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Fossil Leaves of Elaeagnus First Found in Qinghai-Tibet Plateau


September 1, 2014

The Qinghai-Tibet Plateau is the center of diversity and endemism for Elaeagnaceae (silverberry family), as well as for many other taxa. Elaeagnaceae are small, nitrogen-fixing shrubs and trees, consisting of about 90 species in three genera: Elaeagnus L., Hippophae L., and Shepherdia Nutt. About two third of the Elaeagnus species, and all species of Hippophae, are native to the Qinghai-Tibet Plateau and adjacent areas.

Fossil Elaeagnaceae could provide significant evidence for the phylogeny and biogeography of the family and contribute primary data regarding the evolution of the unique Qinghai-Tibet Plateau flora in its dramatic setting of tectonic and climatic change. However, the fossil record of the Elaeagnaceae is limited.

In a recent study, Prof. ZHOU Zhekun and his team of Xishuangbanna Tropical Botanical Garden (XTBG) of Chinese Academy of Sciences collected fossil leaves of Elaeagnus from the Lawula Formation in Kajun village, about 16 km northwest of Gatuo Town, Mangkang County, eastern Tibet, China (fossil locality at 29°45′10″N, 098°25′58″E; 3910 m a.s.l.;). The researchers described four fossil leaves with diagnostic features of Elaeagnus from the late Miocene of eastern Tibet. They compared the fossil leaves to living and fossil species and discussed the taxonomic significance of surficial scales and the biogeographic and paleoenvironmental insights stemming from the discovery.

The researchers found that the well-preserved, densely packed, stellate scales on fossil leaf surfaces were diagnostic of Elaeagnaceae. They assigned those fossil leaves to Elaeagnus tibetensis T. Su et Z.K. Zhou sp. nov., comprising the first confirmed fossil Elaeagnus leaves worldwide.

As the first confirmed leaf fossil record in Elaeagnus, E. tibetensis demonstrated that the genus was already distributed in the Qinghai-Tibet Plateau by the late Miocene. The diversification of Elaeagnaceae and other groups in this region may be closely associated with the uplift of the Qinghai-Tibet Plateau. The characteristic scales on leaf surfaces are likely to be an important functional adaptation to seasonal droughts during early spring.

The study entitled “Miocene leaves of Elaeagnus (Elaeagnaceae) from the Qinghai-Tibet Plateau, its modern center of diversity and endemism” has been published in American Journal of Botany.

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