LATE MIOCENE CHONDRICHTHYANS FROM LAGO BAYANO, PANAMA WITH IMPLICATIONS FOR A MARINE CONNECTION BETWEEN THE CARIBBEAN AND PACIFIC

This novel description of the chondrichthyan fauna of the late Miocene Chucunaque Formation in Lago Bayano, Panama reveals a prolific and highly diverse assemblage. Extensive field efforts resulted in 1426 identifiable dental remains and six non-dental elements; comprising at least 38 taxa, of which at least 12 are new to the documented fossil record of Panama. Comparisons with modern analogs indicates a littoral environment dominated by generalist species (~73%) characterized by having a cutting-grasping type dentition, and a surprisingly large component of mobulid rays (~12%) specialized for filter-feeding. A weighted paleobathymetric analysis estimates a mean average depth of 99 m with a mean maximum depth of 195 m. Previous studies have suggested that the Chucunaque Formation of Lago Bayano had a greater Pacific Ocean affinity based on foraminifera, making this the first Miocene chondrichthyan fauna described from the Pacific shelf of Panama and, consequently, a pivotal piece of evidence in the controversial history of the Central American Seaway. Among the 38 identified taxa, at least 20 bear a morphology comparable to extant species; of which 15 have mixed biogeographic distributions in the present-day Atlantic and Pacific, three are restricted to the Atlantic, and two are restricted to the Pacific. Roughly contemporaneous Caribbean-affiliated fauna, such as that of the Gatun Formation and Alajuela Formation, also exhibit chondrichthyan assemblages with mixed biogeographic affinities; which provides support for the previously purported seaway, ~9 to 10 million years ago, connecting the Pacific Ocean to the Caribbean Sea.