Pelycosauria is an extinct group of early synapsids that lived during the late Carboniferous to the early Permian periods, approximately 300 to 250 million years ago. They are often recognized for their distinctive sail-like structures on their backs, formed by elongated neural spines. Pelycosaurs were among the first amniotes, a group that includes mammals and their ancestors. These creatures were primarily carnivorous, although some species were herbivorous. Pelycosaurs are significant in the study of evolution, as they represent a crucial stage in the transition from reptilian ancestors to modern mammals. Their diverse adaptations laid the groundwork for later synapsid evolution.