A Triassic Fauna from Madagascar, Including Early Dinosaurs

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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“…For example, Flynn et al (1999) reported two new sauropodomorph dinosaurs from the early Late Triassic of Madagascar.…”

Section: Taxa Often Mistaken As Dinosaursmentioning

confidence: 99%

The origin and early radiation of dinosaurs

Brusatte

Nesbitt

Irmis

et al. 2010

Earth-Science Reviews

243

214

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“…The analysis resulted in 67 most parsimonious trees (MPTs), each having a length of 127 steps (CI 5 0.520, RI 5 0.712, RC 5 0.370). The strict consensus of these MPTs shows that both Trirachodontinae and Sinognathinae are well supported as monophyletic clades, but the two clades ended with Traversodontidae (see Flynn et al, 1999, for a different definition of the family) as a trichotomy in the strict-consensus tree ( fig. 7A).…”

Section: Descriptionmentioning

confidence: 99%

A New Nonmammalian Eucynodont (Synapsida: Therapsida) from the Triassic of Northern Gansu Province, China, and its Biostratigraphic and Biogeographic Implications

Gao¹,

Fox²,

Zhou³

et al. 2010

American Museum Novitates

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A new trirachodontid eucynodont, Beishanodon youngi, is named and described based on a wellpreserved skull from Triassic lacustrine deposits exposed in the Beishan Hills, northern Gansu Province, China. The new discovery documents the second record of trirachodontid eucynodonts known from China, along with Sinognathus gracilis from the Middle Triassic Ermaying Formation exposed in Shanxi Province. Cladistic analysis supports the placement of the new taxon as the sister group of Sinognathus, and the two together can be classified in Sinognathinae, a new subfamily differentiated from other trirachodontids by possession of several derived character states, including extremely short snout and strongly expanded temporal region. In addition, the stratigraphic and biogeographic significance of the new discovery are discussed. Because trirachodontids have a restricted stratigraphic range in the Triassic, as best documented by the Cynognathus Assemblage Zone of South Africa, discovery of the new fossil of this group from northern Gansu Province in China provides definitive evidence for a Triassic age of the fossilbearing beds exposed in the Beishan Hills; moreover, the fossil beds are assessed as Early Triassic in age based on the evidence from the entire vertebrate fauna.

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“…Recently, Flynn et al (1998Flynn et al ( , 1999Flynn et al ( , 2000 reported a rich tetrapod fauna from the base of the 'Isalo II beds' (Makay Formation of Razafimbelo, 1987) in the southern part of the Morondava Basin, southwestern Madagascar, including procolophonids, prosauropod dinosaurs, sphenodontians, dicynodonts, traversodontid cynodonts, 'eosuchians,' and rhynchosaurs. Dicynodonts, procolophonids, traversodontids, and rhynchosaurs occur throughout the mid-late Triassic, whereas sphenodontians and prosauropods in the fauna suggest a Late Triassic age (Lucas, 1998a).…”

Section: Tracing the Ischigualastian Throughout South Pangeamentioning

confidence: 99%

“…Jalil and Knoll, 2002) come from strata that appear coeval with the Ischigualasto Formation. However, Flynn et al (1999Flynn et al ( , 2000 suggest a pre-Ischigualastian age for their Isalo II fauna on the basis of (1) the absence of aetosaurs, (2) the high diversity of traversodontid cynodonts, and (3) the phylogenetic position of the rhynchosaur Isalorhynchus and the traversodontids Dadadon and Menadon.…”

Section: Tracing the Ischigualastian Throughout South Pangeamentioning

confidence: 99%

Studies on continental Late Triassic tetrapod biochronology. II. The Ischigualastian and a Carnian global correlation

Langer

2005

Journal of South American Earth Sciences

100

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The Ischigualastian represents a key land vertebrate faunachron for the correlation of Late Triassic terrestrial deposits worldwide, based on the abundant and diverse tetrapod fauna of the Ischigualasto Formation, NW Argentina. The first appearance data of the rhynchosaur Hyperodapedon and the dicynodont Jachaleria define its lower and upper limits, respectively. Fossil taxa that characterize the Ischigualastian include Hyperodapedon, the cynodont Exaeretodon, the aetosaur Aetosauroides, and herrerasaurid dinosaurs. On the basis of faunal similarities, the Ischigualastian can be traced throughout south Pangea to encompass the fossil assemblages of the Hyperodapedon assemblage zone, Santa Maria Formation, south Brazil; the Pebbly Arkose Formation, Zimbabwe; and the Lower Maleri Formation, India. This correlation contradicts tetrapod-based Late Triassic biochronologies that divide the Carnian epoch into two land vertebrate faunachrons, Otischalkian and Adamanian, on the basis of the succession of faunas in some North American continental sequences. However, the extension of these biochronologic units into south Pangea is based mainly on dubious records of index fossils, the taxonomic status of which are not clearly understood. By reassessing the taxonomic status and distribution of tetrapod taxa, this article defines an updated correlation basis for the Late Triassic of Pangea. q

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A Triassic Fauna from Madagascar, Including Early Dinosaurs

Cited by 74 publications

References 8 publications

The origin and early radiation of dinosaurs

The origin and early radiation of dinosaurs

A New Nonmammalian Eucynodont (Synapsida: Therapsida) from the Triassic of Northern Gansu Province, China, and its Biostratigraphic and Biogeographic Implications

Studies on continental Late Triassic tetrapod biochronology. II. The Ischigualastian and a Carnian global correlation

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