Mummified fossil of Keteleeria from the Late Pleistocene of Maoming Basin, South China, and its phytogeographical and paleoecological implications

Keteleeria is a small genus of Pinaceae now mainly restricted to eastern Asia. Although this genus has been documented with a wide distribution in the geologic record of Europe, North America, and Asia, its history in low-latitude areas (including South China) has remained obscure. In this paper, a fossil wood of Keteleeria sp. is described from the Late Pleistocene (29-27 ka BP) of the Maoming Basin, South China. This wood is the most ancient megafossil evidence of Keteleeria within the modern distribution area of this genus. The fossil records of Keteleeria suggests that this thermophyllous genus migrated into South China by the Middle Pleistocene escaping from glacial cooling and became widespread over this region in the Late Pleistocene beginning from the interglacial stage preceding the Last Glacial Maximum. The analysis of growth rings in the fossil wood and its comparison with those of modern Keteleeria davidiana (Bertrand) Beissner indicates that in the Late Pleistocene of Maoming Basin (29-27 ka BP) there was a humid climate with less pronounced seasonality of precipitation than that seen in the subtropical monsoonal climate of modern northeastern Vietnam. Apparently, the Maoming Basin was influenced by interglacial regime with summer-monsoon circulation. The previously proposed method to distinguish between evergreen and deciduous conifers based on growth ring anatomy, is not reliable because of the wide variance and ambiguity in its results.