Evolutionary origin and development of snake fangs

Evolution bites: Fang development and the diversity of modern snakes An 'evo-devo' study of venomous snakes has arrived at a new model for the evolution of snake fangs, a subject of some controversy. Many of the advanced snakes alive today use syringe-like fangs to inject venom into their prey. The fangs are either positioned at the front or rear of the upper jaw, and the controversy lies in whether the two arrangements are evolutionarily related. By visualizing tooth-forming epithelium in the upper jaw of 96 snake embryos from 8 species, the study shows that 'front-fanged' and 'rear-fanged' types are strikingly similar in morphogenesis. Front fangs develop from a rear part of the upper jaw that is displaced forward during development, and rear fangs from a specialized zone that stays put. The new model proposes that a posterior subregion of tooth-forming epithelium became developmentally uncoupled from the remaining dentition, allowing the posterior teeth to evolve independently and in close association with the venom gland, becoming highly modified in different lineages. This developmental event could have facilitated the massive radiation of advanced snakes in the Cenozoic era, resulting in the spectacular diversity of snakes seen today. The cover shows a Lataste's viper ( Vipera latastei gaditana ) with the erected fang covered by the fang sheath. Photo by Ruben Schipper. Many advanced snakes use fangs to inject venom into their prey. The fangs may be either at the front or rear of the upper jaw, but biologists have been unable to agree whether these two arrangements are evolutionarily related. It is now shown that front fangs develop in the rear part of the jaw, and that the resemblances between front and rear fangs are so striking during their development that homology is probable. Many advanced snakes use fangs—specialized teeth associated with a venom gland 1 , 2 —to introduce venom into prey or attacker. Various front- and rear-fanged groups are recognized, according to whether their fangs are positioned anterior (for example cobras and vipers) or posterior (for example grass snakes) in the upper jaw 3 , 4 , 5 . A fundamental controversy in snake evolution is whether or not front and rear fangs share the same evolutionary and developmental origin 3 , 4 , 5 , 6 , 7 , 8 , 9 . Resolving this controversy could identify a major evolutionary transition underlying the massive radiation of advanced snakes, and the associated developmental events. Here we