Meeting Abstract
Facial muscles are fundamental to the mammalian experience: swiveling the ears, twitching noses and whiskers, suckling, and communication through facial expression are all dependent on the presence of these muscles. However, the identification of when these soft-tissue structures appeared in the fossil record is a challenge. MicroCT scan reconstructions of the neurovascular canals hosting the maxillary and mandibular branches of the trigeminus (cranial nerve V) in a sample of both extant and fossil taxa reveal changes in morphology corresponding to a hypothesized ancestral, stem mammal transitional, and crown mammal derived conditions. I propose that (1) a concentration of tactile sensory ability at the rostral end of the snout characterizes the stem mammal transitional condition and (2) that the reduction in number of trigeminal nerve foramina and subsequent appearance of the infraorbital foramen near the crown mammal node is an osteological correlate for the presence of specialized whiskers (i.e., mystacial vibrissae), that are actively moved by facial muscles during tactile exploration. The results of this comparative morphological study are placed within the broader context of research on the biomechanical properties of nerves, vertebrate development, and mammalian evolutionary history.
