A study published in the most recent issue of Nature offers new evidence for how snake fangs evolved from regular teeth.
Many advanced snakes use fangs - specialised teeth associated with a venom gland to introduce venom into prey or attacker. Various front- and rear-fanged groups are recognised, according to whether their fangs are positioned anterior (for example cobras and vipers) or posterior (for example grass snakes) in the upper jaw.
A fundamental controversy in snake evolution is whether or not front and rear fangs share the same evolutionary and developmental origin. Resolving this controversy could identify a major evolutionary transition underlying the massive radiation of advanced snakes, and the associated developmental events.
A team, led by Freek Vonk form the Leiden University, The Netherlands, examined this issue by visualising the tooth-forming epithelium in the upper jaw of 96 snake embryos, covering eight species. They used the sonic hedgehog gene as a marker, and three-dimensionally reconstructed the development in 41 of the embryos. They find that both front and rear fangs arise from the back of the upper jaw, but the front fangs migrate forwards during the embryo development. On the other hand, the rear fangs form a specialised zone in the tooth-forming layer that stays put.
The findings suggest that the back region of the tooth-forming layer in the snake jaw became uncoupled from the rest of the teeth during evolution, enabling the back teeth to evolve independently with the venom gland. 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.