3D anatomical atlas of the heads of male and female adult Chamaeleo calyptratus.

The veiled chameleon, Chamaeleo calyptratus, is a model organism in the study of reptile development. The extreme size of its cranial casque relative to other chameleons has been linked to high bite forces and conspecific signaling, yet its unique head anatomy has not been described. In general, detailed accounts of chameleon cranial musculature are scarce and not in formats that are easily accessible for use by researchers and educators. In this study, we provide the first complete description of both the cranial osteology and soft tissues in two adult specimens, exploring differences between sexes. Utilizing contrast-enhancing staining techniques, microCT scanning and deep learning models for segmentation, we have generated the first digital anatomical atlases of the chameleon skull, nervous system, cranial muscles and, in the female, hyolingual muscles. This includes the first maps of chameleon cranial sutures and muscle attachment sites. Our results show that the sexes differ most in the structure of the facial skeleton and the enlarged cranial casque. Many osteological differences are reflected in muscle topology and size, where the male presents a considerably larger jaw adductor. These atlases represent novel insights and potential applications for future research and education in reptile evolution and development. As an example, we have published a series of lesson plans alongside our atlases to help educators bridge the gap between theoretical knowledge and hands-on analysis in comparative anatomy.