Diverse marine fish assemblages inhabited the paleotropics during the Paleocene-Eocene thermal maximum

The Paleocene-Eocene thermal maximum (PETM) was a short interval (120–220 k.y.) of elevated global temperatures, but it is important for understanding biotic responses to climatic warming. Consequences of the PETM for marine fishes remain unclear, despite evidence that they might have been particularly vulnerable to increasing temperatures. Part of this uncertainty reflects a lack of data on marine fishes across a range of latitudes at the time. We report a new paleotropical (~12°N paleolatitude) fish fauna from the Dababiya Quarry Member of Egypt dating to the PETM. This assemblage—Ras Gharib A—is a snapshot of a time when tropical sea-surface temperatures approached limits lethal for many modern fishes. Despite extreme conditions, the Ras Gharib A fauna is compositionally similar to well-known, midlatitude Lagerstätten from the PETM or later in the Eocene. The Ras Gharib A fauna shows that diverse fish communities thrived in the paleotropics during the PETM, that these assemblages shared elements with coeval assemblages at higher latitudes, and that some taxa had broad latitudinal ranges substantially exceeding those found during cooler intervals.