Patterns of jugal foramina in crocodilians, and their importance as phylogenetic information

Neurovascular foramina are an important, but frequently overlooked source of phylogenetic information within Crocodylomorpha. Such structures are poorly documented, despite their occurrence in jugal, premaxilla, maxilla, postorbital, dentary and angular. Morphological study of fossil/extant material identified a diversity of patterns in the distribution of foramina within mesoeucrocodylians. Jugal foramina are absent in archosauromorphs to basal mesoeucrocodylians, but occur in eusuchians, basal neosuchians and derived notosuchians. Within Eusuchia, small foramina (2-5) are present in alligatorids, Crocodylus, Osteolaemus, Diplocynodon and Asiatosuchus, usually facing lateroventrally. Gavialoids may show extraordinary diversity of patterns, for the morphology found in Gavialis gangeticus (several minute foramina, anterior to the orbit) and Piscogavialis (two enlarged foramina, lateral to the orbit). Two ventrally oriented foramina are present in basal neosuchians (Pholidosaurus, Dyrosauridae indet.), supporting their phylogenetic proximity with eusuchians. Derived notosuchians (e.g. Mariliasuchus, Sphagesaurus) have a single enlarged and laterally oriented jugal foramen, which is absent from Notosuchus and baurusuchids. Thalattosuchians seem to lack jugal foramina, which could be an atavism, or evidence for a basal position of this clade, within Mesoeucrocodylia. Jugal foramina seem to be primarily vascular openings, but at least in Gavialis, foramina may be related to dome pressure receptors, with a sensory function. Crocodylomorphs show distinct patterns of jugal neurovascular foramina, consistent with recent phylogenetic proposals. However, jugal foramina are still poorly documented and should be collected for several taxa (e.g. Allognathosuchus, Pristichampsus, Bernissartia, Isisfordia, Sarcosuchus, Elosuchus).