Scientists from the University of Texas at Austin have determined that it is a giant, soft-shelled egg, most likely laid by a mosasaur—an extinct marine reptile that ruled the seas during the ...

Predators likely included some of the fiercest monsters of the seas, such as the sharp-toothed shark Cretoxyrhina and the giant mosasaur Tylosaurus. Like all plesiosaurs, Styxosaurus's limbs were ...