 The Dinosaur Park Formation preserves a great wealth of vertebrate fossils . A wide variety of fish swam the rivers and estuaries , including gars , sturgeons , sharks and rays , among others . Frogs , salamanders , turtles , crocodilians and <unk> also dwelled in the aquatic habitats . Azhdarchid pterosaurs and neornithine birds like Apatornis flew overhead , while the enantiornithine bird Avisaurus lived on the ground alongside multituberculate , marsupial and placental mammals . A number of species of terrestrial lizards were also present , including whiptails , skinks , monitors and alligator lizards . Dinosaur fossils in particular are found with unrivaled abundance and diversity . Huge herds of ceratopsids roamed the floodplains alongside equally large groups of hadrosaurine and lambeosaurine hadrosaurs . Other herbivorous groups like ornithomimids , therizinosaurs , pachycephalosaurs , small ornithopods , nodosaurids and ankylosaurids were also represented . Small predatory dinosaurs like oviraptorosaurs , troodonts and dromaeosaurs hunted smaller prey than the huge tyrannosaurids ; Daspletosaurus and Gorgosaurus , which were two orders of magnitude larger in mass . Intervening predatory niches may have been filled by young tyrannosaurids . A Saurornitholestes dentary has been discovered in the Dinosaur Park Formation that bore tooth marks left by the bite of a young tyrannosaur , possibly Gorgosaurus . 
