A revision of the Mesozoic naiads (Unionoida) of Africa and the biogeographic implications

Naiads have become a top priority in conservation worldwide and therefore studies about their phylogeny, origin and dispersal have greatly increased. A revision of the rich and well preserved Mesozoic African naiad fauna remained one of the last main gaps. The African naiad assemblages are of Mid and Late Jurassic, late Early Cretaceous, and Late Cretaceous age. The associations are composed of representatives of the orders Trigoniida and Unionida, the latter containing two new families and one new superfamily. Jurassic associations consist predominantly of Unionida with a distinct Eurasian link while Early Cretaceous assemblages are dominated by Asian trigoniids. Representatives of the Iridinidae and Etheriidae, African families considered to belong to the Gondwana superfamily Mullerioidea and presently widespread and highly diversified (Iridinidae), remain conspicuously absent in the fossil record till Late Cretaceous times, when a single genus is found. The conclusion that during Early Cretaceous times, a one-directional species transfer took place between Africa and Asia appears inevitable. Alternatively, the striking absence of all Gondwana families (Superfamily Mullerioidea) during Jurassic and Early Cretaceous times indicates that, for freshwater mussels, an impenetrable barrier existed between South America and North Africa, though both continents were (supposedly) still linked during most of that period.