48 
Psyche 
[Vol. 90 
avid corps of amateur collectors, many of whom have made their 
finds available for scientific study. 
The presence of the Geraridae at both Mazon Creek and at 
Commentry may seem somewhat surprising,*^ The Mazon Creek 
locality is roughly 5 to 10 million years older than that at Commen- 
try and the two formed under quite different circumstances. How 
can the presence of Gerarus at both be explained? 
To find an answer, one must look at land mass movements during 
the Carboniferous, and at their influence on climatic patterns and 
continental distributions (see fig. 28). The collision of the continents 
Gondwana and Laurasia during this period had two major conse- 
quences. These were 1) the formation of the Allegheny Mountain 
range in North America; and 2) the alignment of eastern North 
America and western Europe so that they were contiguous at zero 
latititude. The significance of these events for the family Geraridae 
is twofold. One, the separate land masses were fused into a single 
continent, and two, their new position along the equator resulted in 
the formation of extensive coal swamps throughout North America 
and Europe. These events made dispersal of insects from one region 
to the other relatively easy. Although the creation of the Allegheny 
Mountain chain may have acted as a barrier to dispersal for some 
insects (and other animal and plant species), this was probably not 
so for those that were strong fliers. It is likely, therefore, that the 
Geraridae were able to cross the barrier, and in so doing, passed 
from one coal swamp habitat to another. It is assumed, being 
orthopteroids, that they were herbivores, and probably restricted in 
their feeding habits to plants found in these swamps. It is not sur- 
prising, then, that they should have been so widespread and success- 
ful during the Upper Carboniferous. For the same reason, it is not 
surprising that they died out by the end of the Carboniferous when 
climatic changes led to the drying up of the great coal swamps and 
the concomitant extinction of the coal swamp fauna and flora. 
“^Three other genera common to both these localities have previously been 
reported. They are Honialoncura (Carpenter, 1964) and Spilaptera (Carpenter and 
Richardson, 1971) in the order Paleodictyoptera, and Mischoptera (Carpenter and 
Richardson, 1968) in the order Megasecoptera. 
