History and Development of the Marine Invertebrate Faunas Separated by the Central American Isthmus

Abstract

Throughout the vast majority of Tertiary time (almost 65 million years) there was no Panama land bridge, and North and South America were detached from one another. This condition can be traced back to the initial separation of the North American and South American (still attached to Africa) plates in the Jurassic, about 165 million years ago (Pindell and Dewey, 1982). Following the onset of rifting and continental break-up in the early Mesozoic, it is uncertain as to the amount of time during which North and South America were actually isolated. The reconstructions of Pindell and Dewey (1982) and Donnelly (Chapter 4, this volume) suggest an early isolation, shortly after 165 m.y.a. Anderson and Schmidt (1983), however, propose a different scenario for the evolution of middle America, which would have juxtaposed blocks preserving land contact between North and South America much longer, perhaps into the late Cretaceous. Regardless of the preferred reconstruction, most authors agree that no land bridge existed for at least 70 m.y., from the late Cretaceous up until contact was reestablished in the Plio-Pleistocene. The establishment of the Panama land bridge has been well documented from considerations of the interchange between terrestrial faunas arising on both continents (e.g., Simpson, 1940, 1953; Webb, 1976; Marshall et al., 1979, 1982; and others in this volume), although the precise timing of this event is more poorly known. The migration route is also uncertain as some have argued for migration via the Nicaraguan Rise rather than through present-day Guatemala (Durham, 1985).