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South Africa Karoo Basin Faunal Zones
Faunal Zones of the South African Karoo Basin (after Rubridge 1995; Athena Review).
The Beaufort geological group of the South Africa Karoo Basin has a series of eight well-defined Faunal Zones, extending from the Middle Permian to the Middle Triassic period (270-247 mya). Each Faunal Zone is associated with one or more local geological formations, and each contains a number of associated taxa. The eight type fossils are matched in the chart with skull examples, as listed below.
1. Eodicynodon (Abrahamskrall Formation); 2. Tapinocephalus (Abrahamskraal Formation); 3. Pristerognathus (Koonap and Middleton Formations; 4. Tropidostoma (Middleton Formation); 5. Cistecephalus (Middleton and Balfour Formations); 6. Dicynodon (Balfour Formation); 7. Lystrosaurus (Balfour and Katberg Formations); 8. Cynognathus (Burgersdorp Formation).
Fossil evidence of Therapsids ("beast faces"), the ancestors of mammals, first appears in the Middle Permian deposits of the Beaufort Group. Three suborders of Therapsids include the Anomodontia ("undefined teeth"), the Dinocephalians ("terrible heads"), and the Theriodonta ("beast teeth"). The theriodonts became one of the two synapsid survivors of the great Permian–Triassic extinction event, the other being the dicynodonts, part of the Anomodontia.
Theriodonts split into two groups, Therocephalians ("beast heads") who died out after the Early Triassic; and cynodonts ("dog teeth") including Cygnognathus, whose carnivorous forms became progressively smaller during the Triassic. By the Late Triassic the first mammals evolved from small, shrew-sized cynodonts called trithelodonts. .
Reference:
Rubridge, B.S. (ed.) 1995. Biostratigraphy of the Beaufort Group.
South African Commission on Stratigraphy, Biostratigraphic Series
1, pp.1-45.
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