Palate evolution in early‐branching crocodylomorphs: Implications for homology, systematics, and ecomorphology

Abstract

Living crocodylomorphs have an ossified secondary palate with a posteriorly positioned choana that enables their semi-aquatic, predatory ecology. In contrast, the earliest branching members of Crocodylomorpha have an open palate with anteriorly positioned choanae. The evolution of an ossified secondary palate and a posteriorly positioned choana features strongly in hypotheses of broad-scale phylogenetic relationships within Crocodylomorpha. Renewed investigations into palatal morphology among extinct members of the clade show surprising variability in the anatomy of the palate, with at least one and potentially a second independent occurrence of "eusuchian-type" palate outside of Eusuchia. Understanding the trajectory of crocodylomorph palatal evolution is, therefore, a key to inferring crocodylomorph interrelationships and ecomorphology. To document early-branching crocodylomorph palatal anatomy, we developed an anatomical comparative dataset using computed tomography scan data and literature, comprising 12 early-branching crocodylomorph taxa. To understand discrete phenotypic changes in palatal structure, we compiled a phylogenetically broadly sampled character-taxon matrix from the existing literature, and revised its palatal characters, adding 10 new palatal characters. Our comparative anatomical investigations allow us to propose an adapted hypothesis for the closure of the palate and the posterior migration of the choana. Our phylogenetic findings corroborate previous research showing that non-crocodyliform crocodylomorphs ("sphenosuchians") are paraphyletic, with the exclusion of the clade Hallopodidae. Non-mesoeucrocodylian crocodyliforms ("protosuchians") are paraphyletic, but form three monophyletic clades: Notochampsoidea, Shartegosuchoidea, and Gobiosuchidae. We find a potential association between secondary palate development and dietary shifts, particularly with regard to hypothesized origins of herbivory. Grant sponser(s): NRF AOP grants (98800 and 118794), DSI-

Unique trackway on Permian Karoo shoreline provides evidence of temnospondyl locomotory behaviour

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A taxonomic revision and cranial description of Terrestrisuchus gracilis (Archosauria, Crocodylomorpha) from the Upper Triassic of Pant‐y‐Ffynnon Quarry (southern Wales)

“…Another, poorly developed ridge forms the anterior margin of the first fossa (f1). This represents the choanal ridge ( sensu Dollman & Choiniere 2022) or ‘spout‐like’ ridge ( sensu Walker 1990). The choanal ridge is well developed in Sphenosuchus acutus , Kayentasuchus walkeri , Dibothrosuchus elaphros and Junggarsuchus sloani (Walker 1990; Wu & Chatterjee 1993; Nesbitt 2011; Dollman & Choiniere 2022; Ruebenstahl et al .…”

Dispatches from the age of crocodiles: New discoveries from ancient lineages

“…Numerous changes occurred in the heads of crocodylomorphs along the line to the modern, crown clade, yet patterns and processes underlying this great transformation remain unclear. Dollman and Choiniere (2022) explore the acquisition of the characteristic secondary bony palate evolved along the line to eusuchians. Several morphological changes occurred during the protosuchian‐eusuchian transformation that have bearing on the systematics and biomechanics of crocodyliforms.…”