millions of years 
1983] 
Burnham — Geraridae 
3 
Fig. I. Geological Time Table of the Carboniferous. Note the different ages of 
the Commentry and Mazon Creek localities. 
basing his taxonomic decisions on small differences in wing vena- 
tion (Handlirsch, 1906b, 1911, 1922). This approach, while render- 
ing the decision making easier, is nevertheless open to criticism. 
Studies on intraspecific variation in some Permian Protorthoptera 
have shown, for instance, that two fore wings belonging to the same 
specimen will exhibit noticeable differences in venation (Carpenter, 
1966). From these findings we can conclude that intraspecific varia- 
tion in the Protorthoptera was high, and that the variation Hand- 
lirsch saw was no greater than that seen in a single specimen. 
Further evidence that suggests Handlirsch was unrealistic in his 
representation of species diversity comes from the low probability of 
finding only one individual per species (for all species collected) in a 
random sample of living insects. Similarly, we cannot reasonably 
expect to find only one specimen per species in a paleontological 
sample, particularly when fossilization was catastrophic (and hence 
random) as is true for the Mazon Creek biota. 
Nevertheless, in spite of these drawbacks to the study of fossil 
insects, the field can be immensely rewarding. This is because it 
provides us with concrete evidence (in the form of fossils) of what 
early insect life was like. Without such proof, we would be guided 
