Biology Reference
In-Depth Information
Figure 2.8
Midden of the bushy-tailed pack rat (
Neotoma cinerea
). Photograph courtesy of
Terry Vaughan.
bottom to top changes in local vegetation and climate from old to young.
The packrat uses part of the midden as a urinal perch, which eventually
solidifi es into a shiny mass further protecting the fossil plant fragments.
Comparisons of overlapping sequences from different shelters have allowed
reconstruction of the North American dry-habitat communities and envi-
ronments back 50,000 years (Betancourt et al. 1990).
GRASSLANDS AND THE INTERIOR LOWLANDS
In the eighteenth century, as French explorers and fur traders moved south
from Canada, they encountered grassland unfamiliar to western Europeans
in its vast extent. They applied the closest name they had for the vegeta-
tion, calling it
prairie
, French for “meadow” (fi g. 2.9). The central part of
North America is mostly a relatively low, fl at to rolling region between the
Appalachian Mountains and the eastern foothills of the Rocky Mountains.
The physical features refl ect its geologic development, beginning about
100 Ma, which contributed to conditions suitable for grasslands. At that
time sea levels were higher than at present by up to 300 m, owing to the
absence of glaciers, the displacement of water from tectonic activity (e.g.,
