The discovery of primitive , dinosaur-like ornithodirans , in Middle Triassic strata supports this view . Analysis of their fossils suggests that the animals were indeed small , bipedal predators . The discovery of primitive , dinosaur-like ornithodirans such as Marasuchus and Lagerpeton in Argentinian Middle Triassic strata supports this view ; analysis of recovered fossils suggests that these animals were indeed small , bipedal predators .