The struggle of early mammals in developing an upright stance was no easy feat.
### Uncovering the Complex Evolution of Upright Posture in Early Mammals
The evolution of upright posture in early mammals, a significant milestone in their history, has long been a subject of interest for scientists. A groundbreaking study published in PLOS Biology has shed new light on this topic, revealing a more complex and non-linear evolutionary process than previously thought.
The study, led by Robert Brocklehurst from Harvard University's Museum of Comparative Zoology, delves into the evolutionary path that led to the development of upright posture. Contrary to the linear progression model proposed earlier, the research suggests that the transition was a dynamic and experimental process, involving bursts of anatomical changes and diverse experiments with movement.
The evolution of upright posture followed a complex branching process, with different mammalian ancestors trying various ways of moving before settling on upright walking. This indicates that mammals explored multiple paths before converging on the efficient upright posture.
The transition involved significant changes in limb bone shape and mechanics. For instance, the humerus (upper arm bone) underwent changes in length, torsion, bending strength, and muscle leverage to support upright movement.
To better understand this evolutionary journey, researchers used a computational model to connect bone shape with function and posture. This analysis revealed how different bone structures could support either sprawled or upright postures, providing insights into the adaptive landscapes that early mammals navigated.
The study's findings challenge the previously held linear progression model, revealing instead a more dynamic and experimental evolutionary path. The complexity of the evolutionary process highlights the adaptability and resilience of early mammals as they transitioned to upright posture.
Mammals trace their origins to the earliest stem mammals more than 300 million years ago. The study's focus on understanding bone function and mechanics, rather than just shape, has been instrumental in uncovering the evolutionary story of upright posture in mammals.
Monotremes, with their reptilian features and sprawled stance, were critical in the study. The research points to a period of diversification in stem mammals, rather than a straight-line path to an upright posture.
The study was originally published by Cosmos. It compared fossil bones to those of living animals, including salamanders, reptiles, upright therian mammals, and monotremes. Brocklehurst's team analyzed the humerus bones of over 200 species of tetrapods.
The mass extinction at the end of the Permian period about 252 million years ago led to the extinction of many synapsids, the ancestors of mammals. After this mass extinction, mammals continued to evolve as mostly small, nocturnal creatures under the shadow of dinosaurs.
The development from a reptile-like sprawling mode of locomotion to a more upright (parasagittal) posture was a significant factor in the evolution of mammals. The study reveals that the hallmark forelimb posture and function of modern mammals emerged surprisingly late in synapsid evolution.
The authors of the study suggest that fossils were not stepping-stones but animals evolving to explore a wide range of ecologies, niches, and habitats. This approach offers a fresh perspective on the evolution of early mammals, emphasizing their adaptability and resilience in the face of environmental changes.
During the study, researchers found that the evolution of upright posture in early mammals was a complex and non-linear process, with various medical-conditions and technological advancements playing crucial roles in this transition. For example, the team used a computational model to better understand the function and posture of different bone structures, shedding light on the various ways mammals adapted to different environments. Additionally, the study showcased how technology enabled scientists to delve deeper into the science of evolution, uncovering previously unknown facts about the complex evolutionary history of our ancestors.
