Angiosperms versus gymnosperms in the Cretaceous

In a letter to Sir Joseph Hooker dated July 22, 1879, Charles Darwin described the abrupt origin, highly accelerated rate of diversification, and rise to dominance of flowering plants (angiosperms) in the Mid-Cretaceous (100 to 110 Ma) as an “abominable mystery” (1, 2). Knowledge of the paleobotanical record has greatly increased since Darwin’s day. The currently available fossil record clearly documents a sudden and rapid increase in the diversification and geographical extent of angiosperms since the Mid-Cretaceous, resulting in the ecological dominance of flowering plants in almost all terrestrial biomes on Earth today. It has been widely assumed that this major expansion of angiosperms outcompeted other land plants, most particularly the gymnosperms (mainly conifers). As a botany student in the mid-1960s, I was taught this not as a hypothesis but as an “established fact.” In PNAS, Condamine et al. (3) use all of the available fossil and molecular data for conifers to test the competing hypotheses that competition from angiosperms, climate change, or time alone led to the decline of conifers to the benefit of angiosperms. Results from detailed numerical analyses suggest that the increased extinction rates of conifers in the Mid- and Late Cretaceous are most parsimoniously interpreted as a response to the rise of angiosperms, and the alternative hypotheses of climate change or time alone as drivers of the conifer demise are falsified (3). Within the gymnosperms today (12 families, 79 genera, 985 species), the Pinidae (conifers) is the major group with 6 families, 65 genera, and 627 species (4), such as pines, spruces, and firs. Conifers often occur in relatively harsh environments today such as in boreal areas, at high elevations, and/or on poor or shallow soils. However, conifers were a dominant and widespread component of the Earth’s flora in the Mesozoic, especially in … [↵][1]1Email: john.birks{at}uib.no. [1]: #xref-corresp-1-1