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Natural History

500 million years ago, this critter had a really bad day Add to ...

ROM researchers unearth fossils so well-preserved, they include eyeballs and internal organs

Reading time 11 minutes
The dawn
of life
By Ivan Semeniuk
Researchers from the Royal Ontario Museum are busy drilling, chiselling and carefully dislodging one well-preserved fossil after another at a recently discovered site in the Rocky Mountains. (Courtesy Royal Ontario Museum)

High up in the mountains of British Columbia’s Kootenay National Park, the exact location a secret, Jean-Bernard Caron shows me a slab of rock pried from the cliff face where we are standing. I can see something embedded in the surface, that to my untrained eye is little more than a grey-on-grey blob the size of a flattened tennis ball – nothing that I would suspect as having once been alive.

But to Dr. Caron, curator of invertebrate paleontology at the Royal Ontario Museum, the blob is immediately recognizable as Sidneyia inexpectans, an ancient species of arthropod that would have looked like a cross between a jumbo shrimp and a sowbug. Dr. Caron points out the traces of feather-like appendages. Then he tells me exactly what it was doing the moment it died.

“Defecating, actually,” he says, indicating a darker splotch projecting from what I presume was the creature’s rear end. “He was a bit stressed, I guess, during burial.”

No kidding. One minute, about 508 million years ago, the hapless arthropod was ambling along the seafloor near an underwater cliff. The next, it was caught up in a mudslide and swept into oxygen-starved waters, where it suffocated under a thick blanket of silt along with a menagerie of other weird beasts.

Now, those creatures are seeing the light of day for the first time since their abrupt demise. At a recently discovered site – dubbed Marble Canyon, after a local trail – Dr. Caron and a small band of researchers are busy drilling, chiselling and carefully dislodging one well-preserved specimen after another. Their aim, he says, is not just finding fossils – they have extracted roughly 10,000 on this seven-week expedition alone – but chronicling the emergence of life as we know it.

“It’s the story of how animal life changed from its earliest forms into things with bona fide guts, limbs, eyes, and ways of feeding,” he says. “That’s an amazing transformation.”

In the process of trying to understand it, Dr. Caron is systematically uncovering what looks to be a national treasure.

The site “provides spectacularly preserved examples of animals that are poorly known or unknown based on what we have already,” says Derek Briggs, a paleontologist at Yale University. Those examples, taken together, promise to create an unprecedented portrait of evolution’s inner workings.

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This guy could be your ancestor, and other discoveries from fossils found in B.C.'s Marble Canyon

Before there were dinosaurs

Evolutionary biologists call it the Cambrian explosion. Long before even insects were scuttling around on land, marine life was branching out as never before or since – a grand experiment in biodiversity that lasted some 50 million years and produced every major division in the animal kingdom we see today. It was during the Cambrian period that worms became worms, molluscs became molluscs, and our earliest vertebrate ancestors first started wriggling around in the murky depths.

We know about the Cambrian explosion because of the Burgess Shale, a famous fossil trove 40 kilometres north of Marble Canyon. Its collection of weird life forms gave scientists an initial picture of the Cambrian explosion; Marble Canyon – with its high concentration and great diversity of specimens – is exciting because it samples a different ecosystem, providing researchers with a broader and more nuanced portrait of a crucial phase in the annals of life.

ROM curator of invertebrate paleontology Dr. Jean-Bernard Caron and his have team uncovered thousands of specimens at the Marble Canyon site, including dozens of examples of a primitive fish that may have been a remote ancestor to all land vertebrates. (Courtesy Royal Ontario Museum)

Thanks to a fluke of geochemistry, the characters in that portrait are recorded in extraordinary detail. Seawater contained more dissolved calcium during the Cambrian period than it does today. After each fresh mudslide, a coating of lime would precipitate out of the water and over newly deposited layers of silt, creating a cement-like coating that stifled bacterial growth and kept the creatures from decaying.

Specimens feature not just shells and other hard bits, but include the remains of soft tissues, such as appendages, parts of circulatory systems, eyeballs with retinas and corneas, internal organs, partly digested gut contents, and, in some cases, hints of muscle and nerve fibres. They are snapshots in stone of ancient animals as they once appeared in life.

“You see them from toe to nose,” says Dr. Caron.

Canyon critters

Sidneyia inexpectans

With muscular legs and crushing pincers this carnivorous arthropod roamed the seafloor in search of prey, and may have used its flipper-like tail to propel itself from danger. The largest specimens measure about 20 centimetres across.

Marrella splendens

A small but flamboyantly designed arthropod that grew up to 2.5 centimetres in size. Its Viking-like horns, swept back over a segmented body, likely served as a protective shield that was light to carry and less effort to grow than a full, mineralized shell.

Isoxys acutangulus

A small swimming creature up to a few centimetres in size whose exoskeleton included a saddle-like carapace with sharp points on either end. The purpose of the points is unclear but may they may have aided in protection against predators.

Haplophrentis carinatus

An enigmatic bottom dweller. Its conical shell suggests it was related to molluscs but its lineage remains obscure. The shell and lid served as protection from predators, but the creature could also extend two appendages, presumably to help it move through the mud. About two centimetres long.

Metaspriggina walcotti

A primitive, boneless, jawless fish that was our closest known relative 508 million years ago. It had upward and forward facing eyes suggesting it scavenged on the bottom and had to keep a wary lookout for predators swooping down from above. Typically about five centimetres long.

Sidenyia inexpectans was a carnivorous arthropod the size of a salad plate that roamed the Cambrian sea floor. It's named after Sidney Walcott, son of Charles Walcott who discovered the Burgess Shale formation in British Columbia in 1909. (Courtesy Royal Ontario Museum)

The result can often seem bizarre. For example, there is Marrella, a tiny bottom-dwelling arthropod with impressive Viking-helmet-like spikes emanating from its head. Or how about Isoxys, a bug-eyed multilegged swimmer that in its day would have looked like a self-propelled taco shell.

To scientists, the preservation of soft tissues is crucial for two reasons. For one thing, most animals at the time did not have shells, and so would have simply vanished from the geologic record. The Marble Canyon fossil bed gives us a much more detailed picture of who was on the scene and how they may have interacted with each other.

What’s more, the fine anatomical details offer clues to the ways that evolution was driving animal life to new heights during the Cambrian period. This is particularly true of arthropods, a group that accounts for most of the world’s animal diversity, including crustaceans, insects and spiders. Their predecessors similarly dominated the Cambrian period, and make up the lion’s share of the Marble Canyon fossils.

Darwin's Lego

Today, arthropods are paragons of evolutionary stability. Insects have six legs, for example – a defining feature that hasn’t changed in 400 million years. They are, biologically speaking, a model of conservatism. Yet, the Marble Canyon fossils show that during the Cambrian period, when arthropods first emerged, they were changing a lot, and often. The modular, segmented nature of the arthropod body likely made it amenable to experimentation, like a living Lego kit to which could be added more segments, more legs and more elaborate armour.

It may be the best example scientists have to help them understand just how and why evolution, constantly at work, sometimes goes into creative overdrive. “The hypothesis is that under certain special conditions … the potential to evolve is released,” says Cedric Aria, a PhD candidate at the ROM who is studying the Marble Canyon arthropods.

Apart from a few species such as Sidneyia, which could grow to be 20 cm long and crush prey between pincer-like claws, Cambrian creatures often measured just a centimetre or two. Yet their aquatic habitat was the African savannah of its time, the original Serengeti where the great drama of animal survival first played out.

Among the diminutive characters operating in this alien world was Metaspriggina walcottii>, a limbless, boneless creature that moved through the water like a snake – and it is the most important discovery to have emerged from Marble Canyon to date.

Dr. Caron carts pool noodles to the dig site. The team cuts the noodles and uses them to wrap and protect large chunks of shale for transport back to the ROM. (Courtesy Royal Ontario Museum)

Scientists knew about Metaspriggina before – two partial specimens were discovered at the Burgess Shale; but no one had a clue what it was. At Marble Canyon, Dr. Caron and his team found dozens more – enough to paint a vivid picture of a primitive fish about the size of a baby finger. It is solid proof that our own remote forebears were already on the scene at Marble Canyon.

The first vertebrates would not haul themselves up onto land for about another 150 million years, but Metaspriggina’s anatomy already carries the seeds of a future upright-walking and talking human. For example, it had a notochord, the predecessor of the spine; and it had a series of gill arches in its head, the first pair of which, Dr. Caron proposes, eventually evolved into the vertebrate jaw.

Many of the Metaspriggina specimens found at Marble Canyon were fossilized in groups of adults, suggesting they congregated in life, just as fish now gather in schools. It is the earliest-known example of animals working together in this way.

Pool noodles and gleaming eyes

The first time I met Dr. Caron, last August, he was in Banff, Alta., looking for pool noodles. His plan was to wrap them around the fragile, fossil-bearing slabs that were piling up by the hundreds at the worksite. Later, we drove across the provincial border into British Columbia and parked at a campground. The rest of our journey would take place on foot.

There is no trail that leads to the Marble Canyon site. Getting there means navigating an exhausting tangle of charred logs and detritus left in the wake of a forest fire that swept through the area a decade ago. I followed Dr. Caron’s compact and agile frame as we bushwhacked our way up a steep slope, the Day-Glo orange-and-pink pool noodles strapped to his backpack.

Many of the fossils recovered at the Marble Canyon site are split in half when slabs of shale are cracked open. Each half has the potential to reveal different details about an animal's physiology, thanks to the preservation of soft tissue. (Courtesy Royal Ontario Museum)

By the time we arrived, late-afternoon shadows were creeping across the mountainside; the crew working there had called it a day. Fossil-spotting calls for good light so that paleontologists can make out the monochromatic residue of long-dead creatures as they delve into the strata. (In particular, fossilized eyes tend to glint in the sunlight.) Rainy days are the least productive: When the rocks are wet, whatever contrast the fossils have is gone and it is impossible to work.

We settled in at the field camp, a cluster of tents nestled in a stand of burnt timber surrounded by an electrified fence to discourage grizzly bears. With the summer nearing its end and various supplies running out, dinner was a splendid feast consisting of a little bit of everything.


200,000 years ago

Anatomically modern humans appear

2.58 million years ago

Earth enters a period of successive ice ages. Glaciers expose shale formations in the Rocky Mountains

66.5 million years ago

An asteroid impact coincides with the mass extinction of dinosaurs, along with many other groups of animals

80 million years ago

Formation of the Rocky Mountains begins

225 million years ago

First appearance of mammals

240 million years ago

First dinosaurs appear

252 million years ago

Worst mass extinction event in geologic history. Up to 96% of marine species eliminated

395 million years ago

First land vertebrates emerge

428 million years ago

A millipede-like arthropod, the first known land animal, emerges

462 million years ago

First jawed fish appear

508 million years ago

Mudslides trap a wide assortment of Cambrian creatures that will eventually appear as fossils in the Burgess Shale and Marble Canyon formations

560-80 million years ago

The earliest known animals, ancestors of sponges and jellyfish, appear in the geologic record

The next morning we clambered up to the site. The exposed rock face that the researchers are investigating is just a few metres high and about 10 across. But it is riddled with past life, arranged in fossil-rich bands that run horizontally through the rock. The work consists of pulling the rock out in chunks and then splitting them open with a hammer and chisel along the horizontal layers. The soundtrack of the workday is a steady chorus of hammers tapping, punctuated with an occasional gasp when something really good turns up.

During the summer of 2014 – the first full field season at Marble Canyon – the team collected about two tonnes worth of specimens representing 60 species, a quarter of which are entirely new to science.

The fossil hunter

Canada’s central role in the discovery of the Cambrian explosion dates back to 1886, when geologist Richard McConnell of the Geological Survey of Canada investigated reports of “stone bugs” – strange fossils in the mountains near Field, B.C.

Similar reports eventually reached Charles Walcott, head of the Smithsonian Institution in Washington. He began exploring the region in 1907, and two years later discovered the breathtaking Burgess Shale.

Ever since, it has been heavily mined as a source of information about the Cambrian period. But public fascination with the site and its weird life forms did not take off until 1989, following the publication of Wonderful Life, by the late Harvard professor and science popularizer, Stephen Jay Gould.

It was Mr. Gould’s book that would first introduce Dr. Caron to the splendors and the mystery of the Cambrian explosion. Growing up in France, he was already a committed fossil hound by age 10 and on the way to turning his bedroom into a mini-museum. By the time he was 15 he knew enough to talk his way into volunteering at research digs around France, Spain and elsewhere in Europe. Often the youngest person present, he learned firsthand how fieldwork is done. By his early twenties that experience won him his dream summer job – an invitation to work with a ROM expedition to the Burgess Shale.

It was his first visit to Canada, but he was already hooked; he later earned his Ph.D based on the ROM’s Burgess Shale collection. In 2006 he became a curator at the museum. While the Burgess Shale has already yielded many important fossils, Dr. Caron’s scientific goal was to expand the window on evolution that it offered. That meant looking elsewhere.

In 2008 he brought a few colleagues to a mountainous area south of the original Burgess Shale finds, following up on a report that German hikers had spotted some fossils there. The Caron group eventually came across a thin section of sediment-bearing fossils. Encouraged, they returned in 2012 and worked their way westward, trying to follow the ribbon of shale that marked what had once been the Cambrian seafloor. At first, they had no luck; then, they came across an open area where landslides and winter avalanches had tumbled rocks down a broad slope.

‘We began to find fossils hand over fist,” says Robert Gaines, a geologist at Pomona College in Claremont, Calif., who works with Dr. Caron. “They were just lying there under the sun.”

Even for trained experts, such an abundance of fossils was extraordinary. They traced the fossils to a small cliff further up the slope that was poking out from an overburden of younger debris. It was just what Dr. Caron was looking for: another doorway back to the Cambrian.

The small group began to work the site, and soon had an impressive haul, including Metaspriggina. Dr. Caron was ecstatic, but kept the find quiet until the specimens could be examined in detail and descriptions of them prepared for publication. A year ago, the discovery was announced. Here was a new Cambrian fossil site in Canada that could prove to be as important as Walcott’s original Burgess Shale find.

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Toothbrushes, glue and some newspaper: A look at the delicate process of caring for fossils

National treasures

As a scientist and an immigrant, Dr. Caron marvels at Canada’s rich paleo heritage – something most Canadians are either unaware of or take for granted. From coast to coast there are fossil sites that document virtually every important breakthrough in evolution before mammals took centre stage, including such world heritage sites as Newfoundland’s Mistaken Point, Nova Scotia’s Joggins Fossil Cliffs, Miguasha National Park in Quebec, Alberta’s Dinosaur Provincial Park and, of course, the Burgess Shale.

With so many locations to choose from, Dr. Caron says, it’s possible to chronicle the story of animal life almost entirely with fossils harvested within the nation’s borders. No other country, including Russia or the United States, can make such a claim. It is this vision that propels Dr. Caron’s dream of a new fossil gallery at the ROM that would rival any in the world. It would provide a comprehensive portrait of the dawn and diversification of life while putting visitors in touch with their deepest evolutionary roots. The ROM has launched a capital campaign to finance the gallery, and Dr. Caron hopes it can open by 2017, in time for Canada’s 150th birthday.

In the meantime, there may be even more treasure troves waiting to discovered beyond Marble Canyon.

“There are whole stretches of the Rockies that have similar geology and that have not been looked at,” says Hans Larsson, a professor at McGill University and chair of the paleontology division of the Geological Association of Canada.

The Marble Canyon dig site is about 40 kilometres south of the Burgess Shale, a famous fossil trove. (Courtesy Royal Ontario Museum)

The issue highlights a larger problem for paleontologists in Canada: Although the country is uncommonly wealthy in fossils, there are few paying positions available for scientists with the relevant expertise. There are also limited resources available to protect sites as painstaking work proceeds.

In the case of Marble Canyon, the site’s proximity to the highway means that protection from souvenir hunters is an additional concern. So far, that protection consists of keeping quiet about the site’s exact location. There are also occasional visits from Parks Canada staff (whose numbers have shrunk because of government cuts) augmented by a surveillance system with cameras. In the future, Parks Canada may decide to restrict public access to the mountainside where the fossils are located – though such a measure would be difficult to enforce.

“We’re still looking at all the management options and trying to assess the level of risk to this site,” says Todd Keith, a land-use specialist with Parks Canada.

Where do we come from?

Dr. Caron turned 40 while working at the Marble Canyon site last summer. Bespectacled and soft-spoken, he conveys less the image of an Indiana Jones than that of a librarian of nature tending to sacred volumes of fine-grained rock.

It is in these geological tomes that Dr. Caron is seeking the deeper patterns that underlie life in all its forms. It’s a scientific quest, certainly, but one with an existential dimension. “In the end” Dr. Caron says, “it’s a fundamental question that most human beings will ask at some point: Where do I come from?”

Standing beside him at the rock face, holding a piece of a fossilized animal in the palm of my hand, I can feel the weight of the past. It is like an anchor, hidden beneath the primordial waters of the Cambrian, but tied to my own identity with an unbroken strand of DNA. The creatures of Marble Canyon are strange in appearance, but in their struggles to survive they are eminently recognizable.

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