Paleontologists working in Niger's Tnr Desert have unearthed the fossilized remains of a crocodile that might give even Steve Irwin pause. Indeed, according to a report published today in the journal Science, this bigger, badder cousin of modern crocs measured up to 40 feet long and weighed in at eight metric tons. Dubbed Sarcosuchus imperator, the Cretaceous beast may have preyed on dinosaurs.

Researchers first recovered remains of Sarcosuchus in the Tnr Desert in 1964. Its paleontological significance, however, remained largely unexplored. The newly discovered skulls and partial skeletons, described by University of Chicago paleontologist Paul C. Sereno and colleagues, add significantly to what is known about the 110-million-year-old monster. "This new material gives us a good look at hypergiant crocodiles," Sereno remarks. "There's been rampant speculation about what they looked like and where they fit in the croc family tree, but no one had enough of the skull and skeleton to really nail any of the true giant crocs down until now." (In the image at the right, a Sarcosuchus skull dwarfs that of a modern crocodile.) Features in Sarcosuchus's skull and jaw, the researchers report, link it to two fish-eating fossil crocodilians known as Pholidosaurus and Terminonaris. Sarcosuchus, however, turned up in rivernot marinedeposits and has feeding anatomy indicative of a more generalized diet. Sarcosuchus's long, broad snout is especially interesting, featuring at its tip a large bulbous growth, or nasal bulla. "We're still wondering what it's for," Sereno remarks. "Crocodilians are among the most vocal reptiles, so I wouldn't doubt that it may have been involved in both sound and smell."

Though it may have been the largest, Sarcosuchus certainly wasn't the only croc around during the Cretaceous. The Niger site alone has yielded the remains of six crocodilian species, including one "not much more than an Oreo cookie" in size, Sereno notes. "That's the fascinating thing about crocodile evolution," he muses. "It seems like modern crocodiles have been trimmed at each end of their size range, with the little ones and the big ones disappearing."