Early ornithischian dinosaurs: the Triassic record

Irmis, Randall B.; Parker, William G.; Nesbitt, Sterling J.; Liu, Jun

doi:10.1080/08912960600719988

Cited by 135 publications

(263 citation statements)

References 47 publications

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“…Taken together, these data indicate that the formation spans the Carnian-Norian boundary. Therefore, the oldest dinosaurs from the Ischigualasto Formation are late Carnian in age, not early Carnian as previously reported (e.g., Rogers et al, 1993;Martinez and Alcober, 2009), and some Ischigualasto dinosaurs, notably Pisanosaurus, may be Norian in age (Irmis et al, 2007b;Langer et al, 2010).…”

Section: Dating the Origin Of Dinosaursmentioning

confidence: 54%

“…Sereno (1991b) suggested that the holotype was a chimera of at least two taxa, but there seems to be little basis for this proposal (Irmis et al, 2007b). The phylogenetic position of Pisanosaurus is highly controversial: it has been identified as the most basal known ornithischian (Sereno, 1991b(Sereno, , 1999Butler, 2005;Irmis et al, 2007a;Butler et al, 2008a), or as a possible heterodontosaurid (Bonaparte, 1976), and even its ornithischian affinities have been questioned (Thulborn, 2006;Irmis et al, 2007b).…”

Section: Late Triassic Ornithischians -Fossil Record and Distributionmentioning

confidence: 99%

“…The phylogenetic position of Pisanosaurus is highly controversial: it has been identified as the most basal known ornithischian (Sereno, 1991b(Sereno, , 1999Butler, 2005;Irmis et al, 2007a;Butler et al, 2008a), or as a possible heterodontosaurid (Bonaparte, 1976), and even its ornithischian affinities have been questioned (Thulborn, 2006;Irmis et al, 2007b). This uncertainty results from character conflict in the holotype: cranial material shares derived character states with ornithischians and specifically heterodontosaurids (e.g., the degree and pattern of occlusal wear facets) whereas the postcranial skeleton contains numerous plesiomorphic character states, including possibly an anteriorly directed pubis (seen in no other ornithischian: e.g., Sereno, 1986Sereno, , 1999Butler et al, 2008a; but see Irmis et al, 2007b).…”

Section: Late Triassic Ornithischians -Fossil Record and Distributionmentioning

confidence: 99%

“…In combination, these two discoveries prompted a comprehensive reassessment of the Late Triassic ornithischian record (Irmis et al, 2007b; see also Butler et al, 2006a), which is summarized in Table 2. Following this reassessment, only three Late Triassic body fossil specimens are currently considered ornithischian, and all are from a relatively small geographical area in southern Gondwana.…”

Section: Late Triassic Ornithischians -Fossil Record and Distributionmentioning

confidence: 99%

“…Reanalysis of existing specimens has improved our understanding of character evolution on the lineage leading to Dinosauria (e.g., Sereno and Arcucci, 1994a,b;Langer and Benton, 2006;Brusatte et al, 2010b) and has changed our understanding of the distribution of early dinosaurs in time and space (Parker et al, 2005;Irmis et al, 2007b;Nesbitt et al, 2007). Most recently, quantitative analyses, which take into account this avalanche of new morphological and geological data, have examined in unprecedented detail the macroevolutionary, biogeographical, and paleoecological changes associated with the rise of dinosaurs (e.g., Brusatte et al, 2008a,b;Nesbitt et al, 2009bNesbitt et al, , 2010.…”

Section: Introductionmentioning

confidence: 99%

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The origin and early radiation of dinosaurs

Brusatte

Nesbitt

Irmis

et al. 2010

Earth-Science Reviews

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243

214

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Dinosaurs were remarkably successful during the Mesozoic and one subgroup, birds, remain an important component of modern ecosystems. Although the extinction of non-avian dinosaurs at the end of the Cretaceous has been the subject of intense debate, comparatively little attention has been given to the origin and early evolution of dinosaurs during the Late Triassic and Early Jurassic, one of the most important evolutionary radiations in earth history. Our understanding of this keystone event has dramatically changed over the past 25 years, thanks to an influx of new fossil discoveries, reinterpretations of long-ignored specimens, and quantitative macroevolutionary analyses that synthesize anatomical and geological data. Here we provide an overview of the first 50 million years of dinosaur history, with a focus on the large-scale patterns that characterize the ascent of dinosaurs from a small, almost marginal group of reptiles in the Late Triassic to the preeminent terrestrial vertebrates of the Jurassic and Cretaceous. We provide both a biological and geological background for early dinosaur history. Dinosaurs are deeply nested among the archosaurian reptiles, diagnosed by only a small number of characters, and are subdivided into a number of major lineages. The first unequivocal dinosaurs are known from the late Carnian of South America, but the presence of their sister group in the Middle Triassic implies that dinosaurs possibly originated much earlier. The three major dinosaur lineages, theropods, sauropodomorphs, and ornithischians, are all known from the Triassic, when continents were joined into the supercontinent Pangaea and global climates were hot and arid. Although many researchers have long suggested that dinosaurs outcompeted other reptile groups during the Triassic, we argue that the ascent of dinosaurs was more of a matter of contingency and opportunism. Dinosaurs were overshadowed in most Late Triassic ecosystems by crocodile-line archosaurs and showed no signs of outcompeting their rivals. Instead, the rise of dinosaurs was a two-stage process, as dinosaurs expanded in taxonomic diversity, morphological disparity, and absolute faunal abundance only after the extinction of most crocodile-line reptiles and other groups.

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Section: Dating the Origin Of Dinosaursmentioning

confidence: 54%

Section: Late Triassic Ornithischians -Fossil Record and Distributionmentioning

confidence: 99%

Section: Late Triassic Ornithischians -Fossil Record and Distributionmentioning

confidence: 99%

Section: Late Triassic Ornithischians -Fossil Record and Distributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The origin and early radiation of dinosaurs

Brusatte

Nesbitt

Irmis

et al. 2010

Earth-Science Reviews

Self Cite

243

214

View full text Add to dashboard Cite

show abstract

References

2012

Dinosaur Paleobiology

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Morphological Diversity and Evolution of the Jugal in Dinosaurs

Sullivan

2016

The Anatomical Record

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In dinosaurs, as in other reptiles, the homologue of the mammalian zygomatic bone is the jugal. The dinosaurian jugal was primitively triradiate, with posterior, dorsal and anterior processes that respectively contacted the quadratojugal, the postorbital, and the maxilla and lacrimal. However, the jugal evolved along different lines in the three major dinosaurian clades. In theropods this cranial element remained relatively conservative in morphology, apart from being reduced to a rod-like structure in most birds and a few non-avians. In sauropodomorphs the jugal eventually became small, plate-like and nearly restricted to the area below the orbit, even being excluded from the ventral margin of the skull in many derived taxa. Among ornithischians the jugal was highly variable, but in many cases became large and/or adorned with ornamental features such as horns, flanges, and rugosities. The jugal does not appear to have been a site of muscle attachment in most non-avian dinosaurs, but represented an important structural element in the akinetic dinosaurian skull. The conspicuous jugal ornaments seen in many ornithischian dinosaurs, like the less striking ones documented in some saurischians, may have played an important role in the social behavior of the species that possessed them. In many cases they have a weapon-like aspect suggesting use in aggressive displays, if not actual combat, adding to the evidence that agonistic behavior was likely widespread among ornithischians in particular. Anat Rec,

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Early ornithischian dinosaurs: the Triassic record

Cited by 135 publications

References 47 publications

The origin and early radiation of dinosaurs

The origin and early radiation of dinosaurs

References

Morphological Diversity and Evolution of the Jugal in Dinosaurs

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