Dawn of the Reptiles

We have discussed the dawn of the dinosaurs, multiple times depending on the taxa discussed in any given week, the dawn of mammals, birds, amphibians, and a number of other introductory taxa. Some of these have been composed of disarticulated nearly complete skeletons and some have included single limbs or even single bones. One of the most complete purported "first" taxa is one of the earliest diapsids, a small reptile with two holes in its lateral skull wall (from which we gather the meaning of the word diapsid). Discovered in 1932, the fossil of Petrolacosaurus kansanensis (Lane 1945) comes from the Pennsylvanian age of the Carboniferous (approximately 302 MA) and includes the skull, pectoral girdle, elements of the hind and fore limbs, and a large portion, if not the entirety, of the axial or vertebral skeleton.