Late Cenozoic (Oligocene and Miocene)

Late Cenozoic (Oligocene and Miocene)

According to palaeontologists, Oligocene and upper Miocene deposits with freshwater fish are relatively infrequent in Africa, but these rare deposits indicate one further step towards the building of the modern AFFs, with the first documented presence of Oriental-derived groups, such as Bagridae († Bagrus sp. , 30 Mya; but see Gayet & Otero, 1999), Clariidae († Clarias sp. ,30 Mya) and Cyprinidae (Otero, 2001) , along with continuous records of Mochokidae , Cichlidae , Alestidae , Protopteridae and Polypteridae ( Otero & Gayet, 2001) . Additionally, Otero et al. (2017) described an ichthyological fauna from the late Oligocene locality of Lokone, Kenya (~28 Mya), that includes † Protopterus sp. , † Polypterus sp. , † Heterotis sp. , † Gymnarchus sp. , † Hydrocynus sp. , one species of the extinct alestid genus † Sindacharax , along with other possible remains of alestids, a claroteid, a cichlid and † Distichodus sp. As inferred, the palaeoenvironmental conditions of north Africa and the Arabic region during the Oligocene – Miocene must have been warm and humid, possibly similar to the present climatic conditions found in much of tropical Africa.

OBJECTIVES OF THIS STUDY

The relative contributions of direct marine-to-freshwater shifts, vicariance events and dispersal events to construction of the AFF fauna have not recently been evaluated critically. Herein, I attempted to provide a time-calibrated phylogenetic test to determine the multiple evolutionary origins of the AFF fauna. Data on these lineages are based on a literature review of their diversity, habitat preferences, phylogenetic relationships, time divergence and fossil records. Recent morphology-based and molecular-based phylogenetic works provide the backbone of this study: (1) of identifying most-inclusive monophyletic groups of AFFs (a few of them secondarily extended their distribution to another continental region); (2) of identifying the closest outgroups of each of these lineages, including their sister group (= their phylogenetic position); (3) of inferring the ecological preferences (relative to salinity) of their most ancient common ancestors by outgroup comparisons and maximum-likelihood (ML) criterion; (4) of inferring the geographical origins of their most ancient common ancestors using ancestral range estimation methods; (5) of estimating the age (within maximal and minimal limits when available) of the evolutionary events (regarding the salinity preference and continental distributions) leading to the initial presence of each Afrotropical freshwater group; and (6) of comparing these ecological distribution patterns against geology, palaeoclimate and sea-level fluctuations to uncover possible common processes.