Therapsida is a group of synapsid reptiles that lived during the late Permian period and are considered ancestors of mammals. They are characterized by features such as differentiated teeth and a more advanced jaw structure, which allowed for a varied diet. Therapsids played a crucial role in the evolution of mammals, showcasing adaptations that would later be seen in their descendants. This group includes several subgroups, such as cynodonts, which are particularly important as they exhibit traits similar to modern mammals. Therapsids thrived during the Mesozoic era, and their evolutionary innovations laid the groundwork for the rise of mammals after the mass extinction event that ended the dinosaurs.