By Sean Henahan, Access Excellence

T-rex's position as undisputed king of the carnivores was cast in doubt with the announcement in 1995 of the discovery in Argentina of a  new dinosaur is called giganotosaurus carolinii. Giganotosaurus lived about 95 million years ago in the early part of the Late Cretaceous Period. The monster lived 25 million years before T-Rex and, at nine tons, weighed half again as much.

Comparison of T-Rex and Giganotosaurus

There are enough differences between Giganotosaurus and T. Rex to suggest the two were not closely related. The teeth alone tell quite a story. The teeth of Tyrannosaurus were longer and wider, but more variable in size. While the tyrannosaur's teeth were suited for biting right through flesh and bone, those of Giganotosaurus were shorter, less variable and narrower, and are much better adapted for slicing flesh.

"They are unusual teeth that are laterally compressed whereas those of T. Rex are circular. They [Giganotosaurus's teeth] are for cutting." Giganotosaurus's blade-shaped serrated teeth up to eight inches long indicate it sliced through the flesh of its victims rather than crunching through bones like T. Rex. says Dr. Jack Horner, Curator of Paleontology at the Museum of the Rockies in Montana.

Horner was among the experts asked to render an opinion on the significance of the Giganotosaurus find. "It is certainly the largest meat eating dinosaur skull I have ever seen. I would agree that the skull has been reconstructed accurately and is bigger than our T. Rex skull," he said.

The volume of new dinosaur discoveries in South America in recent years has brought new information and debate about the world of the dinosaurs. Newfound similarities between African and South American specimens has stirred debate among geologists as well as paleontologists.

"Giganotosaurus ushers in a whole new era in our understanding of carnivorous dinosaurs from the southern hemisphere," says Dr. Peter Dodson, a research associate with the Academy and professor of veterinary anatomy and geology at the University of Pennsylvania. "It is an extremely large and well preserved animal. This is the first time we have had such complete knowledge."

Giganotosaurus was discovered by Argentinian scientist Dr. Rodolfo Coria, Director of the Carmen Funes Museum in Plaza Huincul, Argentina.

"In recent years we have found one of the plant eating dinosaurs (rebbachisaurs) from the same period as Giganotosaurus, which is very similar to one found in Africa," says Coria. "We also have crocodiles from the same level and locality which are similar to those in Africa. That is why we are proposing that 100 million years ago Africa and South America were still connected indicating the separation was more than 10 million years later than previously thought. We have whole ecosystems which support this."

The body of new research implies that the continents stayed together longer and the southern continents were a much greater mass than previously believed. It also suggests the center of dinosaur evolution was located in the Southern Hemisphere. Many questions have also been raised about North-South dinosaur migrations in the Americas.
 
Visitors to the Academy of Natural Sciences in Philadelphia will soon be able to compare the monsters for themselves. Complete skeleton reconstructions of both T-Rex and Giganotosaurus  will be on display only at the Academy, June 14 through September 14.