3-D morphology of grass short cell phytoliths: Unlocking the evolution of grasses and grassland ecosystems

Author(s): Caroline Stromberg

Year: 2015


Grass-dominated ecosystems occupy >40% of Earth’s land surface today. Documenting when this prominent biome emerged was traditionally hampered by the rarity of identifiable grass fossils. Recently, phytoliths have emerged as a vital tool for tracking the evolutionary history of grasslands. Key to understanding ancient grassland composition is studying the 3-D morphology of silica grass short cell (GSSC) phytoliths. GSSCs have long been known as broadly diagnostic within grasses, but a landmark paper (Piperno and Pearsall 1998) demonstrated the full taxonomic potential of GSSC shape. For example, 3-D shape distinguishes between forms that look similar in one view, such as saddle-types in bamboos and chloridoids.

Incorporating study of 3-D morphology in phytolith analysis of Cretaceous-Cenozoic (66-2 million years ago (Ma)) samples from the Americas, Europe, and Asia has radically changed our understanding of grassland evolution. This work shows that open-habitat grasses (e.g., pooids, panicoids) diversified 10-20 million years before becoming ecologically dominant in North and South America, suggesting that different environmental factors promoted diversification vs. dominance. GSSC analysis also reveals that (C3) stipoid pooids dominated early savanna/grassland vegetation rather than tropical (C4) grasses as previously thought. Ongoing investigation of GSSC 3-D shape promises to further revolutionize our view of grassland evolution.

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3-D morphology of grass short cell phytoliths: Unlocking the evolution of grasses and grassland ecosystems. Caroline Stromberg. Presented at The 80th Annual Meeting of the Society for American Archaeology, San Francisco, California. 2015 ( tDAR id: 394920)