Herrerasauridae is an extinctfamily ofcarnivorousdinosaurs, possiblybasal to eithertheropods or even all ofsaurischians, or even their own branching fromDracohors, separate from Dinosauria altogether. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago (theCarnian stage of theLate Triassic),[2] before becoming extinct by the end of the Carnian stage. Herrerasaurids were relatively small-sized dinosaurs, normally no more than 4 metres (13 ft) long,[3][4] although the holotype specimen of "Frenguellisaurus ischigualastensis" (nowadays considered a synonym ofHerrerasaurus ischigualastensis) is thought to have reached around 6 meters (20 ft) long. The best known representatives of this group are fromSouth America (Brazil,Argentina), where they were first discovered in the 1930s in relation toStaurikosaurus and 1960s in relation toHerrerasaurus. A nearly complete skeleton ofHerrerasaurus ischigualastensis was discovered in theIschigualasto Formation inSan Juan, Argentina, in 1988. Less complete possible herrerasaurids have been found inNorth America andAfrica, 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 resembletheropods and often present a mixture of very primitive and derived traits. Theacetabulum is only partly open, and there are only twosacral vertebrae, the lowest number among dinosaurs. Thepubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficiallytetanuran-like terminal expansion, especially prominent inH. ischigulastensis. The hand is primitive in having fivemetacarpals 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 hingedmandible, which is also found in theropods.
It is not clear where herrerasaurids lie on the early dinosaur evolutionary tree. They are possibly basal theropods or basal saurischians.[5] Early researchers even proposed that they represented an early lineage ofsauropodomorphs. Some analyses, such as Nesbittet al. 2009, have foundHerrerasaurus and its relatives in Herrerasauridae to be very basal theropods,[6] while others (such as Ezcurra 2010) have found them to be basal to the cladeEusaurischia, that is, closer to the base of the saurischian tree than either theropods or sauropodomorphs, but not true members of either.[7] The situation is further complicated by uncertainties in correlating the ages of late Triassic beds bearing land animals.[3]
The discovery of the HerrerasauridGnathovorax indicates that the family falls outside theTheropoda andSauropodomorpha in the cladistic analysis undertaken on the genus when it was described, but remains squarely withinSaurischia as basal members of the order.[18][19] An unnamed herrerasaurid from theCarnian of Brazil was described and possibly belongs to a new morphotype of relatively large proportions, informally known as the "BigSaturnalia". In the phylogenetic analysis within this study, herrerasaurids are recovered as non-eusaurischiansaurischians.[20]
Fernando Novas (1992) defined Herrerasauridae asHerrerasaurus,Staurikosaurus, and their most recent common ancestor.[21]Paul Sereno (1998) defined the group as the most inclusive clade includingH. ischigualastensis but notPasser domesticus.[22] Langer (2004) provided first phylogenetic definition of a higher leveltaxon,Herrerasauria, asHerrerasaurus but notLiliensternus orPlateosaurus.[3] According to current phylogenetic studies, all of these definitions describe the same clade.
The firstcladogram presented follows one proposed analysis by Novaset al. in May 2011. In this review,Herrerasaurus is found to be a basal saurischian, but not a theropod.[23] The second cladogram is based on an analysis by Sueset al. in April 2011. This review classifiedHerrerasaurus as a basal theropod.[24]
Baron & Williams (2018) found Herrerasauria (includingDaemonosaurus,Caseosaurus andSaltopus) outside Dinosauria.[12] A similar result was provided by the phylogenetic analysis by Cau, 2018:[27]
Novas et al., 2021 revised the fossil record ofSouth American early dinosaurs and supported that Herrerasauria is part ofSaurischia but diverging earlier than bothSauropodomorpha orTheropoda, and further corroborated with the hypothesis thatChindesaurus,Daemonosaurus andTawa are members of the clade.[28] In 2024, Andrea Cau reclassified Herrerasauria within Theropoda.[29]
^Griffin, C. T.; Wynd, B. M.; Munyikwa, D.; Broderick, T. J.; Zondo, M.; Tolan, S.; Langer, M. C.; Nesbitt, S.J.; Taruvinga, H. R. (2022). "Africa's oldest dinosaurs reveal early suppression of dinosaur distribution".Nature.609 (7926):313–319.Bibcode:2022Natur.609..313G.doi:10.1038/s41586-022-05133-x.PMID36045297.S2CID251977824.
^Garcia, Maurício S.; Müller, Rodrigo T.; Dias-Da-Silva, Sérgio (2019-07-04). "On the taxonomic status of Teyuwasu barberenai Kischlat, 1999 (Archosauria: Dinosauriformes), a challenging taxon from the Upper Triassic of southern Brazil".Zootaxa.4629 (1):146–150.doi:10.11646/zootaxa.4629.1.12.ISSN1175-5334.PMID31712541.S2CID198274900.
^Kischlat, E.-E. (1999). "A new dinosaurian "rescued" from the Brazilian Triassic:Teyuwasu barberenai, new taxon".Paleontologia Em Destaque, Boletim Informativo da Sociedade Brasileira de Paleontologia.14 (26): 58.
^Novas, F. E. (1992). "Phylogenetic relationships of the basal dinosaurs, the Herrerasauridae".Palaeontology.35:51–62.
^Sereno, P. C. (1998). "A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria".Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen.210 (1):41–83.doi:10.1127/njgpa/210/1998/41.
^Novas, Fernando E.; Ezcurra, Martin D.; Chatterjee, Sankar; Kutty, T. S. (2011). "New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of central India".Earth and Environmental Science Transactions of the Royal Society of Edinburgh.101 (3–4):333–349.Bibcode:2010EESTR.101..333N.doi:10.1017/S1755691011020093.S2CID128620874.
^Garcia, M. S.; Müller, R. T.; Pretto, F. A.; Da-Rosa, Á. A. S.; Dias-Da-Silva, S. (2021). "Taxonomic and phylogenetic reassessment of a large-bodied dinosaur from the earliest dinosaur-bearing beds (Carnian, Upper Triassic) from southern Brazil".Journal of Systematic Palaeontology.19:1–37.Bibcode:2021JSPal..19....1G.doi:10.1080/14772019.2021.1873433.S2CID232313141.
