The shock study shows that the evolution of the forelegs of mammals began to emerge 270 million years ago, some 40 million years before the onset of the first dinosaurs during the Triassic Period. The members in question belonged to a group of ancient mammals known as synapsids, which separated from sauropsids, which included dinosaurs, birds, crocodiles and lizards, about 312 million years ago. Research has also shown that no other vertebrate has evolved on such a high number of members. For example, birds have wings and almost all lizards walk on all fours.
The author of the study, Jacqueline Lungmus, research assistant at the Field Museum in Chicago and PhD student at the University of Chicago, said: "In addition to fur, the diversified form of the anterior paw is one of the most emblematic features of mammals.
"We were trying to understand where this comes from, whether it's a recent feature or it's a particular feature of the group of animals to which we belong since the beginning. "
Despite this, the first synapsids, called pelycosaurs, looked like gigantic swelling lizards, but they are actually closer to us than are the dinosaurs.
Ken Angielczyk, co-author of the study and curator of the Field Museum, said, "If you saw a pelycosaur walking down the street, you would not think it looks like a mammal – you'd say," C & # 39; is a crocodile of strange appearance. "
The team examined the bones of the arms of hundreds of fossil remains of therapids, another mammalian ancestor, and pelycosaurs, to reach their conclusion.
Ms. Lungmus added, "Modern mammals are the only surviving therapies. This is the group we are part of today.
"Therapidides were the first members of our family to truly diversify, and instead of crocodile-like pelycosaurs, therapids included light carnivores, sturdy burrowers, and tree-dwelling plant eaters.
"This is the first study to quantify the shape of the forelegs on a large sample of these animals.
The therapsids are the first synapsids to increase the variability of their forelegs. This study radically repels this trait in time.
"Prior to this study, paleontologists had been the first to be able to retrace definitively the diversity of the forelegs of mammals before 160 million years ago.
"Our work has repelled this for more than a hundred million years."
"It's something very cool in our evolutionary lineage.
"These animals are part of the same group as us, what makes this research fascinating is that they are our parents."