October 25, 2024 This article has been reviewed according to Science X's editorial process and policies . Editors have highlightedthe following attributes while ensuring the content's credibility: fact-checked peer-reviewed publication trusted source proofread by Harvard University Mammals, including humans, stand out with their distinctively upright posture, a key trait that fueled their spectacular evolutionary success. Yet, the earliest known ancestors of modern mammals more resembled reptiles, with limbs stuck out to their sides in a sprawled posture.
The shift from a sprawled stance, like that of lizards, to the upright posture of modern mammals, as in humans, dogs, and horses, marked a pivotal moment in evolution. It involved a major reorganization of limb anatomy and function in synapsids—the group that includes both mammals and their non-mammalian ancestors—eventually leading to the therian mammals (marsupials and placentals) we know today. Despite over a century of study, the exact "how," "why," and "when" behind this evolutionary leap has remained elusive.
Now, in a study published in Science Advances , Harvard researchers provide new insights into this mystery, revealing the shift from a sprawled to upright posture in mammals was anything but straightforward. Using cutting-edge methods that blend fossil data with advanced biomechanical modeling, the researchers found that this transition was surprisingly complex and nonlinear, and occurred much later than previ.
