Discussion and conclusions
The mollusc shells from the Oligocene Gongkang
Formation in Nanning Basin are exceptionally well
preserved. Altogether, the assemblages are remarkably
diverse and more than 25 species of bivalves and
gastropods have been described by Odhner (1930) and
Yen (1936). Despite these thorough studies, the two
impressively large viviparid species described herein
are new to science. Surely, these gastropods have not
been overlooked by previous workers, but simply were
not present in the outcrops exposed in the early 20th
century, which may indicate a significant sampling
bias. Moreover, several strange taxa of unresolved
affinities, such as the unionids Tuberonaia tuberosa
(Odhner, 1930) and Rhombunio spinifer Odhner,
1930, the gastropod Sinomelania leei Yen, 1936, and the newly described Macromargarya nanningensis,
have been documented from the Nanning Basin, suggesting
a high rate of endemism in the Palaeogene
Nanning Lake.
Discussion and conclusionsThe mollusc shells from the Oligocene GongkangFormation in Nanning Basin are exceptionally wellpreserved. Altogether, the assemblages are remarkablydiverse and more than 25 species of bivalves andgastropods have been described by Odhner (1930) andYen (1936). Despite these thorough studies, the twoimpressively large viviparid species described hereinare new to science. Surely, these gastropods have notbeen overlooked by previous workers, but simply werenot present in the outcrops exposed in the early 20thcentury, which may indicate a significant samplingbias. Moreover, several strange taxa of unresolvedaffinities, such as the unionids Tuberonaia tuberosa(Odhner, 1930) and Rhombunio spinifer Odhner,1930, the gastropod Sinomelania leei Yen, 1936, and the newly described Macromargarya nanningensis,have been documented from the Nanning Basin, suggestinga high rate of endemism in the PalaeogeneNanning Lake.
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