Providence – Researchers had found what appears to be the first pre-reptile to ever walk on four legs. Its name is Bunostegos akokanensis and it was a ‘pareiasaur parareptile‘ that had the size of a cow and the looks of a rhino and inhabited the Earth 269 million years ago. The study was released in the Journal of Vertebrate Paleontology.

Before the findings, scientists believed that all pareiasaurs who lived in the supercontinet of Pangea were sprawlers who had limbs that would jut out from the side of the body and then continue out or slant out from the elbow. However, Bunostegos’s limbs stood rigid and erect.

Artist’s impression of Bunostegos. Credit: Marc Boulay/ Wired

“A lot of the animals that lived around the time had a similar upright or semi-upright hind limb posture, but what’s interesting and special about Bunostegos is the forelimb. In that it’s anatomy is sprawling-precluding and seemingly directed underneath its body, unlike anything else at the time,” reportedly said Morgan Turner, lead author of the research and a student at the University of Washington.

The discovery let Turner and her team characterize, under the supervision of Professor Christian Sidor, how Bunostegos may had looked. The most important findings involve the forelimbs, particularly four main characteristics that let the animal stand differently than the rest, with its legs beneath the body.

First of all, its shoulder joint is facing down in a way that the humerus, the bone that goes from the shoulder to the elbow, would go straight down underneath, restricting the humerus from sticking out to the side.

On the other side, sprawlers’ humerus twisted, but Bunostegos’ bone do not, which suggests that, to actually reach the ground with its feet, the elbows and shoulders were aligned under the animal’s body. Its elbow joint also works like a hinge, enabling back and forth movements similar to the motion human’s knees do.

Lastly, its ulna is longer than its humerus, just like most upright walkers. “Many other sprawling four-legged animals have the reverse ratio,” Turner explained.

According to the lead author of the study, it would not be a surprise if scientists eventually find peers of Bunostegos with straight posture, since for the long walks after meals the upright posture might have been necessary for survival.

“Posture, from sprawling to upright, is not black or white, but instead is a gradient of forms,” Turner said. “There are many complexities about the evolution of posture and locomotion, we are working to better understand every day. The anatomy of Bunostegos is unexpected, illuminating, and tells us we still have much to learn.”

Source: Journal of Vertebrate Paleontology