Eoraptor

Dating to roughly 231 million years ago, Eoraptor lunensis is one of the earliest known dinosaurs. Barely a meter long and about 10 kilograms, it retained many primitive skeletal features and had a mix of tooth shapes, some leaf-like and some more blade-like, that point to an omnivorous diet. Paul Sereno and colleagues described it in 1993 from the Ischigualasto Formation of Argentina, a Late Triassic site that has yielded several of the world's oldest dinosaurs. Its small size and generalized anatomy make it an important reference for reconstructing what the very first dinosaurs looked like before the group diversified into its major branches.