First record of the rare dicynodont Colobodectes from the southern Karoo Basin of South Africa has implications for middle permian continental biostratigraphy

Abstract

Colobodectes is a dicynodont therapsid known from five partial skulls. All are from the western and north-western part of the Beaufort Group in the Karoo Basin and occur in close stratigraphic proximity to the contact between the Ecca and Beaufort groups. Although the provenance of all specimens is near the base of the late middle Permian (Guadalupian) Abrahamskraal Formation, their precise age is uncertain as a result of diachroneity of the base of the formation and the absence of index taxa to correlate this horizon with the biostratigraphy established in the southern Karoo Basin. Here we describe an additional specimen of Colobodectes recently discovered from a locality low in the Abrahamskraal Formation in the southern Karoo Basin. Given the unusual associated fauna at this locality, the occurrence of Colobodectes provides an interesting correlation between the base of the Abrahamskraal Formation in the Northern Cape Province and lower Abrahamskraal Formation in the southwestern part of the basin. It occurs at a similar level to the dicynodont Lanthanostegus, adds an additional species to the transition between the Eodicynodon and Tapinocephalus assemblage zones (AZ), and provides a link between the basal Beaufort rocks in the Northern and Eastern Cape provinces. This supports earlier work proposing that the Eodicynodon AZ is present only on the southwestern side of the Karoo Basin and that the transition from a marine to continental depositional environment occurred later toward the North and East.