Herrerasaurus 1902021 221740430 2008-06-25T21:48:41Z CommonsDelinker 2304267 Removing "Herreramodel.jpg", it has been deleted from Commons by [[commons:User:MichaelMaggs|MichaelMaggs]] because: per [[w:commons:Commons:Deletion_requests/Image:Herreramodel.jpg]]. {{Taxobox | name = ''Herrerasaurus'' | fossil_range = [[Late Triassic]] | image = Herrerasaurus_BW.jpg | image_width = 250px | image_caption = Artist's restoration of ''Herrerasaurus ischigualastensis'' | regnum = [[Animal]]ia | phylum = [[Chordate|Chordata]] | classis = [[Reptile|Sauropsida]] | superordo = [[Dinosaur]]ia | ordo = [[Saurischia]] | subordo = ?[[Theropoda]] | infraordo = [[Herrerasaur]]ia | familia = [[Herrerasaur]]idae | genus = '''''Herrerasaurus''''' | genus_authority = [[Osvaldo Reig|Reig]], 1963 | subdivision_ranks = [[Species]] | subdivision = * ''H. ischigualastensis'' <small>Reig, 1963 ([[Type species|type]])</small> | synonyms = * ''Ischisaurus'' <small>Reig, 1963</small> * ''Frenguellisaurus'' <small>[[Fernando Novas|Novas]], 1986</small> }} '''''Herrerasaurus''''' (meaning "Herrera's lizard," after the name of the rancher who discovered the first [[fossil]] of the animal) was one of the earliest [[dinosaur]]s. All known specimens of this [[carnivore]] have been discovered in northwest [[Patagonia]], [[Argentina]], in late [[Triassic]] [[Period (geology)|Period]] rocks (early [[Carnian]] [[faunal stage|stage]], around 228&nbsp;[[mya (unit)|million years ago]]). The [[type species]], ''Herrerasaurus ischigualastensis'', was described by [[Osvaldo Reig]] in 1963<ref name="Reig1963"/> and is the only [[species]] assigned to the [[genus]]. For many years, the classification of ''Herrerasaurus'' was unclear, as the animal was initially known from very fragmentary remains; it has been [[hypothesis|hypothesized]] to be a [[basal (phylogenetics)|basal]] [[Theropoda|theropod]], a basal [[sauropodomorpha|sauropodomorph]], a basal [[saurischia]]n, or not a dinosaur at all. However, with the discovery of a mostly-complete skeleton and skull in 1988,<ref name ="Sereno1988">{{cite journal|last=Sereno|first=P.C. |coauthors=Novas, F.E.; Arcucci, A.B.; and C. Yu |year=1988 |title=New evidence on dinosaur and mammal origins from the Ischigualasto Formation (Upper Triassic, Argentina)|journal=Journal of Vertebrate Paleontology |volume=8 |issue=3, supplement |pages=26A}}</ref><ref name ="Sereno1992">{{cite journal |last=Sereno |first=P.C. |coauthors=and Novas, F.E. |title=The complete skull and skeleton of an early dinosaur |journal=Science |volume=258 |year=1992 |pages=1137–1140 |doi=10.1126/science.258.5085.1137 |pmid=17789086}}</ref> ''Herrerasaurus'' has been classified as either an early theropod or an early saurischian in at least five recent surveys of theropod evolution. This medium-sized [[bipedalism|bipedal]] reptile is a member of the [[Herrerasaur]]idae, a group of similar animals which were among the earliest of the dinosaurian [[evolutionary radiation|radiation]]. ==Description== ''Herrerasaurus'' was a lightly-built bipedal carnivore with a long tail and a relatively small head. Its length is estimated at 3 to 6&nbsp;[[metre|meters]] (10 to 20&nbsp;[[foot (unit of length)|ft]]),<ref name ="Sereno1992"/> and its hip height at more than 1.1&nbsp;meters (3.3&nbsp;ft).<ref name=GSP88>{{cite book|last=Paul |first=G.S. |year=1988 |title=Predatory Dinosaurs of the World |location=New York |publisher=Simon and Schuster |pages=248–250 }}</ref> It may have weighed around 210–350&nbsp;[[kilogram]]s (463–772&nbsp;[[pound (mass)|lb]]).<ref name=GSP88/> In a large specimen at first thought to belong to a separate genus, ''Frenguellisaurus'', the skull measured 56&nbsp;[[centimetre|centimeters]] (1.8&nbsp;ft) in length.<ref name=GSP88/> ===Skull=== ''Herrerasaurus'' had a long, narrow [[skull]] that lacked nearly all the specializations that characterized later dinosaurs,<ref name="Sereno1993">{{cite journal|last=Sereno|first=P.C. |coauthors=and Novas, F.E. |year=1993 |title=The skull and neck of the basal theropod ''Herrerasaurus ischigualastensis'' |journal=Journal of Vertebrate Paleontology |volume=13 |pages=451–476}}</ref> being not that different from those of more primitive [[archosaur]]s such as ''[[Euparkeria]]''. It had five pairs of [[fenestrae]] (skull openings) in its skull, two of which were for ocular and nasal openings. Between the eyes and the nostrils were two [[antorbital fenestra]]e and a pair of tiny, 1-centimeter-long (0.4&nbsp;in) slit-like holes called promaxillary fenestrae.<ref name="Sereno07">{{cite journal |last=Sereno |first=P.C. |authorlink= |title=The phylogenetic relationships of early dinosaurs: a comparative report |journal=Historical Biology |volume=19 |issue=1 |pages=145–155 |date=2007 |doi=10.1080/08912960601167435 |id=ISSN 0891-2963 }}</ref> Behind the eyes were large [[Skull#Temporal Fenestra|infratemporal fenestrae]]. These holes helped reduce the weight of the skull. ''Herrerasaurus'' had a flexible joint in the lower jaw; this allowed the animal to slide its lower jaw back and forth and deliver a grasping bite.<ref name="Sereno1993"/> This cranial specialization is unusual among the dinosaurs but has evolved independently in some [[lizard]]s.<ref name="McDowell1954">{{cite journal|last=McDowell|first=S.B., Jr.|coauthors=and C.M. Bogert|year=1954|title=The systematic position of ''Lanthanotus'' and the affinities of the anguinomorphan lizards|journal=Bulletin of the American Museum of Natural History |volume=105 |pages=1–142}}</ref> The rear of the lower jaw also had fenestrae. The jaws were equipped with large serrated teeth for biting and eating flesh, and the neck was slender and flexible.<ref name="Sereno1993"/><ref name="Novas1994">{{cite journal|last=Novas|first=F. E.|year=1994|title=New information on the systematics and postcranial skeleton of ''Herrerasaurus ischigualastensis'' (Theropoda: Herrerasauridae) from the Ischigualasto Formation (Upper Triassic) of Argentina|journal=Journal of Vertebrate Paleontology|volume=13|issue=4|pages=400–423}}</ref> ===Limbs=== ''Herrerasaurus'' had relatively short forelimbs, which were less than half the length of its hind limbs. The [[humerus|upper arm]] and [[radius|forearm]] were rather short, while the [[manus (zoology)|manus]] was elongated. The first two fingers and the thumb bore curved, sharp claws for grasping prey. Its fourth and fifth digits were small stubs without claws.<ref name="Sereno1992"/><ref name="Sereno1993b">{{cite journal|last=Sereno|first=P.C.|year=1993|title=The pectoral girdle and forelimb of the basal theropod ''Herrerasaurus ischigualastensis''|journal=Journal of Vertebrate Paleontology|volume=13 |pages=425–450}}</ref> ''Herrerasaurus'' was bipedal. It had strong hind limbs with short [[femur|thighs]] and rather long feet, indicating this animal was most likely a swift runner. The balancing tail, partially stiffened by overlapping vertebral processes, also indicates an adaptation for speed.<ref name="Langer04">{{cite book |last=Langer |first=Max C. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=25–46 |chapter=Basal Saurischia }}</ref> ===Derived and basal characteristics=== This dinosaur is an enigmatic creature, showing traits that are found in different groups of dinosaurs. Although it shared most of the characteristics of dinosaurs, there were a few differences, particularly in regard to the shape of its hip and leg bones. Its pelvis was similar to that of saurischian dinosaurs, but it had a bony [[acetabulum]] (where the [[femur]] meets the [[pelvis]]) that was only partially open. The [[ilium (bone)|ilium]], the main hip bone, was supported only by two [[sacrum|sacrals]], a [[basal (phylogenetics)|basal]] trait,<ref name="Langer04"/> but the [[pubis (bone)|pubis]] pointed backwards, a [[derived]] trait that parallels what is seen in [[dromaeosaurid]]s and [[bird]]s. Additionally, the end of the pubis had a booted shape, similar to what is present in [[avetheropoda|avetheropods]], and the [[vertebra]]l [[vertebral body|centra]] had an ''[[Allosaurus]]''-like [[hourglass]] shape.<ref name=GSP88/> ==Classification== [[Image:Herrerasaurus_DB.jpg|thumb|''Herrerasaurus''.]]''Herrerasaurus'' gives its name to its family, [[Herrerasaur]]idae, of the mid- to late Triassic, though where it and its close relatives lie on the early dinosaur evolutionary tree is unclear. They are possibly [[Basal (phylogenetics)|basal]] theropods or basal [[saurischian]]s but may in fact predate the [[saurischian]]-[[ornithischian]] split.<ref name="BrinkmanSues"/> Other members of the [[clade]] may include ''[[Eoraptor]]'' from the same [[Ischigualasto|Ischigualasto Formation]] of Argentina as ''Herrerasaurus'', ''[[Staurikosaurus]]'' from the [[Santa Maria Formation]] of southern Brazil,<ref>{{cite journal|last=Colbert|first=E.H.|year=1970|title=A saurischian dinosaur from the Triassic of Brazil|journal=American Museum Novitates|volume=2405|pages=1–39}}</ref> ''[[Chindesaurus]]'' from the Upper [[Petrified Forest]] ([[Chinle Formation]]) of Arizona,<ref>{{cite journal|last=Long|first=R.A.|coauthors=and Murry, P.A.|year=1995|title=Late Triassic (Carnian and Norian) Tetrapods from the Southwestern United States|journal=New Mexico Museum of Natural History and Science, Bulletin '''4'''|pages=1–254}}</ref> and possibly ''[[Caseosaurus]]'' from the [[Dockum Group|Dockum Formation]] of Texas,<ref>{{cite journal|last=Hunt|first=A.P.|coauthors=Lucas, S.G.; Heckert, A.B.; Sullivan, R.M.; and Lockley, M.G.|year=1998|title=Late Triassic Dinosaurs from the Western United States|journal=Geobios|volume=31|issue=4|pages=511–531|doi=10.1016/S0016-6995(98)80123-X}}</ref> 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]],<ref>{{cite journal|last=Chatterjee|first=S.|coauthors=and Creisler, B.S.|year=1994|title=''Alwalkeria'' (Theropoda) and ''Morturneria'' (Plesiosauria), new names for preoccupied ''Walkeria'' Chatterjee, 1987 and ''Turneria'' Chatterjee and Small, 1989|journal=Journal of Vertebrate Paleontology|issue=1|pages=142|unused_data=|volume14}}</ref> and ''[[Teyuwasu]]'', known from very fragmentary remains from the Late Triassic of Brazil, might be related.<ref>{{cite journal|last=Kischlat|first=E.-E.|year=1999|title=A new dinosaurian “rescued” from the Brazilian Triassic: ''Teyuwasu barberenai'', new taxon|journal=1st Simp. Brasil. Pal. Vert, Paleontologia em Destaque|volume=14|issue=26|pages=58}}</ref> Novas (1992) defined the group as ''Herrerasaurus'', ''Staurikosaurus'', and their most common ancestor.<ref name="Novas1992">{{cite journal|last=Novas|first=F. E.|year=1992|title=Phylogenetic relationships of the basal dinosaurs, the Herrerasauridae|journal=Palaeontology|volume=35|pages=51–62}}</ref> Sereno (1998) defined the group as the most inclusive clade including ''H. ischigualastensis'' but not ''[[House Sparrow|Passer domesticus]]''.<ref name=PCS98>{{cite journal |last=Sereno |first=P.C. |year=1998 |title=A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria |journal=Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen |volume=210 |issue=1 |pages=41–83 }}</ref> Langer (2004) created a higher level [[taxon]], infraorder Herrerasauria.<ref name="Langer04"/> ==History== [[Image:Herrerasaurusskeleton.jpg|thumb|left|''Herrerasaurus'' skeleton, North American Museum of Ancient Life.]] ''Herrerasaurus'' was named by [[paleontologist]] Osvaldo Reig after Victorino Herrera, an Andean [[goatherd]] who first noticed its [[fossil]]s in outcrops near the city of San Juan in 1959.<ref name="Reig1963"/> These rocks, which later yielded ''[[Eoraptor]]'',<ref name=Serenoetal1993>{{cite journal|last=Sereno|first=P.C.|coauthors=Forster, C.A.; Rogers, R.R.; and Monetta, A.M.|year=1993|title=Primitive dinosaur skeleton from Argentina and the early evolution of Dinosaurs|journal=Nature|volume=361|issue=6407|pages=64–66|doi=10.1038/361064a0}}</ref> are part of the [[Ischigualasto|Ischigualasto Formation]] and date from the late [[Ladinian]] - early [[Carnian]] stages of the Late [[Triassic]] period.<ref name="Rogers93">{{cite journal|last=Rogers|first=R. R.|coauthors=Swisher III, C.C.; Sereno, P.C.; Monetta, A.M.; Forster, C.A.; and Martinez, R.N. |year=1993|title=The Ischigualasto tetrapod assemblage (Late Triassic, Argentina) and 40Ar/39Ar dating of dinosaur origins|journal=Science|volume=260|pages=794–797|doi=10.1126/science.260.5109.794|pmid=17746113}}</ref> Reig named a second dinosaur from these rocks in the same publication as ''Herrerasaurus'';<ref name="Reig1963"/> this dinosaur, ''Ischisaurus cattoi'', is now considered a [[Synonym (taxonomy)|junior synonym]] and a [[juvenile (organism)|juvenile]] of ''Herrerasaurus''.<ref name="Novas1994"/> Two other partial skeletons, with skull material, were named ''Frenguellisaurus ischigualastensis'' by [[Fernando Novas]] in 1986,<ref>{{cite journal|last=Novas|first=F. E.|year=1986|title=Un probable terópodo (Saurischia) de la Formación Ischigualasto (Triásico superior), San Juan, Argentina|journal=IV Congreso Argentino de Paleontología y Bioestratigrafía, Mendoza, november 23-27|volume=2|pages=1–6}}</ref> but this species too is now thought to be a synonym.<ref name="Novas1994"/> Reig believed ''Herrerasaurus'' was an early example of a [[Carnosauria|carnosaur]],<ref name="Reig1963">{{cite journal|last=Reig|first=O.A.|year=1963|title=La presencia de dinosaurios saurisquios en los "Estratos de Ischigualasto" (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina)|journal= Ameghiniana|volume=3|issue=1|pages=3–20}}</ref> but this was the subject of much debate over the next 30 years, and the genus was variously classified during that time. In 1970, Steel classified ''Herrerasaurus'' as a [[prosauropod]].<ref name="Steel70">{{cite journal|last=Steel|first=R.|year= 1970|title =Part 14. Saurischia. Handbuch der Paläoherpetologie/Encyclopedia of Paleoherpetology|journal= Gustav Fischer Verlag, Stuttgart|pages=1–87}}</ref> In 1972, [[Peter M. Galton]] classified the genus as not diagnosable beyond [[Saurischia]].<ref name="Galton73">{{cite journal|last=Galton|first=P.M.|year=1973|title=On the anatomy and relationships of ''Efraasia diagnostica'' (Huene) n.gen., a prosauropod dinosaur (Reptilia: Saurischia) from the Upper Triassic of Germany.|journal=Paläontologische Zeitschrift|volume=47|issue=3/4|pages=229–255}}</ref> Later, using [[cladistics|cladistic]] analysis, some researchers put ''Herrerasaurus'' and ''Staurikosaurus'' at the base of the dinosaur tree before the separation between ornithischians and saurischians.<ref name="Paul1984">{{cite journal|last=Paul|first=G.S.|year=1984|title=The segnosaurian dinosaurs: relics of the prosauropod-ornithischian transition?|journal=Journal of Vertebrate Paleontology |volume=4|pages=507–515}}</ref><ref name="Novas1989">{{cite journal|last=Novas|first=F. E.|year=1989|title=The tibia and tarsus in Herrerasauridae (Dinosauria, incertae sedis) and the evolution and origin of the dinosaurian tarsus|journal=Journal of Paleontology |volume=63|pages=677–690}}</ref><ref name="Novas1992"/><ref name="BrinkmanSues">{{cite journal|last=Brinkman|first=D.B.|coauthors=and Sues, H.-D.|year=1987|title=A staurikosaurid dinosaur from the Upper Triassic Ischigualasto Formation of Argentina and the relationships of the Staurikosauridae |journal=Palaeontology |volume=30 |pages=493–503}}</ref> Several researchers classified the remains as non-dinosaurian.<ref name="Gauthieretal89">{{Citation| last =Gauthier| first =J.A., Cannatella, D., Queiroz, K., Kluge, A.G., and Rowe, T.| contribution =Tetrapod phylogeny| year =1989| title =The Hierarchy of Life| editor-last =Fernholm| editor-first =K. Bremer, & Jörnvall, H. | volume =| pages =337–353| place=Amsterdam| publisher =Elsevier Science Publishers B. V.| id = }}</ref> [[Image:Herrerasaurus ischigualastensis.jpg|thumb|Skull cast of ''Herrerasaurus ischigualastensis'', Valle de la Luna.]] A complete ''Herrerasaurus'' skull was not found until 1988, by a team of paleontologists led by [[Paul Sereno]].<ref name="Sereno1992"/><ref>{{cite episode|title=The Nature of the Beast |episodelink= |series=The Dinosaurs!|serieslink= |airdate=1990 |season= |number=3}}</ref> Based on the new fossils, authors such as [[Thomas R. Holtz, Jr.|Thomas Holtz]]<ref name="Holtz95">{{cite journal |last=Holtz |first= T.R., Jr.|coauthors= and Padian, K. |year=1995 |title=Definition and diagnosis of Theropoda and related taxa |journal=Journal of Vertebrate Paleontolology |volume=15 |issue=3, supplement |pages=35A }}</ref> and [[Jose Bonaparte]]<ref>{{cite journal|last=Bonaparte |first=J.F. |coauthors=and Pumares, J.A. |year=1995 |title=Notas sobre el primer cráneo de ''Riojasaurus incertus'' (Dinosauria, Prosauropoda, Melanorosauridae) del Triásico superior de La Rioja, Argentina |journal=Ameghiniana |volume=32 |pages=341–349}}</ref> classified ''Herrerasaurus'' at the base of the saurischian tree before the divergence between prosauropods and theropods. However, Sereno favored classifying ''Herrerasaurus'' (and the Herrerasauridae) as primitive theropods. These two classifications have become the most persistent, with Rauhut (2003)<ref name="Rauhut03">{{cite journal |last=Rauhut|first=O.W.M. |title=The interrelationships and evolution of basal theropod dinosaurs |journal=Special Papers in Palaeontology |volume=69 |pages=1–213 |publisher= |date=2003 }}</ref> and Bittencourt and Kellner (2004)<ref name="BittenKellner">{{cite journal| last =Bittencourt| first =J. |coauthors=and Kellner, W.A. |title=The phylogenetic position of ''Staurikosaurus pricei'' from the Triassic of Brazil |journal=Journal of Vertebrate Paleontology |volume=24 |issue=3, supplement |pages=39A |date=2004 |doi=}}</ref> favoring the early theropod [[hypothesis]], and Max Langer (2004),<ref name="Langer04"/> Langer and [[Michael J. Benton|Benton]] (2006),<ref name="LangerBenton06">{{cite journal |last=Langer |first =M.C| coauthors=and Benton, M.J. |title=Early dinosaurs: a phylogenetic study |journal=Journal of Systematic Palaeontology |volume=4 |issue=4 |pages=309–358 |date=2006 |doi=10.1017/S1477201906001970 }}</ref> and Randall Irmis and his coauthors (2007)<ref name=RIetal07>{{cite journal |last=Irmis |first=Randall B. |coauthors=Nesbitt, Sterling J.; Padian, Kevin; Smith, Nathan D.; Turner, Alan H.; Woody, Daniel; and Downs, Alex |year=2007 |title=A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs |journal=Science |volume=317 |pages=358–361 |doi=10.1126/science.1143325 |pmid=17641198}}</ref> favoring the basal saurischian hypothesis. If ''Herrerasaurus'' was indeed a theropod, it would indicate that theropods, [[sauropodomorph]]s, and [[ornithischian]]s diverged even earlier than herrerasaurids, before the middle [[Carnian]] (age of the Ischigualasto Formation), and that "all three lineages independently evolved several dinosaurian features, such as a more advanced ankle joint or an open acetabulum".<ref name="Palaeos">{{cite web |last=White |first=A.T. |coauthors=and Kazlev, M.A. |title=Theropoda: Basal Theropods |publisher=Palaeos.com |date=2003 |url=http://www.palaeos.com/Vertebrates/Units/340Theropoda/340.100.html |accessdate=2007-07-20 }}</ref> This view is further supported by [[ichnology|ichnological]] records showing large tridactyl footprints that can be attributed only to a theropod dinosaur, dating from the [[Ladinian]] (Middle Triassic) of the Los Rastros Formation in Argentina and predating ''Herrerasaurus'' by 3 to 5 million years.<ref>{{cite journal|last=Forster|first=C.A.|coauthors=Arcucci, A.B.; Marsicano, C.A.; Abdala, F.; and May, C.L. |year=1995 |title=New vertebrate material from the Los Rastros Formation (Middle Triassic), La Rioja province, northwestern Argentina|journal=Journal of Vertebrate Paleontology |volume=15 |issue=3, supplement |pages=29A}}</ref><ref>{{cite journal|last=Arcucci|first=A. C.|coauthors=Forster, C.; May, Abdala, F.; and Marsicano, C. |year=1998 |title=Una nueva icnofauna de la Formación Los Rastros, Triásico Medio, en la Quebrada de Ischichuca Chica (Provincia de La Rioja, Argentina) |journal=Acta Geológica Lilloana |volume=18 |pages=152 }}</ref> The importance of ''Herrerasaurus'' and ''Eoraptor'' lies in the fact that their remains allow for directly testing the idea of dinosaurs being a [[monophyly|monophyletic]] group, i.e. all dinosaurs have a common ancestor. The monophyly of dinosaurs was explicitly proposed in the 1970s by Bakker,<ref name="Bakker1974">{{cite journal|last=Bakker|first=R.T.|coauthors=and Galton, P.M.|title=Dinosaur monophyly and a new class of vertebrates |journal=Nature |volume=248 |pages=168–172 |doi=10.1038/248168a0|year=1974 }}</ref><ref name="Bonaparte1976">{{cite journal|last=Bonaparte|first=J. F.|year=1976|title=''Pisanosaurus mertii'' Casimiquela and the origin of the Ornithischia|journal=Journal of Paleontology|volume=50|pages=808–820.}}</ref> and nine cranial and about fifty postcranial [[synapomorphy|synapomorphies]] (common anatomical traits derived from the common ancestor) have been listed. However, an extensive study of ''Herrerasaurus'' by Sereno indicates that only one cranial and seven postcranial synapomorphies in Bakker's original list are actually supported while additional synapomorphies were discovered.<ref name="Sereno1992"/> ==Paleoecology== Although ''Herrerasaurus'' shared the body shape of the large carnivorous dinosaurs, it lived about 230 [[million years ago]], a time when dinosaurs were small and insignificant. It was the time of non-dinosaurian reptiles, not dinosaurs, and a major turning point in the Earth's ecology. The vertebrate fauna of the Ischigualasto Formation and the slightly later [[Los Colorados Formation]] consisted mainly of a variety of [[crurotarsi|crurotarsal]] [[archosaur]]s and [[synapsids]].<ref>{{cite journal|last=Bonaparte|first=J. F.|year=1982|title=Faunal replacement in the Triassic of South America|journal=Journal of Vertebrate Paleontology |volume=2 |pages=362–371 }}</ref><ref name="Bonaparte1979">{{cite journal|last=Bonaparte|first=J.F.|year=1979|title=Faunas y paleobiogeografía de los tetrápodos mesozoicos de América del Sur|journal=Ameghiniana, Revista de la Asociación Paleontológica Argentina|volume=16|issue=3–4|pages=217–238 |language=Spanish}}</ref> For instance, in the Ischigualasto Formation, dinosaurs constituted only about 6% of the total number of fossils.<ref name="CompleteDinosaur">{{Citation| first =Michael J.| last =Benton| author-link =| editor-last =Farlow| editor-first =James O.| editor2-last =Brett-Surman| editor2-first =M.K.| contribution =Origin and early evolution of dinosaurs| contribution-url =http://books.google.com/books?id=FOViD-lDPy0C&pg=PA212&lpg=PA212&dq=%22ischigualasto+formation%22+%226+percent%22&source=web&ots=N7LHhehm_c&sig=6QtMrZaVqjWpW8fNTG8X1rQ_aUc#PPA204,M1| title =The Complete Dinosaur| year =1999| pages =204–215| place =| publisher =Indiana University Press| url =| doi =| isbn =0-253-21313-4}}</ref> By the end of the [[Triassic]] Period, dinosaurs were becoming the dominant large land animals, and the other archosaurs and synapsids lost diversity.<ref name="CompleteDinosaur2">{{Citation| first =J. Michael| last =Parrish| author-link =| editor-last =Farlow| editor-first =James O.| editor2-last =Brett-Surman| editor2-first =M.K.| contribution =Evolution of the archosaurs| contribution-url =http://books.google.com/books?id=FOViD-lDPy0C&pg=PA201&lpg=PA201&dq=archosaur+diversity+decline&source=web&ots=N7LHhejhUf&sig=uy-qcUtW1XVgym8X9s33l6juBLg#PPA201,M1| title =The Complete Dinosaur| year =1999| pages =191–203| place =| publisher =Indiana University Press| url =| doi =| isbn =0-253-21313-4}}</ref> Studies suggest that the [[natural environment|paleoenvironment]] of the Ischigualasto Formation was a volcanically active floodplain covered by forests and subject to strong seasonal rainfalls. Vegetation consisted of [[fern]]s (''[[Cladophlebis]]''), sphenopsids ([[horsetail]]s), and giant [[conifer]]s (''Protojuniperoxylon'').<ref name="Bonaparte1979"/> The plants formed an [[upland (geology)|upland]] [[riparian zone|riparian]] forest.<ref name="Sereno1992"/> ''Herrerasaurus'' remains appear to have been the most common among the carnivores of the Ischigualasto Formation.<ref name = "Rogers93"/> It lived in the jungles of Late Triassic [[South America]] alongside another early dinosaur, ''[[Eoraptor]]'', as well as ''[[Saurosuchus]]'',<ref>{{cite journal|last = Sill|first=W.D.|year=1974 |title=The anatomy of ''Saurosuchus galilei'' and the relationships of the rauisuchid thecodonts |journal=Bulletin of the Museum of Comparative Zoology |volume=146 |pages=317–362 }}</ref> a giant land-living meat-eating [[rauisuchia]]n; ''[[Venaticosuchus]]'', an [[ornithosuchidae|ornithosuchid]]; and the predatory [[chiniquodontidae|chiniquodontid]] [[cynodont]]s.<ref name = "Rogers93"/> Herbivores were much more abundant than carnivores and were represented by [[rhynchosaur]]s such as ''[[Hyperodapedon]]'' (formerly ''[[Scaphonyx]]''); [[aetosaur]]s; [[kannemeyeriidae|kannemeyeriid]] [[dicynodont]]s such as ''[[Ischigualastia]]'', and [[traversodontidae|traversodontid]]s such as ''[[Exaeretodon]]''. These non-dinosaurian herbivores were much more abundant than early ornithischian dinosaurs like ''[[Pisanosaurus]]'' <ref>{{cite journal |last=Bonaparte |first=J.F. |year=1970 |title=Annotated list of the South American Triassic tetrapods |journal=Gondwana Symposium Proceedings and Papers |volume=2 |pages=665–682}}</ref> and therefore more likely prey for ''Herrerasaurus'' than were the early dinosaurs. ==Paleobiology== [[Image:Herrerasaurus .jpg|thumb|''Herrerasaurus'' skull, at the [[Field Museum]] in Chicago.]] The teeth of ''Herrerasaurus'' indicate it was a [[carnivore]]; its size indicates it would have preyed upon small and medium-sized animals. It may have fed on other dinosaurs, such as the [[herbivore|herbivorous]] ''[[Pisanosaurus]]''. However, since ''Herrerasaurus'' lived during an era when other dinosaurs were uncommon, more plentiful prey would have included [[rhynchosaur]]s and [[aetosaur]]s. ''Herrerasaurus'' itself may have been preyed upon by giant [[rauisuchia|rauisuchid]]s like ''[[Saurosuchus]]'', as puncture wounds were found in one skull.<ref name="Sereno1993"/> [[Coprolite]]s (fossilized dung) containing small bones but no trace of plant fragments, discovered in the Ischigualasto Formation, have been assigned to ''Herrerasaurus'' based on fossil abundance. The mineralogical and chemical analysis of these coprolites indicate that the carnivorous animal had the ability to digest bones.<ref>{{cite journal |last=Hollocher |first=K.T. |coauthors=Alcober, O.A.; Colombi, C.E.; and Hollocher, T.C. |title=Carnivore coprolites from the Upper Triassic Ischigualasto Formation, Argentina: chemistry, mineralogy, and evidence for rapid initial mineralization |journal=PALAIOS |year=2005 |volume=20 |pages=51–63 |doi=10.2110/palo.2003.p03-98 }}</ref> <!--Similar studies made on coprolites assigned to a large Cretaceous theropod (most probably ''[[Tyrannosaurus]]'') and concluding to the ability of dinosaurs to dissolve ingested bones, further strengthen the assertion.<ref>{{cite journal | last = Chin | first =K. |coauthors = Tokaryk, T.T., Erickson, G.M., and Calk, L.C. | year = 1998 | title =A king-sized theropod coprolite| journal = Nature | volume = 393 | pages = 680–682 | doi =10.1038/31461}} </ref> Karen's paper said the opposite, that they were passing the bones quickly without digestion--> ==References== {{reflist|2}} ==External links== {{wikibooks|Wikijunior Dinosaurs/Herrerasaurus}} {{Wikispecies|Herrerasaurus}} {{portalpar|Dinosaurs}} * [http://www.ucmp.berkeley.edu/diapsids/herrerasaurus.html Introduction to ''Herrerasaurus''], from the University of California Museum of Paleontology [[Category:Dinosaurs of South America]] [[Category:Saurischians]] [[Category:Triassic dinosaurs]] [[ca:Herrerasaure]] [[cs:Herrerasaurus]] [[de:Herrerasaurus]] [[es:Herrerasaurus]] [[fr:Herrerasaurus]] [[it:Herrerasaurus ischigualastensis]] [[la:Herrerasaurus ischigualastensis]] [[hu:Herrerasaurus]] [[nl:Herrerasaurus]] [[ja:ヘレラサウルス]] [[pl:Herrerazaur]] [[pt:Herrerassauro]] [[ro:Herrerasaurus]] [[ru:Герреразавр]] [[sk:Herrerasaurus]] [[fi:Herrerasaurus]] [[sv:Herrerasaurus]] [[zh:艾雷拉龙]]