for National Geographic News
A rare fossil found in Australia suggests dinosaurs were able to traverse the vast prehistoric continent of Gondwana much later than thought, scientists report.
The hundred-million-year-old fossil belonged to a two-legged meat-eater, or theropod, that is closely related to Megaraptor namunhuaiquii, a giant, big-clawed carnivore from Argentina, says a team led by Nathan Smith of the University of Chicago's Field Museum.
The discovery could help redraw the world map during the dinosaur era, researchers add.
That's because the newfound Australian dinosaur shows that animals could travel across Gondwana during the Cretaceous period, about 145 to 65 million years ago.
This in turn suggests that Gondwana's Southern Hemisphere landmasses broke up later than traditionally thought.
The study is based on the unidentified theropod's arm bone, which was discovered at Dinosaur Cove in southeastern Australia in 1989.
The fossil has unique features that solidly link it to the South American Megaraptor that was first described in 1998, Smith said.
"Megaraptor has a huge hand with a big [clublike] claw and a very strange forearm, so if you had to pick one bone to refer to, then the ulna [arm bone] might be that bone," Smith said.
The length of the fossil bone, 7.6 inches (19.3 centimeters), suggests the dinosaur was about half the size of Megaraptor.
This size difference could be because it is a smaller species or because it was a juvenile, Smith said.
The still-nameless Australian specimen is described this week in the journal Proceedings of the Royal Society B.
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