Similarities between South American and African freshwater fishes
The primary freshwater fishes of South America and Africa are remarkably similar. The Dipnoi and Osteoglossomorpha among archaic fishes link South America, Africa, and Australia. The more recent distributions of the Characiformes and Cichlidae also link South America and Africa.
A question arising from these parallels is whether this similarity is due to dispersal or vicariance. Some researchers believe that the Ostariophysi originated in Southeast Asia and dispersed to South America from Africa across a direct land bridge. However, land bridges work particularly poorly for freshwater fishes because rivers seldom run lengthwise along such bridges. Other researchers favor dispersal of Ostariophysi through North America, but this is not supported by recent distributions or by fossil evidence. Among 13 putative African–South American clades, only three clades – lepidosirenid lungfishes, polypterid bichirs, and doradoid catfishes – clearly fit the simple continental drift–vicariance model, with a common ancestor inhabiting fresh waters of the African– South American landmass before the opening of the Atlantic Ocean (Lundberg 1993). Distributions of other groups, such as cichlids and characins, are more difficult to explain this way because they have evolved more recently, so perhaps some dispersal has taken place in addition to vicariant events. An explanation for the distribution of a freshwater galaxiid in South America and Australia is a good example of the argument over dispersal versus vicariance.