Biology Reference
In-Depth Information
the Old World—oldest records in Latin America are in the middle to late
Eocene—and progressively moved northward. It eventually reached the
northern part of its range, where it came and went in the southeastern
United States with swings in Neogene and Quaternary temperatures.
MEXICO, THE ANTILLES, CENTRAL AMERICA
In northern Latin America, there are several fl oras available for recon-
structing middle Miocene through Pliocene vegetation and terrestrial en-
vironments for particular times and places. However, these are not suffi -
ciently distributed stratigraphically to reveal detailed ecosystem evolution
through time, or concentrated geographically to reveal their composition
or distribution at any given time over a broad area. That history must be
extrapolated from several widely separated fossil fl oras and cautiously in-
terpreted from multiple lines of evidence and within the context of global
to regional climatic trends and local orogenic history. A case in point is the
Mint Canyon fossil fl ora, now located along the coast of southern Califor-
nia. It is part of a terrane to the west of the San Andreas Fault that has been
transported about 300 km from the south. Although it therefore provides
an indication of late Miocene vegetation and environments in the Sonoran
region of present-day coastal Sonora and Sinaloa, there are no other diverse
and well-preserved Neogene fl oras in the region to document long-term
trends. The Mint Canyon fl ora is a sclerophyllous (thick-leaved) shrubland/
chaparral and woodland of
Acacia
,
Bursera
,
Caesalpinia
,
Cardiospermum
,
Cassia
,
Celtis
,
Fouquieria
,
Mahonia
,
Persea
,
Robinia
, and
Sapindus
, with a gal-
lery forest of
Juglans
,
Platanus
,
Populus
, and
Salix
. The MAP is estimated
at 500 mm (currently 228 mm in Guaymas, Sonora). The appearance of
the shrubland/chaparral-woodland-savanna as a recognizable ecosystem in
Mexico was probably in about the middle Miocene and derived from ele-
ments preadapted to arid conditions by rain shadow and edaphic factors like
those found in the middle Eocene Green River fl ora of Colorado-Utah and
in the Oligo-Miocene Pié de Vaca fl ora of Puebla. It likely reached its full
development between the middle Miocene and Pliocene, fl uctuated with
the cold/dry and warm/moist intervals of the Quaternary, and it is currently
expanding with desertifi cation brought on by human activity.
To the southeast, middle Pliocene vegetation in coastal southern Ve-
racruz and the adjacent highlands is preserved in the Paraje Solo Forma-
tion. This is a large fl ora of over 100 taxa identifi ed from about 150 types
of spores and pollen (Graham 1976). It conforms to most expectations
about paleovegetation for this time and place, but it also includes two
