AFRICA, THE “ODD MAN OUT” OR “MAN OUT OF LUCK”: DETERMINING THE CAUSE OF TROPICAL AFRICAN FORESTS COMPOSITIONAL AND TAXONOMIC PAUCITY TO OTHER TROPICAL REGIONS BY INVESTIGATION OF THE PALEOBOTANICAL RECORD

The taxonomic and compositional attributes of modern tropical African forests differs markedly in a number of respects from forests in the Neotropics and tropical Asia. In comparisons of diversity, endemism, and species richness of some important families (ex. Arecaceae, Lauraceae, and Myrtaceae) in the forests of all three tropical regions, African forests are always the lesser. Richards (1973) referred to Africa as the “odd man out” due to these attributes. The last of these characteristics may be due to any of the following hypotheses: (1) these families have only recently dispersed or arrived on the African continent, resulting in limited time for diversification on this landmass compared to the other regions, (2) extinctions or extirpations within these clades were greater in number or rate compared to that experienced in the Neotropics and Indo-Malesia, (3) the depauperate groups have had lower speciation rates in Africa compared with the other tropical regions, or (4) a combination of 2 or 3 of the former. The African paleobotanical record provides a means to test the first two hypotheses, especially with new evidence from fossils recently recovered from the Late Oligocene (28 – 27 Ma) Chilga assemblages of northwestern Ethiopia. The arecaceous record is particularly telling because the family is of similar composition and diversity to the other tropical regions in the Late Cretaceous, but their richness and diversity diminishes after a number of apparent extinction events during the Cenozoic. The mechanisms of these extinctions are not known, but may be due to both climatic and faunal changes. Other families, such as the Myrtaceae, may also be species poor in Africa today due to extinctions.