HERENDEEN, PATRICK S.1* and BONNIE FINE JACOBS2. 1Department of Biological Sciences, George Washington University, Washington DC 20052; 2Environmental Science Program, Southern Methodist University, P.O. Box 750395, Dallas, TX 75275-0395. - Fossil legumes from the Eocene of Tanzania.
The Leguminosae has a diverse and abundant fossil record, which has
been well documented from numerous Tertiary age localities, primarily
in North America, Europe, and Asia. The record from these areas shows
a sudden appearance of diversity in the middle Eocene. The available
fossil data have been useful in providing minimum ages of clades
within the family and in providing historical context for modern
biogeographic patterns. However, several holes exist in the known
record, one of the most significant being a lack of fossils from low
paleolatitudes. The fossils described in this paper are significant
therefore because they are from the Eocene of Tanzania. The fossils
were recovered from lacustrine sediments from the Mahenge site
(Singida District) in central Tanzania. The deposit represents a small
paleolake that formed in a kimberlite eruption crater. The fossil
plant assemblage is strongly dominated in taxonomic diversity and
abundance by members of the legume family, which is represented by
fossil leaves and fruits. The Caesalpinioideae is documented by leaves
of several taxa, including the extant genus Aphanocalyx, which
includes ca. 15 species primarily in western and central tropical
Africa today. Fossil leaves of another caesalpinioid taxon are similar
to leaves of the extant genera Cynometra, Julbernardia,
and Guibourtia, but precise relationships remain to be
determined. The Mimosoideae is represented by at least two taxa, one
of which is the genus Acacia. There are no confirmed
papilionoids in the assemblage. Also present are two types of legume
fruits, one of which is moniliform and most specimens show evidence of
seed predation, possibly by bruchid beetles. Thus the Mahenge site is
a valuable addition to our understanding of the fossil history of the
Leguminosae by providing much needed insight on legume diversity at
low latitudes during the early Tertiary.
Key words: Africa, Eocene, Leguminosae, Tertiary