Muons penetrate much further than X-rays, they do essentially zero damage, and they are provided for free by the cosmos.
Image credit: Science Source/Digital Globe.
Edited by Douglas H. Erwin, Smithsonian National Museum of Natural History, Washington, DC, and accepted by the Editorial Board March 10, 2015 (received for review January 2, 2015)
Significance
Many mechanisms of the Cambrian Explosion have been proposed, but rigorous quantitative analyses of biodiversity dynamics are scarce, although they may shed light on important factors. Using a comprehensive database and sampling standardization, we dissect global diversity patterns. The trajectories of within-community, between-community, and global diversity during the main phase of the Cambrian radiation revealed a low-competition model, which was probably governed by niche contraction and the increase of predation at local scales. At continental scales, the increase of beta diversity was controlled by the high rate of community turnover among adjacent continents. This finding supports the general importance of plate tectonics in large-scale diversifications.
Abstract
The fossil record offers unique insights into the environmental and geographic partitioning of biodiversity during global diversifications. We explored biodiversity patterns during the Cambrian radiation, the most dramatic radiation in Earth history. We assessed how the overall increase in global diversity was partitioned between within-community (alpha) and between-community (beta) components and how beta diversity was partitioned among environments and geographic regions. Changes in gamma diversity in the Cambrian were chiefly driven by changes in beta diversity. The combined trajectories of alpha and beta diversity during the initial diversification suggest low competition and high predation within communities. Beta diversity has similar trajectories both among environments and geographic regions, but turnover between adjacent paleocontinents was probably the main driver of diversification. Our study elucidates that global biodiversity during the Cambrian radiation was driven by niche contraction at local scales and vicariance at continental scales. The latter supports previous arguments for the importance of plate tectonics in the Cambrian radiation, namely the breakup of Pannotia.
Footnotes
- ↵1To whom correspondence should be addressed. Email: na-lin13{at}hotmail.com.
Author contributions: L.N. and W.K. designed research, performed research, analyzed data, and wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. D.H.E. is a Guest Editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1424985112/-/DCSupplemental.
The Cambrian Explosion
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