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Cyclicity in the Fossil Record Mirrors Rock Outcrop Area


Cyclicity in the Fossil Record Mirrors Rock Outcrop Area

Andrew B Smith et al. Biol Lett.


In a recent article, Rohde & Muller (Rohde & Muller 2005 Nature 434, 208-210) identified a strong 62 Myr cyclicity in the history of marine diversity through the Phanerozoic. The data they presented were highly convincing, yet they were unable to explain what process might have generated this pattern. A significant correlation between observed genus-level diversity (after removal of long-term trends) and the amount of marine sedimentary rock measured at a surface outcrop in Western Europe is demonstrated. This suggests that cyclicity originates from long-term changes in sedimentary depositional and erosional regimes, and raises the strong possibility that the cyclicity apparent in the record of marine fossils is not a biological signal but a sampling signal.


Figure 1
Figure 1
Plots of area of marine sediments exposed at an outcrop in Western Europe (France and the UK: open circles) and the numbers of short-lived (i.e. <45 Myr duration) genera (squares) plotted against geological stages from the Upper Norian to the Middle Eocene. (a) Log transformed plots that are not detrended, (b) detrended log transformed plots, (c) first and second order sequence stratigraphical cycles (from Hardenbol et al. (1998)). Black rising wedges: transgressive phases; light grey declining wedges: regressive phases. For details of time-scale and how sediment outcrop area was measured see Hardenbol et al. (1998).
Figure 2
Figure 2
Cross-correlation plot of log transformed outcrop area of marine sediment regression residuals against log transformed, short-lived generic diversity regression residuals. Dashed line, 4 s.e.

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