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Longrich NR, Currie PJ.Longrich NR, et al.Proc Natl Acad Sci U S A. 2009 Mar 31;106(13):5002-7. doi: 10.1073/pnas.0811664106. Epub 2009 Mar 16.Proc Natl Acad Sci U S A. 2009.PMID: 19289829Free PMC article.