Scientists unearth a ‘petrified aquarium’ of 62-million-year-old fish fossils
An unexpected haul of nearly 500 fossilized fish in Egypt provides an unprecedented picture of how sea life rebounded from the asteroid that killed the dinosaurs.
Paleontologists excavating a 62.2-million-year-old rock layer in Egypt have uncovered a petrified aquarium. The unexpected cache of fossilized fish—containing about 500 specimens from more than 20 types of ray-finned fish—offers a tantalizing look at how sea life bounced back from the asteroid impact that brought the Cretaceous to a crashing, fiery finale.
“When we arrived at the site and began finding well-preserved fish specimens in the sediment, we knew we were dealing with something exceptional,” says National Geographic Explorer Sanaa El-Sayed, a paleontologist at Mansoura University in Egypt. She and her colleagues published their findings on Wednesday in the journal Science Advances.
The dating of the rock layer places the ancient swimmers about four million years after the end of the Age of Dinosaurs and near the dawn of the Paleocene epoch. Paleontologists have spent decades piecing together how life reemerged once the blazes extinguished and the global “impact winter” subsided. On land, ferns underwent a major boom about a hundred thousand years after the extinction event. Fossil sites like Corral Bluffs in Colorado document how mammals, reptiles, and plants formed new forests a million years after the impact.
(These ancient fish swam with the dinosaurs. They may not survive us.)
But how life in Earth’s oceans recovered has been much more mysterious. The new fish fossils from the Egyptian site, called Qreiya 3, show which aquatic survivors lucked out and seized the seas for millions of years to come.
“Qreiya 3 provides one of the clearest views yet of how modern marine ecosystems emerged,” says National Geographic Explorer Hesham Sallam, a paleontologist also at Mansoura University and an author on the study.
The initial excavations have uncovered only a small portion of what’s preserved, he says, and yet the site already “reveals that many fish groups important in today’s oceans were present only four million years after the extinction of the dinosaurs.”
Percomorph proliferation
Qreiya 3 is what paleontologists call a lagerstätte, a “storage place” where fossils are preserved in exceptional detail. The exquisite preservation allowed El-Sayed and her colleagues to identify many of the Qreiya 3 fish fossils as belonging to known groups. They found at least 21 distinct types of ray-finned fish across nine larger groups. But there was one large fishy family that was preserved in greater abundance than any of the others: the percomorphs.
Prior to the End-Cretaceous mass extinction event, percomorphs were relatively rare in Earth’s oceans. Today, more than 17,000 species of percomorphs exist, and they include everything from tuna and seahorses to perches and deep-sea anglerfish.
“Percomorphs were already present before the extinction,” El-Sayed says, “but they seem to have expanded dramatically afterward.”
Ocean food webs devastated by the mass extinction provided the percomorphs with ample opportunities to rapidly evolve into a variety of new forms, from needle-toothed, eel-like predators to small fish hiding among ancient reefs. El-Sayed was especially excited to find fossils of a predatory percomorph that was an ancient relative of tuna and mackerel. No one before had found tuna relatives so old, she says, but a specimen with telltale teeth provided the clues they needed to show the fishes were present so long ago.
(Spectacular fossil fish reveal a critical period of evolution)
“That was one of the most exciting moments of the project,” El-Sayed says, because it “captured the early history of lineages that would later become major components of modern oceans.”
The findings also close a 10-million-year void in the fossil record, she adds.
El-Sayed and her colleagues named the gap the “Patterson Gap” in 2023 after Colin Patterson, a British paleontologist who noted a seeming lack of bony fish fossils across the rock layers that record the K/Pg extinction and early Paleocene.
“The lack of body fossils preserved during the Paleocene made it quite challenging to precisely resolve the timing and structure of the fish evolution following the K/Pg,” Sibert says, but the Qreiya 3 fossils now fill that gap.
Elizabeth Sibert, a paleontologist from Woods Hole Oceanographic Institute who was not involved in the work, says she was excited to see the diversity of fish revealed by the discovery. The findings, she says, provide "fossil evidence for fish communities during what was a critical time.”
Bouncing back
The percomorph proliferation El-Sayed found is comparable to phenomena seen on land following the extinction event. Just as tiny placental mammals—including our ancestors—and beaked birds were present before the asteroid strike, both groups underwent an evolutionary burst after the extinction event, leading to a broader array of species and forms.
Just because the fish at Qreiya 3 were thriving 62 million years ago, however, does not mean the story was the same in waters everywhere, the researchers say. El-Sayed and her team note that other ocean fossils from around the same time preserved elsewhere around the world indicate that life recovered differently across the planet.
(These fish are 'living fossils'—among the most primitive animals on Earth)
“Some regions may have retained more archaic communities for longer,” El-Sayed says, “While tropical settings may have seen the earlier assembly of more modern-looking fish faunas.”
The pattern is as expected for a global disaster, and it may be that habitats closer to the equator may have been hotspots for life’s recovery. Excavations, like those in the blistering Egyptian desert, will continue to find even more fish to fill in the fossil gap. Together, those findings will form a petrified constellation of sites that can reveal how life, both on land and in the sea, rebounded from even its darkest days.
