Imagine a crocodile almost as long as Tyrannosaurus Rex and just as fierce. That's SuperCroc, the giant Sarcosuchus fossil discovered by Paul Sereno, a National Geographic Explorer-in-Residence. Crocodiles and their ancestors are some of the most successful animals that ever lived. At the time of T. Rex, crocs ranged in size from 2 feet long to over 40 feet long. They lived on land, in swamps, and in the sea. Some (like SuperCroc) were fierce predators. Some were heavily armored plant eaters. Later on, some might even have climbed trees. And when all of the dinosaurs (except birds) went extinct, the crocs lived on, becoming the crocodiles, alligators, and gharials of today.