Fangs have evolved independently time after time among many lineages of venomous snakes, but are rarely seen in other reptiles. Now, scientists have revealed that microscopic features of snake teeth - that may have evolved for an entirely different purpose - make them uniquely capable of developing into fangs.

"It's always been a mystery why fangs have evolved so many times in snakes, but rarely in other reptiles," says lead author Alessandro Palci from Flinders University. "Our study answers this, showing how easy it is for normal snake teeth to turn into hypodermic needles."

The fangs that snakes use to deliver venom are essentially modified teeth that are either grooved, so the venom is directed down the groove, or tubular, with the venom running through a canal within the teeth. These fangs can be located at the back or the front of the mouth, and can be fixed in place or hinged.

In order to understand why such a sophisticated delivery system evolved multiple times among different snake lineages, Palci and his team used modelling, fossils and hours of microscope observations to demonstrate that snakes have tiny in-foldings at the base of their teeth, which may have evolved to help the teeth attach more firmly to the jaw - useful if you need to latch onto prey. These wrinkles are the likely precursor to fangs - as they became deeper and extended to the tooth tip, they created the groove needed to deliver venom over successive generations.

"This helps us understand how venomous snakes evolved, which is important not only because snakes are interesting but because venomous snakes are also medically significant," says Palci.

Of almost 4000 species of snakes in existence, around 600 are considered 'medically significant' to humans, according to the researchers, meaning that if you are bitten you will very likely require treatment in a hospital.

Co-author Michael Lee says the research emphasises how evolutionary quirks that develop to solve one problem can end up solving another to boot.

"Our work highlights the opportunism and efficiency of evolution," says Lee.

The findings are published in a study in Proceedings of the Royal Society B.