The skull of the Round Island boa, Casarea dussumieri Schlegel, based on high-resolution X-ray computed tomography

The skull of the rare bolyeriid snake Casarea dussumieri is described in detail based on high-resolution X-ray CT data. Bolyeriids are unique in their possession of a separate suborbital ossification and a maxilla subdivided into two movably jointed parts, which may be the result of paedomorphic truncation of the development of the maxilla from multiple ossification centers. Comparison of the skull of C. dussumieri to that of larger booids suggests additional paedomorphic features including reduction of the dorsal lamina of the nasal and prefrontal and reduction of their contacts with the frontal, limited posterior extent of the posterior free process of the supratemporal, and reduction of the coronoid and splenial. The observations herein do not resolve competing phylogenetic hypotheses based on morphology, which either place tropidophiids as the sister-taxon of bolyeriids, Acrochordus and colubroids, or place bolyeriids as the sister-taxon of the other three. But these observations provide no support whatsoever for the heterodox placement of tropidophiids at the base of alethinophidian snakes, as obtained recently with molecular data.