Macrofossils, cuticles, and phytoliths: an update on the paleoecology and biogeography of the grasses

GALLAHER, T.J.; IGLESIAS A.; PIPO, M.L.; STROMBERG, C.A.E.; CLARK L.G.

Natal

Congreso; VI Monocot International Conference on Comparative Biology of Monocotyledons, and 7th International Symposium on Grass Systematics and Evolution; 2018

Monocots

The timing of the origin and diversification of the grass family has become the subject of intense debate particularly with regards to the taxonomic placement of recently described grass phytoliths and cuticle from the Maastrichtian of India. Here, we report on new quantitative analyses of phytoliths from multiple sources and a newly discovered early-mid Campanian fossil grass cuticlefrom James Ross Island, Antarctica. Time calibrated phylogenetic analyses and ancestral area estimations using macrofossils, fossil cuticles and phytoliths support an Early Cretaceous Gondwanan origin of the Poaceae. Ancestral habitat estimations using extant taxa indicate that grasses first evolved in forest-associated habitats and may have occupied key positions in forest margins, allowing lineages to more readily evolve into either deep shade or open habitats. In the Late Cretaceous or Paleocene, the PACMAD and Pooideae moved from forest associated ecosystems to open habitats, more than 30 Ma before the spread of grass-dominated vegetation in the Oligocene-Miocene. Our temporal estimations also suggest that C4 photosynthesis evolved first in the Chloridoideae in the Eocene or Oligocene, approximately 15-20 Ma earlier than other C4 PACMAD lineages and long before the rise to dominance of C4 grasslands within the last 10 Ma.