These animals are thought to be the closest outgroup to the clade Amniota. Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. Commonly accepted fact that Sertol cells are terminally differentiated in amniota was recently changed. Notably, this appears to be the ancestral tooth condition in Amniota. Heaton's originally classified the diadectomorphs as amphibians, outside of and sister to Amniota.