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>More recent texts that I have seen suggest that 85% of all species of
>animals and plants (not just the dinosaurs) were wiped out at the K/T
>boundary. If this is a single-event catastrophy, the loss of 85% of species
>represents the loss of 99.9% of individuals. While not being a strong
>argument in its self, the proportion of organisms that were effected by the
>K/T event is much greater than you anticipate.
Can you provide references to these texts? I'd like to see how the figure
was estimated because they would seem to place the K-T event in the same
ballpark as the Permo-Triassic extinction - which would be a genuinely new
development in the story. In the past studies of this type involved
simulations that produced a rather wide range of possible extinction
magnitudes depending on the simulation's assumptions (e.g., selective vs.
nonselective extinction). The most often referred to paper on this is David
Raup's estimates for the magnitude of the Permo-Triassic extinction...
Raup, D. M. 1979. Size of the Permo-Triassic bottleneck and its
evolutionary implications. Science, 206, 217-218.
...which he estimated at somewhere between 76% and 96% of all marine
species. I've always found it understandable that journalists, but curious
that scientists (who should know better), only cite the upper figure.
However, the compendia these types of studies are based upon usually
contain biostratigraphic data that are resolved only to stage level. This
practice (which is perfectly understandable from the standpoint of the
compendium compiler) overestimates the true magnitude of any boundary
extinctions by treating all taxa whose last appearance is recorded anywhere
in the stage (e.g., Maastrichtian) as if they all went extinct
simultaneously at the boundary. For example, such datasets might count
rudists and inoceramids as victims of a K-T boundary extinction despite the
fact that it is tolerably well-established that these clades were gone at
least tens of thousands to hundreds of thousands of years prior to the
boundary and/or any impact debris layers. [Note: Raup's study did not argue
or imply that all the Permo-Triassic extinctions took place only at the
P-Tr boundary horizon.] Such data are also bedeviled by many systematic
problems that...
Patterson, C. & Smith, A. B. 1987. Is periodicity of mass extinctions a
taxonomic artefact? Nature, 330, 248-251.
Smith, A. B. & Patterson, C. 1988. The influence of taxonomic method on the
perception of patterns of evolution. Evolutionary Biology, 23, 127-216.
...and, most recently,...
Smith, A. B. 1994. Systematics and the Fossil Record: Documenting
Evolutionary Patterns. Blackwell, London.
...have discussed at length.
Norm MacLeod
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Norman MacLeod
Senior Scientific Officer
N.MacLeod@nhm.ac.uk (Internet)
N.MacLeod@uk.ac.nhm (Janet)
Address: Dept. of Palaeontology, The Natural History Museum,
Cromwell Road, London, SW7 5BD
Office Phone: 0171-938-9006
Dept. FAX: 0171-938-9277
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