The Burgess Shale
Soft-Bodied Fossils and the Cambrian Seafloor
- 9 chapters
- 18m
- Biology & Evolution
- Free · no sign-up
The book explains how these fossils formed through taphonomy and diagenesis, details the geology of the IUGS heritage site, and examines the Burgess Shale biota. Chapters cover the work of scientists like Simon Conway Morris and Stephen Gould, whose competing theories about evolutionary pathways shaped modern paleontology.
Anyone interested in ancient marine ecosystems or the origins of complex life will find this exploration of exceptional fossils both fascinating and accessible.
Listen
-
Read this chapter
Charles Walcott discovered the Burgess Shale on 30 August 1909, and returned the next year with his family to begin quarrying on Fossil Ridge. He spent nearly every year until 1924 collecting over 65,000 specimens, describing them until his death in 1927. At the time, he tried to classify the fossils into known groups, which led many to see them merely as oddities. It wasn’t until 1962 that Alberto Simonetta revisited the site, revealing that Walcott had only begun to uncover the true significance of what was found there.
Walcott’s original classifications of most Burgess Shale fossils are now considered wrong, though they were accepted during his time. He did change his mind on one point when challenged. Later interpretations benefited from advances in knowledge and techniques that weren’t available to him. Excavations resumed at the Walcott Quarry under Harry Blackmore Whittington’s influence, with a new site, the Raymond Quarry, established higher up Fossil Ridge. Whittington, working with students Derek Briggs and Simon Conway Morris from the University of Cambridge, re-evaluated the fossils thoroughly. They found the creatures were far more unusual and diverse than Walcott had thought. Some had strange features—like Opabinia, with five eyes and a long snout like a vacuum cleaner hose, or Hallucigenia, which was first reconstructed upside down, walking on spines that appeared bilaterally symmetrical.
In the mid-1970s, Parks Canada and UNESCO designated the Burgess Shale a World Heritage Site, which brought stricter rules and protections, making fossil collecting more difficult politically. Still, the Royal Ontario Museum continued the work, with curator Desmond Collins identifying new fossil sites both above and below the original Walcott quarry. These locations keep turning up organisms faster than scientists can study them. Then in 1989, Stephen Jay Gould’s book Wonderful Life brought the Burgess Shale to public attention. Gould argued that the fossils showed life forms were far more diverse and unusual back then, with many evolutionary experiments that didn’t survive. His view relied heavily on Simon Conway Morris’s reevaluation of Walcott’s original findings, though Conway Morris strongly disagreed, claiming almost all Cambrian creatures fit into today’s major animal groups.
The Burgess Shale has drawn paleoclimatologists interested in understanding Earth’s long-term climate changes, including predictions about the future. According to Peter Ward and Donald Brownlee in their 2003 book The Life and Death of Planet Earth, scientists study the fossil record there to learn about the climate during the Cambrian explosion. This research helps predict what Earth’s climate might look like 500 million years from now, as the Sun continues to warm and CO2 and oxygen levels fall, potentially heating the planet to temperatures unseen since the Archean Eon, before plants and animals existed. The site was registered as a World Heritage Site in 1980 and later included in the Canadian Rocky Mountain Parks WHS designation in 1984.
In 2012, scientists announced the discovery of a second Burgess Shale site in Kootenay National Park, located to the south. Just fifteen days later, in 2013, researchers collected fossils at this new location and found fifty animal species buried in the ancient seafloor.
-
Read this chapter
The Burgess Shale site was recognized by the International Union of Geological Sciences in October 2022 as part of its list of 100 geological heritage sites around the world. That organization describes an IUGS Geological Heritage Site as a location with international scientific importance, one that serves as a reference point and has helped shape geological science over time. The Burgess Shale was included because it shows exceptional soft-tissue preservation and contains the most complete record of Cambrian marine ecosystems, specifically from the Wuliuan stage.
-
Read this chapter
The Burgess Shale fossils come from the Stephen Formation, dark mudstones about 505 million years old, laid down at the base of a 160-meter-tall cliff. That cliff was made of calcareous reefs from the Cathedral Formation, which probably formed just before the Burgess Shale did. One leading idea is that part of the reef broke off and slid away, maybe for kilometers, before faults reactivated around 509 million years ago, breaking the formation apart. This left a steep cliff, its limestone bottom protected from tectonic pressure. Farther from the reef, rocks are hard to work with because tectonic forces created vertical fractures that split the beds and disrupted the fossils. The Walcott quarry yielded such exceptional specimens because it was right at the edge of that Cambrian cliff.
Originally, scientists believed the Burgess Shale formed in an environment lacking oxygen, which they thought helped preserve soft-bodied creatures by preventing decay and creating unique chemical conditions. This lack of oxygen was also thought to reduce burrowing organisms, since their tracks are rare in layers with soft-body fossils, usually limited in depth. However, newer research shows oxygen was actually present in the sediment throughout deposition. Another possible explanation involves brine seeps, though that idea is explored more fully in the section titled "Burgess Shale type preservation."
The Burgess Shale is sometimes treated as a distinct formation, the Burgess Shale Formation, rather than just a part of the larger Stephen Formation. This distinction highlights the unique geological character of the site where these remarkable fossils are found. The area has been studied for its exceptional preservation of soft-bodied creatures from the Cambrian period, offering insights into early marine life. While it sits within the broader Stephen Formation, some researchers prefer to recognize it as its own unit due to its distinct features and fossil record. This approach underscores the importance of the Burgess Shale in understanding ancient seafloor ecosystems.
-
Read this chapter
The Burgess Shale preserves organisms that were quickly buried by sediment carried by water currents, before they had time to decay. These currents may have moved the creatures long distances before final burial. The fossils are most often found as extremely thin carbonaceous films, less than a micrometre thick.
There are many other comparable Cambrian lagerstätten, and such fossil assemblages are actually more common in the Cambrian than in any other geological period. This is largely because burrowing activity was much more limited back then. As bioturbation became more widespread throughout the Cambrian, environments that could preserve soft-bodied organisms grew increasingly rare. The fossil record of animals from before the Cambrian is sparse and unclear, as noted with the Ediacaran biota.
-
Read this chapter
The Burgess Shale biota looks like what you'd expect from middle Cambrian rock layers. Even though hard-part-bearing creatures make up only about 14 percent of what's found there, that same small percentage shows up in other sites from the same time period. So there’s no reason to think the soft-bodied animals are especially rare or strange. Many of them show up in other exceptional fossil sites too, ones that are different ages and locations.
The Burgess Shale biota shows a wide variety of ancient sea creatures, but most weren’t swimming freely through the water. Instead, the majority were bottom dwellers—some moving around on the seafloor, others stuck in place. About two-thirds of the organisms fed by eating organic matter buried in the mud, while nearly a third filtered tiny particles from the water above. Less than ten percent were predators or scavengers, yet because these creatures were larger, their total biomass was evenly split among all feeding types—filter feeders, deposit feeders, predators, and scavengers alike.
Many of the creatures found in the Burgess Shale belong to evolutionary lineages that lead to today’s animal groups, even though some of the animals are more closely related to modern species than others. These fossils show us early forms of life from the Cambrian period, and while many represent ancient stem group members, certain phyla include both stem and crown group specimens. This means we’re looking at both distant relatives and direct ancestors of the creatures alive today. The Burgess Shale offers a unique glimpse into that time, revealing soft-bodied organisms that otherwise wouldn’t have been preserved.
-
Read this chapter
The Burgess Shale fossils are found embedded in black rock as thin layers of carbon, a preservation method that presents challenges for photography. Even so, researchers have developed ways to capture better images using different techniques. Among these are backscatter SEM, elemental mapping, and camera lucida drawing, each offering unique advantages for studying the delicate structures.
After researchers have gathered their images, they must carefully consider how decay and taphonomy affected the fossils before attempting to reconstruct their anatomy accurately. By examining the combination of shared characteristics, scientists can determine the taxonomic relationships of the specimens.
-
Read this chapter
Overview
Opabinia regalis is an ancient creature from the Burgess Shale in British Columbia, dating back 505 million years. It was a small, soft-bodied animal about seven centimeters long, with a segmented body and flaps along its sides, ending in a fan-shaped tail. Its head held five eyes, a backward-facing mouth, and a clawed proboscis that likely helped it gather food from the seafloor. Only around twenty good specimens have been found, and fewer than two dozen are known from the Greater Phyllopod bed, making up less than 0.1% of the community there. When first studied in 1975, its unusual features led scientists to think it didn't belong to any known group, possibly related to early ancestors of arthropods and annelids. Later research, especially from the late 1990s onward, supported its placement as a basal arthropod, closely linked with radiodonts like Anomalocaris and gilled lobopodians such as Kerygmachela and Pambdelurion. At the time, Opabinia was seen as evidence for the "explosive" origin of complex life during the Cambrian period, but later discoveries of similar animals and the idea of stem groups helped explain this rapid evolution without needing unique processes.
History of discovery
In 1911, Charles Doolittle Walcott discovered nine nearly complete fossils of Opabinia regalis in the Burgess Shale, along with a few specimens he classified as Opabinia ? media, which he described in 1912. The name comes from Opabin Pass, located between Mount Hungabee and Mount Biddle, near Lake O’Hara in British Columbia. Nearly fifty years later, in 1966–1967, Harry B. Whittington found another well-preserved specimen and, in 1975, published a thorough analysis based on detailed dissection and photographs taken from multiple angles. His study did not include Opabinia ? media, since Walcott’s specimens of that form could not be identified. In the 1960s, Russian paleontologists described fossils from Siberia and named them Opabinia norilica, but Whittington judged them too poorly preserved to confirm their placement in the genus Opabinia.
Occurrence
All known Opabinia fossils have been found in one specific layer of rock called the Phyllopod bed, located within the Burgess Shale of British Columbia. In 1997, Briggs and Nedin reported on a specimen from Emu Bay Shale in South Australia that was far better preserved than earlier finds. They concluded this creature, named Myoscolex, was closely related to Opabinia. However, this interpretation was later disputed by Dzik, who instead suggested Myoscolex was not a relative of Opabinia but rather an unusual annelid worm, more similar in characteristics to Pikaia.
-
Read this chapter
Overview
Anomalocaris is an extinct genus of marine arthropod known from the Burgess Shale and other Cambrian deposits, with the type species A. canadensis found in British Columbia and A. daleyae in Australia’s Emu Bay Shale. The name means “unlike other shrimp,” and it was first described in 1892 based only on frontal appendages mistaken for a shrimp’s body. It wasn’t until the late 20th century that complete specimens were identified, revealing its large eyes, swimming flaps, and grasping appendages. Estimated up to about 38 centimeters long, Anomalocaris was among the largest Cambrian animals and likely one of the first apex predators, though other early predators have since been found in older rocks. It is the type genus of Anomalocarididae, a family that once included all radiodonts but now only closely related taxa.
History of research
Anomalocaris was first found in 1886 by Richard G. McConnell on Mount Stephen in British Columbia, along with trilobites and two unknown specimens. Henri-Marc Ami collected more in August 1891, and Joseph Frederick Whiteaves described them in 1892 as the abdomen of a phyllocarid crustacean, naming it Anomalocaris canadensis. For decades, scientists misidentified parts of this creature, including a mouthpiece mistaken for a jellyfish and appendages thought to belong to other animals. In 1928, Kai Henriksen proposed that Tuzoia was the front half of Anomalocaris, an idea later supported by artists like Elie Cheverlange and Charles R. Knight. The true nature of Anomalocaris wasn't understood until 1966, when Harry B. Whittington and his team at the Geological Survey of Canada began a major revision. Simon Conway Morris identified Laggania as a composite fossil in 1978, while Derek Briggs realized in 1979 that Anomalocaris appendages were legs, not abdomens. Whittington eventually linked the mouthpart Peytoia with frontal appendages, showing they belonged to the same creature. By the late 1980s, researchers realized these fossils represented a single group of large arthropods now known as radiodonts or anomalocaridids. In 2011, compound eyes found in Australia confirmed Anomalocaris was indeed an arthropod, and led to the naming of a new species, A. daleyae. As Stephen Jay Gould said, "The story of Anomalocaris is a tale of humor, error, struggle, frustration, and more error, culminating in an extraordinary resolution."
Reassigned species
In 2021, two species previously assigned to *Anomalocaris*—*A. saron* and *A. magnabasis*—were moved to a new genus called Houcaris, but later analysis showed H. saron actually belongs to the family Amplectobeluidae, while H? magnabasis, thought to be closely related, doesn't form a natural group with other Houcaris species. Also in 2021, A. pennsylvanica was reassigned to Lenisicaris. The following year, a specimen previously treated as an unnamed Anomalocaris or a whole-body A. saron got its own genus, Innovatiocaris. In 2023, A. kunmingensis was moved to Guanshancaris, also in the Amplectobeluidae family. Multiple studies suggested that A. briggsi was never a true Anomalocaris and was reassigned to Echidnacaris in 2023.
-
Read this chapter
Overview
Hallucigenia is a genus of ancient creature known from Cambrian-era fossils found in Burgess Shale-type deposits in Canada and China, as well as from isolated spines scattered across the globe. The name itself reflects how strange this animal looked when first studied; its type species, H. sparsa, was initially reconstructed upside down and backwards. These creatures belong to a group called lobopodians, which are part of a larger collection of early animals known as panarthropods, from which modern velvet worms, water bears, and arthropods eventually evolved.
History of discovery and naming
Hallucigenia sparsa was first described by Charles Walcott in 1911 as a polychaete worm, but Simon Conway Morris reinterpreted it in 1977, naming it Hallucigenia for its "bizarre and dream-like appearance." He proposed the animal walked on its spines, with legs interpreted as tentacles, and suggested a mouth inside those tentacles. An alternative idea saw it as an appendage of a larger creature, like Anomalocaris had been earlier. In 1991, Lars Ramskold and Hou Xianguang reinterpreted Hallucigenia as a lobopodian, a worm-like animal related to velvet worms, and inverted its structure, with tentacles as legs and spines as protection. They also argued the blob-like "head" was just a stain from decay. Hallucigenia was first found in the Burgess Shale of British Columbia, and three species are now known, including H. fortis and H. hongmeia from China’s Maotianshan Shales.
Description
Hallucigenia was a small, tubular creature measuring half a centimeter to over five centimeters long, with up to ten pairs of delicate legs ending in claws. Its body had either a smooth surface or uneven segments. Scientists once couldn't tell which end was head or tail, but research in the mid-2010s revealed the longer end was indeed the head, with a mouth and possibly simple eyes. Different species had varying head shapes—elongated in H. sparsa, rounded in H. fortis. In 2002, Desmond Collins suggested that some fossils might represent two sexes: one with a sturdy trunk and globular head, the other thinner and smaller. Hallucigenia's spines were made of nested layers, with tiny triangular scales on H. sparsa and a net-like pattern of holes on H. hongmeia, possibly showing remnants of papillae. Some specimens even had signs of a simple gut.
Read
Free to download, keep and share. For general information only — not professional medical, legal or financial advice. Please consult a qualified professional.