Ross: The Dunesland Heritage of Illinois 25 



the southwest, others from the southeast. Some of the typical prairie 

 forms, such as the leafhoppers on the prairie grasses, may have 

 spread fairly directly from the south. There is some evidence that 

 the many forms of life that inhabit the swales and the Dead River 

 may also have arrived directly from the south. These could have 

 spread northward via the ponds and lagoons left in central Illinois 

 after retreat of the glaciers. Finding bits of evidence that will help 

 to unravel these northward patterns of dispersal is a laborious but 

 a highly intriguing occupation. A great deal remains to be done 

 before we will have more than a general understanding of these 

 patterns of northward spread following the glaciers. 



EXTINCT LIFE 



During this long historj^ of Illinois life, many species of plants 

 and animals were unable to survive and became extinct. It is thought 

 that extinction of species may have been especially pronounced during 

 the Ice Age, when the ranges of some animals changed geographi- 

 cally and in size. The best evidence we have for this statement con- 

 cerns large mammals. Some of the extinct large animals that once 

 ranged over Illinois were the giant ground sloth, the giant beaver 

 (as large as a bear), the American mastodon, and two species of 

 mammoths. Other extinct large mammals, which may have been 

 rarer and less widely distributed in the Illinois area, were a musk-ox, 

 a peccary, and the giant or royal bison. Too few remains of these 

 animals have been found, however, to allow us to know exactly where 

 these animals belonged in the scheme of natural communities then 

 occurring in the area. 



It is likely that many other kinds of life also became extinct 

 during this period. This is suggested by our knowledge of certain 

 insects. A small stonefly is now known only from the streams in 

 Rocky Branch and one neighboring ravine and from a single stream 

 near Ottawa, Ontario, Canada. Two distinctive caddisflies are now 

 known only from one small spring in southern Illinois. It seems 

 plausible to assume that these and a goodly number of other kinds 

 of animals may have become as rare as these before man altered the 

 environment. Following the same reasoning further, it is likely that 

 still other species of which we have no record diminished in numbers 

 and ultimately became extinct. 



Although a large number of species may have become extinct, 

 truly remarkable numbers of living things have persisted to the 

 present. Illinois has probably 25,000 different kinds of plants and 

 animals — about 2,500 species of plants, about 20,000 species of insects. 



