[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: theP-T boundary

Ron Dass <radass@orion.neca.com> wrote

>        On the other hand, most estimates I've seen say about 95% of all
>species checked out at the end of the Permian. 

Have you seen most "estimates" of 95% or most "quotes" of that figure ? 

If I may quote from David M Raup, Extinction: Bad Genes or Bad Luck ?, 
OUP, 1993, pp 72-74

"Many readers will have heard that 96 percent of all species living near the 
of the Permian were killed in the big mass extinction at that time. This number 
comes from the reverse rarefaction graph of Figure 4.2. This estimate is 
probably an exaggeration, because the extinction of species is not completely 
random. If extinction is focused on certain genera and families, killing will 
concentrated in these groups. If reverse rarefaction is used to estimate 
species kill from the extinction rates of genera or families, any departure 
random (Field of Bullets) killing will exaggerate species kill.

I am slightly embarrassed by the wide use of the figure of 96 percent for the 
Permian because I was responsible for it in a 1979 article presenting the 
reverse-rarefaction method. Although my article contained ample caveats 
about the random-killing assumption and although I said that the 96 percent 
estimate was an upper limit, all too many users of the number have neglected 
to mention the caveats. In truth, I probably did not exert myself to emphasize 

The article Raup referred to : Raup D M, Size of the Permo-Triassic 
bottleneck and its evolutionary implications, Science 1979; 206: 217-18.
In this Raup actually gave a range of 80-96% species extinction.

Alper gave somewhat lower figures : Land animals 80%, Marine animals 
probably over 90% (Alper J, Earth's near-death experience, Earth (January) 
1994; 3 (1): 42-51) though he had not cited any primary source. 

I have not seen any other estimate which specified the 95/96% extinction of 
species at P-T boundary. Is there any other published estimate (not citing 
Raup) which independently came to such a high figure ?

Gautam Majumdar                 gautam@majumdar.demon.co.uk