Meeting Abstract
With over 200 taxa in twelve genera, chameleons exhibit an incredible amount of diversity in their morphology, ecology and behavior. While much of their anatomical diversity is evident from their extreme body size variation and diverse external ornamentations, many of the internal structural differences that contribute to their variation has been less well examined. Among the most variable skeletal features in chameleons is the number of presacral and caudal vertebrae, as well as the number of sternal and parasternal ribs. Our previous work has expanded the known variation of these axial skeletal elements and suggested that both phylogenetic and ecological differences may help drive some of this variation. Here, we performed phylogenetic comparative methods on rib and vertebral counts from micro-CT scans of chameleon specimens to provide further insight into the chameleon axial skeleton. We tested for effects of arboreality and body size, along with other ecological factors, on the observed variation in axial skeletal element counts. Further, we performed ancestral state reconstructions to assess where in the phylogeny specific changes in morphology occurred. In total, vertebral and rib counts from more than 60% of the described species diversity and all twelve genera were included in our analysis. From these analyses, we show that arboreality is a significant predictor of the number of certain axial skeleton elements. We also find a previously unknown synapomorphy for one of the twelve chameleon genera, which show a reduction in cervical vertebrae and ribs relative to all other genera. These results suggest that both ecological and phylogenetic factors have played important roles in shaping patterns of axial skeleton variation in the Chamaeleonidae. More broadly, these results also provide insight into the morphological evolution of the axial skeleton across disparate ecologies and environments.
