LATE CRETACEOUS AMMONITES AND OTHER MOLLUSKS OF COSTA RICA AND THEIR PALEOECOLOGY

Abundant molluscan fossils are preserved in Late Cretaceous (Campanian-Maastrichtian; 83-66 Ma) deposits of the NW region of Costa Rica facing the Pacific Coast. However, recent studies of this fauna only characterize rudist bivalves, in part because most of the fossil material is deposited at the paleontology collection from the Escuela Centroamericana de Geología (ECG) pending description and identification. Here we document the ammonite and non-rudist molluscan fauna, including nerineid gastropods, acteonellid gastropods, belemnites, inoceramid bivalves, among other gastropods and bivalves. This research combines faunal descriptions with detailed stratigraphic context to (1) provide the first comprehensive description of the Late Cretaceous of Costa Rica, and (2) utilize these data to analyze paleoecological and paleobiogeographical patterns in this fauna. Preliminary faunal analyses show a mixed combination of cosmopolitan, Caribbean, North Pacific, and European taxa living in a tropical rudist-reef dominated environment. Taxon distributions through time also support previous work suggesting dispersal east-to-west from Europe through the open channel between North and South America (Johnson 1999; Johnson et al., 2002), followed by dispersal north through the proto-Caribbean and Caribbean volcanic arcs until the Gulf of Mexico and Western Interior Seaway (Johnson 1999; Johnson et al., 2002). Another current would continue south along the Pacific coast of South America until Peru (Phillip and Jaillard, 2004). His east-to-west global current is proposed to continue across the Pacific guyot islands as far as Oman and India (Skelton and Wright, 1987). Continuing work will fill out the gap in the molluscan record between the Pacific coast of the Americas between California and northern Peru and confirm patterns of faunal communication between the Pacific and proto-Gulf of Mexico and Caribbean parts of the Tethys.