Abstract Detail


DeVore, Melanie [1], van der Hoek, Yntze [2], Pigg, Kathleen [3].

Sedges with a tussock-like growth habit from the latest early Eocene Republic flora of the Okanogan Highlands and their bearing on grazing mammal evolution.

Several specimens of a fossil sedge showing the modern tussock growth habit characteristic of some woodland species of Carex (Cyperaceae) are described from the latest early Eocene flora of Republic, northeastern Washington, USA. Compressed compact corm-like plant bases up to 2.5 cm high and 1.4 cm wide bear elongate leaves with tightly imbricated leaf bases. Around a dozen leaves are found in attachment per corm. They are up to 8 cm long x 0.1 cm wide with parallel veins and are preserved flowing around the corm. Corms are lobed basally, and one bears an attached vegetative offshoot, demonstrating that these plants reproduced asexually. One laterally-oriented rhizome 3 cm long x 0.4 cm across bears rounded to lensoid leaf scars and attached leaves up to 4 cm long x 0.1 cm wide. Fragmentary pistillate and staminate inflorescences have also been found. These are around 2.5 cm long x 1 cm across and cylindrical, with membranous glumes that appear to have a hyaline margin and a midrib with a scabrid awn.  Although we have no exact modern analogue for the Republic locality we have suggested similarities with upland African forest communities, particularly ones with folivores.  In forest-dominated biomes today such as those of lowland Gabon and the Virunga Mountains of Rwanda, we find grazers such as the ruminant buffalo (Syncerus caffer) with diets consisting mainly of Cyperaceae and Poaceae associated with open habitats.  Documentation of Cyperaceae plants with a tussock growth habit at Republic suggests that a sedge-dominated microhabitat, similar to those favorable for forest grazers in montane vegetation today was also present 50 Mya.  Whereas the African savannah has often been used as a model for the radiation of middle Miocene grasslands and affiliated faunas, we suggest that earlier evolution within large mammalian woodland grazers proceeded open savannah-land biota. We believe a model for understanding the evolution of grazers in these systems would be to look at the diets of large ruminants today, in lowland Afrotropical rainforests and Afromontane forests. Buffalo provide an excellent initial analogue for developing a more robust model for the radiation of grazers into savannah habitats.  We propose a model of grazers being a guild that evolved first within forests to take advantage of microhabitats such as wetlands and gap clearings dominated by sedges and grasses, and then radiated into savannahs.

1 - Georgia College & State University, Biological And Environmental Sciences, Campus Box 081, Milledgeville, GA, 31061, United States
2 - Dian Fossey Gorilla Fund, Musanze, Rwanda
3 - Arizona State University, School Of Life Sciences, PO Box 874501, Tempe, AZ, 85287, United States


Presentation Type: Poster
Session: P, Paleobotany Posters
Location: Virtual/Virtual
Date: Wednesday, July 29th, 2020
Time: 5:00 PM Time and date to be determined
Number: PPB006
Abstract ID:581
Candidate for Awards:None

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