A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet

Cabreira, Sérgio Furtado; Kellner, Alexander W. A.; Dias‐da‐Silva, Sérgio; Silva, Lúcio Roberto da; Bronzati, Mario; Marsola, Júlio C. A.; Müller, Rodrigo Temp; Bittencourt, Jonathas S.; Batista, Brunna Jul’Armando Rezende; Raugust, Tiago; Carrilho, Rodrigo; Brodt, André; Langer, Max C.

doi:10.1016/j.cub.2016.09.040

Cited by 159 publications

(298 citation statements)

References 24 publications

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“…, ; Cabreira et al. ; Baron et al. ) and some of this uncertainty may derive from the widespread amount of ontogenetic and intraspecific variation present among these groups (Griffin & Nesbitt, ).…”

Section: Discussionmentioning

confidence: 99%

Developmental patterns and variation among early theropods

Griffin

2018

Journal of Anatomy

129

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Understanding ontogenetic patterns is important in vertebrate paleontology because the assessed skeletal maturity of an individual often has implications for paleobiogeography, species synonymy, paleobiology, and body size evolution of major clades. Further, for many groups the only means of confidently determining ontogenetic status of an organism is through the destructive process of histological sampling. Although the ontogenetic patterns of Late Jurassic and Cretaceous dinosaurs are better understood, knowledge of the ontogeny of the earliest dinosaurs is relatively poor because most species-level growth series known from these groups are small (usually, maximum of n ~ 5) and incomplete. To investigate the morphological changes that occur during ontogeny in early dinosaurs, I used ontogenetic sequence analysis (OSA) to reconstruct developmental sequences of morphological changes in the postcranial ontogeny of the early theropods Coelophysis bauri and Megapnosaurus rhodesiensis, both of which are known from large sample sizes (n = 174 and 182, respectively). I found a large amount of sequence polymorphism (i.e. intraspecific variation in developmental patterns) in both taxa, and especially in C. bauri, which possesses this variation in every element analyzed. Megapnosaurus rhodesiensis is similar, but it possesses no variation in the sequence of development of ontogenetic characters in the tibia and tarsus. Despite the large amount of variation in development, many characters occur consistently earlier or later in ontogeny and could therefore be important morphological features for assessing the relative maturity of other early theropods. Additionally, there is a phylogenetic signal to the order in which homologous characters appear in ontogeny, with homologous characters appearing earlier or later in developmental sequences of early theropods and the close relatives of dinosaurs, silesaurids. Many of these morphological features are important characters for the reconstruction of archosaurian phylogeny (e.g. trochanteric shelf). Because these features vary in presence or appearance with ontogeny, these characters should be used with caution when undertaking phylogenetic analyses in these groups, since a specimen may possess certain character states owing to ontogenetic stage, not evolutionary relationships.

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Section: Discussionmentioning

confidence: 99%

Developmental patterns and variation among early theropods

Griffin

2018

Journal of Anatomy

129

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“…This may be because the taxon sample used in that study contrasted with that used by Cabreira et al . (), from which the matrix analysed here was obtained. The supertree likelihoods also support the crocodylomorphs as derived rauisuchians, rather than as the sister group to the Aetosauria, as proposed by Brusatte et al .…”

Section: Discussionmentioning

confidence: 99%

“…For dinosaurs, we used a topology based on Cabreira et al . () for trees A, B, E and F, and a topology based on Baron et al . () for trees C, D, G and H. For trees A–D, we preserved the pseudosuchian relationships within the backbone trees (Ezcurra () in trees A and C and Nesbitt () in trees B and D), but used a pseudosuchian topology based on Brusatte et al .…”

Section: Methodsmentioning

confidence: 99%

Archosauromorph extinction selectivity during the Triassic–Jurassic mass extinction

et al. 2018

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Many traits have been linked to extinction risk among modern vertebrates, including mode of life and body size. However, previous work has indicated there is little evidence that body size, or any other trait, was selective during past mass extinctions. Here, we investigate the impact of the Triassic–Jurassic mass extinction on early Archosauromorpha (basal dinosaurs, crocodylomorphs and their relatives) by focusing on body size and other life history traits. We built several new archosauromorph maximum‐likelihood supertrees, incorporating uncertainty in phylogenetic relationships. These supertrees were then employed as a framework to test whether extinction had a phylogenetic signal during the Triassic–Jurassic mass extinction, and whether species with certain traits were more or less likely to go extinct. We find evidence for phylogenetic signal in extinction, in that taxa were more likely to become extinct if a close relative also did. However, there is no correlation between extinction and body size, or any other tested trait. These conclusions add to previous findings that body size, and other traits, were not subject to selection during mass extinctions in closely‐related clades, although the phylogenetic signal in extinction indicates that selection may have acted on traits not investigated here.

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“…), probably bipedal and faunivorous/omnivorous (Barrett ; Barrett & Upchurch ; Cabreira et al . ). Subsequent anatomical transformations occurred across the skeleton in an apparently stepwise fashion, evidenced by the Late Triassic and Early Jurassic fossil record (e.g.…”

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confidence: 97%

Rapid transformation in the braincase of sauropod dinosaurs: integrated evolution of the braincase and neck in early sauropods?

2017

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Sauropod dinosaurs were quadrupedal herbivores with a highly specialized body plan that attained the largest masses of any terrestrial vertebrates. Recent discoveries have shown that key traits associated with sauropod gigantism appeared stepwise during the Late Triassic and Early Jurassic in evolutionary ‘cascades’ of associated changes, in which a ‘head and neck’ cascade has been suggested as an important module. Here, we investigate the evolutionary transformation of the sauropodomorph braincase, using discrete anatomical characters, prompted by the reanalysis of a Middle Jurassic (Bathonian) sauropodiform braincase from England. Our analysis shows that sauropod braincases are highly distinct, and occupy a different region of morphospace than their evolutionary relatives. This resulted from anatomical transformations including a set of changes in the surface attachments of craniocervical musculature, which may indicate integrated evolution between neck elongation and transformation in braincase anatomy. Neck elongation in Late Triassic and Early or Middle Jurassic taxa is potentially associated with episodes of skull reduction, indicating that the ‘head and neck’ cascade was activated more than once in the evolutionary history of Sauropodomorpha. The re‐activation of this cascade in the Jurassic may have impacted on the differential survival of sauropodomorph lineages through the Early and Middle Jurassic.

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A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet

Cited by 159 publications

References 24 publications

Developmental patterns and variation among early theropods

Developmental patterns and variation among early theropods

Archosauromorph extinction selectivity during the Triassic–Jurassic mass extinction

Rapid transformation in the braincase of sauropod dinosaurs: integrated evolution of the braincase and neck in early sauropods?

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