As per a new study, a pre-reptile may have been the earliest known to walk upright on all fours. The analysis of bones of the Bunostegos Akokanensis, a 260-million-year-old pre-reptile, found that it likely stood upright on all fours, like a cow or a hippo, making it the earliest known creature to do so.
To date, all of the known Pareiasaurs that roamed the supercontinent of Pangea in the Permian Era a quarter of a billion years ago were sprawlers whose limbs would jut out from the side of the body and then continue out or slant down from the elbow (like some modern lizards).
Lead author Morgan Turner expected the Bunostegos to be a sprawler too, but the bones of the animal's fore limbs tell a different story.
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 the Bunostegos is the fore limb, in that its anatomy is sprawling, precluding and seemingly directed underneath its body--unlike anything else at the time, said Turner.
He added that the elements and features within the fore limb bones won't allow a sprawling posture. That is unique. Co-author Linda Tsuji said "imagine a cow-sized, plant-eating reptile with a knobby skull and bony armor down its back." The study appears in the Journal of Vertebrate Paleontology.