What the world's first snakes looked like has been revealed by scientists, showing they had tiny hind limbs, ankles and toes.
Snake evolution is widely debated. Research published in January said four species had been found dating to between 140 and 167 million years ago, 70 million years earlier than the previous oldest specimen.
Another recent study found snakes did not become simplified lizards over time but instead gained more complex vertebral columns as they evolved – turning previous thinking of their origins "on its head".
Snakes are very diverse, with over 3,400 living species in a wide range of habitats including land, water and trees. However, where and how they evolved has remained a mystery – as well as what they looked like.
Researchers from Yale University, publishing their findings in the journal BMC Evolutionary Biology, have now analysed fossils, genes and anatomy of 73 snake and lizard species. Scientists looked for similarities and differences between species to create a large family tree of the evolutionary history of snakes.
Findings showed snakes probably first evolved on land and not at sea, originating in the warm and forested ecosystems of the ancient supercontinent of Laurasia, in the Southern Hemisphere, around 128 million years ago – a period when many mammals and birds appeared on Earth.
They said the ancestral snake probably had a tiny set of hind limbs and was a stealth hunter. It probably preyed on soft-bodied vertebrate and invertebrate that were fairly large in size compared to what would have been targeted by lizards living at the time.
However, scientists say it had not yet developed the ability to manipulate prey far larger than itself by using constriction to attack, like many modern species.
It was also nocturnal in comparison to many ancestral reptiles, which were active in the daytime. Snakes became diurnal around 50 million years ago when Colubroidea appeared – an extremely successful family that now makes up around 85% of living snake species.
Lead author Allison Hsiang said: "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. 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."