Green Web or megabiased clock? Plant fossils from Gondwanan Patagonia speak on evolutionary radiations
Author for correspondence:
Peter Wilf
Tel: +1 814 865 6721
Email: pwilf@psu.edu
Received: 31 July 2014 Accepted: 12 September 2014
Peter Wilf1 and Ignacio H. Escapa2
1 Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA;
2 CONICET, Museo Paleontol ogico
Egidio Feruglio, Avenida Fontana 140, 9100 Trelew, Chubut, Argentina
New Phytologist (2015) 207: 283–290
doi: 10.1111/nph.13114
Key words: divergence dating, evolutionary radiations, geochronology, Gondwana, molecular clocks, paleobotany, Patagonia.
Summary
Evolutionary divergence-age estimates derived from molecular ‘clocks’ are frequently correlated with paleogeographic, paleoclimatic and extinction events. One prominent hypothesis based on molecular data states that the dominant pattern of Southern Hemisphere biogeography is post-Gondwanan clade origins and subsequent dispersal across the oceans in a metaphoric ‘Green Web’. We tested this idea against well-dated Patagonian fossils of 19 plant lineages, representing organisms that actually lived on Gondwana. Most of these occurrences are substantially older than their respective, often post-Gondwanan molecular dates. The Green Web interpretation probably results from directional bias in molecular results. Gondwanan history remains fundamental to understanding Southern Hemisphere plant radiations, and we urge significantly greater caution when using molecular dating to interpret the biological impacts of geological events.
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EXCERPT:
We urge significantly greater caution when using molecular dates in the explicit context of geologic time and Earth history. The fossil record is always incomplete, but its exciting potential is only beginning to develop in many parts of the world. Future improvements in molecular dating seem very likely, but for now, fossils and geochronology provide the only rigorous, enduring temporal framework for evolutionary radiations.
EXCERPT:
We urge significantly greater caution when using molecular dates in the explicit context of geologic time and Earth history. The fossil record is always incomplete, but its exciting potential is only beginning to develop in many parts of the world. Future improvements in molecular dating seem very likely, but for now, fossils and geochronology provide the only rigorous, enduring temporal framework for evolutionary radiations.
