Evidence from South Africa for a protracted end-Permian extinction on land.

Earth's largest biotic crisis occurred during the Permo-Triassic Transition (PTT). On land, this event witnessed a turnover from synapsid- to archosauromorph-dominated assemblages and a restructuring of terrestrial ecosystems. However, understanding extinction patterns has been limited by a lack of high-precision fossil occurrence data to resolve events on submillion-year timescales. We analyzed a unique database of 588 fossil tetrapod specimens from South Africa's Karoo Basin, spanning ∼4 My, and 13 stratigraphic bin intervals averaging 300,000 y each. Using sample-standardized methods, we characterized faunal assemblage dynamics during the PTT. High regional extinction rates occurred through a protracted interval of ∼1 Ma, initially co-occurring with low origination rates. This resulted in declining diversity up to the acme of extinction near the Daptocephalus-Lystrosaurus declivis Assemblage Zone boundary. Regional origination rates increased abruptly above this boundary, co-occurring with high extinction rates to drive rapid turnover and an assemblage of short-lived species symptomatic of ecosystem instability. The "disaster taxon" Lystrosaurus shows a long-term trend of increasing abundance initiated in the latest Permian. Lystrosaurus comprised 54% of all specimens by the onset of mass extinction and 70% in the extinction aftermath. This early Lystrosaurus abundance suggests its expansion was facilitated by environmental changes rather than by ecological opportunity following the extinctions of other species as commonly assumed for disaster taxa. Our findings conservatively place the Karoo extinction interval closer in time, but not coeval with, the more rapid marine event and reveal key differences between the PTT extinctions on land and in the oceans.

Rapid turnover of top predators in African terrestrial faunas around the Permian-Triassic mass extinction.

Catastrophic ecosystem disruption in the late Permian period resulted in the greatest loss of biodiversity in Earth's history, the Permian-Triassic mass extinction (PTME).1 The dominant terrestrial vertebrates of the Permian (synapsids) suffered major losses at this time, leading to their replacement by reptiles in the Triassic.2 The dominant late Permian predatory synapsids, gorgonopsians, were completely extirpated by the PTME. The largest African gorgonopsians, the Rubidgeinae, have traditionally been assumed to go extinct at the Permo-Triassic boundary (PTB).3,4,5 However, this apparent persistence through the sustained extinction interval characterizing the continental PTME6 is at odds with ecological theory indicating that top predators have high extinction risk.7 Here, we report the youngest known large-bodied gorgonopsians, gigantic specimens from the PTB site of Nooitgedacht 68 in South Africa. These specimens are not rubidgeine, and instead are referable to Inostrancevia, a taxon previously thought to be a Russian endemic.8 Based on comprehensive review of the South African gorgonopsian record, we show that rubidgeines were early victims of ecosystem disruption preceding the PTME and were replaced as top predators by Laurasian immigrant inostranceviines. The reign of this latter group was short-lived, however; by the PTB, gorgonopsians were extinct, and a different group (therocephalians) became the largest synapsid predators, before themselves going extinct. The extinction and replacement of top predators in rapid succession at the clade level underlines the extreme degree of ecosystem instability in the latest Permian and earliest Triassic, a phenomenon that was likely global in extent.