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Massive trove of Canadian fossils gives near-unprecedented glimpse of Cambrian explosion

A site in the Kootenay National Park has proved a fantastic source of fossils from the Cambrian explosion, 542 million years ago.

In 2012, geologists discovered a major haul of fossils in Canada’s Kootenay National Park, in the Rocky Mountains near Calgary, Alberta. The find looked like it could shed further light on one of the most critical periods in the history of life on Earth, the Cambrian explosion, 542 million years ago - and the first study of its specimens, published in the journal Nature Communications, reveals that the find will “increase our understanding of early animal evolution” in an almost unparalleled way.

While there is evidence that life existed on Earth at least 3.5 billion years ago, life as we know it - multi-cellular and adapted to almost every part of the planet - appeared in what is called the Cambrian explosion, 542 million years ago. This was the era before animals colonised land, and indeed this period coincided with the first era of algae-like plants adapting to survive above water on the edges of bodies of water.

Over the course of around 80 million years the rate of evolution accelerated vastly, and the ancestors of almost all of the major phyla we see today first emerged. Quite why this happened is the subject of debate among scientists - it could have been any number of environmental or genetic factors - but there seemed to have been a relative frenzy of evolutionary competition.

The previously-dominant Ediacarans, which looked a bit like large floating sacks, were usurped and made extinct by the emergence of creatures that developed physical characteristics we still see today, like internal layering that separates digestive tracts from other organs, or having distinct “fronts” and “backs” (a trait known as bilateral symmetry). For an idea of what creatures exist today that missed out on all this, look to jellyfish.

In the rush to try and fill each new ecological niche, there were thousands of experiments that resemble nothing like anything that lives today. There was the spiky grazer Orthrozanclus and the superhero shrimp Stanleycaris; the bristleworm Insolicorypha and the arthopod Marrella, with huge spines on its head. There were also trilobites, thousands and thousands of different trilobites.

But these creatures lived in the sea, and were usually no more than a few centimetres in length at most. When they died - as they no doubt did by the million - they will have been eaten by other scavenging animals within a short time of settling on the sea floor. Our fossil record is dependent entirely on what were ancient landslides, when massive amounts of rock fell into the sea to crush entire shorelines, fossilising them. The few sites where this has happened, with whole ecosystems frozen in stone, are amazing - and none is better than the Burgess Shale. Nowhere else are the soft bodies of the ancient Cambrian explosion better-preserved, with detail so fine it’s possible to make out individual antennae or legs.

The original Burgess Shale find was in 1909, in the Yoho National Park, by palaeontologist Charles Walcott. It was formed by what’s known as a Lagerstätte formation, a particular kind of sedimentary preservation that happens so quickly not even microbes have time to break the tissue down, which is key to preserving as much detail as possible. Walcott spent decades gathering more than 65,000 fossils from the site, with its major significance only realised in the 1960s. And, while the Shale itself extends beyond the Yoho National Park, the best fossils were always found at Walcott’s original site.

However, it appears that the site in Kootenay National Park now rivals it for importance. The team of researchers - from institutes including the Royal Ontario Museum, the University of Toronto, and Uppsala University - gathered as many as 3,000 fossil specimens representing 50 different species in only 15 days.

The study’s lead author, Jean-Bernard Caron from the Royal Ontario Museum, said: "This new discovery is an epic sequel to a research story that began at the turn of the previous century, and there is no doubt in my mind that this new material will significantly increase our understanding of early animal evolution. The rate at which we are finding animals – many of which are new – is astonishing, and there is a high possibility that we'll eventually find more species here than at the original Yoho National Park site, and potentially more than from anywhere else in the world.”

Some of the preservation is so good that internal organs are visible. There’s also further evidence to support that hypothesis that Pikaia gracilens - a 4cm-long creature that looks a bit like an eel with tentacles - is the earliest known creature with the characteristics of vertebrates. It could even be the common ancestor of all vertebrates alive today.