Petrolacosaurus

Petrolacosaurus ("rock lake lizard") is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, 40-centimetre (16 in) long reptile, and one of the earliest known reptiles with two temporal fenestrae. This means that it was near the base of Diapsida (it may have been the basal taxon), the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs (which survived to the modern day as birds) and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of Araeoscelidia, a short-lived early branch of the diapsid family tree which went extinct in the mid-Permian.