Biology Reference
In-Depth Information
tains in the later part of the Cretaceous (Pinaceae, extinct members of the
Betulaceae and Myricaceae), but without the prominent cool deciduous as-
sociation found in the northern forests. There are mangrove habitats and
versions of mangrove vegetation, but without
Rhizophora
(ferns of the
Acros-
tichum
type, possibly some palms), and beach/strand/dune vegetation along
the coast (other palms, possibly
Ephedra
), but fossils from this community
are few and the composition is not well known.
Similar conditions and vegetation are encountered over the even lower-
lying, inundated, and fragmented lands of southern Central America all the
way to northwestern South America. Between 10°N and 10°S, the approxi-
mate MAT at low to middle elevations ranges between at least 25°C and
28°C. In the Cretaceous, nappe structures (strata stacked like a slanting
deck of cards) are forming along the northern coast of Venezuela as suc-
cessive overriding rock layers are pushed against the mainland by compres-
sion between the South American and North American plates. There are
uplands in the Guiana and Brazilian shields, while the volcanic Cordillera
Occidental of the Northern Andes is being sutured onto the mainland by
subduction and by westward movement of South America away from Af-
rica. That same movement around 100-90 Ma is disrupting an expanse of
land called West Gondwana that extends across western Africa and eastern
South America. The interior is locally dry through continentality, and the
dryness is augmented in places by coarse and sandy substrate. The vegeta-
tion includes
Ephedra
, as well as forerunners of the Welwitschiaceae whose
descendents now grow only in the Namib Desert of South Africa. Moister
areas are covered by a Cretaceous paratropical rain forest, which differs
from a rain forest not because of the climate, or because lowlands are not
available, but in composition and physiognomy—the angiosperms that form
a characteristic component of the modern community are just diversifying
and radiating. As the Cretaceous closes, iridium-rich aerosols will settle
onto the landscape around Recife, for example, and a massive tsunami will
deposit conglomerates along the Brazilian coast when the asteroid hits at
Chicxulub. The angiosperms may have fi rst appeared in West Gondwana,
and some early ones probably became preadapted to deciduousness by the
dryness and fl uctuating rainfall. This would impart some survival advan-
tage when dispersal from whatever place of origin brought them into con-
tact with areas of dryness, seasonal temperatures and light regimes, and
unpredictable moist habitats.
Along the western slopes of the proto-Central Andes, there is a large
swamp or shallow inland sea with numerous dinosaurs that will leave one
of the world's largest concentrations of footprints. Offshore from Bolivia,
