Biology Reference
In-Depth Information
Figure 5.5
Cross-section of dicotyledon-
ous wood,
Paraphyllanthoxylon abbottii
,
from the Paleocene Black Peaks Forma-
tion, Big Bend National Park, Texas.
Note absent or poorly developed growth
rings. From Wheeler 1991. Used with
permission from the Botanical Society of
America, St. Louis.
crocodilians, four amphibians, three fi sh, and two birds. The faunal evi-
dence suggests a fl ood plain / swamp community in the lowlands experi-
encing occasional dry intervals, as shown by fi lled mud cracks; while in
the surrounding uplands, the paleobotanical evidence reveals tropical to
subtropical forests growing under moist conditions. Winter temperatures
were above 5°C and frost free. In the Green River basin in southwestern
Wyoming (Smith et al. 2008) there are also extensive fl oras, with some
189 species of macrofossils (Wilf 2000), and faunas that span the late Pa-
leocene / early Eocene warm interval. The MAT rose from 12°C to an es-
timated high of 21°C. As will be seen in chapter 6, fl oras slightly younger
(middle Eocene) and to the west of the mountains (e.g., Republic, Prince-
ton) have a signifi cant moist microthermal component owing to the onset
of cooling temperatures, increasing elevations, and moisture-laden winds
coming unimpeded off the Pacifi c Ocean in the absence of any signifi cant
elevation in the Cascade Mountains or the Coast Ranges.
Thus, enhanced topographic diversity at the end of the early Eocene
(less-eroded Appalachian Mountains in the east, rising Rocky Mountains in
the west) allowed for a mosaic of eight ecosystems in North America north
of Mexico within an overall dense, uniquely warm, and moist vegetation.
There was a now a much-restricted polar broad-leaved deciduous forest in
the inland and upland regions of the far north, a widespread notophyllous
broad-leaved evergreen forest, a paratropical rain forest, and a lowland neo-
