Biology Reference
In-Depth Information
Figure 9.3
Representative Tertiary fl oras of northern Latin America plotted on the global
paleotemperature curve. Note the few representatives of northern temperate elements prior to
the middle Miocene temperature decline and the greater number after that event.
America. In line with the observation that a land bridge is a sea barrier
(Woodring 1966), closure also began differentiating a Pacifi c and a Carib-
bean marine fauna (Lessios 2008). In addition to marine biological infor-
mation, there is also the independent geochemical evidence for establishing
the time of closure discussed in chapter 2. It is possible to augment the data
further by plotting similarity values in spore and pollen types for Eocene
through Pleistocene fl oras on either side of the isthmus (Graham 1992).
For the Eocene the value is 2.6 percent; for the Pliocene around 3.5 Ma,
it is 8.9 percent; and with the inclusion of recent studies on the Quater-
nary, similarity for the interval calculates at 29.7 percent. Revision in age
assignments for some fl oras now “make for an even nicer pattern” (Lau-
rel Collins, pers. comm. to Robyn Burnham, 1994). When evidence from
terrestrial faunas is added (Stehli and Webb 1985; Webb 2006), closure,
to the extent that large mammals were able to move relatively unimpeded
across essentially continuous land surfaces, had been completed by around
2.5 Ma.
Quercus
fi rst appears in southern Central America in the late Mio-
cene Gatún fl ora, which is also when a slight increase in drier elements
(e.g., grasses) becomes evident in the region. This marks the time when
the Cordillera Central of Panama reached suffi cient heights to cast a slight
