Biology Reference
In-Depth Information
southward with cooling in the middle Miocene and later times, then fl uctu-
ated with the climate changes of the Quaternary. However, the number of
Tertiary fl oras available to document these trends in northeastern North
America is not great.
Those that are available, such as the early Miocene Brandon Lignite
fl ora of Vermont, and others to the south, like the Eocene Wilcox fl ora in
Kentucky and Tennessee, reveal deciduous forest elements in the highlands
during and after about the middle Eocene. A widespread and extensive de-
ciduous forest with Asian exotics developed in the Oligocene, Miocene, and
Pliocene. By the Oligocene, and especially in the Miocene, the deciduous
forest expanded from its Cretaceous-Paleocene polar broad-leaved decidu-
ous forest and boreotropical progenitors and coalesced with other members
elsewhere to become the most widespread ecosystem across the middle lati-
tudes of the Northern Hemisphere. It extended from eastern North Amer-
ica north of Mexico, across the Plains in scattered populations, into western
North America, over Beringia into eastern Asia, and across to Europe. The
Peace Creek fl ora in central Florida, after 2.8 Ma, near the beginning of ex-
tensive Northern Hemisphere glaciations, includes some of the last occur-
rences of present-day Asian taxa in North America—from Japan,
Pterocarya
and
Sciadopitys
(Japanese umbrella pine), and from southeast Asia possibly
Ginkgo
and
Dacrydium
(Hansen et al. 2001).
Tertiary vertebrate fossils from deciduous forest habitats in eastern
North America are few, but the late Miocene to early Pliocene Gray Fossil
Site, Washington County, Tennessee, 7-4.5 Ma, is yielding new and inter-
esting discoveries (DeSantis and Wallace 2008; Shunk et al. 2006; Liu, in
press). They document faunistic affi nities between eastern North Ameri-
can and eastern Asia that parallel those long recognized in the plant fossil
record (Graham 1966, 1972; Wen 1999; chap. 9 below). The fi nds include
the lesser panda (
Pristinailurus bristoli
), peccary (
Tayassuidae
), rhino (
Te -
leoceras
), camel (cf.
Megatylopus
), Eurasian badger (
Arctomeles dimologon-
tus
), as well as the greatest concentration of fossil tapirs (
Tapirus polkensis
)
on record (Wallace and Wang 2004). These lacustrine sediments will un-
doubtedly continue to yield material important for better understanding the
Neogene environments of the southeastern United States and the disjunct
biotic affi nities with eastern Asia.
In the midcontinent region from the Eocene through the Miocene, there
was a shift from dense forest to savanna to grassland (Strömberg 2002,
2004, 2005). There were open areas with grasses and shrubs, a version of
a grassland/savanna, between a seemingly early 27 Ma and 17 Ma based
on phytoliths (Strömberg 2002), and certainly by 18 Ma based on graz-
