Biology Reference
In-Depth Information
is still in the early stages of uplift). At 17 Ma, there is still no continuous
land southward from southern Central America and the landscape consists
of islands and peninsulas. The available fossil fl oras from Central America
are either older (early Miocene) or younger (late Miocene), but the vegeta-
tion was probably similar to that of the present without most of the drier
Pacifi c elements, as refl ected by an increase in grasses toward the end of
the late Miocene, and without the few northern deciduous elements (
Alnus
,
Quercus
) that will arrive this far south in the late Miocene and afterward
(Gatún fl ora).
Hoorn (1993, 1994) has studied spores and pollen from the early to late
Miocene Basins of Solimões, Brazil, and Amazonas, Colombia, Peru. A walk
through these basins at about 17 Ma encounters the vegetation of the fol-
lowing ecosystems: mangrove, beach/strand/dune, freshwater herbaceous
bog/marsh/swamp, aquatic, lowland neotropical rain forest, lower to upper
montane broad-leaved forest.
The mangrove community—represented by
Acrostichum
,
Avicennia
,
Hi-
biscus
,
Pelliceria
,
Rhizophora
—increases in abundance and extent at times
of high sea level in the Miocene, and sediment analysis indicates incursions
come from both the east (Guiana Shield sediment type) and from the west
(Andean type). There are also fringing mudfl ats with
Crenea maritima
as
today.
The presence of the beach/strand/dune community is inferred from the
coastal setting and sediments (sand) even though pollen of the prominent
species (e.g., grasses, composites) cannot be distinguished from those that
grow in other habitats.
The freshwater herbaceous bog/marsh/swamp community, with associ-
ated riparian and swamp forest, is represented by widespread
Alchornea
,
Annona
(also present in other adjacent communities),
Bactris
,
Cyperus
,
Eu-
terpe
,
Ficus
,
Ludwigia
,
Mauritia
palm swamps, and
Virola
.
Aquatic vegetation is indicated by the presence of
Botryococcus
and
Pe-
diastrum
(algae),
Azolla
and
Ceratopteris
(aquatic ferns), and
Pachira
.
Lowland neotropical rain forest is the prominent forest community,
together with the lower elevation phases of the lower to upper montane
broad-leaved forest, with abundant ferns,
Amanoa
, and Bombacaceae (
Ca-
tostemma
,
Quararibea
),
Crudia
,
Humiria
,
Licania
,
Pouteria
. Freshwater bi-
valves from the Amazon Basin in northeastern Peru at the MMCO around
16 Ma show seasonal oxygen isotope variation in growth bands correlated
with the annual migration of the ITCZ and support other evidence that
a climate suffi cient to sustain a tropical rain forest is present (Kaandrop
et al. 2005).
