The Scenario

A part of the world now occupied by Mongolia provides the setting for this 72-million-year-old scene. A small family of primitive ceratopsians belonging to the genus Protoceratops flees over the crest of a large sand dune, pursued by a pair of fleet-footed theropods from the genus Velociraptor. In the right foreground, a solitary mother Oviraptor observes the chase while guarding her nest of eggs. A pack of theropods belonging to the genus Sauronithoides pursues a flock of the flightless bird Mononykus in the middle distance, while a pair of ankylosaurs from the genus Pinacosaurus watches from a distant sand dune.

The Environment

The fossils are preserved in the sandy sediments of the Djadokhta Formation. The large, angled strata contained within the thickest major beds suggest that many of these deposits represent the remains of extensive fields of wind-blown sand dunes. Less common beds of mud and clay suggest that ponds occasionally formed between the dunes, and coarse-grained beds of conglomerate attest to the presence of streams, at least at times, within the general area. Nonetheless, the climate was rather arid and vegetation was sparse in relation to the forested flood plains that existed at the same time in the middle of the North American continent, near present-day Alberta, Montana, Wyoming, Colorado, and Utah.