Fossil-rich Welsh quarry yields trove of soft-bodied animals at dawn of modern life | Science

Between 540 million and 485 million years ago, during the Cambrian period, so many new, complex animal life forms arose that paleontologists speak of the Cambrian Explosion or the Biological Big Bang. But by 400 million years ago, almost all of those species disappeared, eventually replaced by the ancestors of most modern animals. There have been few clues about what happened in between, but fossils from 462 million years ago recently discovered in a quarry in central Wales are filling in that gap, researchers report today in Nature Ecology & Evolution.

“It is wonderful,” says Douglas Erwin, a paleontologist at the Smithsonian Institution’s National Museum of Natural History who was not involved with the work. There are “some beautiful specimens, including some surprising discoveries.”

The Welsh fossils, discovered by a paleontologist couple who live near the quarry, reveal some Cambrian life forms held on for millions of years longer than paleontologists had thought before going extinct, and certain classes of modern animals got their starts earlier than expected. There are also some familiar creatures, including arthropods such as crustaceans and horseshoe crabs, as well as sponges, starfish, and worms. Many of them by that point already had long histories and continue to thrive to this day, so their presence among the fossils isn’t surprising. But the quarry also holds strange creatures thought to have arisen and vanished during the Cambrian period, such as opabiniids, which had five eyes and a long proboscis, and scaly slugs called wiwaxiids. Newcomers spotted in the deposits include modern families of glass sponges and a group of crustaceans called horseshoe shrimp, which were thought to have arisen much later.

“This is muddying the water,” says Joanna Wolfe, a Harvard University biologist who helped characterize the site’s opabiniids for a publication last year in Nature Communications but was not involved in the broader analysis published today. Many researchers had assumed Cambrian critters would be long gone by the time of the Welsh fossils. Instead, “a lot of the groups that are modern are surviving alongside those [early] things,” Wolfe marvels.

Joe Botting and Lucy Muir, who have Ph.D.s in paleontology but chose to work mostly as amateurs, discovered the site, called Castle Bank, a decade ago, but at the time it didn’t seem very interesting. Only when the COVID-19 pandemic stopped them from traveling—even as far as Cardiff to work at Amgueddfa Cymru-National Museum Wales, where they are honorary research fellows—did they take a closer look at what was in the 10-meter-wide quarry in a sheep field. A narrow swath of shale overflowed with fossils, including preserved soft-bodied animals. They began to suspect they had stumbled on a deposit that could rival Canada’s Burgess Shale, a world-famous source of fossils from 500 million years ago. “We are still finding new things every time we go,” Botting says.

But most of the specimens were too tiny for them to closely analyze without high-power microscopes, which they didn’t have at home. At first they balked when the quarry’s landowner suggested the couple crowdsource funds to buy the instruments. However, an initial try quickly yielded about $20,000, more than twice their original goal. The subsequent microscopic analysis of the site’s fossils has now revealed so many details that “we can draw conclusions about what [the animals] ate” and where and how they lived, says Julien Kimmig, a paleontologist at the State Museum of Natural History Karlsruhe who was not involved with the work. He is particularly thrilled that Castle Bank has fossils of both hard-body and soft-body organisms, as they are not usually preserved in the same place. “That gives us a complete idea of the diversity there,” he explains.

So far, the researchers say they have found 170 species. “There is every reason to expect that the diversity of the fauna will continue to climb as the authors continue their research,” Erwin predicts. But even the currently documented diversity emphasizes the underappreciated importance of this time, called the Ordovician, which set the stage for the world’s current biodiversity. “It’s a period that we don’t know very much about,” Muir says. “But by the end of it, [ecosystems] are completely different.”

Many of the specimens are remarkably small. Most vary from the size of a sesame seed to that of a pencil eraser. During the Cambrian, life could be small, “but not that small,” says Kimmig, who suggests the Ordovician fossils may signal a miniaturization trend for life.

The smallness of many of the fossils may lead to differing opinions on what some of them are, Wolfe predicts. “It’s difficult to know for sure exactly what you are seeing,” she says. For example, Muir and Botting have come across a six-legged arthropod that they say could be a marine ancestor of insects. “It can’t really be an insect because it’s marine,” Botting says. “But we don’t know where insects evolved from.”

This fossil “is quite remarkable,” Erwin says, “but I suspect many paleontologists may want more convincing specimens.” Botting agrees: “We are desperate to get another.”

Erwin says more studies will be needed to fully appreciate the implications of Castle Bank for understanding evolution. But if nothing else, he says, the work is “further illustration of how much there is still left to discover by getting out in the field and finding exciting new fossils.”

Kimmig is already convinced the site will make history. The Welsh quarry, he says, “could definitely be as famous” as the Burgess Shale.

Between 540 million and 485 million years ago, during the Cambrian period, so many new, complex animal life forms arose that paleontologists speak of the Cambrian Explosion or the Biological Big Bang. But by 400 million years ago, almost all of those species disappeared, eventually replaced by the ancestors of most modern animals. There have been few clues about what happened in between, but fossils from 462 million years ago recently discovered in a quarry in central Wales are filling in that gap, researchers report today in Nature Ecology & Evolution.

“It is wonderful,” says Douglas Erwin, a paleontologist at the Smithsonian Institution’s National Museum of Natural History who was not involved with the work. There are “some beautiful specimens, including some surprising discoveries.”

The Welsh fossils, discovered by a paleontologist couple who live near the quarry, reveal some Cambrian life forms held on for millions of years longer than paleontologists had thought before going extinct, and certain classes of modern animals got their starts earlier than expected. There are also some familiar creatures, including arthropods such as crustaceans and horseshoe crabs, as well as sponges, starfish, and worms. Many of them by that point already had long histories and continue to thrive to this day, so their presence among the fossils isn’t surprising. But the quarry also holds strange creatures thought to have arisen and vanished during the Cambrian period, such as opabiniids, which had five eyes and a long proboscis, and scaly slugs called wiwaxiids. Newcomers spotted in the deposits include modern families of glass sponges and a group of crustaceans called horseshoe shrimp, which were thought to have arisen much later.

“This is muddying the water,” says Joanna Wolfe, a Harvard University biologist who helped characterize the site’s opabiniids for a publication last year in Nature Communications but was not involved in the broader analysis published today. Many researchers had assumed Cambrian critters would be long gone by the time of the Welsh fossils. Instead, “a lot of the groups that are modern are surviving alongside those [early] things,” Wolfe marvels.

Joe Botting and Lucy Muir, who have Ph.D.s in paleontology but chose to work mostly as amateurs, discovered the site, called Castle Bank, a decade ago, but at the time it didn’t seem very interesting. Only when the COVID-19 pandemic stopped them from traveling—even as far as Cardiff to work at Amgueddfa Cymru-National Museum Wales, where they are honorary research fellows—did they take a closer look at what was in the 10-meter-wide quarry in a sheep field. A narrow swath of shale overflowed with fossils, including preserved soft-bodied animals. They began to suspect they had stumbled on a deposit that could rival Canada’s Burgess Shale, a world-famous source of fossils from 500 million years ago. “We are still finding new things every time we go,” Botting says.

But most of the specimens were too tiny for them to closely analyze without high-power microscopes, which they didn’t have at home. At first they balked when the quarry’s landowner suggested the couple crowdsource funds to buy the instruments. However, an initial try quickly yielded about $20,000, more than twice their original goal. The subsequent microscopic analysis of the site’s fossils has now revealed so many details that “we can draw conclusions about what [the animals] ate” and where and how they lived, says Julien Kimmig, a paleontologist at the State Museum of Natural History Karlsruhe who was not involved with the work. He is particularly thrilled that Castle Bank has fossils of both hard-body and soft-body organisms, as they are not usually preserved in the same place. “That gives us a complete idea of the diversity there,” he explains.

So far, the researchers say they have found 170 species. “There is every reason to expect that the diversity of the fauna will continue to climb as the authors continue their research,” Erwin predicts. But even the currently documented diversity emphasizes the underappreciated importance of this time, called the Ordovician, which set the stage for the world’s current biodiversity. “It’s a period that we don’t know very much about,” Muir says. “But by the end of it, [ecosystems] are completely different.”

Many of the specimens are remarkably small. Most vary from the size of a sesame seed to that of a pencil eraser. During the Cambrian, life could be small, “but not that small,” says Kimmig, who suggests the Ordovician fossils may signal a miniaturization trend for life.

The smallness of many of the fossils may lead to differing opinions on what some of them are, Wolfe predicts. “It’s difficult to know for sure exactly what you are seeing,” she says. For example, Muir and Botting have come across a six-legged arthropod that they say could be a marine ancestor of insects. “It can’t really be an insect because it’s marine,” Botting says. “But we don’t know where insects evolved from.”

This fossil “is quite remarkable,” Erwin says, “but I suspect many paleontologists may want more convincing specimens.” Botting agrees: “We are desperate to get another.”

Erwin says more studies will be needed to fully appreciate the implications of Castle Bank for understanding evolution. But if nothing else, he says, the work is “further illustration of how much there is still left to discover by getting out in the field and finding exciting new fossils.”

Kimmig is already convinced the site will make history. The Welsh quarry, he says, “could definitely be as famous” as the Burgess Shale.