who have studied the fossilized animal , which was 5 to 6 years old when it died , believe it was an ancestor of the fearsome T. Rex . `` Raptorex really is a pivotal moment in the history of the group where most of the biological meaningful features about Tyrannosaurs came into being , '' said lead author Paul Sereno , a paleontologist at the University of Chicago . `` And the surprising fact is that they came into being in such a small animal , '' he added . Based on estimates of other similar-sized theropods , or `` beast-footed '' dinosaurs , Sereno and his colleagues estimate an adult Raptorex was about 9 feet tall and weighed about 143 pounds . By contrast , the Tyrannosaurus rex , which topped the prehistoric food chain until dinosaurs went extinct about 65 million years ago , was believed to weigh at least five tons . Scientists hypothesize that Raptorex ran its prey down , using its enlarged skull , powerful jaws and sharp teeth to dispatch animals much larger than itself . Like the T. rex , the Raptorex also had tiny forelimbs , they said . `` We
-LRB- CNN -RRB- -- A pint-sized version of the Tyrannosaurus rex , with similarly powerful legs , razor-sharp teeth and tiny arms , roamed China some 125 million years ago , said scientists who remain startled by the discovery . An adult Raptorex was about 9 feet tall and weighed about 150 pounds , scientists say . The predator , nicknamed Raptorex , lived about 60 million years before the T. rex and was slightly larger than the human male , scientists said . The findings , to be released Friday in the journal Science , are based on fossilized remains discovered in lake beds in northeastern China . They show a dinosaur with many of the specialized physical features of Tyrannosaurus rex at a fraction of its size . `` The most interesting and important thing about this new fossil is that It is completely unexpected , '' said Stephen Brusatte , co-author of the article , in a conference call with reporters . `` It 's becoming harder and harder to find fossils like this that totally throw us for a curve , '' added Brusatte , a paleontologist with the American Museum of Natural History . Scientists