In looking at snake genomes, serpent anatomy and new clues from early snake fossils, researchers at Yale concluded the earliest ancestral snakes lived on land, not in the water.

"We infer that the most recent common ancestor of all snakes was a nocturnal, stealth-hunting predator targeting relatively large prey, and most likely would have lived in forested ecosystems in the Southern Hemisphere," Allison Hsiang, a paleontologist and postdoctoral researcher at Yale University, explained in a press release.

The comprehensive analysis of genetics and fossil records allowed snake experts at Yale to reconstruct a massive family tree. In retracing both ongoing and extinct lineages, researchers revealed evolutionary patterns that allowed them to paint a clearer picture of the planet's earliest snakes.

"Our analyses suggest that the most recent common ancestor of all living snakes would have already lost its forelimbs, but would still have had tiny hind limbs, with complete ankles and toes," said study co-author Daniel Field. "It would have first evolved on land, instead of in the sea. Both of those insights resolve longstanding debates on the origin of snakes."

The study posits that the earliest ancestors of modern snakes -- a group that includes 3,400 living species -- populated the forest floors of the middle Early Cretaceous period, some 128.5 million years ago. Like their modern relatives, ancestral snakes seized their prey with sharp, hooked teeth and swallowed them whole.

It's perhaps their origins on the floors of the forest -- where the earliest humans and their primate ancestors lived and foraged for food -- that makes snakes such a longstanding boogieman of the human psyche.

"Primate brains, including those of humans, are hard-wired to attend to serpents, and with good reason," said senior study author Jacques Gauthier, a geophysicist professor and curator of fossil vertebrates at the Yale Peabody Museum of Natural History. "Our natural and adaptive attention to snakes makes the question of their evolutionary origin especially intriguing."

The new research was published in the journal BMC Evolutionary Biology.