Sclerosperma fossils from the late Oligocene of Chilga, north-western Ethiopia

Author(s)
Friðgeir Grímsson, Bonnie F. Jacobs, Johan L.C.H. Van Valkenburg, Jan J. Wieringa, Alexandros Xafis, Neil Tabor, Aaron D. Pan, Reinhard Zetter
Abstract

The palm family, Arecaceae, is notoriously depauperate in Africa today, and its evolutionary, paleobiogeographic, and extinction history there are not well documented by fossils. In this article we report the pollen of two new extinct species of the small genus, Sclerosperma (Arecoideae), from a late Oligocene (27–28 Ma) stratum exposed along the Guang River in Chilga Wereda of north-western Ethiopia. The pollen are triporate, and the two taxa can be distinguished from each other and from modern species using a combination of light and scanning electron microscopy, which reveals variations in the finer details of their reticulate to perforate exine sculpture. We also report a palm leaf fragment from a stratum higher in the same section that is in the Arecoideae subfamily, and most likely belongs to Sclerosperma. The implications of these discoveries for the evolutionary history of this clade of African arecoid palms is that their diversification was well underway by the middle to late Oligocene, and they were much more widespread in Africa at that time than they are now, limited to West and Central Africa. Sclerosperma exhibits ecological conservatism, as today it occurs primarily in swamps and flooded forests, and the sedimentology of the Guang River deposits at Chilga indicate a heterogeneous landscape with a high water table. The matrix containing the fossil pollen is lignite, which itself indicates standing water, and a variety of plant macrofossils from higher in the section have been interpreted as representing moist tropical forest or seasonally inundated forest communities.

Organisation(s)
Department of Palaeontology
External organisation(s)
Southern Methodist University, National Herbarium of The Netherlands, Don Harrington Discovery Center
Journal
Grana
Volume
58
Pages
81-98
ISSN
0017-3134
DOI
https://doi.org/10.1080/00173134.2018.1510977
Publication date
10-2018
Peer reviewed
Yes
Austrian Fields of Science 2012
105118 Palaeontology
Keywords
ASJC Scopus subject areas
Ecology, Evolution, Behavior and Systematics, Plant Science
Portal url
https://ucris.univie.ac.at/portal/en/publications/sclerosperma-fossils-from-the-late-oligocene-of-chilga-northwestern-ethiopia(866818f3-7827-4231-bcb8-c9153420f7ef).html