The development of the osteocranium in the snake Psammophis sibilans (Serpentes: Lamprophiidae).

Non-avian reptiles are good models to investigate structural and developmental differences between amniotes. Investigations of craniofacial development in a complete series of embryos from oviposition up to hatching are still relatively rare. Consideration of a complete series can reveal developmental events that were previously missed, and thus correct or confirm theories about developmental events. The Egyptian Sand snake, Psammophis sibilans, has been a key species in descriptions of the snake skull development. However, published work was based on a limited sample of specimens collected from the wild. Here, we supplement previous descriptions with an illustrated account of skull development in P. sibilans based on a staged series of embryos and histological sections. Our findings largely agree with those of previous authors, although we record differences in developmental timing, confirming the presence of an egg tooth in this species. We add further observations on the enigmatic fenestra X, showing that it closes rather than merging with the prootic notch. Our observations revealed the likely contribution of the tectum posterius to the occipital roof, the presence of an internal carotid foramen (possibly transitory or variable), and the formation of the initial laterosphenoid pillar.