When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa

Abstract

A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian-Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74-80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U-Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions.

Keywords: Guadalupian; Karoo; Permian; U–Pb geochronology; biostratigraphy; tetrapod extinction.

Figure 1.

Minimum stratigraphic ranges of tetrapod genera across the mid-late Permian boundary in the Karoo Basin. The shaded triangles on the left indicate uncertainty surrounding the age of biozone boundaries (electronic supplementary material, Methods). Genera from the Tropidostoma AZ presented here are only those believed to occur in the lowest part of that AZ. The age of the marine extinctions is taken from the literature cited in the text. Star, dated horizon presented here; Wuchi., Wuchiapingian. (Online version in colour.)

Figure 2.

Map of the lowest Beaufort Group in the South African Karoo Basin. Star, locality of tuff sample (K1202-B1) on the farm Puntkraal, Sutherland district, Northern Cape Province. Alternating long and short dashed lines, boundaries of the sectors used when calculating the stratigraphic position of fossil specimens. The Philippolis sector is isolated as no fossil material has been found in the lowest Beaufort strata between the eastern limit of the Victoria West sector and the vicinity of Philippolis. (Online version in colour.)

Figure 3.

Generic richness and generic last-appearance events. (a) Raw generic richness data for composite stratigraphic section. H, Hoedemaker Member; K, Karelskraal Member; P, Poortjie Member; T, Tropidostoma AZ. (b) Uncertainty band (shaded) for best-fit composite sequences of last-appearance events per five composite sequence units (solid lines). Dashed lines, percentile outcomes for 300 random reordering events using the same genus durations. (c) Uncertainty band for total generic richness within the upper Abrahamskraal Formation and lower Teekloof Formation. The position of lithostratigraphic boundaries can be constrained to uncertainty bands (hatched boxes on x-axis). (Online version in colour.)

Figure 4.

Recalibrated ages for Permian Beaufort Group biozones. Dated horizons are shown in lithostratigraphic position. Hashed boxes, uncertainty surrounding stratigraphic position of assemblage zone boundaries relative to dated horizons. New date in bold. All units are scaled to time. Asterisk, date obtained from [27].