HR: 09:35h
AN: U31B-07 INVITED     [Abstracts]
TI: Origin and History of Magnolias
AU: * Hebda, R J
EM: rhebda@royalbcmuseum.bc.ca
AF: Royal British Columbia Museum, 675 Belleville Street, Victoria, BC V8W 9W2 Canada
AU: Irving, E
EM: tirving@pgc-gsc.nrcan.gc.ca
AF: Pacific Geoscience Centre, P.O. Box 6000, Sidney, BC V8L 4B2 Canada
AB: The classic disjunct distribution of living magnolias between southeast Asia and the Americas has been a puzzle for more than a century and a half. We propose a scheme for the origin and history of magnolias to explain this distribution by integrating paleogeographic, paleoclimatic, paleobotanical, and phytogeographic data. Our scheme is based on paleomagnetically determined latitudes. We assume that the moist warm temperate climate favoured by most extant magnolias has always been their preference. Molecular analyses (largely chloroplast DNA) reveal that several North American species are distinct and basal forms suggesting that magnolias likely originated in North America, a conclusion supported by the fossil record. We identify four evolutionary stages: (1) Ancestral magnolias originate in the Late Cretaceous of North America in high mid-latitudes ($45\deg$-$60\deg$N) at low altitudes under greenhouse climates. (2) During the exceptionally warm climate (super-greenhouse) of the Eocene, magnolias spread eastwards via the Iceland-Faroes isthmuses, to Europe and then across west and central Asia possibly to east Asia, still at low altitudes and high mid-latitudes. (3) With global cooling from the mid-Cenozoic, magnolias shift their core range to lower mid-latitudes ($30\deg$-$45\deg$N), become extinct in Europe and southern Siberia, breaking the once continuous distribution into two. (4) In the late Cenozoic, as ice-house conditions develop, magnolias diversify rapidly and expand southward into moist warm temperate uplands in newly uplifted mountain ranges of South and Central America, southeast Asia and the High Archipelago between southeast Asia and Australia. The late Cenozoic evolution of magnolias is characterized by the impoverishment of northerly species and diversification of southerly species. Thus, the centre of origin is not the center of diversity today. Disjunction at the generic level likely occurred as part of the mid-Tertiary southward displacement of the northern hemisphere "boreotropical" flora, assisted by the development of north-south water barriers to floral interchange, especially the Turgai Straight across eastern Siberia in the Late Eocene.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
SC: Union [U]
MN: 2004 AGU Fall Meeting