Herrerasaurus flourished at a time just before dinosaurs became the dominant land animals. Its remains help clarify the sequence of anatomic changes that occurred during early dinosaur evolution. It closely resembled the common ancestor of all dinosaurs, and it retained the carnivorous habits and features of predatory animals that were ancestral to dinosaurs and their relatives. Although some features, such as their three-toed feet, resemble those of true theropod dinosaurs, they lack some features that distinguish theropods from saurischians, such as overlapping wrist bones and an opposable thumb.
Fragmentary fossil remains of Herrerasaurus were first discovered in the early 1960s, but it was not until 1988, when several skeletons were discovered in the Ischigualasto Formation of northwestern Argentina, that researchers could complete the first picture of the animal.