Herbivorous dinosaur jaw disparity and its relationship to extrinsic evolutionary drivers

Disparity, the diversity of form and function of organisms, can be assessed from cladistic or phenetic characters, and from discrete characters or continuous characters such as landmarks, outlines, or ratios. But do these different methods of assessing disparity provide comparable results? Here we provide evidence that all metrics correlate significantly with each other and capture similar patterns of morphological variation. We compare three methods of capturing morphological disparity (discrete characters, geometric morphometric outlines and geometric morphometric landmarks) in coelurosaurian dinosaurs. We standardize our study by focusing all our metrics on the mandible, so avoiding the risk of confounding disparity methods with anatomical coverage of the taxa. The correlation is strongest between the two geometric morphometric methods, and weaker between the morphometric methods and the discrete characters. By using phylogenetic simulations of discrete character and geometric morphometric data sets, we show that the strength of these correlations is significantly greater than expected from the evolution of random data under Brownian motion. All disparity metrics confirm that Maniraptoriformes had the highest disparity of all coelurosaurians, and omnivores and herbivores had higher disparity than carnivores.

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“…; Hopkins ; Maclaren et al . ; Romano ) have shown similar results, but more or less strongly. On the other hand, Mongiardino Koch et al .…”

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confidence: 53%

Morphological disparity in theropod jaws: comparing discrete characters and geometric morphometrics

et al. 2019

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“…As such, the separation of the ‘Norian-Rhaetian’ and ‘Early Jurassic’ morphospaces observed in our PCoA results cannot be attributed to the phylogenetic position of the taxa within each time interval (Figs 13 and 14). Thus, one possible explanation for this splitting is that changes in the vegetation across the Triassic/Jurassic boundary [49,50] leaded to the shift in morphology seen in the jaw feeding apparatus of Norian-Rhaetian to Early Jurassic taxa (but see [51]–in that study, the results of morphological and biomechanical disparity analyses of the mandible of sauropodomorphs shows an overlap in the morphospace associated with Late Triassic and Early Jurassic taxa). As for the phylogenetic groupings, features of non-anchisaurian massopods such as Coloradisaurus and Yunnanosaurus huangi , which also has a dentition markedly different from that of its closest relatives [52], contribute to the great morphospace range occupied by that assemblage of sauropodomorphs (Fig 14).…”

Section: Discussionmentioning

confidence: 98%

Skull remains of the dinosaur Saturnalia tupiniquim (Late Triassic, Brazil): With comments on the early evolution of sauropodomorph feeding behaviour

2019

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Saturnalia tupiniquim is a sauropodomorph dinosaur from the Late Triassic (Carnian–c. 233 Ma) Santa Maria Formation of Brazil. Due to its phylogenetic position and age, it is important for studies focusing on the early evolution of both dinosaurs and sauropodomorphs. The osteology of Saturnalia has been described in a series of papers, but its cranial anatomy remains mostly unknown. Here, we describe the skull bones of one of its paratypes (only in the type-series to possess such remains) based on CT Scan data. The newly described elements allowed estimating the cranial length of Saturnalia and provide additional support for the presence of a reduced skull (i.e. two thirds of the femoral length) in this taxon, as typical of later sauropodomorphs. Skull reduction in Saturnalia could be related to an increased efficiency for predatory feeding behaviour, allowing fast movements of the head in order to secure small and elusive prey, a hypothesis also supported by data from its tooth and brain morphology. A principal co-ordinates analysis of the sauropodomorph jaw feeding apparatus shows marked shifts in morphospace occupation in different stages of the first 30 million years of their evolutionary history. One of these shifts is observed between non-plateosaurian and plateosaurian sauropodomorphs, suggesting that, despite also having an omnivorous diet, the feeding behaviour of some early Carnian sauropodomorphs, such as Saturnalia , was markedly different from that of later Triassic taxa. A second shift, between Late Triassic and Early Jurassic taxa, is congruent with a floral turnover hypothesis across the Triassic-Jurassic boundary.

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“…Further analyses upon evolutionary trends in sauropodomorph cranial feeding adaptations are still ongoing. MacLaren et al () showed that the disparity of mandibular shape is in line with diversity of herbivorous dinosaur taxa, which increased throughout the Mesozoic. According to their study, biomechanical disparity peaks with increased variation in sauropods in the Late Jurassic, but then decreases thereafter in the Cretaceous.…”

Section: Discussionmentioning

confidence: 99%

Cranial Musculature in Herbivorous Dinosaurs: A Survey of Reconstructed Anatomical Diversity and Feeding Mechanisms

Nabavizadeh

2019

The Anatomical Record

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Herbivorous dinosaurs exhibited diverse cranial feeding mechanisms. Although osteological, microwear, and biomechanical research has revealed some of this diversity, the evolutionary reorientation of cranial musculature throughout nonavian herbivorous Dinosauria and its influence on feeding mechanisms requires more study. Here, cranial muscle reconstructions in herbivorous dinosaurs are reviewed and informative anatomical characters are compared across 142 dinosaur genera (84 ornithischians, 36 sauropodomorphs, and 22 herbivorous nonavian theropods), both through examination of specimens and literature. Traits include those relating to the temporal region, adductor chamber, palate, and mandibular attachments, such as the coronoid elevation and retroarticular process. Findings reveal many combinations of anatomical traits influencing a diversity of feeding mechanisms. Some primarily more orthal feeders, including herbivorous theropods, nonsauropod sauropodomorphs, basal ornithischians, and derived stegosaurs (which also show varying degrees of coinciding slight palinal motion and long‐axis hemimandibular rotation), possess traits indicative of more prominent temporal musculature and moderately sized palatal musculature. However, orthal feeding sauropods and pachycephalosaurs possess traits indicative of greatly reduced, low‐angled temporal musculature, and enhanced palatal musculature producing a primarily vertical, orthal feeding vector. Among ankylosaurs, hadrosaurids, and neoceratopsians, a rostrolabial temporal muscle expansion is present (with a tall coronoid elevation in hadrosaurids and ceratopsids) for greater temporal muscle support and mechanical advantage for complex palinal feeding motions. This also aids in long‐axis hemimandibular rotation against the predentary in hadrosaurs and ankylosaurs. This diversity in cranial muscle architecture provides an informative spectrum of numerous adaptations acquired given the evolution of various anatomical constraints in the skull. Anat Rec, 303:1104–1145, 2020. © 2019 American Association for Anatomy

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Herbivorous dinosaur jaw disparity and its relationship to extrinsic evolutionary drivers

Cited by 32 publications

References 50 publications

Morphological disparity in theropod jaws: comparing discrete characters and geometric morphometrics

Morphological disparity in theropod jaws: comparing discrete characters and geometric morphometrics

Skull remains of the dinosaur Saturnalia tupiniquim (Late Triassic, Brazil): With comments on the early evolution of sauropodomorph feeding behaviour

Cranial Musculature in Herbivorous Dinosaurs: A Survey of Reconstructed Anatomical Diversity and Feeding Mechanisms

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