Meeting Abstract
P3.141 Wednesday, Jan. 6 A histological investigation of cranial kinesis in geckos: testing predictors of joint type PAYNE, S.L.**; VICKARYOUS, M.K.; University of Guelph, Ontario, Canada; University of Guelph, Ontario, Canada spayne@uoguelph.ca
Cranial kinesis is a widespread feature of gekkotan lizards. Based on previous biomechanical studies, it is speculated that most joints involved in cranial kinesis are synovial (defined by the presence of a synovial cavity lined with articular cartilage). However, detailed investigations of tissue structure of most cranial joints are lacking. We examined the anatomy and histology of cranial kinesis in three representative species of geckos: Eublepharis macularius, Tarentola annularis, and Chondrodactylus bibronii. Particular focus was given to the articulations of the quadrate bone, whose anterior-posterior rotation is responsible for the movement known as streptostyly. Heads were non-invasively imaged using micro-computed tomography (microCT), and then serially sectioned and stained with Masson’s Trichrome. For all species investigated, the histology clearly demonstrates that many joints involved in cranial kinesis are not synovial. More specifically, the quadrate-articular and epipterygoid- pterygoid joints are synovial, whereas the frontal-parietal and quadrate-pterygoid joints are syndesmoses (fibrous), and the epipterygoid-prootic and quadrate-otooccipital joints are synchondroses (cartilaginous without a synovial cavity). Our data indicate that the osteology cannot conclusively predict the presence of a synovial joint. For instance, the condyle-like skeletal structure at the cephalic end of the quadrate, while suggestive of a synovial joint, was not found to correspond to one. Available data also indicates that synovial joints are difficult to predict based on the degree of mobility. We conclude that in geckos, multiple synovial joints are not required for streptostyly. In addition, we propose that synovial joints are exclusive to elements derived from the neural crest.
