Mammal fossils in Africa, map
The 6-volume work (3760 pages) Mammals of Africa, by Jonathan Kingdon and others https://www.bloomsbury.com/uk/mammals-of-africa-9781408122570/
shows a map of all the known mammalian fossil sites (Volume 1, page 41).
Here we see Hadar (8), Turkana (14), Olduvai (24), Laetoli (25), Taung (33), Sterkfontein (32), all famous for hominin fossils.
Mammalian fossils are only found in savanna areas and other relatively dry parts of Africa. That does not mean that there were no mammals living and evolving in wet parts of Africa. It simply shows where fossils can be preserved and found.