For all the fame of Tyrannosaurus rex and its relatives, their origins have been difficult to pin down. Now paleontologists have unveiled a skeleton of a primitive tyrannosauroid that backs up what many have suspected: The hulking predators evolved from smaller, long-armed creatures.
The classic view of T. rex ancestry was that it evolved from a long line of large meat eaters that stretched back more than 80 million years to the Jurassic. An alternative idea, proposed in the 1920s, suggested that the tyrannosaurs of 65 million years ago descended from a group of more diminutive predators called the coelurosaurs, which is now known to include Velociraptor. The theory didn't catch on, but it was revived in the 1990s and sometimes dubbed the "tyrannoraptor hypothesis." Yet despite many similarities between tyrannosaur and coelurosaur anatomy, there was no dinosaur that seemed transitional.
That gap is now filled by the 132-million-year-old Eotyrannus, found by an amateur collector in 1997 on the Isle of Wight, off the southern coast of England. Although isolated bones of primitive tyrannosaurs had been reported before, this 5-meter-long skeleton beats them hands down. It's about 40% complete and includes the front half of the skull. In the April issue of Cretaceous Research, a group from the University of Portsmouth, United Kingdom, and the Museum of Isle of Wight Geology describes several features that link Eotyrannus with tyrannosaurs, such as a blunt snout and fused nasal bones. Other traits are much more primitive, and it has long arms and hands like Velociraptor--just as the tyrannoraptor theory predicts. "This is one of the first specimens to confirm that," says team member Darren Naish of the University of Portsmouth.
The new specimen will help clarify how tyrannosaur traits evolved, says paleontologist Tom Holtz of the University of Maryland, College Park. For example, Eotyrannus implies that the advanced biting style of the tyrannosaurs evolved in a predator that could still grab with its arms. As for the tyrannoraptor idea, Holtz says Eotyrannus "is great confirmation."