Biology Reference
In-Depth Information
animals living along the shore were preserved in lowland, swamp, and near-
coastal sediments. Many of the fossil fl oras and faunas of central and south-
eastern North America actually mark the position of the sea in Cretaceous
through Cenozoic times (fi g. 2.10). The Cretaceous Lance Formation of
Wyoming contains the fi rst record of Mesozoic mammals in North Amer-
ica. The Scollard Formation of Alberta, Canada, includes the Bug Creek
fauna, which represents the greatest assemblage of Mesozoic animals in the
world; and in the southeast, the extensive Claiborne fl ora of Tennessee and
Kentucky has provided much information on the biota and climates of this
ocean-bordering region during middle Eocene time.
In western North America, the volcanism associated with formation
of the cordilleras and plateaus also created conditions ideal for the pres-
ervation of fossils. As lava poured onto the landscape, it blocked streams,
creating numerous lakes and marshes that provided habitats for the biota
and basins for accumulating their remains. Ash and other sediments fi lled
these lakes and charged the waters with silicates; there were algal blooms
of silica-requiring diatoms; and the result is siltstone, diatomite, and vol-
canic shale (fi g. 2.13) at numerous sites with exquisitely preserved fossils
(fi g. 2.14). The early Eocene Wind River Formation of Wyoming has more
than a hundred species of vertebrates; the middle Eocene Green River
Formation of Colorado and Utah has an extensive fi sh fauna and caddisfl y
mounds up to 9 m tall along the margin of the paleo-lake Gosiute (Leggitt
and Cushman 2001); and both contain other kinds of insects and abundant
plant fossils. Other similar assemblages are found in the Eocene/Oligocene
Florissant Beds of Colorado, the middle Eocene Clarno of Oregon, the
middle Eocene Republic of Washington, the middle Eocene Princeton of
British Columbia, and the Miocene Trout Creek and Succor Creek fl oras of
southeastern Oregon.
In the Arctic and boreal regions, adjacent New England, and in the up-
per midwestern United States, small depressions were dredged by glaciers,
fi lled by meltwater and precipitation, and accumulated deep, low pH de-
posits of
Sphagnum
and other remains (fi g. 2.3). The lakes and peat bogs
provided innumerable sites for the preservation of spores, pollen, seeds,
and plant and animal fragments that have yielded considerable information
on the late Quaternary biota and environments.
The gradual retreat of the epicontinental sea from the interior lowlands
and coastal plains, volcanism in the western cordillera, and glaciation in the
Arctic, boreal, and alpine regions are among the geologic events creating
conditions favorable for the preservation of more than two hundred fossil
fl oras of Cretaceous and Tertiary age alone. There are many more smaller
