was initially overlooked so it is unclear how common this pathology actually is. Palaeoecology Following the extinction of the dinocephalians and (in South Africa) the basal therocephalians Scylacosauridae and Lycosuchidae, gorgonopsians evolved from small and uncommon forms into large apex predators. Through the Middle to Upper Permian, in South Africa the dicynodonts were the most common animals, whereas the pareiasaurs Deltavjatia and Scutosaurus were the most abundant in the gorgonopsian-bearing Russian formations. During the Upper Permian, the South African Beaufort Group was a semi-arid cold steppe featuring large, seasonal (ephemeral) rivers and floodplains draining water sources much farther north into the Karoo Sea, with some occurrences of flash floods after sudden, heavy rainfall; the distribution of carbonates is consistent with present-day caliche deposits which form in climates with an average temperature of and of seasonal rainfall. The gorgonopsian-bearing Salarevskian Formation in western Russia was also probably deposited in a semi-arid environment with highly seasonal rainfall, and featured hygrophyte and halophyte plants in coastal areas, as well as more drought-resistant conifers at higher elevations. The Moradi Formation was an arid desert, primarily dominated by the captorhinid reptile Moradisaurus and the pareiasaur Bunostegos''. It featured voltzian conifers, and has environmentally been compared to the interior Namib Desert or the Lake Eyre basin. Extinction Gorgonopsians went extinct at the end of the Upper Permian during the Permian-Triassic extinction event, which was primarily caused by volcanism which formed the Siberian Traps. The resultant massive spike in greenhouse gases caused rapid aridification due to: temperature spike (as much as 8–10 °C at the equator, with average equatorial temperatures of 32–35 °C, or 90–95 °F, at the beginning of the Triassic), acid rain (with pH as low as 2 or 3 during eruption and 4 globally, and the subsequent dearth of forests for the first 10 million years of the Triassic), frequent wildfires (though they were already rather common throughout the Permian), and potential breakdown of the ozone layer (possibly briefly increasing UV radiation bombardment by 400% at the equator and 5000% at the poles). Among therapsids, small therocephalians and large herbivorous anomodonts managed to cross the Permian–Triassic boundary, and survived respectively until the Middle and Upper Triassic, but only small-bodied species of cynodonts survived into the Jurassic, whose descendants would include mammals. The niches gorgonopsians left open were eventually filled by the archosaurs (including crocodiles and dinosaurs) during the early stages of the Triassic. See