Decoupled taxonomic radiation and ecological expansion of open-habitat grasses in the Cenozoic of North America

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 34; pp. 11980 - 11984
• Main Author: Stromberg, C.A.E
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 23.08.2005; National Acad Sciences
• Subjects: Ancient civilizations; Cenozoic; Climate change; Colorado; Demography; Ecology; Ecosystem; Environment; Environmental changes; Eocene; Forest habitats; Fossils; geographical distribution; Geologic Sediments; Grasses; grasslands; Habitats; Idaho; Miocene; Montana; Nebraska; North America; Oligocene; Paleoclimatology; paleoecology; Phylogeny; Physical Sciences; phytogeography; Phytoliths; Plains; Plant ecology; Poaceae; Poaceae - anatomy & histology; Poaceae - genetics; Radiation; species diversity; Taxonomy; Vegetation; Wyoming; Montana; Wyoming; Colorado; Idaho; Nebraska; North America
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0505700102

Because of a dearth of Cenozoic grass fossils, the timing of the taxonomic diversification of modern subclades within the grass family (Poaceae) and the rise to ecological dominance of open-habitat grasses remain obscure. Here, I present data from 99 Eocene to Miocene phytolith assemblages from the North American continental interior (Colorado, Nebraska, Wyoming, and Montana/Idaho), constituting the only high-resolution mid-Cenozoic record of grasses. Analyses of these assemblages show that open-habitat grasses had undergone considerable taxonomic diversification by the earliest Oligocene (34 million years ago) but that they did not become ecologically dominant in North America until 7-11 million years later (Late Oligocene or Early Miocene). This pattern of decoupling suggests that environmental changes (e.g., climate changes), rather than taxonomic radiations within Poaceae, provided the key opportunity for open-habitat grasses to expand in North America.