MICROANATOMY OF THE MANDIBULAR SYMPHYSIS IN LIZARDS

Although the mandibular symphysis is a functionally and evolutionarily important feature of the vertebrate skull, little is known about the soft‐tissue morphology of the joint in squamate reptiles. Lizards evolved a diversity of skull shapes and feeding behaviors, thus it is expected that the morphology of the symphysis will correspond with functional patterns. Here we present new histological data illustrating the morphology of the joint in a number of lizard taxa. The symphyses of all taxa exhibit dorsal and ventral fibrous portions of the joints that possess an array of parallel and woven collagen fibers. The middle and ventral portions of the joints are complemented by contributions of Meckel's cartilage. Kinetic taxa have more loosely‐built symphyses with large domains of parallel‐oriented fibers whereas hard biting and akinetic taxa have symphyses primarily composed of dense, woven fibers. Whereas most taxa maintain unfused Meckel's cartilages, iguanids and geckos independently evolved fused Meckel's cartilages however the joint's morphologies suggest different developmental mechanisms. Fused Meckel's cartilages may be associated with the apomorphic lingual behaviors exhibited by iguanids (tongue translation) and geckoes (eye wiping). These morphological data shed new light on the functional, developmental, and evolutionary patterns displayed by the heads of lizards. Grant Funding Source : West Virgina NASA Space Grant Consortium