Synapsids are one of the major groups of terrestrial vertebrates. They first appear in the Carboniferous period and since that time have gone through many radiation and extinction events. But what did these first stem-mammals look like, how did they live and how do they differ from modern mammals? These may sound like simple questions, but there is an underrepresentation of terrestial deposits from the Permian. How then can we understand larger-scale evolutionary patterns when so much data is missing?