Scientists have discovered an ancient pre-reptile that was likely one of the first animals to stand on four legs like a cow or hippo.
The Bunostegos akokanensis walked the supercontinent of Pangea 260 million years ago, Brown University reported. During this era, most pareiasaurs had limbs that jutted out from the sides of their bodies and slanted down from the elbow similar to modern lizards'; this new analysis reveals Bunostegos was an exception to the rule.
"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," said Morgan Turner, lead author of the study. "The elements and features within the forelimb bones won't allow a sprawling posture. That is unique."
The researchers observed that Bunostegos' humerus was not twisted like those of sprawlers, suggesting that if the elbow and shoulders were aligned under the body the foot would be able to reach the ground. Sprawling pareiasaurs had mobility at the elbow, but Bunostegos had more limited elbow mobility. The animals' forearm bones form a hinge-like joint that were only able to swing back and forth like a human knee, and not from side to side. The researchers believe other animals with similar posture that lived during Earth's early days will one day be revealed.
"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."
The findings were published in a recent edition of the Journal of Vertebrate Paleontology.
