The Guadalupian Epoch

The Guadalupian Epoch of the Permian Period: 271 to 260 million years ago

Introduction

The Guadalupian Stage was named after the Guadalupe Mountains of New Mexico, U.S.A., where rocks and fossils of this age are known. These rock strata and fossils were formed during the middle Permian period, and as part of the recent revision of Permian stratigraphy (in order to attain a standard global correlation) the old division of lower and upper Permian has been supplemented, if not replaced, by a newer arrangement. In this the Guadalupian epoch refers to the Middle Permian (with the Lopingian as the Late Permian).

The first two-thirds of this epoch were characterized by a continuation of the temperate and tropical climate zones established during the preceding Kungurian Age. But the drying climate meant the end of the great tropical coal forests that had dominated the equatorial belt for so long and provided a haven for numerous stem tetrapods, reptiles, fish, invertebrates, and plants. The last third experienced a drop in temepratures, the Kamura cooling event (Isozaki et al 2007), during which tropical coral reefs and many marine organisms died out. Finally, vulcanism led to a Greenhouse crisis, anoxia, and a mass-extinction at the end of the epoch (Retallack 2005 Retallack et al 2006)

During this period, evolutionary turn-over was high, and on land a series of animal dynasties successed each other.

At the top of the middle Permian food chain were giant carnivores, such as the Eotitanosuchids and the appropriately named "terrible heads" or Dinocephalians. These latter included Titanophoneus pictured above) and Anteosaurus. Some, such as Ivantosaurus and Anteosaurus were the largest land carnivores of the Permian period, reaching 5 or more meters in length, and dwarfing even the bigger fin-back Dimetrodons of the Early Permian.

These animals were among the most primitive of the therapsids. In older books they are called "mammal-like reptiles" because they were on the evolutionary road to mammals, and may have even had the very beginnings of a primitive warm-blooded metabolism, although the presence of fur (shown in the Titanophoneus illustrated above) at this early stage is probably dubious. These creatures preyed on their equally if not bigger herbivorous contemporaries, the moose-like Estemmenosuchids, the great Tapinocephalids (upto 2 tonnes live weight) with their immensely thickened skulls allowing head-butting territorial behavior, and the bizarre armoured and possibly semi-aquatic pareiasaurs.

In addition to this megafauna a diverse selection of smaller reptiles inhabited the undergrowth, and stem temnospondyl amphibians, although diminished from their early Permain heyday, still frequented ponds, rivers, and lakes. Some, like the aquatic Melosaurus, was an Eryops-type predator reaching 2 to 3 meters . This creature was clearly able to eat just about anything it could wrap its huge mouth around (mostly fish and smaller tetrapods and reptiles).

Among the smaller animals that would have ended up in Melosaurus' stomach were Discosauriscus, an aquatic batrachosaur Seymouriomorpha) that was very close to the base of the true reptiles. Ironically, whilst reptiles had evolved from batrachosaurs millions of years earlier, these Carboniferous relics had continued as "living fossils", retreating back to the ponds as their last refuge

While animals were undergoing a change so were plants, with xerophyletic (dry-adapted) species of ferns, seed-ferns, conifers and ginkgos coming into prominence. The Glossopteris flora dominates in Gondwanaland. These new plants mark the transition between the Paleophytic (the old spore-bearing moisture loving coal swamp plants) and the Mesophytic (gymnospermous) era of plant evolution. Significantly, whereas animal life has its big transition at the very end of the Permian, plant life switches over to a more modern flora some ten to twenty million years previous. The same pattern is seen in in the late Mesozoic era, where modern flowering plants appear long before the extinction of the dinosaurs and their contemporaries.

"Life on much of the supercontinent Pangea resembled central Asia today: Large inland areas, far from moderating oceans, suffered baking summers and bitter winters. At tropical and subtropical latitudes, summer monsoon rains bathed the continent's east coast. Those conjectures come from a computer model that uses coastlines and topography-plus a few laws of physics, like the equations for air movements and heat transport-to predict the climate 250 million years ago. The idealized, squared-off coastline of this map simplified the calculations done in 1993 by Chicago's Alfred Ziegler and John Kutzbach of the University of Wisconsin-Madison (illustration by Allen Carroll). Rainfall and temperature data determine the biome regions where evolution unfolded, from tundra to tropics. Wind patterns can predict ocean currents like the upwellings that fostered plankton, a clue to today's oil deposits. And comparisons to the actual climate and biome, deduced from fossil and geologic evidence, improve the computer model-refining predictions of future climate change, like global warming."

The Guadalupian epoch ended with a deteriorating environment, Greenhouse conditions, and several series of mass-extinctions; both the great dinocephalians and other taxa on land, and varuious invertebrates in the sea. In teh following, Lopingian, age, new types of mammal-like reptiles would dominate the land.