oa South African Journal of Science - Alpha and sigma taxonomy of Lystrosaurus murrayi and L. declivis, Triassic dicynodonts (Therapsida) from the Karoo Basin, South Africa - research

Volume 115 Number 3-4
  • ISSN : 0038-2353
  • E-ISSN: 1996-7489



Permo-Triassic dicynodont (Therapsid) fossils attributed to the genus Lystrosaurus1 are known from the South African Karoo Basin, including two Triassic taxa referred to as L. (Dicynodon) murrayi2 and L. (Ptychognathus) declivis3. Distinction of the two taxa has been recognised inter alia by Brink4, Cluver and King5, Botha and Smith6, Grine et al.7 and Botha-Brink et al.8 However, in this instance, the appropriateness of alpha taxonomy may be questioned, recognising that boundaries between these species of Lystrosaurus are not necessarily clear, especially for specimens close to the time of divergence postdating the Permo-Triassic boundary, 252 million years ago. The question has arisen as to whether only one species occurred.9 Thackeray10 proposed the following hypotheses:
• HT – that one species existed and
• HBB – that there were two taxa, clearly distinct at the species level.

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