Fossilized remains of four ancient snakes between 140 and 167 million years old are changing the way we think about the origin of snakes, and how and when it happened.

The discovery by an international team of researchers, including University of Alberta professor Michael Caldwell, rolls back the clock on snake evolution by nearly 70 million years.

"The study explores the idea that evolution within the group called 'snakes' is much more complex than previously thought," says Caldwell, professor in the Faculty of Science and lead author of the study published today in Nature Communications. "Importantly, there is now a significant knowledge gap to be bridged by future research, as no fossils snakes are known from between 140 to 100 million years ago."

New knowledge from ancient serpents

The oldest known snake, from an area near Kirtlington in Southern England, Eophis underwoodi, is known only from very fragmentary remains and was a small individual, though it is hard to say how old it was at the time it died. The largest snake, Portugalophis lignites, from coal deposits near Guimarota in Portugal, was a much bigger individual at about a metre long. Several of these ancient snakes (Eophis, Portugalophis and Parviraptor) were living in swampy coastal areas on large island chains in western parts of ancient Europe. The North American species, Diablophis gilmorei, was found in river deposits from some distance inland in western Colorado.

This new study makes it clear that the sudden appearance of snakes some 100 million years ago reflects a gap in the fossil record, not an explosive radiation of early snakes. From 167 to 100 million years ago, snakes were radiating and evolving toward the elongated, limb-reduced body shape characterizing the now well known, ~100-90 million year old, marine snakes from the West Bank, Lebanon and Argentina, that still possess small but well-developed rear limbs.

Caldwell notes that the identification of definitive snake skull features reveals that the fossils -- previously associated with other non-snake lizard remains -- represent a much earlier time frame for the first appearance of snakes.

"Based on the new evidence and through comparison to living legless lizards that are not snakes, the paper explores the novel idea that the evolution of the characteristic snake skull and its parts appeared long before snakes lost their legs," he explains.

He adds that the distribution of these newly identified oldest snakes, and the anatomy of the skull and skeletal elements, makes it clear that even older snake fossils are waiting to be found.

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