The long-lived Lake Nanning and its endemic and non-endemic fossil biota

Long-lived lakes are famous for the development of taxonomically and morphologically diverse endemic faunas, which usually radiated from a rootstock of only a few early colonisers. Examples of such radiations are known from several continents. Eocene? to Oligocene sediments of Lake Nanning in southern China (Guangxi Province) have yielded rich and diversified fossil biota. Although research on these fossils started in the early 20th century, Lake Nanning has not found its way onto the map of long-lived lakes. Providing an overview of the flora and fauna recorded from Lake Nanning, we intent to change this now.

Gastropods (Viviparidae, Stenothyridae), bivalves (Unionidae), ostracods and fish have successfully radiated in Lake Nanning, and developed a variety of endemic species, many of which still await formal description. Several mollusc species have developed peculiar morphologies, some of them reminiscent of (unrelated) marine taxa. Shell thickening, spines, carinae, nodes and restricted apertures in bivalves and gastropods are interpreted as armour to prevent predation by giant shell crushing carp, which are documented by their teeth. Four different, successive macro-mollusc associations are defined, which can likely be used for relative dating of the lake sediments. The molluscs of Lake Nanning are outstandingly well preserved and provide a great opportunity to study a remarkable endemic lake radiation, as well as life-life interactions with their predators.

In addition, a pilot palynology study has generated data on palaeoecology. Palynomorph assemblages from different lake stages are dominated by cool temperate conifer pollen and freshwater algae. This suggests that the sediments were deposited during or after Eocene-Oligocene cooling, and supports the biostratigraphy based on rare mammal finds. The presence of well-preserved palynomorphs throughout the succession makes the sediments of Lake Nanning one of the most important Oligocene climate archives of the region.