This undated photo released by National Geographic shows University of Chicago Professor Paul Sereno, left, and McGill University Associate Professor Hans Larsson excavating the fossil skull of a 100-million-year-old croc in Niger. The animal, which they nicknamed BoarCroc, was one of several crocs that inhabited a lost world now buried in the sands of the Sahara. (AP Photo/National Geographic, Mike Hettwer) ** NO SALES, NO ARCHIVE **