Amazing Planet

Giganotosaurus Was The T. Rex Of South America

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In 1993, an amateur fossil hunter and full-time mechanic named Ruben Carolini made an incredible discovery in southern Argentina—the massive leg bone of a carnivorous dinosaur. Soon two of Argentina's most celebrated paleontologists were on the case, and by 1995, when they were done unearthing the monster, they made a bold pronouncement to the world: Giganotosaurus carolinii ("giant southern lizard of Carolini") was an even larger carnivore than Tyrannosaurus rex, the most famous giant meat-eater of all time.

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Model of Gigantosaurus in Slovakia's DinoPark

A Giant In A Land Of Giants

So we all know that dinosaurs were big (the most famous ones, anyway). But Patagonia, the southern tip of South America, was home to the biggest of the big. Seriously—the long-necked dinosaur Argentinosaurus had vertebrae the size of a human being. So maybe it's not surprising that such massive prey would demand a massive predator. And massive Giganotosaurus was. Up to 47 feet long and nearly 14 tons by some estimates, the dinosaur may have made T. rex's 40 feet and 9 tons look positively runty. What's more, it's quite possible it hunted in packs, since there's strong evidence its close relative Mapusaurus did. Though (possibly) larger than Tyrannosaurus, it had a leaner build and may have been a faster runner as well—as fast as 31.3 miles per hour to T. rex's 25.

But what exactly was Giganotosaurus's relationship to T. rex? At first glance, they looked a lot alike—it would be awfully hard to choose which one you'd rather have running you down. They had to be closely related, right? Actually, aside from the fact that both were theropods, they weren't even close. Giganotosaurus's nearest relatives have been dug up in Africa (South America and Africa had not been long separated 100 million years ago), while T. rex and company are firmly based in Canada and the US. Giganotosaurus had a small, more reptile-like brain, while Tyrannosaurus's bore a closer resemblance to the bird-like dinosaurs. Finally, the southern dinosaur had slashing, knife-like teeth instead of Tyrannosaurus's crushing, conical chompers—further evidence, perhaps, of pack hunting, since it was better equipped to deal death by a thousand cuts than one single killing blow.

A Controversial Mystery

You may have noticed that we're using a lot of "may have" and "could have been" language when talking about Giganotosaurus's size. That's because even though it's been more than 20 years since their discovery, we've only found seven partial skeletons—the most complete is still missing about 30 percent of its bones. By contrast, fossil hunters have found about 50 Tyrannosaurus rex specimens, including several that are nearly complete. So while the most complete Giganotosaurus was comparable to T. rex in length but much slighter in build, orphaned leg bones and fragments of jaws have suggested a much larger animal.

That incompleteness of data has led some modern researchers such as dinosaur anatomist Scott Hartman, to believe that T. rex, with its massive head and barrel chest, remains the size champion between the two. Regardless, neither one was the real biggest land-dwelling carnivore discovered thus far. That honor goes to Spinosaurus, a fish-eating predator who probably lived a lot like a modern-day crocodile.

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