Fish have a missing chapter in their past. It begins 66 million years ago, when an asteroid struck Earth and transformed life permanently. The collision eradicated the non-avian dinosaurs and set off one of the greatest mass extinctions ever experienced by the planet.
Dinosaurs tend to dominate this account. Yet scientists have also spent years pursuing another question: what became of fish?
For almost 10 million years following the asteroid impact, the fossil record becomes remarkably sparse. Scientists know that many fish now inhabiting the world’s oceans ultimately emerged, but the route from dinosaur-era seas to the modern marine world has remained uncertain.
Fossils uncovered in Egypt are now beginning to restore those lost pages.
Exploring ancient oceans
The newly reported fossils were found in Egypt’s Eastern Desert and are 62.2 million years old. They fall close to the middle of a little-understood interval that starts after the asteroid strike and continues into the early age of mammals.
The location has produced fossil remains from 21 types of fish across nine separate orders. Crucially, it also contains the earliest known fossil skeletons for several fish groups that remain widespread in today’s seas.
These include jackfish, popular game fish found worldwide, as well as moonfish and pipefish, the family to which seahorses also belong.
The discoveries close an important gap in the evolutionary history of modern marine life. They indicate that many fish groups recognised today had emerged just a few million years after the extinction event that reorganised Earth’s ecosystems.
Unravelling the fish fossil mystery
Researchers have long grappled with what is known by some as Patterson’s Gap: an early Cenozoic Era interval in which fish fossils are exceptionally rare.
The lack of fossils left scientists with two central possibilities. Had some fish groups persisted beyond the extinction for longer than thought? Or was the fossil record simply too patchy to reveal the story properly?
“We have this 10-million-year gap with a very limited fossil record. We know the asteroid impacted the marine environment, but it was unclear how the oceans came to have these modern fishes,” said Sanaa El-Sayed, a graduate student at the University of Michigan.
“It was mind-blowing that this site is now helping us answer the questions of when and where and what was present in the modern ocean just a few million years after the dinosaurs went extinct.”
The Egyptian site provided a rarity for this era: an extensive assemblage of well-preserved fish skeletons.
Evidence for a major ocean reset
The fossils produced a notable result.
Scientists did not uncover the fish groups that many researchers had expected may have endured past the end of the Cretaceous Period.
Instead, the site was chiefly populated by percomorphs, an enormous group now comprising thousands of species, including tuna, bass, cichlids and mackerel.
These results reinforce the view that the extinction event did indeed remove many older fish lineages. New groups subsequently grew quickly and became dominant within marine ecosystems.
“This gap early in the Cenozoic record leads to two interrelated questions,” said Matt Friedman, co-author of the study and director and curator of the U-M Museum of Paleontology.
“First, did the fish that we generally assume went extinct at the end of the Cretaceous Period really not limp into the next interval, called the Paleogene, and we’ve just missed them because the record is poor?”
“Second, when did the more familiar modern groups appear? The gap represents a long span of time during which we have poor grasp of what happened, and it’s frustratingly coincident with one of the most interesting intervals of Earth’s more recent history.”
The Egyptian fossils offer some of the strongest evidence so far that fish communities resembling those of the modern world emerged remarkably early.
Tropical origins of modern fish
The research also points towards a broader trend.
On comparing the Egyptian fossils with other sites from soon after the extinction, researchers found that many early percomorph fish were concentrated in tropical areas. Regions at higher latitudes seemed to host fewer of them.
As time passed, these fish groups became more widely distributed throughout the world’s oceans.
“There is a coarse but intriguing geographic pattern to how these modern-looking faunas arose,” said Friedman. “Maybe they developed in the tropics, for instance, and then spread to higher latitudes as climates changed or as these groups dispersed.”
“That will be something to test more critically as we continue to improve the record.”
The proposal aligns with scientists’ understanding of present-day biodiversity. Tropical seas still support some of Earth’s most diverse marine communities and frequently serve as hubs of evolutionary innovation.
Looking beyond established fossil hotspots
The discovery underlines that major fossil finds can emerge from places examined less intensively than the traditional fossil hotspots.
“It’s always good to look at other places for finding fossils. We can’t keep focusing on Europe and North America,” El-Sayed said.
Fresh finds from Egyptian sites such as this are exposing some of the oldest known representatives of this fish group.
Scientists say the discoveries may eventually alter our understanding of modern fish evolution. The site is especially significant because its age has been determined as 62.2 million years with exceptional accuracy.
More secrets still lie buried
Despite this finding, substantial questions are unresolved. Fossils from the period directly after the asteroid impact remain incomplete, and researchers anticipate that future discoveries will bring further surprises.
“What we are seeing now is only a small light illuminating a long and previously dark corridor in the early history of modern marine fish evolution,” said Hesham Sallam, founder of the Mansoura University Vertebrate Paleontology Center (MUVP) in Egypt. “This Egyptian site shows that many important answers are still waiting to be discovered.”
For the moment, Egypt’s fossils provide one of the clearest pictures so far of how ocean life rebounded after one of the darkest events in Earth’s history.
They indicate that many fish living in today’s seas can trace their origins to a swift recovery that started only a few million years after the asteroid altered the trajectory of life on Earth.
The complete study was published in the journal Science Advances.
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