Herrerasaurus

Herrerasaurus was an early dinosaur from the Triassic of Argentina.

Description
Herrerasaurus is estimated to have measured 3 meters or more in length and up to 350 kilograms in weight. It had a fairly typical theropod body plan, but its skull more resembled those of earlier and more primitive archosaurs.

Classification
Herrerasaurus and its closest relatives form the family Herrerasauridae. However, where the herrerasaurs fit in the early evolutionary tree of dinosaurs is unclear. Most studies have found them to be basal theropods, although it is possible that they are basal saurischians or even non-dinosaurian archosaurs.

Discovery
Incomplete remains of Herrerasaurus were discovered in the Ischigualasto Formation of Argentina, and named in 1963 by paleontologist Osvaldo Reig after the rancher who first noticed the fossils. It was first believed that the remains were from an early type of carnosaur, but over the following years Herrerasaurus was classified on separate occasions as a theropod, a prosauropod, an indeterminate saurischian, and non-dinosaurian.

The next significant discovery of Herrerasaurus fossils was in 1988, when a complete skull was discovered by Paul Sereno and colleagues.

Environment
It is believed that the Ischigualasto Formation was a volcanically active floodplain during the Middle and Late Triassic period when Herrerasaurus lived. The climate was typically warm and moist, although the area experienced seasons throughout the year. Ferns and conifers were likely the dominant vegetation, forming high-altitude forests. It coexisted with the early dinosaur Eoraptor, which was also found in the Ischigualasto Formation.

Diet
Herrerasaurus was a carnivore, and likely preyed on smaller animals. Coprolites found in the Ischigualasto Formation have been assigned as belonging to Herrerasaurus, and if this identification is correct it is evidence that the dinosaur could digest bone.

Pathologies
One specimen of Herrerasaurus exhibits unusual pitting in the skull bones. This has been attributed to an infected head injury that later healed. It is likely that these injuries were obtained during a fight with another Herrerasaurus.