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 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. The first tyrannosaurs evolved about 170 million years ago, when they split from the group of feathered predators that later gave rise to birds. 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: 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. 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.
– 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.)