Eosuchus lericheiis a gavialoid crocodylian from late Paleocene marine deposits of northwestern Europe, known from a skull and lower jaws, as well as postcrania. Its sister taxon relationship with the approximately contemporaneous speciesEosuchus minorfrom the east coast of the USA has been explained through transoceanic dispersal, indicating a capability for salt excretion that is absent in extant gavialoids. However, there is currently no anatomical evidence to support marine adaptation in extinct gavialoids. Furthermore, the placement ofEosuchuswithin Gavialoidea is labile, with some analyses supporting affinities with the Late Cretaceous to early Paleogene “thoracosaurs.” Here we present novel data on the internal and external anatomy of the skull ofE. lericheithat enables a revised diagnosis, with 6 autapormorphies identified for the genus and 10 features that enable differentiation of the species fromEosuchus minor. Our phylogenetic analyses recoverEosuchusas an early diverging gavialid gavialoid that is not part of the “thoracosaur” group. In addition to thickened semi‐circular canal walls of the endosseous labyrinth and paratympanic sinus reduction, we identify potential osteological correlates for salt glands in the internal surface of the prefrontal and lacrimal bones ofE. lerichei. These salt glands potentially provide anatomical evidence for the capability of transoceanic dispersal withinEosuchus, and we also identify them in the Late Cretaceous “thoracosaur”Portugalosuchus. Given that the earliest diverging and stratigraphically oldest gavialoids either have evidence for a nasal salt gland and/or have been recovered from marine deposits, this suggests the capacity for salt excretion might be ancestral for Gavialoidea. Mapping osteological and geological evidence for marine adaptation onto a phylogeny indicates that there was probably more than one independent loss/reduction in the capacity for salt excretion in gavialoids.
