Permian

The Permian Period, is the last period of the Paleozoic Era and famous for its ending epoch event, the largest mass extinction known to science. The Permian Period was named after the kingdom of Permia in modern-day Russia by Scottish geologist Roderick Murchison in 1841. The Permian period marked great changes in the Earths climate and appearance. The climate in the Permian was quite varied. At the start of the Permian, the Earth was still at the grip of an Ice Age from the Carboniferous. Glaciers receded around the mid-Permian period as the climate gradually warmed, drying the continents interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles. Trilobites and other marine groups became extinct, and a group of small reptiles (diapsids) appeared. These were the ancestors to most modern reptiles and the ruling dinosaurs as well as pterosaurs and crocodiles. Thriving also, were the early ancestors to mammals (synapdia), which included some large reptiles such as dimetrodon. Reptiles grew to dominate among vertebrates, because their special adaptations enabled them to flourish in the drier climate. The warm zone spread in the northern hemisphere, where extensive dry desert appeared. The rocks formed at that time were stained red by iron oxides, the result of intense heating by the sun of a surface devoid of vegetation cover. The old types of plants and animals died out. The three primary subdivisons of the Permian Period are given below from youngest to oldest, and include faunal stages also from youngest to oldest.

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Sea levels in the Permian remained generally low, and near-shore environments were limited by the collection of almost all major landmasses into a single continent - Pangaea. One continent, even a very large one, has less shoreline than 6 to 8 smaller ones. This could have in part caused the widespread extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms. Permian marine deposits are rich in fossil mollusks, echinoderms, and brachiopods. Fossilized shells of two kinds of invertebrates are widely used to identify Permian strata and correlate them between sites: fusulinids, a kind of shelled amoeba-like protist that is one of the foraminiferans, and ammonoids, shelled cephalopods that are distant relatives of the modern nautilus.

Terrestrial life in the Permian included diverse plants, fungi, arthropods, and various types of tetrapods. The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian there was a major transition in vegetation. The swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria, were replaced by the more advanced conifers, which were better adapted to the changing climatic conditions. Lycopods and swamp forests still dominated the South China continent because it was an isolated continent and it sat near or at the equator. Oxygen levels were probably high there.

The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. The ginkgos and cycads also appeared during this period. Rich forests were present in many areas, with a diverse mix of plant groups. A number of important new insect groups appeared at this time, including the Coleoptera (beetles) and Diptera (flies). Permian tetrapods consisted of temnospondyli, lepospondyli and batrachosaur amphibians and sauropsids and synapsid (pelycosaurs and therapsids) reptiles.

This period saw the development of a fully terrestrial fauna and the appearance of the first large herbivores and carnivores. Early Permian terrestrial faunas were dominated by pelycosaurs and amphibians, the middle Permian by primitive therapsids such as the dinocephalia, and the late Permian by more advanced therapsids such as gorgonopsians and dicynodonts. Towards the very end of the Permian the first archosaurs appeared (proterosuchid thecodonts); during the following Triassic period these latter would evolve into more advanced types and eventually into dinosaurs. Also appearaing at the end of the Permian were the first cynodonts, which would go on to evolve into mammals during the Triassic.

Another group of therapsids, the therocephalians (such as Trochosaurus), appeared in the Middle Permian. During this time, amphibians remained common, including various Temnospondyli and Lepospondyli. Synapsids became the dominant type of animal, represented by the Pelycosaurs during the Early Permian and Therapsids during the Middle and Late Permian, and distingusihed by the appearance and possession of mammal-like characteristics (hence the old term, mammal-like reptiles). These were accompanied by Anapsids or Parareptiles, which included both lizard-like and large herbivorous forms, and primitive diapsids.

The Permian ended with the most extensive extinction event recorded in paleontology: the Permian-Triassic extinction event. 90% to 95% of marine species became extinct, as well as 70% of all land organisms. It is also the only known mass extinction of insects. On an individual level, perhaps as many as 99.5% of separate organisms died as a result of the event. Recovery from the Permian-Triassic extinction event was protracted; on land ecosystems took 30 Million years to recover.