Plant–insect and –fungal interactions in Taxodium-like wood fossils from the Oligocene of southwestern China

Abstract

Cupressaceae fossil tree stumps from the early Oligocene Lühe coal mine in southwestern China contain abundant quartz-petrified damage traces. The wood fossils were assigned to Taxodioxylon (very similar to extant Taxodium) based on wood anatomy analysis. Within the woods, three types of arthropods- and one fungus-mediated ichnofossils LHIF 1–4 (Lühe wood ichnofossils 1–4) were observed. The boring wood types for LHIF 1–3 are comparable to extant longicorn beetles (Cerambycidae), snout beetles (Curculionidae), and wood wasps (Siricidae). The polyporous structured traces of LHIF 4 were attributed to the invasion of stem canker fungus (Polyporaceae). This first-ever report of Taxodium-like fossil from the Oligocene of southwestern China points to Yunnan serving as a refugium for some lineage of gymnosperms at that time. Furthermore, the extensive traces of arthropods and fungus discovered from the fossil wood have filled a gap in fossil records for insect herbivory in this region. The wood stumps and decomposers suggest a swamp-like environment. The disappearance of Taxodium after the Oligocene supports incremental aridification and changes in winter season temperature conditions, which shifted the late Paleogene mixed deciduous broad-leaved and needle-leaved forest into the present evergreen broad-leaved forest.