Snake forebear had two back legs but no front legs

by Lucas Joel
Friday, August 21, 2015

This artist's rendering of the common ancestor of modern snakes shows it with two small hind legs. Credit: Julius T. Csotonyi.

The more than 3,400 species of snakes alive today may have descended from one ancestor that lacked forelimbs, but which had small vestigial hind limbs complete with ankle bones and toes, according to a new study published in BMC Evolutionary Biology.

Allison Hsiang, a postdoctoral researcher at Yale University, and her colleagues used data from the fossil record, as well as the anatomy and genomes of modern snakes, to reconstruct a family tree that mapped when particular traits emerged during the course of snake evolution. From this, the researchers generated a picture of how the ancestral snake looked.

“We infer that the snake was a nocturnal, stealth-hunting predator targeting relatively large prey, and most likely would have lived in the Southern Hemisphere,” Hsiang said in a statement. The snake was nonconstricting, which means it did not coil around and suffocate its prey like modern-day boas and pythons do. Instead, it would seize its prey with needle-sharp teeth and swallow them, like present-day garter snakes.

The study also offers answers to two long-standing questions about snake evolution: where and how it evolved. “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. It would have first evolved on land, instead of in the sea,” said Daniel Field, also of Yale and a co-author of the study, in a statement.

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