Snake fossils found in the areas around the world could push back the date when researchers believe the animals first evolved by 65 million years. Until these recent discoveries, the oldest-known snake fossils dated back to 102 million years before our present time.

Eophis underwoodi, found near Oxford, England, lived around 167 million years ago. The creatures grew to be about 10 inches long, researchers believe. Living in swamps, these creatures likely ate fish, tadpoles, and insects, and were the oldest of the four ancient snakes discovered by paleontologists.

Diablophis gilmorei lived in western Colorado 155 million years ago, and likely had a diet similar to the slightly smaller E. underwoodi.

Parviraptor estesi lived 11 million years after D. gilmorei. The two-foot-long creature made its home near modern-day Swanage, England.

Portugalophis lignites is the largest of the new finds, stretching four feet in length. This animal, which lived 155 million years in the past, may have made a diet of small mammals, birds, frogs, and even small dinosaurs. It was discovered in a coal mine in central Portugal.

Snakes evolved from lizards, slowly losing their legs over millions of years, as the limbs fell into disuse. Investigators believe the animals which formed the newly-discovered fossils may have possessed short stumps of limbs, similar to those found in some other remnants of primitive snakes. However, it is likely these animals slithered along the ground as their primary means of locomotion.

Paleontologists and biologists previously believed that the thin, long skull structure that marks modern snakes evolved after the creatures became legless, and began slithering across the ground. These new findings suggest the distinctive skulls were present in even the earliest snake species. Some modern snakes today are believed to be among the oldest varieties of these animals. The newly-disocvered snakes appear to be closely-related to those older species, researchers determined.

Still, the animals "are still very much snakes, there is no question about the affinity of these living forms, but they don't show quite the mobility of the skull that you would see in a boa or a python," Michael Caldwell of the University of Alberta said.

The first of the discoveries was identified when Caldwell examined a specimen, believed to be from a lizard, stored in a drawer at the Natural History Museum in London, England. Examination of the maxilla - the bone that holds teeth - revealed Parviraptor estesi to be a a form of snake.

Discovery and analysis of the four ancient snake fossils was detailed in the journal Nature Communications.