Lystrosaurus species composition across the Permo–Triassic boundary in the Karoo Basin of South Africa

Abstract

Lystrosaurus is one of the few therapsid genera that survived the end-Permian mass extinction, and the only genus to have done so in abundance. This study identifies which species of Lystrosaurus have been recovered from Permian and Triassic strata to determine changes in the species composition across the Permo-Triassic (P-T) boundary in the Karoo Basin of South Africa. Data generated from museum collections and recent fieldwork were used to stratigraphically arrange a total of 189 Lystrosaurus specimens to determine which species survived the extinction event. Results reveal that L. curvatus and L. maccaigi lived together on the Karoo floodplains immediately before the extinction event. L. maccaigi did not survive into the Triassic in South Africa. L. curvatus survived, but did not flourish and soon became extinct. Two new species of Lystrosaurus , L. murrayi and L. declivis , appeared in the Early Triassic. It is possible that L. murrayi and L. declivis occupied different niches to L. maccaigi and L. curvatus , and had special adaptations that were advantageous in an Early Triassic environment. We suggest that L. maccaigi may be used as a biostratigraphic marker to indicate latest Permian strata in South Africa and that, in support of previous proposals, the genus Lystrosaurus should not be used as a sole indicator of Triassic-aged strata. Our field data also show that L. curvatus may be regarded as a biostratigraphic indicator of the P-T boundary interval. ᮀ End-Permian extinction, Karoo Basin, Lystrosaurus , PermoTriassic.

Vertebrate Paleontology of Nooitgedacht 68: A Lystrosaurus maccaigi-Rich Permo-Triassic Boundary Locality in South Africa

“…The material lacks the gentle curving snout seen in L. curvatus and overly large orbits that characterise both L. curvatus and L. maccaigi (Grine et al 2006). Furthermore the angle of the orbits is not consistent with that of L. maccaigi, but appears to be more similar to that of L. murrayi or L. declivis (Botha and Smith 2007). This interval is overlain by a very fine-grained, horizontally laminated sandstone.…”

“…Remarks: The material is assigned to Lystrosaurus for the same reasons given above and to the species L. declivis on the basis of a snout that is longer than the length of the skull roof, prefrontal bosses, a prominent frontonasal ridge, a longitudinal, premaxillary ridge and the absence of postorbital bosses (Cluver 1971;Grine et al 2006;Botha and Smith 2007) (Fig. 17.7d).…”

“…Lystrosaurus murrayi (Huxley, 1859 Remarks: The material is assigned to Lystrosaurus for the same reasons given above and to the species L. murrayi on the basis of a shorter, curved snout compared to other Lystrosaurus species, the absence of postorbital bosses, the anterior surface of the snout lying at right angles to the parieto-preparietal plane and weakly developed prefrontal bosses, frontonasal ridge and longitudinal, premaxillary ridge (Cluver 1971;Grine et al 2006;Botha and Smith 2007) (Fig. 17.7e).…”

“…Following the lithologic descriptions and stratigraphic interpretations of Retallack et al (2003), Smith and Botha (2005), and Botha and Smith (2006), we place the PermoTriassic boundary at Nooitgedacht 68 at the contact between a thick (8 m at Loskop, 4 m at Spitskop) rubified, thinly laminated heterolithic mudrock section and a 50 cm thick siltstone body ( Fig. 17.2), below which the last occurrence of the locally abundant L. maccaigi is documented (Botha and Smith 2007).…”

A Burrow Cast With Lystrosaurus Skeletal Remains From the Lower Triassic of South Africa

“…Although taxonomic assignment to species level is not possible with the available skeletal remains, the only species of Lystrosaurus that are known from the uppermost strata of the Palingkloof Member are L. murrayi and L. declivis (Botha and Smith, 2007), so it seems likely that NMQR 3606 represents one or the other. The disarticulation and the distribution of the skeletal elements indicate that the skeleton was disturbed prior to burial.…”