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Paleobotanical Section

Garcia Massini, Juan Leandro [1], Jacobs, Bonnie [1], Pan, Aaron [1].

Palaeoecological significance of the presence of the fern Acrostichum in the Oligocene of the northwestern Ethiopian Plateau.

Several Oligocene leaf fragments displaying morphological affinities with the fern Acrostichum are described from near Gondar on the northwestern Ethiopian Plateau, Ethiopia. The fossils consist of elongate to lanceolate pinnae impressions with an entire margin, numerous secondary veins arising at an acute angle from a thick midvein, and have a characteristic reticulate venation pattern. Modern Acrostichum is a taxon with a pantropical distribution associated with mangrove vegetation communities in brackish or saltwater environments, and occasionally occurs in freshwater settings. The fossil record of this fern shows that only seldom was it associated with mangrove type of taxa, but more often occurred in an environment where stressful conditions, particularly high saline levels in soil, predominated. Its presence in the northwestern Ethiopian Plateau during the Oligocene suggests the existence of an environment characterized by inundated terrains where salt and other minerals accumulated resulting in high concentrations tolerable by Acrostichum. This fern is widespread today, both in western as well as in eastern tropical Africa. Its fossil record shows that during the Paleogene the geographic range of Acrostichum extended from western tropical to northeastern Africa including a greater inland area than today as evidenced by this record.


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1 - Southern Methodist University, Department of Geological Sciences, P.O. Box 750395, Dallas, Texas, 75275-0395, USA

Keywords:
Acrostichum
Ethiopia
Oligocene.

Presentation Type: Oral Paper
Session: 36-4
Location: Salon G - Austin Grand Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 2:45 PM
Abstract ID:240


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