The Silurian–Devonian terrestrial revolution: Diversity patterns and sampling bias of the vascular plant macrofossil record

Abstract

During the mid-Palaeozoic, vascular land plants (i.e., tracheophytes) underwent a great radiation that triggered the development of the land biosphere – the so-called Silurian–Devonian terrestrial revolution. However, little is known about how different plant groups impacted this process. A newly constructed dataset of plant macrofossil genera is used to characterize the tempo and mode of development of Silurian–Devonian vegetation and how it spread out over subaerial habitats. Important fluctuations of diversity and evolutionary rates of vegetation are linked to the diversity dynamics of particular tracheophyte groups. Despite a general increase of taxonomic richness through the Devonian, there was a clear stepwise pattern of origination and extinction events that resulted in the main floral transitions over time, such as the change to a forested landscape. To test if sampling bias may be affecting the observed diversity patterns, the latter were compared with the number of plant macrofossil localities as a proxy for sampling effort. This suggested a highly significant correlation between observed diversity and sampling effort, but it was not homogeneous, suggesting that at least some diversity fluctuations have a potential biological explanation. The sampling-corrected pattern of standing diversity suggests a clear increase of plant richness in the Pragian (Early Devonian) and Givetian (Middle Devonian), which may be related to the early expansion of the tracheophyte clades and the initial diversification of forested ecosystems, respectively. Further works should be focused on elucidate the impact of rock record on our understanding of Devonian plant diversification.