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A comparative study of the cranial osteology of Chionactis occipitalis and Pituophis melanoleucus (Reptilia, Colubridae)
The osteology of the skull of the fossorial snake, Chionactis occipiitalis, is described and illustrated for the first time. It is generally true that fossorial animals show structural adaptations to burrowing, and in order to test whether this is so in Chionactis it was compared to a terrestrial snake, Pituophis melanoleucus. It was found that the general shape of the skull is different. In Chionactis it is more streamlined because the bones have a different shape, fit closer together, and are less ridged. The skull is also sturdier, as a result of closer and more extensive contact between the bones. These characteristics enables Chionactis to move through the sand more easily, and to absorb the forces exerted on the skull through its burrowing activity. The most notable differences between the two snakes is found in the nasal region and the jaw. In Chionactis, the nasal region is narrower dorsoventrally as a result of a recessed jaw, and changes in the position and shape of the bones. The narrow anterior region enables the snake to enter the substrate easily, and the recessed jaw also functions to keep the sand out of its mouth. Some of the other differences in Chionactis include smaller orbits, shorter supratemporals, fewer teeth, and a longer sphenoid complex. It is concluded that the observed differences, the streamlined body, the sturdy skull, the narrow anterior the recessed jaw, and the smaller orbits, are all adaptations to a burrowing habit.