BIOTIC CHANGE IN THE TROPICAL EASTERN PACIFIC AND CARIBBEAN DURING THE NEOGENE – THE EVOLUTION OF WOODRING'S "TERTIARY CARIBBEAN PROVINCE"

The marine biogeographical history of the Tropical Americas is tightly linked to the Central American Seaway (CAS), which connected the eastern Pacific Ocean and Caribbean Sea through much of the Cenozoic. Prior to the closure of the seaway (c. 3 Ma), one large biogeographic province encompassed much of this region, which Woodring (1974) coined the “Tertiary Caribbean Province”. More recently the terms Baitoan and Gatunian Province have been applied to this biogeographic unit, and in the present day, the region includes the now distinctive Caribbean (Atlantic) and Panamic (Pacific) Provinces.

The biogeographic history of this region is reviewed using a large dataset of Middle Eocene-Recent molluscan occurrences compiled from the literature, field surveys, and museum collections. Statistical similarity among faunal assemblages throughout both ocean basins was used to define the extent of biogeographic provinces in each time interval. The known species diversity, number of shared species and similarity in taxonomic composition between the two ocean basins, the number of paciphilic taxa (species of genera whose distribution became constricted to the Pacific), and trends in ecospace utilization and body size were measured through the time series. Changes in faunal composition through the Neogene were also assessed for a number of sedimentary basins within this province.

Analysis of faunal assemblages on both sides of the isthmus indicate that a single biogeographic province extended from northern Peru into the central Caribbean from the Paleogene through early Neogene. Shoaling of the CAS disrupted this province following the latest Miocene (8-6 Ma), ultimately forming what is recognizable as the present-day Caribbean and Panamic provinces by the late Pliocene (4-2 Ma). Similarity between the Pacific and Atlantic components of this province sharply declined in the latest Miocene, while the number of paciphilic taxa recorded from the western Atlantic declined most significantly during the early Pleistocene. Variations in the timing of change for each of these biogeographic metrics suggest that shoaling of the CAS was a prolonged event. Additionally, disruption of the once contiguous tropical eastern Pacific and Caribbean marine province took place much earlier than has been previous recognized.