introduction permian tetrapods

INTRODUCTION

The Permian is the last period of the Paleozoic Era. During the late Carboniferous and the Permian the amniotes diversified in three main lineages (four if we include Diadectomorpha), Synapsida, Eureptilia, Parareptilia. Among early synapsid eupelycosaurs could be traced our remote ancestors, among early eureptilians the ancestors of birds and snakes, among parareptilians, perhaps, the ones of the turtles. The amphibian lineages continued their diversification in the Lower Permian. Frogs and salamanders probably have their origin in temnospondyl branchiosaurs (Temnospondyli), the caecilians, perhaps, from microsaurs (Lepospondyli). There is a continuity in the amniote fauna of late Carboniferous and lower Permian, less there is between the lower and the late Permian. The lower Permian is dominated by carnivorous sphenacodontids and herbivorous edaphosaurs, caseids and captorhinids. The late Permian is dominated by carnivorous and herbivorous therapsids (that are sphenacodontid descendants), and large herbivorous parareptilians. The diapsids remained rare through all the period except at the extreme end, and a rich diapsid fauna is documented in the upper Permian of Madagascar. The most rich lower Permian sites are situated in North America (Texas and Oklahoma) in general they are deltaic-lowland deposits, with some exceptions, the most important of these is the Dolese Quarry at Richards Spur - Fort Sill. Richards Spur documents an highly diversified upland fauna. The fossils are in general disarticulated but very well preserved in Permian fissures that are occasionally discovered during the quarry operations, the surrounding rocks are Ordovician. The lower Permian Irati Formation, in South America, is famous for they mesosaurs that are present also on the other side of Atlantic Ocean in South Africa, proof of a probable ancient connection of the two continents. In Europe, important lower Permian sites are situated in France, Germany and Czech Republic. They are lacustrine deposits with a tetrapod fauna almost exclusively composed of amphibians that are very well preserved also in the soft tissues, but there are some important exceptions, as Bromacker Locality, that recently has yielded skeletons of sphenacodontids, diadectomorphs and seymouriamorphs, and most important, a complete skeleton of a bipedal bolosaurid. The late Permian is not well documented in North America or western Europe but it is in Russia and South Africa, with a fauna of therapsids and parareptilian pareiasaurs. Of interest is the upper Permian of Moradi Formation in Niger, in this site are dominant pareiasaurs and the large captorhinid Moradisaurus. The Permian finished with the terrible Permo-Triassic extinction that wiped out great part of the Paleozoic world, few taxa were able to survive and radiate in the early Triassic recreating for brief period a fauna rich of therapsids as in the upper Permian, but soon the diapsid archosaurs replaced them in the Mesozoic world. The therapsid descendants, the Mammals, regain the scene only after the end of Cretaceous.