Ecological Aspects of the Cretaceous Flowering Plant Radiation

Abstract

The first flowering plant fossils occur as rare, undiverse pollen grains in the Early Cretaceous (Valanginian-Hauterivian). Angiosperms diversified slowly during the Barremian-Aptian but rapidly during the Albian-Cenomanian. By the end of the Cretaceous, at least half of the living angiosperm orders were present, and angiosperms were greater than 70% of terrestrial plant species globally. The rapid diversification of the group, and its dominance in modern vegetation, has led to the idea that the Cretaceous radiation of angiosperms also represents their rise to vegetational dominance.Paleoecological data cast a different light on the Cretaceous radiation of angiosperms. Analyses of sedimentary environments indicate that angiosperms not only originated in unstable habitats but remained centered there through most of the Cretaceous. Morphology of leaves, seeds, and wood is consistent with the status of most Cretaceous angiosperms as herbs to small trees with early successional strategy. The diversification of flowering plants in the Cretaceous represents the evolution of a highly speciose clade of weeds but not necessarily a major change in global vegetation.

Decoupling the spread of grasslands from the evolution of grazer-type herbivores in South America

“…Thus, the rise to ecological dominance of openhabitat grasses lagged taxonomic diversification by at least 20 million years in southern South America. This decoupling ARTICLE parallels the North American record 14 , suggesting that it reflects an evolutionary/ecological phenomenon rather than incomplete fossil records; similar patterns have been recorded in C 4 grasses 14 and several other organisms, such as early flowering plants and certain insect groups 48,49 . If true, the lag implies that different factors influenced pooid and PACMAD diversification versus ecological expansion 14 .…”

Explosive Radiation of Malpighiales Supports a Mid‐Cretaceous Origin of Modern Tropical Rain Forests

“…As we have noted, fossil evidence indicates that tropical rain forest appeared after the K/T event in many areas where Late Cretaceous forests were apparently more open and dry adapted (Tiffney 1984;Wolfe 1987, 1993;Wolfe and Upchurch 1987;Wing and Boucher 1998;Morley 2000;Johnson and Ellis 2002;Ziegler et al 2003). Further expansion and taxonomic diversification of this biome took place during the Cenozoic.…”

“…They can be defined as having a stratified closed canopy, as receiving abundant precipitation, as experiencing equable temperatures, and as containing woody angiosperm species, at least in the understory (Richards 1996;Whitmore 1998;Morley 2000). During the past 20 years the view has become widespread that the expansion and diversification of this vegetation type occurred principally during the past 65 million years, following the mass extinction event at the CretaceousTertiary (K/T) boundary (∼65 Ma [Tiffney 1984;Wing and Boucher 1998;Morley 2000;Johnson and Ellis 2002;Ziegler et al 2003]; Cretaceous and Cenozoic timescales following Gradstein et al [1995] and Berggren et al [1995]). This hypothesis was initially supported by the rarity of large stems (Wheeler and Baas 1991;Wing and Boucher 1998) and large diaspores (Tiffney 1984;Wing and Boucher 1998) of angiosperms in the Cretaceous and by the marked increase in diaspore size in the Early Tertiary.…”

An exceptional role for flowering plant physiology in the expansion of tropical rainforests and biodiversity

“…Wet conditions can thereby be propagated out from areas that would already have high precipitation: ever-wet rainforest would exist in tropical South America with or without the angiosperms, but the area of everwet conditions is dramatically increased with their presence (figure 5). Angiosperms first appeared in the Mid-Cretaceous, which was followed by a more protracted rise to ecological dominance (Tiffney 1984;Wing et al 1993;Wing & Boucher 1998). Global temperatures were warm before and after their ecological spread, but climates differed dramatically.…”