Evolution Watch: King Claw

Ninety million years ago in what is now Argentina, a terrible predator hunted some of the biggest animals ever to walk on land. Meet Megaraptor.

By Shanti Menon|Wednesday, April 01, 1998
RELATED TAGS: DINOSAURS
It was the last day of his expedition, and Fernando Novas was pleased. The Argentine paleontologist, who works at the Museum of Natural Sciences in Buenos Aires, had been looking for carnivorous dinosaurs in northwestern Patagonia, a dinosaur-fossil hot spot. The region had already yielded the 42-foot-long terror Giganotosaurus, possibly the largest carnivore of all time, and the 100-ton Argentinosaurus, the heaviest beast to walk on land. Novas himself had found a curiously birdlike nonflying dinosaur, which he called Unenlagia, and several other predatory species. On the last day of his successful expedition, in January 1996, he decided to check out some bedrock at the top of a hill. Not surprisingly, given the arid, fossil-friendly landscape of northwestern Patagonia, Novas found some bones.

We started to excavate the sandstone around the bones, says Novas. At first glance, the bones appeared to correspond to the hind limb of an herbivore dinosaur. We were very happy—the last day, the last minute of the expedition and we find another animal. But when we followed the excavation, something wrong occurred. The bones didn’t match with an herbivore dinosaur. A very bizarre bone started to emerge from the rock. I couldn’t imagine to which bone of the skeleton it corresponds. When we finished removing all the sandstone from that bone, it was triangular in shape, and then I start to walk around that bone and then I realize that it is a giant claw. And the other bone didn’t correspond to the hind limb of a plant-eating dinosaur, but to the forelimb of a carnivore dinosaur of a very large size. We start to jump, to cry of happiness. We were in front of another meat-eating dinosaur.

Three months later, back in his lab in Buenos Aires, Novas was due for another surprise. He had assumed that the huge claw would be attached to the dinosaur’s hand. But after the fossilized bones had been prepared, he saw that the claw belonged on the second digit of the foot. The claw, compressed on either side to give it a knifelike cutting edge and a pointed tip—was strikingly similar to the killing claw on the foot of Velociraptor, only much bigger. The bone Novas found was nearly a foot long. In a living animal the bone would have been covered with a horn sheath, making it several inches longer. If you remember the movie, they show Velociraptor with a claw of about six inches, says Novas. We are talking about a claw that is 16 inches. This is an animal that is huge.

Novas calls this enormous predator Megaraptor namunhuaiquii (the species name is Mapuche for lance foot). Based on the bones he has found—the claw, a forearm bone, a finger bone, and a foot bone—he estimates that the 90-million-year-old Megaraptor was about 26 feet long, making it at least three times the length of Velociraptor. Megaraptor probably used its formidable foot claw to slash or disembowel lumbering plant eaters. Long-necked, long-tailed sauropods were relatively common, says Novas. They are candidates to be on Megaraptor’s menu.

Despite their similar weaponry, Velociraptor and Megaraptor had quite different forearms, which leads Novas to think the two are not closely related. He believes that Megaraptor represents a new lineage of carnivorous dinosaurs that evolved independently in the Southern Hemisphere. During the Cretaceous period, 140 to 65 million years ago, the continents in the Western Hemisphere formed two distinct landmasses. The familiar Triceratops, Velociraptor, and Tyrannosaurus roamed Laurasia in the north. Gondwanaland, the southern continent, was home to Megaraptor, Argentinosaurus, and Giganotosaurus, all of which probably surpassed their northern counterparts in size. Why were southern dinosaurs so big? Was it something in the water? We don’t know, says Novas. Maybe there was some climatic condition that allowed for these huge sizes. We don’t know enough about the ecosystem. It’s like a jigsaw puzzle. We are slowly adding, year after year, another piece. Novas has just returned to Patagonia, where he hopes to find more pieces of Megaraptor. At the rate that fossil finds are coming out of the area, Novas may well be surprised again.
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