Adapting phytolith analysis for use in Cenozoic paleoecology

Phytolith analysis has become a standard method in archaeobotany and Quaternary paleoecology for reconstructing vegetation types and describing grass communities (closed-habitat grasses vs. open-habitat grasses; C3 vs. C4 grasses) (Piperno 2006). Nevertheless, several aspects of phytolith analysis have not yet been standardized. For example, methods of inference in most phytolith studies rely heavily on local modern analogs that may not be applicable to phytolith assemblages with poorly known modern analogs, such as Cenozoic assemblages (Strömberg 2004). Additionally, laboratory methods and classification vary from study to study, and few published phytolith keys exist.

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Research in the lab addresses these problems in several different ways. First, we are refining our method of phytolith extraction by examining sources of bias (e.g., phytolith size, specific gravity, and shape) that may be introduced during various steps of the procedure and that may hinder inter-study comparisons (Strömberg 2007, 2009).


Second, we have developed a rigorous classification system of phytolith morphotypes (200+) with

Testing the effects of count size on commonly used vegetation indices. From Strömberg (2009).

high predictive power for ecological and paleoecological analyses. For this purpose, we are continually building a comprehensive reference collection of phytoliths from modern plants. We explore the distribution of morphotypes among taxa to assign precise, quantitative, and testable guidelines for interpretation of fossil soil phytolith assemblages (Strömberg 2003).















 
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Grass short cell phytolith morphology in a phylogenetic framework. Red = closed-habitat grasses; white = open-habitat grasses.

Detailed study of grass (short cell) phytoliths is also underway in collaboration with Dolores Piperno (Smithsonian Institution) to establish a more explicit, phylogenetic basis for identification of specific grass clades in the fossil record (see also Prasad et al. 2005, 2011).


Third, work in the lab—some in collaboration with colleagues from other institutions—focuses on comparing phytolith assemblages with macrofossil and pollen floras, isotopic and paleosol data to establish calibrations between different methods of inferring Cenozoic vegetation and climate. For example, an NSF-funded project in collaboration with Nathan Sheldon and Selena Smith, University of Michigan, seeks to intercompare vegetation reconstruction using phytoliths with paleosols and isotopic data through three critical climatic transitions (Eocene-Oligocene, Oligocene-Miocene, middle-late Miocene in southwestern Montana. Read more about this project here.


New research in the lab, led by graduate student Regan Dunn, seeks to develop an a-taxonomic proxy for habitat openness using phytoliths. Read more here.

 
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Phytoliths from modern plants (Strömberg 2003). a. Trichome from Pharus. b. Cystolith from Morus. c. Sclereid from Magnolia. Scale bar = 10 micrometers.