Biology Reference
In-Depth Information
in edaphically dry habitats in the Early to Middle Cretaceous, for example,
in the Barremian of Colombia around 125 Ma. There was an understory of
ferns and allied plants, and angiosperms became more widespread in the
Cenomanian, around 98 Ma.
In Brazil, sediments of the Rio Acre and Marajó formations document
periodic marine incursions into the Amazon Basin, and near Recife there
are tsunami deposits and iridium layers from the asteroid impact at Chicxu-
lub. In the Guyanas, Cretaceous-Paleocene sediments include bauxite,
coals, and lignites, all of which form under warm-moist climates. The
bauxite layers are almost always preceded in the sections by a rise in palm
pollen, consistent with moist, warming conditions. There are also layers
of evaporates (e.g., gypsum) and oxidized iron indicating local drier sites
along the tectonically active and edaphically variable Cretaceous northern
coasts of South America.
As mentioned previously, as South America was separating from Africa,
geomorphic structures called pull-apart basins developed along the eastern
coasts and accumulated plant and animal remains. One of these is the Arar-
ipe Basin near Recife, Brazil, where the Middle Cretaceous (Aptian, Albian)
Crato Formation contains macrofossils of
Isoëtites
(similar to quillworts of
wet-damp habitats),
Equisetites
(horsetail, also mostly of damp habitats),
and ferns, along with various gymnosperms such as cycads, a strobilus of
an
Araucaria
-like plant,
Brachyphyllum
, various remains attributed to the
gymnosperm family Welwitschiaceae (Rydin et al. 2003), some fragmen-
tary angiosperm leaves, and others of Nymphaealean affi nities (Mohr
et al. 2008). Today,
Welwitschia
is a bizarre-looking extreme xerophyte of
the Namib Desert of southwestern Africa. It has two long, strap-shaped
leaves growing along the desert surface from a circular, corky center, at-
tached to a tap root that penetrates several meters into soil. Radiocarbon
dates on the center give average ages of 500-600 years, and some spec-
imens may be 2000 years old. The ecological relationships between this
plant and the Crato specimens are unknown, but the presence of ephedroid
pollen (similar to
Ephedra
, another extreme xerophyte) suggests there were
locally dry habitats along the margins and in what was then the interior part
of the Gondwana continent.
Seeds described as
Musa enseteformis
were included in an interesting
early report for the Paleocene of Colombia by E. W. Berry.
Musa
is the
genus of bananas, and after its discovery, a banana fruit and later seeds
containing
Musa
-like pollen were reported from the Cretaceous of Colom-
bia. Phylogenetically,
Musa
and its relatives are not particularly primitive
(basal) plants, and the origin of the cultivated banana is conventionally
