Brusatte, of the University of Edinburgh's School of GeoSciences, who led the study, said: "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. 
   
   Photo: Steve Brusatte/University of Edinburgh/PA 
   
   "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." 
   
   The work was carried out in collaboration with researchers at the Russian Academy of Sciences, Saint Petersburg State University and the National Museum of Natural History, Smithsonian Institution, US. 
   
   Professor Hans Sues, of the museum, said: "Timurlengia was a nimble pursuit hunter with slender, blade-like teeth suitable for slicing through meat. 
   
   "It probably preyed on the various large plant-eaters, especially early duck-billed dinosaurs, which shared its world." 
   
   The study has been published in the journal Proceedings of the National Academy of Sciences. ||||| Todd Marshall 
   
   Brains came before brawn for tyrannosaurs. The iconic Tyrannosaurus rex, the star of Jurassic Park, emerged as a huge and cunning predator some 80 million years ago. But how it evolved has long been a mystery, because of a gap in the fossil record that began 100 million years ago. 
   
   Now, new remains that include a skull fragment show that this dinosaur started out smaller, the size of a bear, and evolved its big brain before its huge stature. 
   
   The first tyrannosaurs evolved about 170 million years ago, when they split from the group of feathered predators that later gave rise to birds. But they remained in the shadows of larger beasts, such as allosaurs and spinosaurs. They emerged as giants during a 20-million-year gap in the fossil record, when the dinosaur age was coming to an end. 
   
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   A tyrannosauroid fossil called Timurlengia euotica dating back 90 million years fills that gap, helping us understand how T. rex was able to become so big and so dominant, says Stephen Brusatte of the University of Edinburgh, UK. 
   
   The vital clues emerged two years ago when Alexander Averianov of the Russian Zoological Institute in St Petersburg showed Brusatte a braincase that was among many fossils his group had collected in the remote Bissekty formation of Uzbekistan. 
   
   “I’ve studied a lot of tyrannosaurs and a lot of braincases, and after a while I recognised it as a tyrannosaur,” Brusatte says. On further scrutiny, the team concluded it was a new species. 
   
   CT scans 
   
   CT scans revealed that Timurlengia’s brain was large for a dinosaur and that it had structures in the inner ear used for balancing and for hearing low-frequency sounds. Earlier tyrannosaurs lacked those traits, which could have helped T. rex in its niche as an apex predator. 
   
   Yet with a body mass of some 200 kilograms, Timurlengia was much smaller than T. rex, which could weigh over 5 tonnes. 
   
   The fossils support earlier proposals that T. rex evolved “head first” – brain before bulk. 
   
   But how it took over as apex predator remains unclear, although Brusatte says it may have taken advantage of the mysterious disappearance of other large predators. “It looks like the allosaurs go out and tyrannosaurs opportunistically take over,” says Brusatte. 
   
   “This is cool stuff,” says Thomas Holtz of the University of Maryland in College Park. But he notes that the remains of Timurlengia are too fragmentary to reveal other details like the length of its arms. He hopes further fossil discoveries will fill in the gaps. 
   
   The number of tyrannosaur species known has more than doubled in the past 15 years, says Mark Norell of the American Museum of Natural History in New York. “It’s a great time to be working on tyrannosaurs.” 
   
   Other Uzbek fossils collected by Averianov’s team have already yielded important insight into other dinosaurs. They include the oldest horned dinosaurs and the first duck-billed dinosaurs, both of which lived alongside T. rex, says Holtz. 
   
   Read more: Rise and fall of a dinosaur hunter; The making of T. rex 
   
   Journal reference: PNAS, DOI: 10.1073/pnas.1600140113
target: – Though one of the most well-known dinosaurs, Tyrannosaurus rex is actually somewhat of a mystery, having suddenly emerged as a fearsome beast some 80 million years ago. As a 20-million-year gap in the fossil record preceded T. rex, paleontologists have known little about its evolutionary path—until now. The discovery of 90-million-year-old fossils belonging to a previously unknown relative shows T. rex likely developed brains before size, reports New Scientist. Discovered in Uzbekistan in 2012, Timurlengia euotica's large brain and ears used for balancing and hearing low-frequency sounds were "almost identical to T. rex," which also shared certain bone features, researcher Stephen Brusatte tells the BBC. Yet Timurlengia was only "the size of a horse" and weighed less than 500 pounds. "Only after these ancestral tyrannosaurs evolved their clever brains and sharp senses did they grow into the colossal sizes of T. rex," weighing over five tons, Brusatte tells the Telegraph.Timurlengia was "evolving features that would eventually allow T. rex to become this super-dominant top-of-the-food-chain animal," he adds. "Tyrannosaurs had to get smart before they got big." Researchers still don't have a full picture of Timurlengia after uncovering 25 sections of its skeleton—they don't know the length of its arms, for example—but say the "nimble pursuit hunter" had long legs and was a fast runner. Timurlengia also had "slender, blade-like teeth suitable for slicing through meat" and "probably preyed on the various large plant-eaters, especially early duck-billed dinosaurs," an expert says. (One creature alive today has teeth like T. rex.)