The reported age estimates for the Prospect Hill Formation in the Western Cape have ranged from Pleistocene to middle Miocene. This vast difference reflects the diversity of techniques and data (microfossils, ratite eggshell, and Sr isotopes) that have been applied to and collected from outcrops of the formation. The older middle to late Miocene age estimate (based on the presence of the extinct ratite eggshell morphology Diamantornis wardi) has been disputed by more recent work. A reexamination of the fossil eggshell fragments from the Prospect Hill Formation confirms their original species identification. In addition, with increased knowledge of ratite eggshell biostratigraphy across Africa, the presence of Diamantornis wardi in the Prospect Hill Formation demonstrates that the sediments are at a minimum older than 6.5 Ma and most likely older than 9 Ma.

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