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On the other hand, expansion of lakes spread many fishes to new sites, some of which are found today in refugia of small ponds that remained as the connected glacial lakes retreated.One extreme example is the spread of the prickly sculpin across the Continental Divide in British Columbia.It is likely that changing sea levels and shifts of marine regions played a part in the evolutionary pressure. At times during the Pleistocene, subtropical conditions extended to the Carolinas and even Virginia.These periods alternated with cooler-than-normal conditions. The rapid shifts in sea level and latitudinal ecosystems created disturbance and mixing of different ecological assemblages, which in turn accelerated evolutionary pressure. Most of the animals that became extinct at the end of the Pleistocene were large, and both herbivores and carnivores were affected.Pollen is one of the most important tools of correlation in terrestrial settings, and it is often used to extend knowledge from well-dated sequences to less clear situations.Fossil pollen is particularly useful because it is almost indestructible when trapped in lake and bog sediments.
Examples of giant Pleistocene mammals include the giant beaver, giant sloth, stag-moose, dire wolf, giant short-faced bear of the New World, and cave bear of the Old World.The Quaternary is replete with forces of disturbance and evidence for evolution in many living systems.Examples of disturbance include the direct destruction of habitat by glacial advance, the drying of vast plains, increases in size of lakes, a decrease in the area of warm, shallow, continental shelves and carbonate banks, and shifts in ocean currents and fronts. Many genera and even species of shellfish, insects, marine microfossils, and terrestrial mammals living today are similar or identical to their Pleistocene ancestors.Most important, however, is that the record of decline and extinction in many cases precedes evidence for humans in the New World and Australia.Other likely causes for extinction include loss or change of habitats, direct climatic effects, and changes in the length and intensity of summer and winter conditions.
