The first remains of a tyrannosaurus that stalked the southern continents have been identified by scientists from a distinctive hip bone blasted from a cliff face in Australia.
About a quarter of the size of the legendary, and exclusively northern, Tyrannosaurus rex, the dinosaur was about three meters long and would have weighed some 80kg (12st 8lb), about the same as a human. The find sheds lays to rest the belief that tyrannosaurs never made it to the southern hemisphere. Their fossils have previously been found only in the northern hemisphere.
Tyrannosaurs have very distinctive hip bones, which allowed Roger Benson, a dinosaur expert at the University of Cambridge, to make the identification. In the journal Science, Benson and his colleagues say the dinosaur would have lived about 110m years ago.
A surge of finds from that period in recent years have shown that these smaller tyrannosaurs were probably widespread, and ancestors of the T-rex, which weighed about four tonnes and emerged 70m years ago.
Benson said: "Although we have only one bone, it shows that 110m years ago, small tyrannosaurs like ours might have been found worldwide. This find has major significance for our knowledge of how this group of dinosaurs evolved." It was unlikely that a T-rex fossil could be uncovered in the southern hemisphere.
Paul Barrett, a palaeontologist at the Natural History Museum in London and a member of the research team, said: "The absence of tyrannosauroids from the southern continents was becoming more and more anomalous as the representatives of other northern dinosaur groups started to show up in the south. This find shows that tyrannosauroids were able to reach these areas early in their evolutionary history, and also hints at the possibility that others remain to be discovered in Africa, South America and India."
Benson said a key question now was why the early tyrannosaurs seem to have evolved into the giant T-rex only in the north. "It is difficult to explain why different groups succeeded in the north and the south if they originally existed in both places. What we need to know now is just how diverse the early radiation of tyrannosaurs was, why they went extinct, leaving only giant-sized, short-armed species like T-rex, and how successful they might have been in the southern hemisphere. We can only answer these questions with new discoveries."
During the time of the dinosaurs, the world's continents gradually went from a single supercontinent towards something like their present arrangement. The new tyrannosaur is from the mid-stages of this continental break-up, when the southern continents of South America, Antarctica, Africa and Australia had separated from the northern continents, but not from each other.
The distinctive hip bone was one of 100-odd bones and fragments recovered at Dinosaur Cove in Victoria by Australian scientist Tom Rich in 1989. The 30cm-long pubis bone looks like a rod with two expanded ends, one of which is flattened and connects to the hip and the other of which has the shape of a boot.