Ross: The Dunesland Heritage of Illinois 9 



tology. If fossils are sufficiently well preserved that we can identify 

 them at least to family or genus, fig. 8, we can deduce many ecological 

 facts about the time or place in which the fossilized organisms lived 

 — such as whether it was aquatic or terrestrial, humid or dry. All 

 our evidence indicates that, within rather broad limits, like things 

 have lived under about the same climatic conditions for the greater 



Fig. 8. — An insect fossil from on iron nodule or concretion found at Mozon Creek, Illinois; 

 hind wing of on ancestral mayfly, lithoneoro mirifica Carpenter. Actual length of wing about 

 one-half inch. This fossil represents on insect that lived during the Pennsylvonian period, about 

 250 million years ago. (Photograph courtesy of Illinois State Museum.) 



part of their history. If a species has become adapted to different 

 climatic conditions, almost invariably morphological changes of some 

 kind have accompanied or followed the ecological change. 



The second great accumulation of evidence used in unraveling 

 this past comes from investigating the relationships and present 

 geographic distribution of existing forms of life. This evidence com- 

 prises part of the field known as biogeography. If plant or animal 

 groups are studied on a world basis, the relationships and present 

 distribution give us indubitable evidence of at least some past move- 

 ments of floras and faunas. A plant and an insect offer two dramatic 

 examples of these movements. 



The plant is the eastern skunk cabbage. At present, this plant 

 is known only from the temperate deciduous forest of eastern North 

 America and the temperate deciduous forest of China. Because skunk 

 cabbage seeds are not spread easily (unlike others, such as dandelion 

 seeds, which may be carried long distances by wind), it does not seem 

 possible that the species was spread adventitiously from one area to the 



