New Mexico Museum of Natural History has announced that a 300-million-year old fossil of the earliest known example of a plant-eating reptile has been found in southern New Mexico.

The museum stated that the unique structure of the skull, jaws and teeth of the sail-backed reptile suggested that it was a herbivore, an animal which gets its energy from only eating plants. The authority also said that such plant-eating creatures were previously unknown in reptiles older than about 200 million years.

The well-preserved fossil was discovered in near Alamogordo by Ethan Schuth during the field trip in 2013 by a University of Oklahoma geology class. The museum said that the bones were part of an exquisitely preserved but incomplete skeleton.

"The skeleton is that of a sail-backed eupelycosaur, a group of animals that were very successful during the Permian [Period]," the museum said adding that "Eupelycosaurs include the ancestors of mammals, making this new skeleton more closely related to us than to dinosaurs."

After the discovery of the fossil, the field crew spent almost a year on the excavation site while collecting the bones. They spent more time to remove the hard sandstone surrounding the fossils so research could ensue.

Spencer Lucas, a palaeontology curator and his team from the museum determined that the bones were about 300-million-years old and it indicated that this particular species lived during the early part of the Permian Period, which is almost 50 million years before the origin of dinosaurs.

Lucas and research associate Matt Celeskey decided to name this previously unknown species as Gordodon kraineri.

The first part of the name is a combination of two words that came from Spanish word 'gordo,' or fat and the Greek word 'odon,' or tooth, as the researchers found that this previously unknown species had large pointed teeth at the tips of its jaws. The second part of the name, krainer honours an Austrian geologist, Karl Krainer, who contributed to knowledge about the Permian period in New Mexico.

Lucas said in a statement that "Gordodon rewrites the books by pushing back our understanding of the evolution of such specialized herbivory by about 100 million years."

Gordodon was about 5 feet long and weighed an estimated 75 pounds and the researchers believe that this creature have been a selective feeder on high-nutrient plants. As per the experts at the museum other early herbivorous reptiles were not selective, as they used to eat any plants they came across. They also found some similarities between Gordodon and modern animals such as goat and deer.