some large therocephalians after the Middle Permian. Despite the existence of a single continent during the Permian, Pangaea, gorgonopsians have only been found in the Karoo Supergroup (primarily in South Africa, but also in Tanzania, Zambia, and Malawi), the Moradi Formation of Niger, western Russia, and in the Turpan Basin of Xinjiang, China, with probable remains known from the Kundaram Formation in the Pranhita–Godavari Basin of India. These places were semi-arid areas with highly seasonal rainfall. Gorgonopsian genera are all very similar in appearance, and consequently many species have been named based on flimsy and likely age-related differences since their discovery in the late 19th century, and the group has been subject to several taxonomic revisions. They became extinct during a phase of the Permian–Triassic extinction event taking place at the very end of the Permian, in which major volcanic activity (which would produce the Siberian Traps) and resultant massive spike in greenhouse gases caused rapid aridification due to temperature spike, acid rain, frequent wildfires, and potential breakdown of the ozone layer. The large predatory niches would be taken over by the archosaurs (namely crocodilians and dinosaurs) in the Mesozoic. Description Earlier gorgonopsids in the Middle Permian were quite small, with skull lengths of , whereas some later genera attained massive, bear-like sizes with the largest being Inostrancevia up to in length and in body mass. Nonetheless, small gorgonopsians remained abundant until extinction (though small species may actually represent juvenile specimens of other taxa). Like other Permian therapsids, gorgonopsians had developed several mammalian characteristics. These might have included a parasagittal gait (the limbs were vertically oriented and moved parallel to the spine) as opposed to the sprawling gait of amphibians and earlier synapsids. This gait change in therapsids was possibly related to the reduction in tail size and phalangeal formula (the number of bones per digit, which for gorgonopsians was 2.3.4.5.3 like reptiles). Other developments included fibrous lamellar cortical bone and deeply-set teeth. Like reptiles, gorgonopsians lack a secondary palate separating the mouth from the nasal cavity, prohibiting chewing. Skull Anatomy varies incredibly little between gorgonopsians. Many species are distinguished by vague proportional differences, and consequently smaller species may actually represent juveniles of larger taxa. Notably, the vomer at the tip of the snout varies among species in terms of the degree of its expansion, as well as the positions, degree of splay, and shape of the 3 ridges. They