Ecomorphology and Morphological Diversity of Trigeminal Nerve‐mediated Somatosensation in Sauropsids

Abstract

Understanding the morphology of tissues mediating sensory perception is essential to understanding organismal behavior. Cranial somatosensation in living reptiles requires dense innervation of the mandibles by the trigeminal nerve to receive and discriminate between the range of stimuli experienced during sensory behaviors including prey acquisition, feeding, and navigation. Morphological diversity of both the soft tissue and osteological trigeminal system is unexplored across reptiles, and thus relationships between form and function are unknown. Additionally, inferences of facial sensation in extinct vertebrates are often loosely based on qualitative descriptions of bony features of the trigeminal system. Using CT and hand-measured data, we explore morphometric relationships between and among soft tissue (i.e., trigeminal ganglion, inferior alveolar nerve, terminal sensors) and osteological (i.e., trigeminal fossa, inferior alveolar canal, rostral foramina) trigeminal structures of extant representatives from each major clade of sauropsids with diverse sensory strategies. Exploring the trigeminal mandibular division, we find relatively larger trigeminal structures in crocodylians than most birds and lepidosaurs, implying differing levels of sensory ability among taxa. We show canal branching patterns reflect sensory ecologies as well, with only tactile-foraging taxa exhibiting dendritic canals. Finally, we identify phylogenetic and ecologic factors influencing osteological correlate utility and predict sensory ecologies of extinct reptiles, supporting a trend of increasing trigeminal sensation along the crocodylian line. Overall, these findings describe some of the diversity of the reptilian trigeminal system and establish evolutionary patterns of reptile trigeminal ecomorphology.