One of the earliest known true dinosaurs in the Dinosauria order is Eoraptor lunensis. From this predatory bird-like precursor, the birds and dinosaurs emerged. This direct-line ancestor evolved into theropods, birds, sauropods and ornithischians.

Eoraptor emerged during the Late Triassic period, approximately 231.4 million years ago, in what is now Argentina. It is considered one of the earliest and most primitive dinosaurs, exhibiting key dinosaur characteristics such as upright posture, bipedal locomotion, and a predatory lifestyle. Eoraptor belongs to the clade Saurischia and is classified within the family Eoraptoridae.