Herrerasauridae
| Herrerasaurids Temporal range: Late Triassic,
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| Mounted Herrerasaurus ischigualastensis skeleton cast, at the Field Museum in Chicago | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria (?) |
| Clade: | Saurischia (?) |
| Clade: | †Herrerasauria |
| Family: | †Herrerasauridae Reig, 1963 |
| Genera | |
| Synonyms | |
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Herrerasaurids are among the oldest known dinosaurs, appearing in the fossil record 231.4 million years ago (Late Triassic). They became extinct by the end of the Triassic period. Herrerasaurids were small-sized (not more than 4 metres (13 ft) long) carnivorous theropods[1] or basal saurischians.[2][3] 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 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 clearly theropod in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible like all theropods.
Classification
Where herrerasaurids lie on the early dinosaur evolutionary tree is unclear. They are possibly basal theropods or basal saurischians but may in fact predate the saurischian-ornithischian split.[4] 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,[5] 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.[6] The situation is further complicated by uncertainties in correlating the ages of late Triassic beds bearing land animals.[2]
Other proposed members of the clade have included Sanjuansaurus[7] from the same Ischigualasto Formation of Argentina as Herrerasaurus, Staurikosaurus from the Santa Maria Formation of southern Brazil,[8] Chindesaurus from the Upper Petrified Forest (Chinle Formation) of Arizona,[9] and possibly Caseosaurus from the Dockum Formation of Texas,[10] although the relationships of these animals are not fully understood, and not all paleontologists agree. Other possible basal theropods, Alwalkeria from the Late Triassic Maleri Formation of India,[11] and Teyuwasu, known from very fragmentary remains from the Late Triassic of Brazil, might be related.[12] Novas (1992) defined Herrerasauridae as Herrerasaurus, Staurikosaurus, and their most recent common ancestor.[13] Sereno (1998) defined the group as the most inclusive clade including H. ischigualastensis but not Passer domesticus.[14] Langer (2004) provided first phylogenetic definition of a higher level taxon, infraorder Herrerasauria.[2]
Phylogeny
The first cladogram presented here follows one proposed analysis by M.D. Ezcurra in 2010. In this review, Herrerasaurus is a primitive saurischian, but not a theropod.[6] The second cladogram is based on an analysis by M.J. Benton, in 2004. This review indicated Herrerasaurus was a basal theropod.[15]
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References
- ^ Nesbitt, S. J., Smith, N. D., Irmis, R. B., Turner, A. H., Downs, A., and M. A. Norell. (2009). "A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs." Science 326:1530-1533.
- ^ a b c Langer, Max C. (2004). "Basal Saurischia". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.) (ed.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 25–46. ISBN 0-520-24209-2.
{{cite book}}:|editor=has generic name (help)CS1 maint: multiple names: editors list (link) - ^ Langer, M.C (2006). "Early dinosaurs: a phylogenetic study". Journal of Systematic Palaeontology. 4 (4): 309–358. doi:10.1017/S1477201906001970.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Brinkman, D.B. (1987). "A staurikosaurid dinosaur from the Upper Triassic Ischigualasto Formation of Argentina and the relationships of the Staurikosauridae". Palaeontology. 30: 493–503.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Nesbitt, S. J.; Smith, N. D.; Irmis, R. B.; Turner, A. H.; Downs, A.; Norell, M. A. (2009). "A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs". Science. 326 (5959): 1530–1533. doi:10.1126/science.1180350. PMID 20007898.
{{cite journal}}: Unknown parameter|lastauthoramp=ignored (|name-list-style=suggested) (help) - ^ a b Ezcurra, M.D. (2010). "A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny." Journal of Systematic Palaeontology, 8: 371-425.
- ^ Alcober, Oscar A. (2010). "A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina". ZooKeys. 63: 55–81. doi:10.3897/zookeys.63.550.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)CS1 maint: unflagged free DOI (link) - ^ Colbert, E.H. (1970). "A saurischian dinosaur from the Triassic of Brazil". American Museum Novitates. 2405: 1–39.
- ^ Long, R.A. (1995). "Late Triassic (Carnian and Norian) Tetrapods from the Southwestern United States". New Mexico Museum of Natural History and Science, Bulletin 4: 1–254.
{{cite journal}}: Italic or bold markup not allowed in:|journal=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Hunt, A.P. (1998). "Late Triassic Dinosaurs from the Western United States". Geobios. 31 (4): 511–531. doi:10.1016/S0016-6995(98)80123-X.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Chatterjee, S. (1994). "Alwalkeria (Theropoda) and Morturneria (Plesiosauria), new names for preoccupied Walkeria Chatterjee, 1987 and Turneria Chatterjee and Small, 1989". Journal of Vertebrate Paleontology. 14 (1): 142.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Kischlat, E.-E. (1999). "A new dinosaurian "rescued" from the Brazilian Triassic: Teyuwasu barberenai, new taxon". 1st Simp. Brasil. Pal. Vert, Paleontologia em Destaque. 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.
- ^ Benton, Michael J. (2004). "Origin and relationships of Dinosauria". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.) (ed.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 7–19. ISBN 0-520-24209-2.
{{cite book}}:|editor=has generic name (help)CS1 maint: multiple names: editors list (link)
