A preliminary assessment of plant-biotic interactions in the Eocene of South China: Evidence from Liquidambar L. (Saxifragales: Altingiaceae)

The study of fossil plant-biotic (mainly arthropod) interactions offers an opportunity to understand the evolutionary process in palaeoecosystems and their response to climate fluctuation. Despite the importance of such investigations, not much is known about plant-arthropod associations from the Cenozoic floras of Asia. Exceptionally diverse Eocene floras from adjacent Maoming and Changchang sedimentary basins of southern China provide valuable insights into low-latitude palaeoecosystems. These floras indicate different intensities of plant-arthropod interactions and probably viral, bacterial or fungal infection. Two upper Eocene floras from the Maoming Basin are markedly distinct from two approximately contemporaneous middle Eocene floras of the Changchang and Maoming basins in exhibiting much more abundant and diverse plant damage types (DTs). For equivalent comparisons we focus on well-sampled fossil leaves of Liquidambar L. (Altingiaceae) present and relatively abundant in both basins. L. maomingensis and Liquidambar sp. 1 from both upper Eocene Maoming floras exhibit mainly external foliage feeding. In contrast, almost only galling occurs on Liquidambar sp. 2 leaves from the middle Eocene Changchang flora. The differences in the diversity and frequency of DTs in the studied palaeofloras could have been affected by a progressive warming and increase in climate seasonality over the middle-late Eocene interval as well as by habitat conditions and plant successional status. We hypothesize that L. maomingensis and Liquidambar sp. 1 from the Maoming Basin inhabited the early successional riparian forests on an alluvial plain, whereas Liquidambar sp. 2 from the Changchang Basin was a component of more mature plant communities.