appears to have been the highest Paleozoic peak in extinction rate observed in Eureptilia, exceeding even the Permian–Triassic mass extinction. Amphibians were also particularly hard-hit. In December 2011, the fossilized remains of the 'youngest' pelycosaur was described by Modesto et al. as from 260 million years ago in South Africa. This, and slightly older remains of varanopids, documents the fact that this clade, like some caseids, survived Olson's Extinction. This type of animal is called a disaster taxon, an organism that survives a major environmental disruption, perhaps forming the basis for a new adaptive radiation. In the water Fish Extinction rates in fish increased noticeably between the Cisuralian and the Guadalupian, the time of Olson's extinction. However, origination rates also rose, and so there does not appear to have been any substantial decrease in species richness. Using data on chondrichthyan diversity, Koot showed that there was little substantial decline in diversity until the middle of the Guadalupian. Recovery Fauna did not recover fully from Olson's Extinction before the impact of the Permian-Triassic extinction event. Estimates of recovery time vary, where some authors indicated recovery was prolonged, lasting 30 million years into the Triassic. Several important events took place during Olson's Extinction, most notably the origin of therapsids, a group that includes the evolutionary ancestors of mammals. Further research on the recently identified primitive therapsid of the Xidagou Formation (Dashankou locality) in China of Roadian age may provide more information on this topic. References Further reading io9.com: "Why did nearly all life on Earth die 250 million years ago ?" Vancouversun.com: "Canadian researchers spearhead fossil discovery of resilient prehistoric animal." Extinction events Guadalupian life Permian events Permian North America