Biology Reference
In-Depth Information
of Patagonia (Wilf et al. 2003), with palms, cycads, araucarias, and podo-
carps, indicates elevations in the Southern Andes were still relatively low
and were not yet casting a rain shadow to the east.
The vegetation types in the Cretaceous and Paleocene of South Amer-
ica include megaphylls and notophylls in warm megathermal climates of
northern South America, with microphylls becoming more common in the
cooler microthermal conditions toward the south. Late Cretaceous woods
from Patagonia show distinct growth rings. Later, toward the early Eocene,
conditions warmed, and a more quantitative estimate of climates is afforded
by leaf margin analysis from the Laguna del Hunco fl ora of Patagonia (Wilf
et al. 2003). This was the time of maximum LPTM/EECL warmth, and
the MAT was around 18°C, increasing to around 24°C through the section.
At present the MAT is 12°C, and the MAP is 300 mm. Minimum winter
temperatures for the Eocene are estimated at more than 10°C, consistent
with the absence of the temperate
Nothofagus
in the fl ora. Sea surface tem-
peratures in the South Atlantic Ocean are estimated at about 17°C, and
the MAP at about 1200 mm. In vegetation terminology, comparable to that
used for the northern part of the world, after this notophyllous broad-leaved
evergreen forest / paratropical rain forest of the LPTM/EECL interval, the
vegetation at the southern end of the world changed through a microther-
mal deciduous community of
Nothofagus
forest and gymnosperms (middle
Eocene through the Oligocene), to a colder, seasonally dry shrubland and
herbaceous vegetation (steppe) after about the middle Miocene (Barreda
and Palazzesi 2007). Modernization of the southern fl ora involved the ad-
dition of grasses into various ecosystems; the earliest grasses in southern
South America appear in the early to middle Eocene. In addition to grasses,
dry elements present in the Eocene were
Cassia
,
Celtis
, and some Anacardi-
aceae and Fabaceae, probably in coastal sands and similar edaphically suit-
able sites inland. As in northern North America (e.g., in the Eocene Green
River fl ora), these sites afforded habitats and a source of elements available
for later assemblage into expanding versions, then essentially modern coun-
terparts of steppe (shrubland/chaparral-woodland-savanna). In Antarctica,
the Cretaceous and Paleogene vegetation was a rich assemblage of plants
widespread across to Weddellia and adjacent regions. The dramatic change
in store for Antarctica later in the Tertiary and Quaternary is shown by
only two remaining plants that now constitute the angiosperm fl ora of the
continent (
Colobanthus quitensis
, Caryophyllaceae, and
Deschampsia antarc-
tica
, Poaceae). Future changes in store for Antarctica as a result of current
global warming is foreshadowed by the dramatic expansion of
Deschampsia
now covering extensive areas with a layer of grassy green.
