Abstract Detail

Paleobotany

Stromberg, Caroline A. E. [1], Aboulafia, Elie [2], Brightly, William H [1], Crifò, Camilla [1], McManus, Brittany [2], O'Keefe, Casey [1], Schorr, Anna [1], Senske, Ashly [1].

Grass phytolith shape: towards a key to the evolution and paleoecology of grasses and grasslands.

Phytoliths are microscopic bodies made up of opal-A that are precipitated in the tissues of many vascular plants. Grasses in the family Poaceae produce a diverse range of phytolith shapes, including so-called grass silica short cells (GSSC), which are unique to grasses. It has long been known that GSSC shape variation broadly correlates with grass classification, and these differences have been used in paleontology and archaeology to reconstruct, among other things, evolutionary divergences within the grass family (Poaceae), grass community composition in Cretaceous to Holocene ecosystems, and human domestication of grasses. Nevertheless, it remains unclear just how well GSSC morphology reflects relatedness among grasses in light of the new, molecular-based Poaceae phylogenies, which have substantially altered traditional views of grass relationships. In addition, previous work on the phylogenetic significance of GSSC shape have focused mainly on two-dimensional GSSC shape categories, rather than trying to assess three-dimensional shape quantitatively.
To solve this issue, we are attempting to establish a phylogenetically-based, morphological phytolith “key” for more robust assessment of the phylogenetic affinities of fossil phytoliths. This phytolith key focuses on extracted phytolith assemblages, rather than GSSCs in situ in the epidermis, and considers primarily (1) the relative abundances of GSSC shape categories (rondel, pyramidal, crenate/polylobate, saddle, bilobate, cross) produced by grass species, and (2) the detailed three-dimensional shape variation within these categories, although the orientation of GSSCs in the epidermis will also be taken into account. To do so, we study phytolith assemblages extracted from modern grass species from across the Poaceae phylogeny. For each grass species, we first classify the GSSCs into shape categories and calculate the relative abundance distribution of these categories. Second, we use high-resolution light-microscopy images to collect landmark- and semilandmark data to quantitatively compare shapes within each shape category. Preliminary data indicate that both distribution of GSSC shape categories and detailed variation within shape categories provide at least coarse distinctions between clades. Work is ongoing to refine the method and add taxa to determine the phylogenetic resolution of GSSC phytoliths and test hypotheses about GSSC shape evolution.

1 - University Of Washington, Department of Biology, 24 Kincaid Hall, Box 351800, Seattle, Washington, 98195-1800, United States
2 - University Of Washington, Department of Earth and Space Sciences, Johnson Hall Rm-070, Box 351310, Seattle, Washington, 98195-1310, United States

Keywords:
phytoliths
Grasses
Poaceae
grasslands
phylogeny
Systematics
morphometrics
Paleobotany
paleoecology.

Presentation Type: Poster
Session: P, Paleobotanical Section Posters
Location: Exhibit Hall/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 5:30 PM This poster will be presented at 6:15 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PPB002
Abstract ID:712
Candidate for Awards:None