Herrerasaurus ischgualastensis

Herrerasaurus was one of the earliest dinosaurs, living during the Late Triassic of Argentina. It was an agile predator with a flexible jaw joint and grasping hands that probably hunted small and medium-sized animals in its environment. The phylogenetic position of Herrerasaurus has bounced around between basal sauropodomorph, basal to the split between theropods and sauropodomorphs, and even just outside of Dinosauria, although it seems to have settled down of late as a very basal theropod. Time will tell whether this is a permanent position, or if it moves again (the challenge here is that basal members of the major dinosaur groups all look quite similar, since they are closer to the common ancestor of all dinosaurs, making family trees harder to build at the base).