New Cichlid Fossils From The Middle-Late Miocene Alkaline Lakes Of Africa

The African CichlidaeOreochromis(Alcolapia) andOreochromis amphimelascan survive in extremely alkaline environments and represent the only known modern alkaliphilic cichlid fish found in Africa. The presence of fossil cichlids from the Miocene of central Kenya (Tugen Hills) that are morphologically similar toOreochromis(Alcolapia) has been noted in previous works, but the conclusions remained tentative. The purpose of this study is to examine newly discovered fossil cichlids from the Tugen Hills and to compare their osteology with that of extantOreochromis(Alcolapia). This is performed based on a comprehensive collection of comparative material, using microscopy and computed microtomography (mu CT). We provide a revised diagnosis for the genus dagger Rebekkachromis, and revise its systematic relationships by assigning it to the Oreochromini (rather than to the Etiini). Two new species of dagger Rebekkachromisare described, i.e., dagger R. valyricus, sp. nov., and dagger R. vancouveringae, sp. nov., and a morphologically diverse assemblage of co-occurring dagger Rebekkachromisspecimens is documented. Moreover, we found that dagger Rebekkachromishad three sensory canal pores (instead of four) on the lower arm of the preopercle, a feature that distinguishes both the modernOreochromis(Alcolapia) and our fossil specimens from almost all other modern African cichlid fish. Our new data indicate that alkaliphile cichlids similar toOreochromis(Alcolapia) were present in Central Kenya about 10-13 Ma ago and that the ability of African cichlid fishes to thrive in highly alkaline waters had already developed by that time.