Taxonomy, phylogeny and stratigraphical ranges of middle Permian pareiasaurs from the Karoo Basin of South Africa

Abstract

Pareiasaurs were relatively abundant, globally distributed, herbivorous parareptiles of the mid to late Permian. The basal-most forms, all members of the Bradysauria, are restricted to the Guadalupian (mid-Permian) of South Africa and went extinct in the late Capitanian near the top of the Tapinocephalus Assemblage Zone. Currently four species are recognised in 2 this group: Bradysaurus seeleyi, B. baini, Embrithosaurus schwarzi and Nochelesaurus alexanderi. Those taxa have historically been poorly defined and based on a limited number of specimens, leaving the taxonomic diversity of the group open to doubt and limiting their utility in biostratigraphy. Here we present our fourth and final contribution designed to improve the understanding of this group of pareiasaurs by providing a taxonomic and phylogenetic review, updated stratigraphic ranges and updated diagnoses for each taxon of the Bradysauria. Bradysaurus seeleyi is synonymised with Bradysaurus baini, resulting in three valid mid-Permian pareiasaur taxa: Bradysaurus baini, Embrithosaurus schwarzi and Nochelesaurus alexanderi. Our cladistic analysis of cranial and postcranial characters supports the monophyly of Bradysauria with five synapomorphies. Embrithosaurus schwarzi is recovered as the sister taxon to a clade containing Bradysaurus baini and Nochelesaurus alexanderi. By identifying 157 pareiasaur specimens in fossil collections we show that the Bradysauria are stratigraphically restricted to the Abrahamskraal Formation of the Beaufort Group and suggest a staggered appearance. Bradysaurus baini is first to appear, followed by Nochelesaurus alexanderi, and lastly by Embrithosaurus schwarzi. All three taxa perished during the Capitanian mass extinction, and have their highest occurrences near the top of the Abrahamskraal Formation.

The emblematic South African therocephalian Euchambersia in China: a new link in the dispersal of late Permian vertebrates across Pangea

“…This represents the only therocephalian radiation limited to the Karoo Basin of South Africa. The same is true for middle Permian pareiasaurians, which are also limited to the Wordian–Capitanian of the Karoo Basin [ 20 , 21 ].…”

Saurodesmus robertsoni Seeley 1891—The oldest Scottish cynodont

“…Despite having those basic anatomical components and their significant dorsoventral compression, pareiasaur femora differ from NHMUK PV OR 28877 in a number of ways: they are much broader, the result of a significantly wider shaft, which is at least 50% as wide as the proximal and distal expansions; the direction of the femoral head is subparallel to the plane of the distal expansion; the internal trochanter is located more distally and is subperpendicular to the proximal expansion; the greater (major) trochanter typically extends distally along most of the shaft’s length a flattened postaxial flange (usually resulting in the posterior edge being straighter than the anterior edge); the internal (lesser) trochanter and adductor ridge is usually well developed, elongated, often sigmoid-shaped and somewhat medially positioned, away from the anterior (preaxial) edge of the femur; the dorsal surface of the distal expansion is typically pierced by a large and deep nutrient foramen and groove, elongated along the direction of the shaft; the distal end is not significantly flattened; the distal lateral condyle often extends significantly beyond the distal medial condyle (related to a relatively sprawling or oblique hind-limb posture); the articular surfaces of the condyles are longer than wide, oval in outline, with sharply defined, flattened, and substantial ventral exposure, and are separated by a deep intercondylar groove (sulcus) [ 184 , 185 , 187 , 190 – 197 ] ( Fig 6 ). There is no Triassic record of pareiasaurs, since the clade perished at the Permo-Triassic boundary [ 190 , 191 , 194 ].…”

“…. There is no Triassic record of pareiasaurs, since the clade perished at the Permo-Triassic boundary [190,191,194].…”

Enigmatic humerus from the mid-Permian of South Africa bridges the anatomical gap between “pelycosaurs” and therapsids

“…A temnospondyl affinity for BP/1/7395 is rejected on the basis of its strong degree of ossification, well-defined and strongly convex articular surface, blade-like DPC, and terminally positioned LT (e.g., Pawley, 2007; Pawley & Warren, 2004). A pareiasaur affinity is rejected given the well-defined and strongly convex articular surface, and the lack of a sharp longitudinal ridge on the dorsal aspect where the DPC meets the main body of the bone (Van den Brandt et al, 2021). Deduction implies the owner of BP/1/7395 to have been a synapsid.…”