In Science news, there has been a lot of talk about our early biped ancestors. Yet there have been some amazing breakthroughs in the field of quadrupeds as well. Scientists believe they have determined the first creature to ever walk on four legs.
Living around 260 million years ago, the Bunostegos akokanensis was as large as a cow and ate plants. The Bunostegos akokanensis is an example of a pre-reptile, that is, a vertebrae creature living before the age of the dinosaurs that displayed many mammal-like characteristics. The creatures lived in an age when all of the world’s continents were still joined as one, Pangaea.
Unlike all of the other creatures roaming Pangaea, the Bunostegos akokanensis could stand on all four legs and walk like a cow or hippopotamus, according to the study published in Journal of Vertebrate Paleontology.
“We don’t see upright posture, with the legs underneath the body, in both the forelimb and the hindlimb in a single animal until much later, in mammals and in dinosaurs,” said study co-author Morgan Turner of Brown University. “Bunostegos is much further back on the evolutionary tree than anything else that exhibits this posture [and] hints at a larger story about posture and locomotion evolution.”
“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,” said Turner
What Turner means by ‘sprawling’ is the placement of legs beneath lizards, etc. The legs are not directly underneath the body of a lizard but rather the arms are horizontal to the main frame and the legs are vertically in line with the body and tail.
In Bunostegos, “the elements and features within the forelimb bones won’t allow a sprawling posture. That is unique,” said Turner.
Scientists first identified Bunostegos in 2003 after finding its peculiarly knobby skull buried in the Sahara Desert of northern Niger. A team of paleontologists spent the next three years unearthing the rest of the fossilized skeleton.
Walking on four legs would have allowed the Bunostegos to cover much more ground in a single day- a necessary ability for surviving in the central desert of Pangaea.
“Here’s this big, cow-sized animal in this very arid region,” said Dr. Nick Fraser, a vertebrate paleontologist from the National Museum of Scotland. “You don’t think of big herbivores in arid regions. What was going on there? Do we really understand what the climate was? The more we learn about this creature, the more we will learn about what appears to be an isolated environment in the center of Pangea.”
The study describes in detail the most probably arrangement of the bones in support of their claim to have found the first creature to walk upright on four legs.
The shoulder joints of the Bunostegos is pointing downward- meaning the front arms could not splay out horizontally. Moreover, the humerus is strong and straight, unlike the twisted arm-bones of lizards. This encourages speculation that the bones served as a weight-bearing support pillars.
“Aspects of the anatomy of the shoulder and the forelimb indicate that the humerus could not have jutted out in a ‘sprawling’ posture,” said Dr. Linda Tsuji of the Royal Ontario Museum, study co-author and a member of the team that found the Bunostegos in Niger. “And in Bunostegos we see limited motion at the elbow joint, which is an indication of upright posture in other animals.”
Similarly, the hip joints and femurs are more similar to a cow’s than a lizard’s.
“Posture, from sprawling to upright, is not black or white, but instead is a gradient of forms,” said Turner. “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.”