Dinocephalians were a group of prehistoric reptiles that lived during the late Permian and early Triassic periods, around 270 to 240 million years ago. They are known for their distinctive features, including large skulls and thick bones, which suggest they were robust animals. These creatures were primarily herbivorous, feeding on plants, and they played a significant role in their ecosystems. This group is part of the larger clade called Therapsida, which includes ancestors of modern mammals. Dinocephalians are often recognized for their unique adaptations, such as specialized teeth and body structures, which helped them thrive in various environments during their time on Earth.