Biology Reference
In-Depth Information
rivers from into the Pacifi c Ocean to into the Atlantic Ocean beginning in
the middle Miocene around 15 Ma. Later in the Miocene, the uplift of the
eastern cordillera of the Northern Andes Mountains blocked the fl ow of the
Maracaibo and other rivers to form Lake Maracaibo.
By the Pliocene, alterations in landscape provided habitats for all the
ecosystems except coniferous forest. These included páramo, as revealed by
macrofossils and microfossils of the sedges
Eleocharis
and
Scirpus
,
Gunnera
,
Juncus
,
Ranunculus
,
Rubus
,
Xyris
(Wijninga 1995, 1996a-d; Wijninga and
Kuhry 1990). The timing of uplift in the Northern Andes is known from
several approaches, including fossils and fi ssion-track zircon dates from a
Podocarpus
mire that give an estimated elevation of 2000 m around 4 Ma,
and 2500 m around 3 Ma or near modern heights (Wijninga 1996d). The
vertical arrangement of the vegetation in the Northern Andes approaching
Plio-Pleistocene times is shown in fi gure 7.5.
The third event was a change in climate in Antarctica and southern
South America, as shown in the McCurdo Valley region of the Transant-
Figure 7.5
Altitudinal zonation of vegetation in the Cordillera Oriental of Colombia. From Wij-
ninga and Kuhry 1990. Used with permission from Elsevier Science Publishers, Amsterdam.
