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 not more than 4 metres (13 ft) long. The best known representatives of this group are from South America (Brazil, Argentina), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete 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.
|Mounted Herrerasaurus ischigualastensis skeleton cast, at the Field Museum of Natural History in Chicago.|
It is not clear where Herrerasaurids lie on the early dinosaur evolutionary tree. They are possibly basal theropods or basal saurischians but may predate the saurischian-ornithischian split. Early researchers even proposed that they represented an early lineage of sauropodomorphs. Some analyses, such as Nesbitt et al. 2009, have found Herrerasaurus and its relatives in Herrerasauridae to be very basal theropods, while others (such as Ezcurra 2010) have found them to be basal to the clade Eusaurischia, that is, closer to the base of the saurischian tree than either theropods or sauropodomorphs, but not true members of either. The situation is further complicated by uncertainties in correlating the ages of late Triassic beds bearing land animals.
Other proposed members of the clade have included Sanjuansaurus from the Ischigualasto Formation of Argentina, Staurikosaurus from the Santa Maria Formation of southern Brazil, Chindesaurus from the Petrified Forest (Chinle Formation) of Arizona, and possibly Caseosaurus from the Dockum Formation of Texas, although the relationships of these animals are not fully understood, and not all paleontologists agree. Grzegorz Niedźwiedzki, Stephen L. Brusatte et al. (2014) described a European member of the group on the basis of Norian age fossils discovered in Poland. Other possible basal saurischians include Alwalkeria from the Late Triassic Maleri Formation of southern India, and Teyuwasu, known from very fragmentary remains from the Late Triassic of Brazil.
Fernando Novas (1992) defined Herrerasauridae as Herrerasaurus, Staurikosaurus, and their most recent common ancestor. Paul Sereno (1998) defined the group as the most inclusive clade including H. ischigualastensis but not Passer domesticus. Langer (2004) provided first phylogenetic definition of a higher level taxon, Herrerasauria, as Herrerasaurus but not Liliensternus or Plateosaurus. According to current phylogenetic studies, all of these definitions describe the same clade.
The first cladogram presented follows one proposed analysis by Novas et al. in May 2011. In this review, Herrerasaurus is found to be a basal saurischian, but not a theropod. The second cladogram is based on an analysis by Sues et al. in April 2011. This review classified Herrerasaurus as a basal theropod.
A large phylogenetic analysis of early dinosaurs by Matthew Baron, David Norman and Paul Barrett (2017) found Herrerasauridae within the clade Saurischia, as the sister group to Sauropodomorpha. This was the result of the removal of Theropoda from Saurischia and its placement next to Ornithischia within the newly created clade Ornithoscelida.
A phylogenetic analysis including Herrerasaurids after Cau, 2018:
Alwalkeria (; "for Alick Walker") is a genus of basal saurischian dinosaur from the Late Triassic, living in India. It was a small bipedal omnivore.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Caseosaurus
Caseosaurus ( KAY-zee-o-SAWR-əs) is a dubious genus of herrerasaurid theropod dinosaur that lived approximately 235 to 228 million years ago during the latter part of the Triassic Period in what is now Texas, in North America. Caseosaurus was a small, lightly-built, bipedal, ground-dwelling carnivore, that could grow up to 2 m (6.6 ft) long.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Chilesaurus
Chilesaurus is an extinct genus of herbivorous dinosaur. The type and only species is Chilesaurus diegosuarezi. Chilesaurus lived about 145 million years ago (Mya) in the Late Jurassic period of Chile. Showing a combination of traits from theropods, ornithischians, and sauropodomorphs, this genus has far-reaching implications for the evolution of dinosaurs, such as whether the traditional saurischian-ornithischian split is superior or inferior to the newly proposed group Ornithoscelida.Chindesaurus
Chindesaurus ( CHIN-di-SAWR-əs) is a genus of herrerasaurid dinosaur that lived approximately 235-210 million years ago during the latter part of the Triassic Period in what is now the Southwestern United States. Chindesaurus was a small, bipedal carnivore that could grow up to 2 to 2.3 m (6.6 to 7.5 ft) long.Dinosaur classification
Dinosaur classification began in 1842 when Sir Richard Owen placed Iguanodon, Megalosaurus, and Hylaeosaurus in "a distinct tribe or suborder of Saurian Reptiles, for which I would propose the name of Dinosauria." In 1887 and 1888 Harry Seeley divided dinosaurs into the two orders Saurischia and Ornithischia, based on their hip structure. These divisions have proved remarkably enduring, even through several seismic changes in the taxonomy of dinosaurs.
The largest change was prompted by entomologist Willi Hennig's work in the 1950s, which evolved into modern cladistics. For specimens known only from fossils, the rigorous analysis of characters to determine evolutionary relationships between different groups of animals (clades) proved incredibly useful. When computer-based analysis using cladistics came into its own in the 1990s, paleontologists became among the first zoologists to almost wholeheartedly adopt the system. Progressive scrutiny and work upon dinosaurian interrelationships, with the aid of new discoveries that have shed light on previously uncertain relationships between taxa, have begun to yield a stabilizing classification since the mid-2000s. While cladistics is the predominant classificatory system among paleontology professionals, the Linnean system is still in use, especially in works intended for popular distribution.Eucnemesaurus
Eucnemesaurus (; meaning "good tibia lizard", for its robust tibiae) is a basal sauropodomorph dinosaur genus usually considered to be a synonym of Euskelosaurus. Recent study by Yates (2006), however, indicates that it is valid and the same animal as putative "giant herrerasaurid" Aliwalia.
Eucnemesaurus was named in 1920 by Egbert Cornelis Nicolaas van Hoepen. The type species is Eucnemesaurus fortis. The specific name means "strong" in Latin. It is based on holotype TrM 119, a partial skeleton including vertebrae, part of a pubis, a femur, and two tibiae. The remains were found by Van Hoepen in the late Carnian-early Norian-age Upper Triassic Lower Elliot Formation of the Slabberts district, Orange Free State, South Africa.
Yates assigned the genus to the new family Riojasauridae, with Riojasaurus, usually regarded as a melanorosaurid.Herrerasaurus
Herrerasaurus was one of the earliest dinosaurs. Its name means "Herrera's lizard", after the rancher who discovered the first specimen. All known fossils of this carnivore have been discovered in the Ischigualasto Formation of Carnian age (late 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. Ischisaurus and Frenguellisaurus are synonyms.
For many years, the classification of Herrerasaurus was unclear because it was known from very fragmentary remains. It was hypothesized to be a basal theropod, a basal sauropodomorph, a basal saurischian, or not a dinosaur at all but another type of archosaur. However, with the discovery of an almost 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, with many researchers treating it at least tentatively as the most primitive member of Theropoda.It is a member of the Herrerasauridae, a family of similar genera that were among the earliest of the dinosaurian evolutionary radiation.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Pseudolagosuchus
Pseudolagosuchus (meaning "false Lagosuchus") is a genus of dinosauromorph from the Middle Triassic (Ladinian) Chañares Formation of Argentina. It may be a junior synonym of Lewisuchus, but there is very little overlapping material. It was a small reptile which was probably about 1 meter (3.3 ft) long, 30 centimeters (1 ft) tall, and weighed approximately 2 kilograms (4.4 lb). It is known only from a pubis, a femur, a tibia, and vertebrae. Both Sterling Nesbitt, Christian Sidor et al. (2010) and Matthew Baron, David Norman and Paul Barrett (2017) treated this taxon as being synonymous with Lewisuchus.Sanjuansaurus
Sanjuansaurus ("San Juan Province lizard") is a genus of herrerasaurid dinosaur from the Late Triassic (Carnian) Cancha de Bochas and La Peña Members of the Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina.Saurischia
Saurischia ( saw-RIS-kee-ə, meaning "reptile-hipped" from the Greek sauros (σαῦρος) meaning 'lizard' and ischion (ἴσχιον) meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia). ‘Saurischia’ translates to lizard-hipped.
In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure, though today most paleontologists classify Saurischia as an unranked clade rather than an order.Sauropodomorpha
Sauropodomorpha ( SOR-ə-POD-ə-MOR-fə; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The "prosauropods", which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic (approximately 230 Ma) until their decline and extinction at the end of the Cretaceous (approximately 66 Ma).Staurikosaurus
Staurikosaurus (Pronounced "STORE-ee-koh-SAWR-us", "Southern Cross lizard") is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.