Paleobiology
The teeth of Herrerasaurus indicate that it was a carnivore; its size indicates it would have preyed upon small and medium-sized plant eaters. These might have included other dinosaurs, such as Pisanosaurus, as well as the more plentiful rhynchosaurs and synapsids. Herrerasaurus itself may have been preyed upon by giant rauisuchids like Saurosuchus; puncture wounds were found in one skull.
Coprolites (fossilized dung) containing small bones but no trace of plant fragments, discovered in the Ischigualasto Formation, have been assigned to Herrerasaurus based on fossil abundance. Mineralogical and chemical analysis of these coprolites indicates that if the referral to Herrerasaurus was correct, this carnivore could digest bone.
Comparisons between the scleral rings of Herrerasaurus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals.
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