MICROSTRUCTURE, ONTOGENY, AND EVOLUTION OF SCALE SURFACES IN XENOSAURID LIZARDS

Both scanning electron and light microscopy were used to examine the e pidermal structure of scales taken from several ontogenetic stages of Xenosaurus grandis and Shinisaurus crocodilurus. In addition, scales f rom all xenosaurid species were examined by scanning electron microsco py to determine scale surface variation among genera, species, and sub species. A varied and phylogenetically informative morphology characte rizes the scale surfaces of xenosaurid lizards. Scale surface morpholo gy is conservative among the species and subspecies of Xenosaurus, but is more variable between the two xenosaurid genera. Their scale surfa ces are characterized by folds in the oberhautchen, beta, mesos, and a lpha epidermal layers, forming polygonal ridges of a type previously d escribed for the Iguania. The three species of Xenosaurus possess lent icular scale organs, whereas Shinisaurus has scale organs with spikes (bristles). The spikes of Shinisaurus are formed by the beta and oberh autchen layers, with the alpha layer forming a dome-shaped cap over a dermal papilla. Shinisaurus crocodilurus exhibits a dramatic ontogenet ic change in scale surface morphology, that is here reported for the f irst time in any lizard.