The Permian period was named after the kingdom of Permia, Russia. During the Early Permian the great swamplands, lakes and floodplains of Carboniferous dried out. Their flora, in particular their giant club mosses and calamites, went into fast decline, to be replaced by conifers descending from the uplands, and by other gymnosperms (seed-bearing plants) such as cycads, ginkgoes and seed ferns. A new flora then spread southwards, dominated by the seed fern Glossopteris.
In the Late Carboniferous the areas behind the eye sockets of some of the reptiles had begun to develop arched openings known as temporal fenestra (‘windows’). These openings appear to provide extra space for the attachment of jaw muscles, and muscles appear to attach more readily to edges rather than to flat surfaces. There are thus four main forms of skull: anapsid, synapsid, diapsid and euryapsid (the names refer to the number and disposition of the arched openings. All of the reptiles, birds and mammals can be traced back to the first three of these groups.
Anapsids (‘no arches’) have no skull openings, a characteristic inherited by the earliest reptiles from the fishes and amphibians. The early anapsids, such as Hylonomus, were small insect-eaters. In the Permian and Triassic the procolophonids, small animals with short triangular skulls, had broad teeth adapted to a diet of tough plants and insects. The only surviving anapsids are the turtles, which made their first appearance in the Late Triassic.
Synapsids (‘jointed arches’) have a single pair of skull open-ings and evolved from an anapsid ancestor yet to be discovered. This monophyletic (‘of one race’, i.e. having a common ancestor) group includes all of the now extinct mammal-like reptiles that gave rise to the mammals. Starting from small animals, the synapsids produced animals such as Ophiacodon, which reached lengths of three metres (10 ft). These creatures were known as pelycosaurs, the majority of which were predators, but included were a number of groups that adapted to plant-eating, the first herbivorous land vertebrates. In the Early Permian there appeared the well known predator, Dimetrodon (‘two sizes of teeth’), often mistakenly called a dinosaur, which reached a length of three metres (10 ft). Its tall ‘tail’ regulated its body temperature.
Diapsids (‘two arches’) have two pairs of skull openings and evolved sometime later. This monophyletic group includes the birds, crocodiles, dinosaurs, lizards and snakes. Living along-side the pelycosaurs in the Late Carboniferous was the smaller, lizard-like diapsid Petrolacosaurus. Animals of this general type have been very successful and have been around for over 300 million years.
Euryapsids (wide arches’) have a single pair of facial openings but these are smaller than those in the synapsids. This group is a mixed set of extinct marine reptiles that probably evolved from a number of synapsid ancestors. In Early PerMian times another small animal to be found alongside the pelycosaurs was the euryapsid Araeoscelis. This animal was an early member of a group that was to show a repeated tendency to return to the water.
From the Middle Permian the long-bodied species represented by the pelycosaurs was replaced by different animals, generally known as therapsids. Gorgonopsians (‘gorgon faces’) had a wolf-like body and massive sabre teeth probably used to attack the larger thick-skinned herbivores. Dicynodonts (‘two dog teeth’, i.e. tusks) were herbivores, and some of them were the first animals to have a complex chewing cycle that enabled them to tackle a wide variety of food plants. Dinocephalians (‘fearsome heads’) fall into two groups: the mostly carnivorous anteosaurs (‘early reptiles’), which included giants up to 6 metres and more in length, and the medium to very large herbivorous estemmenosuchids (‘crowned crocodiles’) and tapinocephalians (‘low heads’). Therocephalians (‘beast heads’) were a mixed group of smaller carnivores.
The end of the Permian was marked by Earth’s most severe extinction event. Most of these animals died out. The gorgonopsians disappeared, and the dicynodonts were nearly wiped out. Nearly seventy-five percent of all amphibian and reptile families disappeared. One-half of all marine families were lost. It is the only known mass extinction of insects; sixty percent of all families were killed off. Plants were also affected; their overall diversity was halved, but appeared to follow a pattern of long-term change.
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