The Occurrence of the FernAcrostichumin Oligocene Volcanic Strata of the Northwestern Ethiopian Plateau

Oligocene (28–27 Ma) leaf fragments displaying morphological affinities with the fernAcrostichumare described from volcanic and fluvio‐lacustrine strata near Chilga, west‐southwest of Gondar on the northwestern Ethiopian Plateau. The fossils consist of elongate pinnae impressions and compressions, w...

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Bibliographic Details
Published in:International journal of plant sciences 2006-07, Vol.167 (4), p.909-918
Main Authors: García Massini, J. L., Jacobs, B. F., Pan, A., Tabor, N., Kappelman, John
Format: Article
Language:English
Subjects:
Basalt
Ferns
Fossils
Paleogene period
Petioles
Sediments
Spore dispersal
Spores
Swamps
Taxa
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Summary:Oligocene (28–27 Ma) leaf fragments displaying morphological affinities with the fernAcrostichumare described from volcanic and fluvio‐lacustrine strata near Chilga, west‐southwest of Gondar on the northwestern Ethiopian Plateau. The fossils consist of elongate pinnae impressions and compressions, with secondary veins that arise from a midvein, anastomose, and create a characteristic reticulate venation without included free veinlets. ModernAcrostichumhas a pantropical distribution associated with mangrove vegetation, but it occasionally occurs in freshwater settings. The Paleogene fossil record shows thatAcrostichumusually is preserved in freshwater environments, as it is at Chilga, but elsewhere in Africa it is associated with mangrove taxa. At Chilga,Acrostichumoccurs in a waterlogged terrain, as indicated by independent environmental assessment based on paleosol analyses. This fern occupied a greater geographic range than it does today in Africa, having occurred in the past on the Ethiopian Plateau in addition to the coastal areas at tropical latitudes.
ISSN:1058-5893
1537-5315
DOI:10.1086/504390