On the paranasal and paratympanic sinuses of perinatal Gavialis gangeticus, with notes on the endocast, ossification observations in the braincase, and cervical vertebrae.

Gavialis gangeticus is a critically endangered, enigmatic, long-snouted crocodylian with uncertain phylogenetic affinities. Molecular and morphological data return disparate results for its placement within the larger diversity of Crocodylia. Because of its conservational status, specimens of Gavialis are rarer in museum collections, especially ones of younger ontogenetic age. Here, we use computed tomography (CT) to image a perinatal specimen to investigate cranial morphology, paranasal, and paratympanic pneumaticity. We provide digital reconstructions of the cranial morphology as an open access digital atlas. We also compare this unique specimen to adult morphology based on taxonomically comparative published literature and found some similar, but not identical morphologies across ontogeny (e.g., maxillary sinus, antorbital sinus, recessus epitubaricus, laterosphenoid recess, and otoccipital recess). Other structures, like the basioccipital recess and pterygoid recesses, are morphologically disparate in this hatchling, matching more closely with other published hatchling specimens of different species rather than with adult Gavialis. We include a description of the endocast and associated nervous structures. The scan included the first three cervical vertebrae, so we make observations on vertebral ossification. We intend this descriptive work to be a novel point of comparison for future ontogenetic work in Crocodylia.