Dinosaurs are animals that dominated
terrestrial environments for more than 160 million years, first appearing approximately 230
million years ago. They were extremely varied, abundant and have been found preserved on all seven modern continents. At the end of the
Cretaceous Period, approximately 65 million years ago, a catastrophic
extinction event ended the dinosaurs' dominance on land. However, since birds are
theropods the clade dinosauria still survives in great diversity and abundance. The term "dinosaur" is sometimes used mistakenly to describe other prehistoric animals, such as the synapsid
Dimetrodon, or reptiles like
pterosaurs,
ichthyosaurs,
plesiosaurs and
mosasaurs. Since the first dinosaur
fossils were recognized in the nineteenth century, mounted dinosaur skeletons have become major attractions at
museums around the world and have amassed a large fan base among children and adults alike. They have been featured in best-selling
books and
films such as
Jurassic Park, and new discoveries are regularly covered by the
media.
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Herrerasaurus (meaning 'Herrera's lizard', after the name of the rancher who discovered the first
fossil of the animal) was one of the earliest
dinosaurs. All known specimens of this
carnivore have been discovered in rocks of late
Ladinian age (middle
Triassic according to the
ICS, dated to 231.4
million years ago) in northwestern Argentina. The
type species,
Herrerasaurus ischigualastensis, was described by
Osvaldo Reig in 1963 and is the only
species assigned to the
genus. The names
Ischisaurus and
Frenguellisaurus are
synonymous with
Herrerasaurus.
For many years, the classification of Herrerasaurus was unclear, as the animal was initially known from very fragmentary remains; it has been hypothesized to be a basal theropod, a basal sauropodomorph, a basal saurischian, or not a dinosaur at all. However, with the discovery of a mostly complete skeleton and skull in 1988, Herrerasaurus has been classified as either an early theropod or an early saurischian in at least five recent reviews of theropod evolution. It was a member of the Herrerasauridae, a group of similar animals which were among the earliest of the dinosaurian evolutionary radiation. (see more...)
