Biology Reference
In-Depth Information
models of creation, and it joins the banana from Colombia as examples of
fossil food plants that never fulfi lled their promise (Brown 1934).
A site that has provided useful information on the Neogene history of
ecosystems in the Central Andes is near the settlement of Pislepampa about
20 km northeast of Cochabamba, Bolivia, at an elevation of about 3600 m.
Fieldwork in Bolivia usually begins with an international fi ght into La Paz,
the highest capital city in the world at 4050 m, and our group was no excep-
tion. A vehicle was waiting for us at the airport, and we went directly from
the pressurized cabin of the plane to Cochabamba, and the next morning
to the collecting site. At these heights oxygen, is unsettlingly scarce; it was
also cloudy, dark, very cold and windy, and it is almost always misty or
raining. Fortunately, the samples from Pislepampa, studied in collaboration
with Kathryn Gregory-Wodzicki of the Lamont-Doherty Earth Observatory,
contained a diverse assemblage of plant microfossils 6-7 million years old
that revealed interesting details about the uplift history of the Central An-
des (Graham et al. 2001).
The modern vegetation of Bolivia includes the cloud forest formation, or
the bosque montano húmedo, which grows at an elevation between about
1400 and 3200 m. At its upper limit, it grades into the puna; and at its lower
limit, it intermingles with tropical plants that extend upward along moist
river valleys. In the Pislepampa microfossil fl ora, three pollen types were
of special interest, and they provide an example of the way environmental/
vegetation reconstructions begin based on paleobotanical data. Pollen simi-
lar to
Oreopanax
(fi g. 7.8a) and
Prumnopitys
/
Podocarpus
(fi g. 7.8b) was
recovered, and both species grow today in the cloud forest (fi g. 7.9). In
addition, pollen similar to
Cavanillesia
(Bombacaceae) was present, and
this genus is presently found in the tropical lowlands and extends into the
uplands along river valleys. Finding fossils of plants from 7-6 Ma growing
together today where the ecological parameters can be measured and, thus,
applied to the paleocommunity, is a kind of Holy Grail for tropical vegeta-
tion history studies. The fossil fl ora revealed a paleocommunity of cloud
forest near its lower limits of about 1400 m. The locality is now at 3600 m,
so this information, if used alone, would suggest an uplift of the Central
Andes of around 2200 m since about 7 Ma. When all other paleobotani-
cal, geological, ancillary, and context information from the region is taken
into account (Gregory-Wodzicki 2000; Gregory-Wodzicki et al. 1998),
the consensus is that from one-third to one-half of the present altitude of
the Central Andes has been attained since 10 Ma. Between 5 and 2 Ma, the
eastern cordillera rose at the annual rate of 0.5-3 mm and continues to rise
with a crustal shortening of 10-25 mm. This is geological evidence that
