Biology Reference
In-Depth Information
Viviana Barreda and colleagues (e.g., Barreda et al. 2007) are presently
revising the paleofl oras. Those from the Río Guillermo Formation are now
considered early Oligocene in age and will be important in outlining biotic
and environmental history during this transitory interval. The temperature
history for the middle Eocene is diffi cult to trace in detail for southern
South America, but palynofl oras in the Salta Basin suggest climates were
cooling (Quattrocchio and Volkheimer 1990). This is consistent with leaf-
margin evidence from Chile (Romero 1986), where in the early Eocene Lota
and Coronel fl oras entire-leaf margins are 70 percent (paratropical fl ora),
while by middle Eocene Río Turbio times they are 40 percent, and in the
late Eocene Ñirihuau fl ora of northwestern Patagonia they are 27 percent
(seasonally cool forest). In place of forested vegetation east of the substan-
tially elevated Southern Andes, and with grasses widespread by the end of
this interval, the plant formation was an expanding shrubland/chaparral-
woodland-savanna (i.e., steppe).
Thus, the ecosystems of South America at the end of the early Miocene
included the lowland neotropical rain forest recognizable as an ecosys-
tem since the Paleocene, circa 58 Ma, reaching its maximum extent at the
LPTM/EECL, and retreating from its northern and southern margins since
the early Eocene. By this time, it primarily occupied its present range in
the Amazon Basin and along the east-central coast of Brazil (the Atlantic
forest), with elements extending into other moist lowland habitats. There
was also mangrove (with
Rhizophora
since the middle to early Eocene),
lower to upper montane broad-leaved forest (with a deciduous component
of
Nothofagus
in the south and west of the Southern Andes Mountains),
shrubland/chaparral-woodland-savanna (steppe east of the Southern An-
des; monte east of the Central Andes), beach/strand/dune, freshwater her-
baceous bog/marsh/swamp, and aquatic ecosystems of essentially modern
aspect. Grasses had been present since the early Eocene and versions of
local grassland were likely present (e.g., early pampas), but they expanded
and modernized with further drying and seasonality beginning in middle
Miocene times and later. There was also an early version of the Atacama
Desert, and it further developed with continued uplift of the Central Andes
Mountains. At this time, individual elements to early versions of tundra and
páramo were present at the highest southern latitudes and at the summits
of the highest mountains.
The available record for South America is diffuse across the north, ex-
tensive in the south, and meager in between. It provides a broad but rapidly
improving impression of South American vegetation during the transition
times of the middle Eocene, Oligocene, and early Miocene. It thus indicates
