Know Your Early Diapsids

One of Dr. John Merck's online lectures for one of his geology classes summarizes some aspects of diapsida and specifically references the characters of Petrolacosaurus that have caused it to be assigned to the base of the diapsid family tree. Other sites have information on Petrolacosaurus as well. These include Prehistoric Wildlife which has a short paragraph describing what is known about the small reptile. A more extensive entry and probably the most comprehensive and easy to read entry outside of the Wikipedia article or a scholarly journal entry is that found on the Walking with Monsters version of the wiki sites.