CONICET | Buscador de Institutos y Recursos Humanos

Crocodyliformes are the only group of Archosauriformes that have enclosed the antorbital fenestra and internalized the associated pneumatic cavity multiple times in their evolutionary history. A large-scale phylogenetic analysis of Crocodyliformes allows evaluating the pattern of character evolution of this fenestra in the history of the group. The closure of the antorbital fenestra is optimized as a highly homoplastic process, inferred to occur independently up to eight times. Although this closure is observed in few basal crocodyliforms (e.g., Edentosuchus, the Fruita Form), most transformations are focused in certain mesoeucrocodylian clades. In notosuchians, a closed antorbital fenestra is observed in derived notosuchians (including sebecosuchians). However, the presence of an antorbital fenestra in Notosuchus creates an ambiguous optimization for this character. Furthermore, the presence of a small fenestra in some Cenozoic sebecosuchians (Bergisuchus and Iberosuchus) implies a reopening of the fenestra in the evolution of this group. Among neosuchians, two independent events of closure are optimized on the phylogeny, in Pholidosauridae+Dyrosauridae and in Goniopholidae+Eusuchia. This optimization is due to the condition of basal Thalattosuchia and Atoposauridae, as both have small antorbital fenestra. Given that the homology of the antorbital fenestra of Metriorhynchidae has been recently questioned, an internalized antorbital fenestra could represent an ambiguous synapomorphy of the longirostrine clade composed by Thalattosuchia+Goniopholidae+Pholidosauridae. The evidence at hand indicates the antobital fenestra of Crocodyliformes is one of the most homoplastic analyzed characters of the group, suggesting not only the closure of this opening in multiple groups but also the independent reappearance of a fenestra (that would not be homologous from a phylogenetic point of view) in some notosuchians and, possibly, in basal thalattosuchians.