Meeting Abstract
Vertebrates evolved numerous types of integumentary sensory systems, many of which enhance facial somatosensation. Species with sensitive faces exhibit high densities of trigeminal nerve-innervated receptors at the ends of nerve branches that course through bony canals and foramina in the face and mandibles. These bony features of the trigeminal system are often used to infer facial sensation in extinct vertebrates. However, the form and function of the trigeminal system are diverse in extant reptiles, and its physiological significance and phylogenetic patterns are unclear. Extant reptiles display morphological diversity in proximal (i.e., trigeminal fossa contents and trigeminal division pathways), intermediate (i.e., inferior alveolar canal [IAC] neurovasculature and its relation to teeth and integument), and distal structures (i.e., symphyseal neurovasculature and bill-tip-organs). These structural differences are reflected in the behavioral diversity (e.g., lingual vs. jaw prehension in squamates, tactile-feeding in birds) across Reptilia. Using histological and CT data, we performed morphometric analyses of the maxillomandibular foramen, IAC, and distal mandibular foramina of several extant sauropsids. Comparing IAC branching patterns, we find a more dendritic arrangement in crocodylian IACs in comparison to squamates in which accessory canals transmit mostly vascular tissue to squamate integument, suggesting reduced ability for mandibular sensation. Additionally, crocodylians distribute more neurovasculature branches across smaller areas of the mandible than the squamate taxa sampled, suggesting smaller receptive fields and increased sensory ability. Overall, these findings assist in reconstruction of soft tissues from osteological correlates in fossil taxa and will help uncover patterns of reptilian somatosensory ecology and evolution.
