Biology Reference
In-Depth Information
artifi cial system of nomenclature is used (e.g.,
Triporopollenites
, pollen with
three pores). However, in contrast to the Olmos and other fl oras where
macrofossils of gymnosperms are well represented, there is no winged co-
nifer pollen reported among the thirty pollen types in the Piedras Negras
assemblage. This suggests there was a regional mosaic of gymnosperm
and angiosperm communities, and moist to moderately dry habitats, over
the Cretaceous landscape. These few poorly known fl oras can all be in-
cluded within the moister paratropical sites to more seasonally dry forests
on edaphic- or slope-conditioned drier sites, along with localized marsh,
beach/strand/dune, and aquatic vegetation. A version of the mangrove eco-
system was also likely present (
Acrostichum
,
Spinozonocolpites/Nypa
), but as
noted, diverse, well-preserved, recently studied fossil fl oras of Late Creta-
ceous through early Eocene age are not available for much of Mexico. It is
probable that by the end of the early Eocene, local and moderate highlands
provided enough slope to allow some vegetation gradient from the lowlands
into more upland habitats. The prominent community was likely a version
of the lower to upper montane broad-leaved forest.
In the Antilles, there is an Early Cretaceous fl ora from the Dominican
Republic containing the fern
Gleichenites
, the gymnosperms
Brachyphyllum
and
Zamites
(a cycad), and a few angiosperms. The site was originally lo-
cated in the Isthmian region, and after a brief emergence during which the
fl ora accumulated, it was transported eastward and submerged in the pro-
cess as indicated by overlying marine deposits of Albian age. The affi nities
of the fl ora are widespread but lie primarily with the Cretaceous vegeta-
tion of North America. There are no Cretaceous fl oras known from Central
America, and no Paleocene or early Eocene plants known from Mexico, the
Antilles, or Central America.
SOUTH AMERICA
At 100 Ma, South America was separating from North America with for-
mation of the Gulf of Mexico, and at 90 Ma it was just moving away along
its northeastern coast from Africa. The former common ground between
South America and Africa is called West Gondwana, and it is one region
favored for the origin of the angiosperms about 135 Ma. South America
was connected, or essentially connected, to Antarctica through the shal-
lows of the Drake Passage, and on to Australia (fi g. 2.19; Scotese 2004,
plates 7-9). This region includes a paleobiotic province called Weddellia
(fi g. 5.6), and many members shared in the past (e.g.,
Casuarina
) and at
present refl ect the ancient continuity (e.g.,
Araucaria
, fi g. 2.48;
Nothofagus
,
