Abstract

 
 
 No direct palaeoclimatic proxies have been available to indicate the seasonality or amount of rainfall on the west coast of southern Africa during the Early Pliocene. The Benguela Upwelling System (BUS) is today one of the factors responsible for the present-day aridity on the west coast of southern Africa. The initiation of the BUS is frequently linked to the entrenchment of aridity and the establishment of the current winter rainfall pattern on the west coast; however, marine proxies are inconclusive regarding the effects of past fluctuations in the BUS and sea surface temperatures on the rainfall regime. Neither the fossil evidence nor the fact that plants using the C3 photosynthetic pathway predominate at this time, provide direct evidence of winter rainfall at Langebaanweg. We challenge certain assumptions which are commonly made in the literature regarding the timing of inception of a winter rainfall regime on the west coast and the onset of aridity in the Langebaan region, and provide new evidence as to seasonality of rainfall at Langebaanweg in the Early Pliocene. Herein, the identification of frog species from the genus Ptychadena from Langebaanweg provides new and compelling evidence for a summer rainfall regime, or of at least significant summer rainfall, at 5.1 mya in the southwestern Cape of South Africa.
 
 
 
 
 Significance: 
 
 
 
 Advances understanding of the evolution of the winter rainfall zone on the west coast of South Africa
 Assesses evidence for the inception of aridity and a winter rainfall regime on the west coast of South Africa
 Fossil Ptychadenidae from the Early Pliocene site of Langebaanweg provide evidence for a summer rainfall regime at 5.1 mya on the west coast of the southwestern Cape.
 
 
 
Highlights
Southern Africa is a predominantly summer rainfall region but the Winter Rainfall Zone (WRZ) situated along the southwestern and southern tip of the African continent, lying at the boundary between southern hemisphere temperate and tropical climate systems, is an exception (Figure 1)
We challenge certain assumptions which are commonly made in the literature regarding the inception of a winter rainfall regime on the west coast and the onset of aridity in the Langebaan region, and provide new evidence for rainfall seasonality at Langebaanweg in the Early Pliocene
These two groups correspond to the Summer Rainfall Zone (SRZ) and WRZ, and their breeding periods are delineated by mean annual precipitation in the summer or winter rainfall months, respectively.[17,48]
Summary
Southern Africa is a predominantly summer rainfall region but the Winter Rainfall Zone (WRZ) situated along the southwestern and southern tip of the African continent, lying at the boundary between southern hemisphere temperate and tropical climate systems, is an exception (Figure 1). The southern African amphibian fauna is commonly divided into two main groups – the so-called ‘tropical’ (a term used to describe the speciose tropical frog fauna distributed widely in the northeastern parts of southern Africa) and the unique ‘Cape’ frog faunas of the southwestern Cape which are characterised by extremely high rates of endemism and contain a large number of species with narrow niche envelopes.[16,17,47,48] These two groups correspond to the SRZ (the tropical frog fauna) and WRZ (the Cape frog fauna), and their breeding periods are delineated by mean annual precipitation in the summer or winter rainfall months, respectively.[17,48] The two rainfall regimes have such a high turnover in species that it is evident at a global scale.[49] there are some genera that straddle both rainfall zones, but the population genetics of these taxa suggest deep genetic divisions, such that populations are confined to one zone or the other.[46]
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