Researchers have revealed a new model of snake evolution to explain how fangs specialized from early teeth to introduce venom into prey or attackers; their new weaponry may have enabled the massive expansion of snake species across all continents (except Antarctica) approximately 60 million years ago.

“Understanding the evolution of fangs sheds light on how snakes colonised new environments or adapted to feed on new prey” says Dr Bryan Fry from the Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne.

“The evolution of these unique adaptations has been unravelled for the first time”.

Dr Fry worked with a team from the Netherlands, US, Israel, and Adelaide.

All snakes with hollow front fangs were initially considered to all share a common ancestor but genetic evidence showed that this was not the case. Hollow front fangs instead evolved independently on three separate occasions.

“The true innovation in venom delivery came with the development of hollow-syringe fangs to deliver the venom under high-pressure” added Dr Fry.

A major unanswered riddle was how snake species each developed their weaponry.

“The origin and evolution of the snake venom system has long been an area of great controversy and acrimonious debate. It has only become recently evident that venom is a basal characteristic of the advanced snakes.”

All share a common ancestor that had venom glands but used ordinary teeth to chew the venom, and many lineages independently enlarged the rear-teeth.

“Such innovations allowed the snakes to envenomate new prey items, such as being able to efficiently get past the thick fur of mammals or puncture the hard scales of other snakes”.

Among the species of advanced snakes there is a range of front- and rear-fang groups according to whether their fangs face forward (for example cobras and vipers) or face backward (for example grass snakes) in the upper jaw, but it has perplexed snake biologists for years as to whether or not the fangs shared the same evolutionary and developmental origin

This new evolutionary model reveals that a subset of tooth-forming cells developed independently allowing some teeth to evolve closely with the venom gland into fangs- which have become highly specialized in some species.

Fang evolution was studied by analysing expression of the sonic the hedgehog gene (shh), different levels of shh cause different types of cells to be formed in the developing embryo.

The team examined tooth-forming cells in upper jaw of 96 snake embryos by visualizing the tooth-forming epithelium (layer of skin cells) in the upper jaw of 96 snake embryos, covering eight species.

They used the sonic hedgehog gene as a marker to three-dimensionally reconstruct the development in 41 of the embryos.

“We showed that front fangs actually start their development in the rear end of the upper jaw, and are strikingly similar in structure to rear fangs found in the snakes with less specialised venom delivery teeth but that front-fanged lineage has developed its own trick.”

“As the venom system is an intricate combined system, a better understanding of one part facilitates the study of the other components. So the implications of this study go well beyond being a clever dental exam.”