Tropical American Tertiary Floras and Paleoenvironments: Mexico, Costa Rica, and Panama

Abstract

Three Tertiary microfossil floras from northern Latin America are considered with reference to paleoenvironments and paleoenvironmental trends, especially paleotemperatures: Gatuncillo (middle (?) to late Eocene, Panama), Uscari (early Miocene, Costa Rica), and Paraje Solo (late Miocene, Veracruz, Mexico). The composition of the floras reflect lower temperatures in the late Miocene for terrestrial environments at ca. 18°N latitude, and temperatures comparable to the present for the middle (?) to late Eocene and early Miocene at ca. 9°N latitude. These values are consistent with Tertiary paleotemperature curves derived from 18O and 13C isotope studies of marine invertebrates, and show that the global drop in temperature at the end of the Miocene affected terrestrial biotas at least as far south as 18°N latitude. Comparison of the paleobotanical data with paleotemperature curves further reveals that the late Miocene was not only a likely time for the introduction of northern temperate elements into the Latin American biota (viz., establishment of the floristic and faunal relationship between eastern United States and eastern Mexico), but that earlier times were progressively less favorable because of generally rising temperatures and more tropical conditions. Information on the Tertiary history of vegetation in the Gulf/Caribbean region is also being monitored with reference to the effect of global sea level changes, although the specific influence of these fluctuations cannot as yet be detected.

Identification of a Neurotoxic Venom Component in the Tiger Rattlesnake, Crotalus tigris

“…The first assumption is that vicariance events cannot explain the current distribution of the taxon under investigation. The estimated date of divergence of rattlesnakes from their common ancestor with Agkistrodon is recent enough (20-30 mya; Knight et al, 1993) to preclude vicariance via mountain forming in Central America (40-60 mya; Graham, 1989). Our application of Bremer's method meets this assumption.…”

“…Thus, increased confidence in inferring the ancestral habitat type could emerge only if it can be shown that habitats in the ancestral area have changed little since the initial divergence. Palynological data indicate that pollen typical of the present pine-oak habitats of the region were already present in the middle to late Tertiary (Graham, 1987(Graham, , 1989. Armstrong and Murphy (1979) give vegetational associations of extant rattlesnakes in Mexico.…”

“…We treated habitat in a manner similar to area because we assumed species could disperse into other neighboring habitat types the same way they disperse into neighboring land areas. Palynological evidence suggests the current plant communities have changed little since the middle to late Tertiary (Graham, 1987(Graham, , 1989.…”

Bipolar disjunctions in Carex: Long-distance dispersal, vicariance, or parallel evolution?

“…Raven (1963) suggested that such plants could have migrated at the end of the Pliocene or in Pleistocene, during some of the last cold periods that expanded the polar regions in both hemispheres. Graham (1987) and Ball (1990) agree with Raven (1963) in chronological estimations of migrations, but differ in the proposed mechanism of dispersal. Raven (1963) proposed a direct jump between the adjacent regions of both hemispheres, whereas Graham (1987) and Ball (1990), following Guppy's (1917) hypothesis, suggested a migration pathway through mountain chains (mountain hopping) across tropical regions where climatic conditions were very similar to the polar zones.…”

“…Graham (1987) and Ball (1990) agree with Raven (1963) in chronological estimations of migrations, but differ in the proposed mechanism of dispersal. Raven (1963) proposed a direct jump between the adjacent regions of both hemispheres, whereas Graham (1987) and Ball (1990), following Guppy's (1917) hypothesis, suggested a migration pathway through mountain chains (mountain hopping) across tropical regions where climatic conditions were very similar to the polar zones. The same hypothesis has recently been documented on the basis of AFLP results in Carex canescens, C. echinata, C. lachenalii, and C. magellanica (Vollan et al, 2006).…”