Fungi, a Driving Force in Normalization of the Terrestrial Carbon Cycle Following the End-Cretaceous Extinction

Abstract

Geologists have long recognized the magnitude, abruptness, and the global pattern of the major biotic turnover across the Cretaceous–Paleogene (K–Pg) boundary approximately 65.5 million years ago. It was associated with one of the most catastrophic events in the history of life, involving mass mortality in both terrestrial and marine ecosystems globally; vast amounts of dead biomass covered the Earth’s surface. Of prime importance are data from distal boundary sites. These reveal much about the pattern of extinction, whether overprinted or not by local effects such as cratering and post-impact tsunamis. There are few instructive Cretaceous–Paleogene boundary sequences in terrestrial settings. Such sites include the western interior of the USA, Canada, and New Zealand. The pattern of vegetation turnover in these areas is characterized by a so-called fern-spike: abrupt and marked increase in relative abundance of fern spores in palynological assemblages. The latest Cretaceous palynofloras were a rich and diverse mix of angiosperms and gymnosperms with fern, lycophyte, and moss spores. In New Zealand, the boundary is characterized by total dominance of fern spores, notably in undisturbed, fine-grained sediments at the Moody Creek Mine where turnover from the latest Maastrichtian flora consists of a thin fungal layer followed by a step-wise recovery succession of several ground- and tree-fern taxa. Identification of this ‘fungal-spike’ accords with fungi having played an important role in the devastated terrestrial ecosystems. Fungi may even have facilitated normalization of the global carbon cycle.