Herrerasauridae (1 ene 233230000 año aC – 1 ene 210000000 año aC)

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Herrerasauridae is a family of carnivorous basal saurischian dinosaurs. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago (Late Triassic), before becoming extinct by the end of the Triassic period. Herrerasaurids were relatively small-sized dinosaurs, normally no more than 4 metres (13 ft) long, although the holotype specimen of "Frenguellisaurus ischigualastensis" (nowadays considered a synonym of Herrerasaurus ischigualastensis) is thought to have reached around 6 meters (20 ft) long. The best known representatives of this group are from South America (Brazil, Argentina), where they were first discovered in the 1930s in relation to Staurikosaurus and 1960s in relation to Herrerasaurus. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete possible herrerasaurids have been found in North America, and they may have inhabited other continents as well. Herrerasaurid anatomy is unusual and specialized, and they are not considered to be ancestral to any later dinosaur group. They only superficially resemble theropods and often present a mixture of very primitive and derived traits. The acetabulum is only partly open, and there are only two sacral vertebrae , the lowest number among dinosaurs. The pubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficially tetanuran-like terminal expansion, especially prominent in H. ischigulastensis. The hand is primitive in having five metacarpals and the third finger longer than the second, but resembles those of theropods in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible, which is also found in theropods.

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