Hispanic Corridor: its evolution and the biogeography of bivalve mollusks

DAMBORENEA, S.E.

Vancouver, Canadá

Simposio; 5th International Symposium on the Jurassic System; 1998

International Subcommission on Jurassic Stratigraphy

Biogeography is a powerful tool in recognizing and studying significant biogeographical events such as the opening of a mid-Atlantic seaway between western Tethys and eastern Pacific, which triggered off the fragmentation of Pangea. An updated set of biogeographical data of bivalve mollusks is analyzed in order to understand the development of the Hispanic Corridor during Late Triassic to Middle Jurassic times. The sequence of similarity coefficients between the western Tethys (s.s.) and several cratonic regions of the eastern Pacific shows a number of minor "pulses" of increased similarity along that time, before the major Middle Jurassic peak. These pulses, of which the Pliensbachian is the most significant, are related to eustatic sea level changes. Since not all ecological types are equally represented in the biotic interchange along the Corridor, a shallow intermittent marine connection which preceded rifting by millions of years is indicated. Benthonic bivalve taxa, and especially epifaunal stocks, some of which can be followed "step by step", show this pattern clearly. "Neritic" bivalve species were analyzed separately and, although data are still few, the distribution of some of these taxa along that time can be alternatively explained using a pantropic model, implying planctotrophic larvae and fast ocean currents. In this case, data agree better with a western direction of prevailing currents, since some taxa which are abundant along the eastern Pacific, such as Posidotis and Otapiria, do have isolated records in the eastern (but not the western) Tethys. The rôle of the Pacific as an effective barrier for faunal dispersion is also considered for the same period of time. As one of the biological impacts produced by the opening of the Hispanic Corridor, bivalve diversity increased along the Jurassic.