Biology Reference
In-Depth Information
and it is represented at present in the Luquillo Mountains (chap. 2). It was
probably more tropical on the limited emergent lands of the Antilles in the
Eocene, and somewhat more seasonally temperate, especially at the higher
altitudes, in Miocene and later Tertiary times and in the glacial intervals of
the Quaternary. These conditions and trends were muted, however, by the
insular nature and maritime climates of the islands.
In most instances, paleontological information does not defi ne the tec-
tonic and orogenic history of land fragments but must accommodate itself
to geological reconstructions and the fi ndings of geophysics. In the case of
Puerto Rico, however, the fossil plant record does contribute to refi ning the
submergent-emergent history of the island. Subsidence took place between
the middle Eocene and the middle Oligocene, and the geology suggests that
most of Puerto Rico may have been under water during this time. However,
the presence of lignites with mangrove fossils, along with the extensive
terrestrial San Sebastian fl ora, reveals an emergent coast and documents
densely vegetated uplands in the middle Oligocene.
SOUTH AMERICA
There are few extensive, concentrated, well-preserved macro- or micro-
fossil fl oras of middle Eocene to early Miocene age in South America that
have been studied either suffi ciently or recently to reveal the histories of
ecosystems. Also, in some instances, the primary nomenclature for fossils
from this interval is based on an artifi cial system with biological affi nities
appended in the discussions. (See II, tables 7.1, 7.2, 7.6, and appendices
2.1, 2.2 for a list of plant macro- and microfossils for South America, along
with the associated literature.) Collectively, fossil evidence indicates that
swamps, lagoons, and riverine habitats occupied much of the Amazon Ba-
sin, and that fl ow of the major rivers continued to the west into the Pacifi c
until about the middle Miocene. In the Eocene,
Nypa
and other palms and
Pelliceria
were represented, along with
Retibrevitricolpites
of unknown af-
fi nities, the abundance of which in lowland coastal deposits (e.g., lignites)
suggests it occupied the mangrove habitat. Thus, a version of mangrove
vegetation was present until the middle to late Eocene when
Rhizophora
established an essentially modern counterpart. There was a mudfl at as-
sociation at scattered sites mostly inland to the mangroves that included
the present-day emergent aquatic
Crenea
. This plant grows today along the
northern coast of South America in saline soils subject to periodic drying.
It is known in the fossil record as
Verrutricolporites rotundiporis
, and it ex-
tends back to the late Eocene in the Maracaibo Basin region associated with
