# Remarkable dominance of myctophid otoliths in Upper Miocene Chagres Formation, Caribbean Panama

## TL;DR

Fossils in Panama's Chagres Formation reveal a highly productive marine ecosystem dominated by myctophid fish before the Isthmus of Panama formed.

## Contribution

Discovery of four new species and evidence of a Late Miocene upwelling system through detailed otolith analysis.

## Key findings

- Myctophid otoliths make up over 96% of the assemblage, indicating their dominance in the ecosystem.
- Otolith density is among the highest globally, suggesting a highly productive marine environment.
- Evidence of a coastal upwelling system is supported by taphonomic data and predator fossils.

## Abstract

Marine fossils from the Upper Miocene Chagres Formation in northern Panama offer critical insights into the paleoenvironmental conditions and ecological responses prior to the separation of the Atlantic from the Pacific by the formation of the Isthmus of Panama. Here we present a systematic study based on more than 6,200 otoliths collected from a coastal exposure near the town of Piña, Colón. This assemblage is remarkable for the extraordinary dominance of the family Myctophidae, constituting over 96% of specimens. The otolith density in the sediments is among the richest known globally (278.80 ± 135.59 otoliths/kg). The taxonomic composition is represented by 31 taxa across 12 families, including four new species: namely Chiloconger aflorens sp. nov., Dasyscopelus inopinatus sp. nov., Hoplostethus boyae sp. nov., and Malakichthys schwarzhansi sp. nov. Taphonomic evidence, combined with abundant predatory marine vertebrate fossils and extensive burrow ichnofossils, indicates a dynamic and highly productive nearshore ecosystem. The dominance of myctophids and multiple lines of evidence support the existence of a Late Miocene coastal upwelling system in the region, highlighted by efficient trophic transfer channeled from high primary production to apex predators. These findings provide a nuanced understanding of Neogene marine ecosystems prior to the final emergence of the Isthmus of Panama.