REVISION OF THE ARCHOSAUROMORPH REPTILE <i>TRILOPHOSAURUS</i>, WITH A DESCRIPTION OF THE FIRST SKULL OF <i>TRILOPHOSAURUS JACOBSI</i>, FROM THE UPPER TRIASSIC CHINLE GROUP, WEST TEXAS, USA

Heckert, Andrew B.; Lucas, Spencer G.; Rinehart, Larry F.; Spielmann, Justin A.; Hunt, Adrian P.; Kahle, Robert

doi:10.1111/j.1475-4983.2006.00556.x

Cited by 30 publications

(39 citation statements)

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“…In addition, a downturned dentary and specialized transversely lophate, tricuspid teeth in Trilophosaurus (e.g. Case 1928; Gregory 1945; Heckert et al. 2006), a variety of features indicative of herbivory occurring in rhynchosaurs (e.g.…”

Section: Discussionmentioning

confidence: 99%

A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible

et al. 2010

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Here, we describe a new species of Azendohsaurus from the Middle-Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle-Late Triassic (or even later), 'leafshaped' teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occurs in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.

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Section: Discussionmentioning

confidence: 99%

A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible

et al. 2010

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“…1 and 2). Additionally, although size is often used as a proxy for degree of skeletal maturity in many studies (20,24,(34)(35)(36)(37)(38)(39)(40)(41), size correlates poorly with morphological maturity, as quantified by maturity score in OSA, even though OSA may reconstruct missing data as present and thus raise the maturity score higher than a strict scoring of the individual would give (Figs. 1 and 2).…”

Section: Discussionmentioning

confidence: 99%

Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds

Griffin

Nesbitt

2016

Proc. Natl. Acad. Sci. U.S.A.

127

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Compared with all other living reptiles, birds grow extremely fast and possess unusually low levels of intraspecific variation during postnatal development. It is now clear that birds inherited their high rates of growth from their dinosaurian ancestors, but the origin of the avian condition of low variation during development is poorly constrained. The most well-understood growth trajectories of later Mesozoic theropods (e.g., Tyrannosaurus, Allosaurus) show similarly low variation to birds, contrasting with higher variation in extant crocodylians. Here, we show that deep within Dinosauria, among the earliest-diverging dinosaurs, anomalously high intraspecific variation is widespread but then is lost in more derived theropods. This style of development is ancestral for dinosaurs and their closest relatives, and, surprisingly, this level of variation is far higher than in living crocodylians. Among early dinosaurs, this variation is widespread across Pangaea in the Triassic and Early Jurassic, and among early-diverging theropods (ceratosaurs), this variation is maintained for 165 million years to the end of the Cretaceous. Because the Late Triassic environment across Pangaea was volatile and heterogeneous, this variation may have contributed to the rise of dinosaurian dominance through the end of the Triassic Period.I n comparison with other reptiles, avian biology is highly unusual, characterized by "hollow" bones and postcranial skeletal pneumaticity, feathers, a unique forelimb digit formula, endothermy, and rapid growth rates. However, these peculiarities initially arose in nonavian dinosaurs (1-7) in a gradual process occurring over tens of millions of years (8,9). In addition to their extremely rapid rates of growth, avian ontogeny possesses a characteristically low level of morphological variation within a species relative to that of other reptiles. The majority of individuals in a given avian species undergoes the same morphological changes during ontogeny in the same order at similar body sizes (10, 11), whereas their closest living relatives, crocodylians, possess higher variation (10,(12)(13)(14). How and when this feature of avian biology evolved is poorly constrained.This avian style of development must have evolved after its most recent common ancestor with crocodylians but before the origin of Aves. Most studies of the ontogeny of more-derived theropods (15-17) suggest that the low levels of variation that characterize avian ontogeny were present in close nonavian relatives as well. Closer to the origin of Dinosauria, morphological variation within species is widespread (18-26), but whether this variation is the result of taxonomic diversity, ontogeny, sexual dimorphism, or simple individual variation is not clear (22,23,27). Furthermore, close dinosaurian relatives or "dinosaur precursors" (e.g., Silesaurus, Asilisaurus) possess high intraspecific variation in growth sequences [i.e., sequence polymorphism (28)], suggesting that this condition could be ancestral for Dinosauria (21).In contrast to ...

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“…This opening is evidently an upper temporal (supratemporal) fenestra, and the temporal configuration could thus be described as euryapsid. Only two other euryapsid archosauromorph reptiles are known from the Late Triassic: Trilophosaurus Case, 1928 from the Dockum Group (CarnianNorian) of Texas and the Chinle Formation of Arizona (Gregory, 1945;Long and Murry, 1995;Heckert et al, 2006;Mueller and Parker, 2006) and Teraterpeton Sues, 2003 from the Wolfville Formation (Carnian) of the Fundy basin (Newark Supergroup) in Nova Scotia. Unlike the large temporal openings of Trilophosaurus and Teraterpeton, the supratemporal fenestrae of Doswellia are small and do not extend posteriorly beyond the occipital condyles.…”

Section: Skullmentioning

confidence: 98%

Redescription and phylogenetic relationships ofDoswellia kaltenbachi(Diapsida: Archosauriformes) from the Upper Triassic of Virginia

Dilkes¹,

Sues

2009

Journal of Vertebrate Paleontology

184

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REVISION OF THE ARCHOSAUROMORPH REPTILE TRILOPHOSAURUS, WITH A DESCRIPTION OF THE FIRST SKULL OF TRILOPHOSAURUS JACOBSI, FROM THE UPPER TRIASSIC CHINLE GROUP, WEST TEXAS, USA

Cited by 30 publications

References 0 publications

A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible

A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible

Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds

Redescription and phylogenetic relationships ofDoswellia kaltenbachi(Diapsida: Archosauriformes) from the Upper Triassic of Virginia

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