The Strait of Panama: Fossil Fish, the Great American Schism, and a Ngäbe Paleontologist

A strait that no longer exists

The phrase “Strait of Panama” refers to a seaway that has not existed for millions of years. Before the Central American isthmus finished rising and closing, the waters of the Pacific and the Caribbean flowed into each other across what is now the land bridge, and marine life moved freely between the two oceans through that gap. The slow closure of that seaway, completed a few million years ago, was one of the most consequential geological events of recent earth history, because it separated what had been a single marine fauna into two, and it joined what had been two separate terrestrial faunas into one.

The terrestrial side of that event is famous as the Great American Biotic Interchange, the moment when North and South American land animals began to move across the new bridge. The marine side is sometimes called the Great American Schism: the formation of the Central American isthmus caused a profound divergence and extinction as the Caribbean was isolated from the Pacific, a split first discussed as early as 1876 by Alfred Russel Wallace^[2]. The dedicated great-american-interchange page covers the interchange in depth, and the panama-isthmus-geology page covers the geological mechanics; this page focuses on the marine-fossil evidence that lets scientists read the schism in the rocks.

Reading the schism in fossil fish

The clearest way to study a marine event that happened millions of years ago is through the fossils it left behind, and Panama is unusually well placed for that work because the rocks around the Canal (notably the Upper Miocene Chagres Formation) preserve marine fossils from exactly the period of interest. STRI researchers analysing marine fossils from the Upper Miocene Chagres Formation have now described four new species of fossil fish, most of them belonging to the Myctophidae family, the lanternfishes^[1].

Lanternfish are small, abundant, deep-water or vertically migrating fish named for the rows of light-producing organs (photophores) along their bodies, and they are among the most numerous vertebrates on earth by biomass. Finding them in Miocene Panama fossils tells scientists about the deep-water marine community that existed in the region as the isthmus was closing, which is direct evidence of what the pre-schism fauna looked like and how it changed. Four new species from a single formation is a meaningful addition to that record, because each one is a data point in the reconstruction of an ocean that no longer exists in that form.

The technology: otoliths and a reference collection

The reason these fossil fish can be identified at all is a piece of anatomical good fortune and a lot of institutional infrastructure. The identifications rest on otoliths (the small, dense “ear stones” found in the inner ear of bony fish), which are distinctive enough in shape that a specialist can identify a species from a fossilised otolith alone, much as a forensics specialist can identify a mammal from a tooth. STRI maintains what is described as the most complete reference collection of tropical fish bones in Central America, covering both Caribbean and Pacific species, which is the comparative database against which fossil otoliths are matched^[1].

That infrastructure point matters because fossil identification is only as good as the modern reference material it is checked against. A fossil otolith from the Miocene can only be named if a researcher can compare it to the otoliths of living fish, which is why a comprehensive tropical fish-bone reference collection is the enabling condition for the whole field. STRI’s collection is that enabling condition for Central American marine paleontology, and it is part of the broader research strength that makes Panama a globally significant place to study the deep history of tropical seas.

A species named for Brígida de Gracia

The human story behind the science is worth telling in its own right, because it is both unusual and significant. One of the four newly described fossil fish species was named Hoplostethus boyae in honour of Brígida de Gracia, identified as the first Ngäbe marine paleontologist^[1]. Naming a species for a researcher is a formal scientific recognition, and the choice to name a Panamanian fossil fish for a Ngäbe scientist is a meaningful statement about who does science in and about Panama.

The Ngäbe are the largest indigenous people in Panama, and the Comarca Ngäbe-Buglé is the country’s largest indigenous territory (see ngabe-bugle-comarca-guide). Indigenous Panamanians are historically underrepresented in the scientific establishment that studies the country’s biodiversity, so the emergence of a Ngäbe marine paleontologist, and the formal recognition of her work in a species name, is a small but real marker of change in who gets to produce knowledge about Panama’s natural history. It also connects this deep-time marine page to the living indigenous-conservation story elsewhere in the site, where indigenous communities are increasingly recognised as central to environmental stewardship rather than as subjects of study.

Why deep-time marine paleontology matters now

It is fair to ask why fossil fish from several million years ago matter to a reader interested in Panama today, and the answer is that the deep-time record is the only baseline against which to measure modern change. The Great American Schism isolated Caribbean and Pacific marine faunas from each other; studying the fossils from before and during that isolation shows scientists how marine communities respond when their connectivity is severed, which is directly relevant to understanding how modern reefs and fisheries respond when their connectivity is disrupted today. The coral-restoration-panama page picks up exactly that thread, showing how the same STRI research group uses ancient otoliths to measure how much dietary complexity modern Caribbean reefs have lost.

The connection is that the paleontological record is not an isolated curiosity; it is the control dataset for understanding contemporary ecological change. Knowing what a Caribbean reef food web looked like thousands or millions of years ago is what lets researchers say, quantitatively, how degraded the modern one is. That is the bridge between the fossil fish of the Chagres Formation and the live coral reefs of Bocas del Toro, and it is why a country that invests in marine paleontology is investing in the science that underpins modern marine conservation.

The Strait as something to read in rocks, not visit

For most visitors, the “Strait of Panama” is a concept rather than a destination. There is no seaway to visit, because it closed millions of years ago. What you can see are the rocks that record its closure (exposed along the Canal and in the Chagres Formation), the fossils those rocks contain (in research and museum collections), and the modern separation of Caribbean and Pacific marine life that the schism produced, visible in the different reef and fish communities of Bocas del Toro versus Coiba. For anyone interested in science, the story of the four new fossil fish, the STRI reference collection, and the Ngäbe paleontologist honoured in a species name is one of the clearest examples of how Panama’s deep-time research connects geology, biology, and a changing human story.

What the isthmus closure changed, beyond Panama

The closure of the Central American isthmus was not merely a local geological event; it reshaped the global ocean and climate system, and understanding that scale explains why the fossil record around Panama matters to science far beyond the country’s borders. Before the isthmus closed, the Pacific and the Atlantic (via the Caribbean) exchanged water across the seaway, and that exchange was part of the pattern of ocean circulation that distributed heat around the planet. When the land bridge sealed that gap, it cut off the inter-ocean exchange and reorganised the circulation that had connected the two oceans, a change whose effects on global climate patterns are a central reason the isthmus closure is studied as a planet-scale event rather than only a local one.

On the biological side, the same closure produced the Great American Schism (the separation of the once-connected Caribbean and Pacific marine faunas into two communities that then evolved in isolation from each other). The Caribbean and Pacific coasts of modern Panama, a short drive apart, hold distinctly different marine communities precisely because they have been diverging since the isthmus separated them. That divergence is the marine counterpart to the terrestrial Great American Interchange (the overland mixing of North and South American mammals), and together the schism and the interchange make the isthmus one of the most consequential biogeographic boundaries on earth. The great-american-interchange page covers the terrestrial side; the marine schism is the reason the fossil fish of the Chagres Formation are scientifically valuable. They are snapshots of the fauna caught in the act of being divided.

Otoliths as a time machine

The method that lets scientists read the schism in the rocks deserves explanation, because it is the enabling technology behind most of what this page describes, and it is genuinely elegant. Otoliths (the small, dense “ear stones” in the inner ear of bony fish) grow throughout a fish’s life, laying down layers much like tree rings, and because they are mineralised and species-distinctive in shape, they persist in the fossil record long after the rest of the fish has decomposed. A specialist can pick up a fossil otolith from the Miocene Chagres Formation and identify the species it came from by comparing its shape to the otoliths of living fish, which is exactly how the four new fossil species, including the lanternfish of the Myctophidae family, were recognised and described.

The reason this works as a “time machine” is that a deposit of otoliths from a fossil reef is a census of the fish community that lived there, preserved in stone. Read a 7-million-year-old otolith assemblage from Panama and you have a record of the marine fauna that existed there as the isthmus was closing; compare it to a 7,000-year-old assemblage and a modern one and you can measure how the community changed across that entire interval. That is the same method the coral-restoration-panama page relies on to measure how much trophic complexity Caribbean reefs have lost, and it is the method that gave STRI the basis to name Hoplostethus boyae and the other new fossil species. The reference collection of tropical fish bones that STRI maintains is the comparative database that makes the method work. Without a comprehensive set of modern otoliths to compare fossils against, the fossil stones would be unidentifiable. The collection and the method together are what let Panama’s deep-time marine record speak.

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Last reviewed: 2026-07-03