RELATIONSHIPS OF SEYMOURIA, DIADECTES, AND CHELONIA

Evidence now available supports the concept of close relationshipbetween the seymouriamorphs and diadectids, with the lattera specialized offshoot of the former. Diadectes itself clearlyis not a progenitor of Chelonia. The seymouriamorphdiadectidcomplex may be a sterile line, except for the gephyrostegidswhich, originating very early among seymouriamorphs, may haveled to true reptiles. There is some evidence, mostly highly tentative, that procolophonsand their probable descendants, the pareiasaurs, may have arisenfrom the non-gephyrostegid seymouriamorph stock. Chelonia couldhave found their ancestery within the procolophons or pareiasaurs.If this is the case, and only additional study can confirm ordeny it, then the concept of the Parareptilia, as proposed earlier(Olson, 1947), may retain much of its original meaning, withthe Diadectidae, however, far removed from the ancestry of theChelonia.