The oldest animal to have a skeletal structure that forced it to walk on four legs was a plant-eating reptile named Bunostegos akokanensis that lived in Niger in Africa 260 million years ago. Linda Tsuji of the Royal Ontario Museum and Professor Christian Sidor at the University of Washington are the first to discover the unique bone structure in an animal that lived at a time when all other land animals crawled.
Bunostegos akokanensis roamed ancient Niger with four legs that were directly beneath the animal’s body. The long bone in all of the limbs called the humerus did not have a structure called a twist that would allow the animal to move flat on the ground like all of its contemporaries. The animal’s shoulder was also not capable of moving in a manner that allowed the animal to sprawl on its belly to move. The elbow of all four limbs would not allow the animal to sprawl on the ground.
The area of Niger that the first four-footed animal lived in was extremely arid at the time the extinct animal lived. The researchers consider the animal to have been an evolutionary fluke that came about due to the necessity of traveling long distances to obtain food and water in a very arid climate. Bunostegos akokanensis may have been as large as a cow and had bone armor on its sides and a knobby skull. The animal predates any other known animal that walked on four limbs by as much as 40 million years.
