Analyzing and comparing the buccal anatomy of European colubroid snakes: A reassessment of dentition models

Anatomical analyses reveal the presence of two rear- fanged models among European colubroids, categorized by different types of venom glands and rear maxillary fangs and differences in the features of the maxillary bones. The first model, opisthoglyphous, is characterized by the presence of purely serous venom glands, from which the secretions produced flow in the grooved posterior maxillary fangs. The posterior fangs are separated from the anterior ones by an alveolar diastema and a deviation of the maxillary bone. The second model, blade-fanged, has a venom gland composed of seromucous cells, anatomically positioned in a more recessed position compared to the opisthoglyphous model. In this model the posterior maxillary fangs are enlarged but have distal and mesial keels instead of grooves, but are not separated from the anterior teeth by diastemas or deviations of the maxillary bone. The European group of colubroids, previously composed almost exclusively of snakes considered “aglyphous,” must be reconsidered in light of a system that consists mostly of opisthoglyphous snakes (predominantly the large group of Whip snakes, in addition to some species of Colubridae and Lamprophiidae), “aglyphous” snakes (exclusively Colubridae, including Ratsnakes and Dwarf snakes), and blade-fanged snakes (Natricidae, including Grass snakes and Water snakes). This reassessment is justified and supported by a comparative analysis of various European and non-European species, which confirms that “aglyphous” colubrids are residual forms of a rear-fanged model.