Freshwater fishes, dispersal ability, and nonevidence: "gondwana life rafts" to the rescue.

In a recent issue of Systematic Biology, Briggs (2003: Fishes and Birds: Gondwana Life Rafts Reconsidered, pp. 548–553) examines the current distributions of four vertebrate clades (cichlid fishes, aplocheiloid killifishes, ratites, and parrots), which have been attributed to the Mesozoic fragmentation of Gondwana (Parenti, 1981; Stiassny, 1991; Murphy and Collier, 1997; Farias et al., 1999). Briggs (2003) contests the vicariance hypotheses offered by these authors for cichlids and aplocheiloid killifishes in favor of scenarios reliant on transoceanic marine dispersal. His conclusions are based on the absence of Cretaceous-age fossils for these clades, as well as strict adherence to Myers’ (1938) classification of cichlids and killifishes as secondary freshwater fishes. For fishes, the arguments Briggs uses to explain their current distributions rely on what he perceives to be a valid and absolute distinction: that between so-called primary and secondary freshwater fishes (Myers, 1938) and what this implies regarding their dispersal ability. According to Briggs (2003:549), the current distribution of aplocheiloid killifishes has a simple explanation (our italics):