New research shows snakes evolved on land, not in the sea

The world's first snakes evolved on land, and not in the sea, about 128 million years ago and had tiny hind limbs, ankles and toes, a new study has found.

The original snake ancestor was a nocturnal, stealth-hunting predator that had tiny hindlimbs with ankles and toes, researchers said.

The study, led by Yale University, US, analysed fossils, genes, and anatomy from 73 snake and lizard species, and suggests that snakes first evolved on land, not in the sea, which contributes to a longstanding debate. They most likely originated in the warm, forested ecosystems of the Southern Hemisphere around 128 million years ago, researchers said.

Snakes show incredible diversity, with over 3,400 living species found in a wide range of habitats, such as land, water and in trees. But little is known about where and when they evolved, and how their original ancestor looked and behaved.

While snake origins have been debated for a long time, this is the first time these hypotheses have been tested thoroughly using cutting-edge methods, lead author Allison Hsiang said.

"By analysing the genes, fossils and anatomy of 73 different snake and lizard species, both living and extinct, we've managed to generate the first comprehensive reconstruction of what the ancestral snake was like," said Hsiang.

The team constructed a large family tree and illustrated the major characteristics that have played out throughout snake evolutionary history. The results suggest that snakes originated on land, rather than in water, during the middle Early Cretaceous period (around 128.5 million years ago), and most likely came from the ancient supercontinent of Laurasia.

This period coincides with the rapid appearance of many species of mammals and birds on Earth. The ancestral snake likely possessed a pair of tiny hindlimbs, and targeted soft-bodied vertebrate and invertebrate prey that were relatively large in size compared to prey targeted by lizards at the time.

While the snake was not limited to eating very small animals, it had not yet developed the ability to manipulate prey much larger than itself by using constriction as a form of attack, as seen in modern Boa constrictors.

While many ancestral reptiles were most active during the daytime (diurnal), the ancestral snake is thought to have been nocturnal. Diurnal habits later returned around 50-45 million years ago with the appearance of Colubroidea - the family of snakes that now make up over 85 per cent of living snake species.

The results suggest that the success of snakes in occupying a range of habitats over their evolutionary history is partly due to their skills as 'dispersers'. The research was published in the journal BMC Evolutionary Biology.