LATE MIOCENE CYCLOCARYA (JUGLANDACEAE) FROM SOUTHWEST CHINA AND ITS BIOGEOGRAPHIC IMPLICATIONS

Premise of research. Cyclocarya Iljinskaya (Juglandaceae) is a genus with a single living species that is endemic to central and south China. The genus has an abundant North American and Eurasian fossil record from the Paleocene to the Pliocene, documenting its spread across Europe to western Siberia during the Oligocene and its arrival in Japan by the Miocene. However, there have been no fossil occurrences of Cyclocarya near its modern distribution. In this study, we describe a new species of Cyclocarya from the upper Miocene Nanlin Formation in Lianghe County, western Yunnan Province, southwest China, and discuss its biogeographic implications. Methodology. We examined the fossil fruit using LM and SEM, and we compared its morphology with fruits of fossil Cyclocarya and extant Cyclocarya paliurus (Batalin) Iljinsk. Pivotal results. The fossil fruit of Cyclocarya simipaliurus sp. nov. consists of a small nutlet that is surrounded by a circular and flange-like wing. The nutlet is circular in plan view and oblate in longitudinal view. Nutlet structure and the epidermal characteristics of the wing indicate that this fossil fruit is almost identical to that of the extant species, C. paliurus. Conclusions. The specimen reported here is the only reliable fossil of Cyclocarya known from China. The new fossil species helps to fill a significant gap in the fossil record of Cyclocarya, indicating that the genus had reached the western most boundary of its modern distribution by the late Miocene. Western Yunnan had a warm and humid climate during the late Neogene, and the rapid uplift of the Yunnan Plateau began in the Pliocene. Pleistocene glaciations may have forced Cyclocarya to retreat from western Yunnan, and the uplifted mountains and deep river valleys might have posed barriers for reconnection during the interglacials.