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[dinosaur] Large sphagesaurid notosuchian from Upper Cretaceous of Brazil + crocodylomorph cranial shape



Ben Creisler
bcreisler@gmail.com


Some recent papers:

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Galuber Oliveira Cunha, Rodrigo Santucci, Marco Brandalise Andrade & Carlos Eduardo Maia Oliveira (2019)
Description and phylogenetic relationships of a large-bodied sphagesaurid notosuchian from the Upper Cretaceous Adamantina Formation, Bauru Group, SÃo Paulo, southeastern Brazil.
Cretaceous Research (advance online publication)
doi: https://doi.org/10.1016/j.cretres.2019.104259
https://www.sciencedirect.com/science/article/pii/S0195667119300667


In this work we describe new remains and possible gastroliths of a sphagesaurid (Mesoeucrocodylia: Notosuchia) unearthed from the Adamantina Formation (Bauru Group, Upper Cretaceous) in the municipality of FernandÃpolis-SP, which add new data about the dental, dermal shield, and the post-cranial skeleton morphology of these crocodilians. Phylogenetic analyses place the studied fossil within Sphagesauridae, in a polytomy with Armadillosuchus arrudai and Caryonosuchus pricei. The anatomical comparisons are congruent to the phylogenetic analysis since they also suggest that the specimen herein described is closely related to other larger-bodied Sphagesauridae species, such as Armadillosuchus arrudai. The new skull, appendicular, and dermal elements described in this work may provide data for the elaboration of new phylogenetic characters which can improve cladistic analyses concerning Sphagesauridae species, as well as they may help to better understand the morphological complexity of this family of crocodylomorphs, especially the large-bodied species.

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Now officially published under peer review:


Pedro L. Godoy (2019)
Crocodylomorph cranial shape evolution and its relationship with body size and ecology.
Journal of Evolutionary Biology (advance online publication)
doi: https://doi.org/10.1111/jeb.13540
https://onlinelibrary.wiley.com/doi/10.1111/jeb.13540


Crocodylomorpha, which includes living crocodylians and their extinct relatives, has a rich fossil record, extending back for more than 200 million years. Unlike modern semiâaquatic crocodylians, extinct crocodylomorphs exhibited more varied lifestyles, ranging from marine to fully terrestrial forms. This ecological diversity was mirrored by a remarkable morphological disparity, particularly in terms of cranial morphology, which seems to be closely associated with ecological roles in the group. Here, I use geometric morphometrics to comprehensively investigate cranial shape variation and disparity in Crocodylomorpha. I quantitatively assess the relationship between cranial shape and ecology (i.e. terrestrial, aquatic, and semiâaquatic lifestyles), as well as possible allometric shape changes. I also characterise patterns of cranial shape evolution and identify regime shifts. I found a strong link between shape and size, and a significant influence of ecology on the observed shape variation. Terrestrial taxa, particularly notosuchians, have significantly higher disparity, and shifts to more longirostrine regimes are associated with largeâbodied aquatic or semiâaquatic species. This demonstrates an intricate relationship between cranial shape, body size and lifestyle in crocodylomorph evolutionary history. Additionally, disparityâthroughâtime analyses were highly sensitive to different phylogenetic hypotheses, suggesting the description of overall patterns among distinct trees. For crocodylomorphs, most results agree in an early peak during the Early Jurassic and another in the middle of the Cretaceous, followed by nearly continuous decline until today. Since only crownâgroup members survived through the Cenozoic, this decrease in disparity was likely the result of habitat loss, which narrowed down the range of crocodylomorph lifestyles.

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Free preprint version (posted earlier):

Pedro Lorena Godoy (2019)
Crocodylomorph cranial shape evolution and its relationship with body size and ecology.
BioRxiv (preprint)
doi: http://dx.doi.org/10.1101/724609
https://www.biorxiv.org/content/10.1101/724609v1

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