Researchers have identified a new species of snakes with uniquely broad wing-shaped projections that lived five million years ago.
The fossils of the new genus and species Zilantophis schuberti were discovered from the Gray Fossil Site in the US.
The study, published in the Journal of Herpetology, involved many hours of close examination of hundreds of dark mineral-stained snake fossils.
The biggest surprise was the discovery of vertebrae that did not match any known species of snake, living or extinct.
"Snakes do not have arms or legs, but they have high numbers of vertebrae. These are often the bones that paleontologists use to identify fossil snakes," said Steven Jasinski, a doctoral student at the University of Pennsylvania in the US.
Zilantophis bore uniquely broad wing-shaped projections on the sides of its vertebrae. In life, these were likely attachment sites for back muscles.
These features are what inspired the name of the new genus, derived from Zilant, a winged serpent in Russian mythology.
"It is about as large around as your pointer finger," said Jasinski.
"This animal was probably living in leaf litter, maybe doing a bit of digging and either eating small fish or more likely insects. It was too small to be eating a normal-sized rodent," he said.
"These snake vertebrae are tiny," said David Moscato, who pursued his masters at East Tennessee State University.
"Before we can study them, they have to be meticulously separated from the sediment and other bones. This work is done by dedicated museum workers, students and volunteers," said Moscato.
Based on features of its vertebrae, this new species is thought to be most closely related to rat snakes (Pantherophis) and kingsnakes (Lampropeltis), both of which are relatively common in North America today.
The Gray Fossil Site is one of the richest fossil localities in the US, particularly from the Neogene period, which spans from 23 million to 2.58 million years ago.
At the time that Zilantophis dwelled there, the site was a sinkhole surrounded by forest, attracting a variety of animals.
The local fauna included ancient representatives of familiar North American creatures such as bears, beavers and salamanders.
Others were more exotic, including unique species of rhinoceros, alligator and the site's famous red panda.