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18 June 2018 Convergent Evolution of a Eusuchian-Type Secondary Palate within Shartegosuchidae
Kathleen N. Dollman, James M. Clark, Mark A. Norell, Xu Xing, Jonah N. Choiniere
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Abstract

Shartegosuchids are a poorly known, early-branching group of Asian and North American crocodylomorphs. Shartegosuchids have been hypothesized to have eusuchian-type secondary palates, but a paucity of described material makes assessing this difficult. Our fieldwork in western Mongolia recovered cranial material of a new Shartegosuchus specimen from the Ulan Malgait Formation, which we CT-scanned and digitally reconstructed to investigate its palatal morphology. We then incorporated this new anatomical information into a revised phylogenetic dataset to assess its affinities. Our study confirms that Shartegosuchus has a posteriorly placed choana that is fully enclosed by the pterygoids, but differs from Eusuchia in possessing a secondary palatal fenestra and reduced palatine bones. Shartegosuchus, together with Adzhosuchus, Fruitachampsa, and Nominosuchus, forms the monophyletic group Shartegosuchidae. Shartegosuchidae is nested within a larger clade Shartegosuchoidea, and this clade is an earlier-diverging lineage than Eusuchia, showing that a eusuchian-type secondary palate evolved multiple times in crocodylomorphs, including very early in the group's evolutionary history. The co-occurrence of Nominosuchus in the Ulan Malgait Formation and the Shishigou Formation allows us to assign an early Oxfordian age to Shartegosuchus. The independent evolution of a eusuchian-type secondary palate in an oreinorostral group suggests that the link between platyrostry and a closed secondary palate has been overstated.

© American Museum of Natural History 2018
Kathleen N. Dollman, James M. Clark, Mark A. Norell, Xu Xing, and Jonah N. Choiniere "Convergent Evolution of a Eusuchian-Type Secondary Palate within Shartegosuchidae," American Museum Novitates 2018(3901), 1-23, (18 June 2018). https://doi.org/10.1206/3901.1
Published: 18 June 2018
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KEYWORDS
Crocodylomorpha
Mongolia
palatal fenestra
pterygoid
Ulan Malgait Formation
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