Biology Reference
In-Depth Information
placed in southeastern Asia. Berry's specimens proved to be recent seeds
of the local
Ensete ventricosum
, and the fruit a concretion of nonbiological
origin (Manchester and Kress 1993). An extensive middle to late Paleocene
fl ora occurs in the Cerrejón Formation at Guajira, Colombia, at about 60-
58 Ma. It is presently under study (e.g., Doria et al. 2008), and already
palms (
Nypa
; Gomez-Navarro et al. 2009) and numerous leaf specimens of
the Menispermaceae have been described belonging to four species (
Meni-
spermites cerrejonensis
,
M. cordatus
,
M. guajiraensis
,
M. horizontalis
). The
family is currently widespread in warm regions of the world. The Araceae
was also present (
Montrichardia
;
Pterocardium
; Herrera et al. 2008). The ge-
ology and composition suggest a coastal rain forest, as does the gargantuan
Titanoboa
. Microfossils of Paleocene through middle Eocene age from Co-
lombia are described by Jaramillo and Dilcher (2001) and include abundant
fern spores and pollen of palms, including
Nypa
, along with pollen similar
to
Hibiscus
and
Pelliceria
documenting the presence of an early version of a
mangrove ecosystem (still without
Rhizophora
). Most of the Paleocene spe-
cies are uniquely South American, with only 11.5 percent showing affi nities
with Africa and 5.2 percent with North America.
A discussion of the paleovegetation of northern South America is conve-
nient for introducing current views on the origin of the lowland neotropical
rain forest. Recognition of the formation during its transitory beginning is
based in part on upon the composition that includes prominent representation
of the angiosperm families Fabaceae (Leguminosae), Moraceae, Lauraceae,
and Arecaceae (Palmae; chap. 2). In terms of habitat, the rain forest is found
on relatively fl at terrane in lowlands with high water tables where the eleva-
tion is mostly below 900 m. The climate is warm, with an MAT around 24°C
(monthly minimum about 18°C) and moist (minimum of 1800-1500 mm)
throughout the year without signifi cant seasonality, and the soils are of-
ten sterile, shallow, red, and heavy (clay) laterites. Geographically, these
conditions are presently found mostly between 10°N and 10°S. After the
rain forest had fully differentiated as an ecosystem, it can further be recog-
nized in the fossil record by a syndrome of morphological features, such as
a high percentage of large entire-margined leaves, drip tips, wood with no
or poorly developed growth rings, and by the considerable number of mac-
rofossil and microfossil types in the fl oras, refl ecting the great biodiversity
of the rain forest community.
When these features were fi rst appearing, however, the time of origin of
the lowland neotropical rain forest can only be set within a range of time.
Since a prominent angiosperm component is one criterion for its recogni-
tion, this puts the maximum age as Late Cretaceous circa 90 Ma, when
