There is a marked similarity in the fauna and flora of the Devonian continental facies the world over. Records from such deposits in China containing Early Devonian genera of the armoured fish Cephalaspis and Pterichthys or the widespread Australian records of Bothriolepis, a Late Devonian antiarch, correspond closely to those of the Old Red Sandstone in Europe. Yet, when studied in more detail, specific differences become apparent. It has been suggested that the Baltic fish succession is so rich that the area must have formed a migration centre. This may be so, but the wide distribution of supposed estuarine and freshwater fishes raises many problems. Many of these can be resolved if the continents were closer together during the Devonian than at present.
Cephalaspis
The marine life of the Devonian gives little evidence of faunal provinces. It is true that in the Lower Devonian the brachiopod Australocoelia has been recognized only in the Antarctic, the Falkland Islands, South America, South Africa, and Tasmania and that Australospirifer, Scaphiocoelia, and Pleurothyrella share parts of this distribution. These genera are not known in the marine Lower Devonian of northern continents and seem to establish an “austral” fauna of limited circum-Antarctic distribution at this time (if the southern continents were then united as Gondwana). Elements of this fauna are often called “Malvinokaffric” after the Falkland (Malvinas) Islands and the South African Bokkeveld Beds. At other levels in the Devonian, however, provincial distinctions are not apparent, with the exception of local coral provinces that are distinguishable in areas of Asia.
No comments:
Post a Comment