Scientists discover earliest-known animal able to walk on all fours

Contributed by
Sep 22, 2015, 12:45 PM EDT

A team of scientists at Brown University has identified a chunky, cow-like dinosaur that appears to be one of the first creatures ever to walk on all fours.  Their remarkable findings were published in the current edition of the Journal of Vertebrate Paleontology.  Long before the awesome T-rex thundered through the primeval forests of Earth, Bunostegos akokanensis, an ancient “pre-reptile,” munched on arid desert plants during the Permian era more than 260 million years ago.  The remains of Bunostegos were first discovered in Niger by paleontologist and study co-author Linda Tsuji of the Royal Ontario Museum in 2003 and 2006. 


Studying its fossilized form, the Brown University research team, which included Morgan Turner and Christian Sidor, has deduced that it stood upright on all four legs, making it the earliest known quadrupedal creature to do so. The bulky Bunostegos belonged to an ancient group of para-reptiles called Pareiasaurs, beefy Permian Era herbivores that favored a thick, stocky torso and featured stubby tails, small heads, muscly limbs and flat feet. 

“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 its anatomy is sprawling—precluding and seemingly directed underneath its body—unlike anything else at the time,” noted Turner in a press release. “The elements and features within the forelimb bones won’t allow a sprawling posture. That is unique.”


Technically classified as belly-resting "sprawlers," these creatures sprouted stout limbs that grew out from the sides of their bodies, then continued out or angled down from the elbow joint.  Similar examples would include what we would consider to be modern lizards.  However, this Pareiasaur evolved differently to adapt to the dry, climate of the Pangea supercontinent's desert interior, allowing it to attain much greater mobility and energy efficiency over the vast desert terrain.

“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.”

What do you think of the upright quadrupedal Bunostegos and its dino-cow cuteness?