Where do reef fish come from?

This article was originally presented on Hakai Magazine, Online Journal of Science and Society in Coastal Ecosystems. Read more stories like this at hakaimagazine.com.

Sixty-nine million years ago, an asteroid nearly 10 kilometers across slammed into what is now Mexico’s Yucatan Peninsula. The impact set huge swaths of the planet ablaze. Soot and dust choked the Earth. As the world burned, ocean temperatures plummeted, and once-dominant creatures, including ammonites, plesiosaurs, and mosasaurs, died out—along with 80 percent of the planet’s other animal species.

New life flourishes in the void.

Within three million years, new species of fish flourished on a reef of coral-like algae and large tuberous clams just 500 kilometers from the asteroid’s crater. One day one of these fish—with an elongated snout and a delicate, slender body—died. It sank to the sandy seabed where, along with other animals, its skeletal imprint was compressed into limestone.

The ocean receded, and in the seventh century, Maya builders building temples in the city-state of Palenque began mining fossil-strewn rocks from the now dry seabed. The petrified creatures came to inform Mayan beliefs about a previous world destroyed by fire and flood. A plaque with a stamped fish was taken to the palace, where it was painted and decorated with plaster. Palenque residents used other fossils, including megalodon teeth and stingray spines, as cutting tools or buried them with the dead.

But the skeleton of the long-snouted fish remained buried in the quarry.

When Palenque, like many Maya city-states, collapsed in the 10th century, its temples and their fossils were abandoned and swallowed by the forest. They lay forgotten until Spanish colonists began studying the site in the 1800s. But it wasn’t until the 2000s that researchers took a closer look at the footprints in the limestone.

The fossilized fish found in Palenque are of species that have never been seen before. “It was just like a movie script,” says marine biologist David Bellwood of James Cook University in Australia, who was brought in to help identify the fossilized fish. “We found them on the lids of tombs.”

But the more shocking discovery came after paleontologists traced the limestone back to the quarry from which it was originally mined.

There, after millennia buried in stone, long-snouted fish finally saw the light and upended our understanding of fish evolution.

The researchers identified the fish as a flutemouth, a species whose descendants live on modern coral reefs. Dozens of other fossils recovered from the quarry include two other families of reef fish: damselfish and grouper.

Bellwood and colleagues show in a new study that these fossils represent the earliest known examples of reef fish found anywhere on Earth. Today we think of grouper, flute and damselfly as coral reef fish. But these groups actually appeared in one world before a modern coral that won’t appear on the scene for another 29 million years.

Before this discovery, the oldest evidence of reef fish was from about 50 million years ago: fossils excavated from what is now Monte Bolca in northern Italy. Based on the diversity represented in these Italian fossils, some scientists suspected that reef fish may have appeared earlier – closer in time to the asteroid impact. But no fossils from this period have ever been found. The specimens from the Palenque quarry, which date back to 65 and 63 million years ago, help fill this gap.

Although the grouper, flute-mouthed fish, and fish are the only extant families represented in the Palenque fossil, Bellwood believes that most other reef fish likely evolved around the same time. The study also suggests that reef fish originated in the western Atlantic Ocean, not in the ancient Tethys Ocean, near present-day Italy, as scientists had thought.

“These fossils are really important for understanding the history of coral reef fishes,” said David Wainwright, an evolutionary biologist at the University of California, Davis, who was not involved in the study. Wainwright notes that this study probably isn’t the final word on the origins of reef fish. “We’ll probably end up finding another fossil that’s even older,” he says—perhaps even one from before the asteroid hit.

Bellwood, for his part, is excited about what may still lie in Palenque’s careers. Future excavations could yield even more fossils that further reveal the history of coral reef ecosystems. “Theoretically, there could be all kinds of fossils in there,” he says. “It might just be a magical little place.”

This article first appeared in Hakai Magazine, and is republished here with permission.

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