Dinosaurs and other archosaurs, such as the pterosaurs, dominated the land biota. . .
. . . such as these dinosaurs from the Cretaceous of Mongolia.
Cycads and Bennettitaleans were among the dominant land vegetation.
The first mammals also arrived on the scene in the Mesozoic,descended from a lineage of so-called "mammal-like reptiles," or synapsids. This is Thrinaxodon, an extinct relative of mammals from the Triassic.
Find out more about the Mesozoic paleontology and geology of North America at the Paleontology Portal.