Most long-necked sauropods have spent all their lives on all fours to support their titanic mass. But a first parent of these behemoths as Brachiosaurus A new study shows that the unusual transition between four legged walking and two leg walking has progressed.
Diminutive to hatching, Mussaurus patagonicus (which means "mouse lizard") started life by walking on all fours. But by the time the 200-million-year-old plant eater reached his adult height of 6 meters, he was walking through two legs, which is now Argentina.
The changing length of M. patagonicusThe bones of the arm in relation to his body and his palms turned inward, as an adult had suggested. But for the first time, computer simulations based on a rich fossil record show how a shift in the creature's center of gravity as it grew has allowed bipedal walking, researchers said on May 20 Scientific reports.
The researchers took fossil bone scanners from six individuals M. patagonicus – covering different stages of development of the species, ranging from newborns of 60 grams the size of a baby chicken to a ton and a half of adults the size of a rhinoceros. The researchers added virtual flesh to the digitized bones to create 3D models that allowed them to estimate both the weight and the center of gravity of the M. patagonicus at different stages of his life.
Reconstructions of the newborns showed that the creature's center of gravity was so advanced that the dinosaurs could only move by walking on all fours, says Andrew Cuff, paleontologist of the Royal's Structure and Movement Laboratory. Veterinary College of Hatfield, England. .
As the dinos grew, their center of gravity moved closer to their hips, allowing them to walk on two legs, discovering Cuff and his colleagues. The transition "is incredibly rare," he says. "We had a hard time finding other animals besides humans crossing this transition … Finding it in the fossil record is quite exceptional."
The findings suggest that these adult dinosaurs turned into bipeds because their tail muscles became heavier and heavier as they grew, shifting their center of gravity backwards, explains Stephen Poropat, paleontologist at the Swinburne University of Technology in Melbourne, Australia, who did not participate in the research. "It's not the changing proportions of mussaurusThe front legs require the transition from four-legged walking to two-legged walking as an adult, "he says.
As afterwards, long-necked dinosaurs have grown in size (SN online: 04/09/14), going on two legs was perhaps no longer an option. The massive sauropods probably started on all fours, as M. patagonicus and remained in this state, developing front legs in the shape of a trunk to support their weight. "What we gain from this [study] is that there may be a size limit to the size that you can become a biped in this group, "says Cuff.