Bunostegos akokanensis, a 260-million-year-old pre-reptile may have been the first creature to walk upright on all fours, like a cow or a hippo, new research suggests.
Bone analysis of the animal's fossils showed that it stood like a cow, and could be about the same size.
"Imagine a cow-sized, plant-eating reptile with a knobby skull and bony armour down its back," said study co-author Linda Tsuji of the Royal Ontario Museum in Canada who discovered the fossils in Niger along with a team of paleontologists in 2003 and 2006.
"A lot of the animals that lived around the time had a similar upright or semi-upright hind limb posture, but what is interesting and special about Bunostegos is the forelimb," lead author of the study Morgan Turner, graduate student at Brown University in Rhode Island, US, pointed out.
Bunostegos stood differently than all the rest, with the legs entirely beneath the body, she said.
"Bunostegos was an isolated pareiasaur," Turner noted.
Way back when, Niger was an arid place (like some of it is today) where plants and water sources might well have been few and far between.
Scientists have associated walking upright on all fours with a more energy efficient posture than sprawling.
For the long journeys between meals, Turner said, the upright posture might have been necessary for survival.
The significance of such an early example of the upright posture is that Bunostegos dates very far back on the evolutionary tree, pushing back the clock on when this posture shows up in evolution.
But Turner said she would not be surprised if other animals of the time are eventually also found to have similarities to this posture, which evolved independently in reptiles and mammals several times over the eras.
The findings appeared in the Journal of Vertebrate Paleontology.