Cynodonts from the Uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the TriassicCynognathusAssemblage Zone

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Abstract
The Burgersdorp Formation in the Beaufort Group of the South African Karoo Basin records a diverse and rich vertebrate fauna that is referred biostratigraphically to the Cynognathus Assemblage Zone. Recent collecting efforts, and taxonomic and biostratigraphic studies on this formation, resulted in a proposed subdivision of the Cynognathus Assemblage Zone into three subzones informally known as A, B, and C. Cynodont fossils constitute an important component of the fauna of the uppermost subzone C of the Cynognathus Assemblage Zone. As in the middle subzone B, cynognathids, diademodontids, and trirachodontids are represented in subzone C, although the latter group-instead of Diademodon-is the dominant taxon. The presence of Cynognathus in the faunas of the three subzones confirms that this genus is the correct choice as the index taxon of the assemblage zone. The large size attained by trirachodontid specimens from subzone C represents an unusual characteristic. One complete skull measured 160 mm ...