CHAPTER 4 – BIOGEOGRAPHY OF PRIMITIVE AMNIOTES

The origin of amniotes must have begun by the middle of Pennsylvanian or earlier. The past three decades have seen a revolution in the way terrestrial vertebrate fossils are studied. Studies by Carroll have proposed a transitional sequence of taxa that included gephyrostegids and soleonodonsaurids, which led to a primitive amniote bauplan exemplified by the small, presumably insectivorous members of the Protothyrididae family. Most of the authors consider Diadectomorpha and Seymouriamorpha to be successively more distant outgroups to the Amniota. In most recent works, the Seymouriamorpha has always been considered to be a stem Amniote group and no evidence exists for their inclusion within the Amnoita. Despite minor differences in recent phylogenetic analyses, the phylogenetic relationships and biogeographic distributions of the following taxa are considered by all to be critical to an understanding of the origin of Amniotes. In several papers describing the vertebrates and sediments of the commonly referred early Permian red-bed deposits of New Mexico, particularly the lowermost levels of the Cutler Formation, the somewhat ambiguous age of Permo-Carboniferous has been applied. It is noteworthy that only one theraspid has been reported from the early Permian called the enigmatic Tetraceratops of North-Central Texas.