About 250 million years ago, the continents we know today were united in a single super-continent called Pangaea.  Toward the end of the Jurassic period (about 150 million years ago), Pangaea began to fragment into northern and southern landmasses called L

Map of the world 135 million years ago, when Jobaria herds lived in central Africa

aurasia and Gondwana.  The separation continued through the Cretaceous period (145-65 million years ago) and split the two landmasses into the continents we recognize today.  As the continents drifted apart they took plants and animals with them.

    How did dinosaurs respond to these gradual -- but profound -- changes in their world?  It has been suspected that as the continents became more isolated, different species of dinosaur evolved on each one.  One of the difficulties in proving this theory, however, has been the lack of dinosaur fossils from Southern continents.  Many dinosaurs are known from well-studied continents like North America.  Tyranosaurus and Tricerotops for instance are known only from North America.

In September of 1997, an expedition led by University of Chicago paleontologist Paul Sereno set out for Niger in search of African dinosaurs --  and clues to the mystery of how the break up of the continents affected dinosaur evolution.