Manchester, Steven R. , Doyle, James A. , Sauquet, Hervé .
A myristicaceous seed from the Early Eocene of southern England: implications for the age of Myristicaceae.
Analyses of geographic ranges of Myristicaceae and Annonaceae (Magnoliales) in a phylogenetic context imply that both groups originated in Africa and/or South America and expanded into the Asian tropics, suggesting a Late Cretaceous origin and dispersal to Laurasia as the Tethys closed in the Tertiary. This is consistent with Late Cretaceous molecular dates for crown-group Annonaceae and fossil records of annonaceous seeds in the Maastrichtian of Africa and the Eocene of England and North America. However, molecular age estimates for crown-group Myristicaceae are much younger (Miocene), which poses major problems for explaining the pantropical distribution of the family. The oldest fossils previously attributed to Myristicaceae are wood from the Paleocene of Africa and seeds from the Miocene of Germany. Here we describe a fossil seed from the Early Eocene London Clay Formation at Herne Bay in southern England that significantly extends the record of seeds that can be related to Myristicaceae. Transverse fracturing of the specimen reveals prominent tegminal ruminations of the kind found today only in Myristicaceae. The Early Eocene age might seem to contradict molecular dating of the family as Miocene, but this is uncertain. Because phylogenetic analyses do not resolve whether ruminations are ancestral for the family or arose within it, the fossil could belong either to the crown group or on the stem lineage leading to it, and the same is true for the Paleocene wood and Miocene seeds. Better resolution of relationships in Myristicaceae and more detailed understanding of seed characters are needed to determine whether molecular and fossil data on the age of the family are in conflict, or modern morphology was attained on the stem lineage long before radiation of the crown group.
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1 - Florida Museum of Natural History, Dickinson Hall, P.O. Box 117800, Gainesville, Florida, 32611, USA
2 - University of California, Davis, Section of Evolution and Ecology, One Shields Ave., Davis, California, 95616, USA
3 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, TW9 3DS, United Kingdom
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:30 AM