Biogeographic affinities of Middle and Late Devonian fishes of South Africa

WA Museum Records and Supplements | Updated 1 decade ago

Abstract - South African fossil fish remains spanning much of the Devonian Period have now been reported from the Bokkeveld and Witteberg Groups (West Gondwana). Emsian and Eifelian material is scarce, consisting of fragments of an antiarch, elasmobranchs, the acanthodian Machaeracanthus and a possible dipnoan, represented by a single scale. Recent explorations have focused on Middle Devonian (Givetian) and Late Devonian (Famennian) sites in the south and west of the country. The Givetian ichthyofauna is characterized by a high proportion of sharks to placoderrns and an absence of agnathans, actinopterygians and dipnoans, with only a single crossopterygian (Onychodus sp.).

The better-explored Famennian has a high diversity of endemic forms, and at higher taxonomic levels is comparable to ichthyofaunas from slightly earlier sites in Iran and at Mount Howitt, Australia, reflecting the pan-Gondwanan nature of non-marine fish distributions in the Late Devonian. The Givetian, however, in its diversity of sharks, comparable to that of Antarctica, and absence of thelodonts, antiarchs and major sarcopterygian groups, is interpreted as a depauperate assemblage unaffected by cosmopolitan distributional trends occurring at the time. Three possible explanations are a high-latitude effect, palaeoecological restriction in brackish marginal habitats, or inadequate sampling of the fauna.