Cenozoic Exploration in the Rukwa Rift

After the end-Cretaceous extinction event, it has been suggested that Afro-Arabia entered a period of relative isolation that lasted throughout much of the Paleogene (65 – 24 million years ago), with only occasional small-scale faunal exchange with other landmasses. As this endemic African fauna radiated in isolation, certain mammal groups dominated the landscapes. Many of the endemic forms later became extinct shortly after the collision between the Arabian and Eurasian plates. Our knowledge of African Paleogene faunas has largely been based upon sites from supra-equatorial Africa, particularly throughout what is now the Sahara. Until recently, virtually nothing has been known of Oligocene African terrestrial vertebrate faunas from below the equator, rendering assessments of geographic patterns in these forms all but impossible.

Since the inception of the RRBP, a wealth of new invertebrate and vertebrate forms have been recovered from Nsungwe Formation deposits in the Rukwa Rift Basin, including freshwater crabs, gastropods, fishes, frogs, turtles, crocodylians, birds, rodents, macroscelideans, hyracoids and primates (for an overview, Stevens et al., 2008). Documentation of this diverse fauna from below the equator can help to better characterize regional faunal patterns and examine the role of this paleoecological setting in preserving a broader sampling of vertebrate evolutionary history.

The Rukwa Rift Basin Project is also beginning to reveal an interesting chapter in primate evolutionary history. Dental and postcranial remains of small anthropoid primates, similar to the older parapithecids known from the Jebel Qatrani Formation of Egypt, demonstrate that small members of this group existed until the end of the Oligocene. In the early years of the project, a tiny humerus was recovered, and represents the first anthropoid postcranial element ever recovered from the Paleogene of sub-equatorial Africa. The shape of this bone suggests that the animal was an arboreal quadruped, one that moved around actively within the canopy of trees. Strepsirrhine primates have also been recovered and are currently under study.
Drawing by Haley O’Brien.