| Hylonomus, Protorothyrididae, Protorothyris, Petrolacosaurus, Eureptilia|
Paleothyris was a small, agile, anapsid romeriidan reptile which lived in the Middle Pennsylvanian epoch in Nova Scotia (approximately 312 to 304 million years ago). Paleothyris had sharp teeth and large eyes, meaning that it was a nocturnal hunter. It was about a foot long. It probably fed on insects and other smaller animals found on the floor of its forest home. Paleothyris was an early sauropsid, yet it still had some features that were more primitive, more labyrinthodont-like than reptile-like, especially its skull, which lacked fenestrae, holes found in the skulls of most modern reptiles and mammals.