We look closer at the terrestrial world. Where there are copses of vegetation near ponds and water there are herds of the dicynodont Lystrosaurus. They are stolid and lamb-sized, even as adults, but nevertheless are the largest animals on the planet. They are not very active, and all are living at sea level. Almost motionless, they slowly graze on the low vegetation; moving about leaves them breathless. Two kinds of small carnivores harass their young—the small cynodonts, looking much like strange primitive dogs, and graceful, low-slung but active diapsids known as Proterosuchus. They are ambush predators, for the stalking of prey requires locomotion, and while both are capable of rapid bursts of movement to bring down prey, the low oxygen quickly puts them in respiratory debt. What is striking is that other than these few inhabitants there is little else, and the lack of diversity is perhaps the most striking aspect of this world. A paltry few members of the once common dicynodonts such as Dicynodon dodder about, and there is still a last predatory gorgonopsian or two, but these are the last relics of lineages headed to complete extinction. Even insects are rare here and of few varieties, for their kind suffered great losses in the extinction that by this time has been a succession of paroxysms over several million years, and there has still not been an evolutionary burst of new forms. The heat and low oxygen have not relented; in fact, they continue to trend unfavorably. The oxygen content now is even lower than

Reconstruction of a gorgonopsian, the largest late Permian predator and also a victim of the Permian extinction. The largest of these top carnivores would have reached 10 feet in length.