The origins of modern biodiversity on land

Abstract

Comparative studies of large phylogenies of living and extinct groups have shown that most biodiversity arises from a small number of highly species-rich clades. To understand biodiversity, it is important to examine the history of these clades on geological time scales. This is part of a distinct 'phylogenetic expansion' view of macroevolution, and contrasts with the alternative, nonphylogenetic 'equilibrium' approach to the history of biodiversity. The latter viewpoint focuses on density-dependent models in which all life is described by a single global-scale model, and a case is made here that this approach may be less successful at representing the shape of the evolution of life than the phylogenetic expansion approach. The terrestrial fossil record is patchy, but is adequate for coarse-scale studies of groups such as vertebrates that possess fossilizable hard parts. New methods in phylogenetic analysis, morphometrics and the study of exceptional biotas allow new approaches. Models for diversity regulation through time range from the entirely biotic to the entirely physical, with many intermediates. Tetrapod diversity has risen as a result of the expansion of ecospace, rather than niche subdivision or regional-scale endemicity resulting from continental break-up. Tetrapod communities on land have been remarkably stable and have changed only when there was a revolution in floras (such as the demise of the Carboniferous coal forests, or the Cretaceous radiation of angiosperms) or following particularly severe mass extinction events, such as that at the end of the Permian.

Dinosaur morphological diversity and the end-Cretaceous extinction

“…Unfortunately, records of dinosaur disparity across the entire Mesozoic are not yet available for comparison, and are difficult to compile because of low sample sizes in many stage-level intervals, but the establishment of these patterns should be a major goal of research on dinosaur biodiversity. Furthermore, there are known instances in the fossil record in which major vertebrate clades endured catastrophic diversity and disparity losses, both during mass extinctions and normal background times, but later rebounded [36][37][38][39][40] . A satisfactory understanding of the causes and tempo of the non-avian dinosaur extinction remains difficult, but the compilation of additional biodiversity metrics (such as disparity) and increased study of non-North American taxa is helping to bring clarity.…”

Biological diversity in a changing world

“…The planet has always been changing: current patterns of biodiversity are the result of past environmental conditions and ecological and evolutionary constraints (Benton 2010;Clarke & Crame 2010;Lyons et al 2010). However, current rates and sources of change pose scientists and people in general with new challenges (Chown 2010;Jackson 2010).…”

“…Benton (2010) explores the origins of modern biodiversity on land and contrasts two approaches to view this issue: a phylogenetic expansion view, which focuses on describing how and when current phylogenies were formed, and an equilibrium view, which focuses on developing density-dependent global scale models as general rules for the origins of biodiversity patterns. The paper argues for the former and points out that most land diversity is due to a subset of groups in which there is an increased rate of diversification, and that the availability of empty ecospace has helped shape current patterns.…”

Phylogenomics reveals rapid, simultaneous diversification of three major clades of Gondwanan frogs at the Cretaceous–Paleogene boundary

“…Even though the fossil record indicates mass extinction at the KPB for several taxa, including birds, squamates, and mammals, and subsequent radiation post-KPB (29-31), molecular data often indicate that many clades had diversified, at least in the sense of lineage splitting, before the KPB event (32)(33)(34)(35)(36). Unlike nonavian dinosaurs, whose demise is well documented in the rocks, the fossil record of frogs is so far largely uninformative about survival/ extinction across the KPB (37)(38)(39)(40).…”