Abstract

The Gatun Formation is a late Miocene tuffaceous litharenite (volcanic sandstone) that is exposed on the north side of Lake Gatun, and is cut by the Panama Canal. This formation contains molluscs indicating a shallow nearshore environment, and it has been age-dated by its planktonic foraminifera (Zones N14-N17) and calcareous nannofossils (Zones NN10-NN11).

Examination of Gatun samples collected just east of Cativa, Colon Province, Panama, reveals abundant fish otoliths. Otoliths are the aragonitic elements within the otic capsule of fishes, which allow them to hear and to orient themselves in the water column. Because of their durability, otoliths are often used in paleobathymetric analyses as otoliths provide information about predatory fish living in distinct paleodepth and paleoenvironmental conditions.

The otolith assemblage is dominated by gobiids, lutjanids, bothids, sciaenids, engraulids, haemulids, cynoglossids, and batrachoidids. Myctophids are less common, but are present in relatively substantial numbers. The dominance of neritic gobiids supports the interpretation of deposition in a shallow nearshore environment, with haemulids indicating a sandy substrate. Sciaenids are found in modern euryhaline environments. The presence of myctophids and the absence of macrourids indicates some oceanic influence. No otolith taxon found was exclusively Pacific, and most taxa are restricted to, or more diverse in, the Atlantic Ocean, indicating a close affinity to the assemblages of the modern Gulf of Mexico.