Morphology, taxonomy, phylogeny and stratigraphic ranges of South African middle permian pareiasaurs
Date
2020
Authors
Van den Brandt, Marc Johan
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Abstract
The morphology, taxonomy, phylogeny and stratigraphic ranges of the basal pareiasaurs of the middle Permian of South Africa are revised.
The first detailed cranial description of Nochelesaurus alexanderi is produced, recognising the more distinctive cranial ornamentation, new dental features (non-symmetrical marginal cusp arrangements on both upper and lower jaw teeth, up to ten marginal cusps on lower jaw teeth, incipient horizontal cingulum and medially placed cusps). Updated cranial diagnoses are produced for Embrithosaurus schwarzi, the only taxon with wide maxillary teeth lacking an elongated, central, three cusped trident at the apex of the crown and possessing the largest cheek flange amongst the group of middle Permian pareiasaurs. Bradysaurus baini has one cranial autopomorphy in the large dorsomedially oriented posterior process of the distal paroccipital process of the opisthotic. A large maxillary boss and the ventromedially oriented upper jaw teeth are confirmed as important distinguishing characters.
The first detailed postcranial descriptions are produced for Embrithosaurus schwarzi and Nochelesaurus alexanderi and an updated description for Bradysaurus baini. The three pelvic autopomorphies of Embrithosaurus are confirmed: anterior iliac blades flat and vertical/dorsoventral (not everted or upturned); iIiac blades not parallel but diverge anteriorly, oriented 45-600 off the sagittal plane, and the very thick pelvic symphysis. Bradysaurus baini has one postcranial autapomorphy: osteoderms convex, without a central boss and with very smooth ornamentation.
Bradysaurus seeleyi is synonymised with Bradysaurus baini, reslting in three valid middle Permian pareiasaur taxa: Bradysaurus baini, Embrithosaurus schwarzi and Nochelesaurus alexanderi. A rigorous cladistic analysis of middle Permian pareiasaurs recovers the three basal South African forms as a monophyletic group for the first time, named the Bradysauria, supported by six synapomorphies, indicating a first pulse of pareiasaurian evolution restricted to the South African Karoo. Nochelesaurus and Bradysaurus are sister taxa and Embrithosaurus is the most basal member of the group.
The Bradysauria are stratigraphically restricted to the Abrahamskraal Formation of the Beaufort Group. Bradysaurus baini is first to appear, in the Koornplaats Member, followed by Nochelesaurus in the Swaerskraal Member and by Embrithosaurus in the Moordenaars Member. All three taxa terminate at a similar stratigraphic level in the Karelskraal Member at the top of the Abrahamskraal Formation. The fact that Embrithosaurus is phylogenetically the most basal genus, suggests a long ghost linage for the genus.
Description
A dissertation submitted in fulfilment of the requirements for the degree Doctor of Philosophy
in Palaeontology in the Faculty of Science, University of the Witwatersrand, Johannesburg, 2020