[6] In 2008 Sahney and Benton[1] confirmed that this was not just a turnover (gradual replacement of one faunal complex by another) but a real extinction event in which a significant drop in the biodiversity of tetrapods on a global scale and community level occurred.
The extinction may have taken place in two phases: Edaphosauridae and Ophiacodontidae died out around the Kungurian–Roadian boundary, while Caseidae and Therapsida diversified; later in the Roadian or slightly later Sphenacodontidae died out,[3] although this was apparently the result of a slow decline over 20 Ma, which spanned from the Sakmarian through the Kungurian,[19] and Caseidae also went into decline, over an even longer period.
[14] 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,[22] survived Olson's Extinction.
[23] 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.
[1] Several important events took place during Olson's Extinction, most notably the rise of therapsids, a group of sphenacodontoid synapsids 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.