Biology Reference
In-Depth Information
respective regions. However, the process is too complex to overemphasize
a single explanatory factor.
THE BIOTAS OF THE EASTERN UNITED STATES AND EASTERN MEXICO
The origin of a northern aborescent temperate element in the Latin Ameri-
can biota is complex (fi g. 9.2). Fossils in the middle Pliocene Paraje Solo
fl ora of Veracruz document that a number of northern temperate plants
were already established in eastern Mexico prior to the Pleistocene, so the
origin of the fl oristic affi nity does not date exclusively from this time. That
still leaves open a number of questions: First, were these elements wide-
spread in the Tertiary, or even in the Cretaceous, and their range divided
by development of the Chihuahuan Desert across south Texas and northern
Figure 9.2
Floristic affi nities between eastern United States and eastern Mexico as repre-
sented by
Liquidambar
(sweet gum). From Martin and Harrell 1957. Used by permission from
the Ecological Society of America, Washington, DC.
