Range change in Metasequoia:: relationship to palaeoclimate

Metasequoia was widely distributed across the mid and high latitudes of the Northern Hemisphere during the Cretaceous, and experienced range contraction associated with Tertiary climatic cooling and drying. We compile occurrences of Metasequoia from the literature, museum collections and new localities, and plot them in a plate tectonic framework to document these range changes through time. We note two pulses of range contraction: Eocene-Oligocene associated with cooling at high latitudes, and Late Miocene-Pliocene associated with cooling and drying in mid latitudes. Only the northern limit of the taxon's range changed during these intervals. Because of its apparent climate sensitivity, Metasequoia might be used to reconstruct palaeoclimate. To test this hypothesis, we assemble the climatic tolerances of living Metasequoia glyptostroboides under natural and cultivated conditions and compare them with palaeoclimate reconstructions across the genus' former range. The fossil record of Metasequoia shows that ancient members of the genus regenerated under similar conditions to those preferred by living M. glyptostroboides (mean annual temperature of 9-17 degrees C and mean annual precipitation of 953-2039 mm). However, some data suggest that early Tertiary representatives may have tolerated mean annual temperatures as high as 20-22 degrees C. Thus, the climate tolerance of Metasequoia appears to have evolved little since the Cretaceous, suggesting that it has potential as a palaeoclimate indicator when used in coordination with other climate proxies. However, Metasequoia alone cannot provide great precision. (C) 2007 The Linnean Society of London.