Horse-sized dinosaur species find linked to T. rex development
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.
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.
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.
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.
"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.