The name “Burgess Shale” refers to the fossil ridge-line between Wapta Mountain and Mount Field in Yoho National Park, home to many well-preserved 505 million year old fossils – regarded as one of the world’s most important fossil sites.
This small fossil bed sits high above the Trans-Canada Highway where it cuts across the continental divide on the BC-Alberta border. Measuring less than 200m in length and 30m in height, the Burgess Shale fossils were first brought to the attention of researchers by Charles Walcott in 1909, and was later given the title of a World Heritage Site by UNESCO in 1981.
For more than 80% of the time that Earth has existed, there was minimal life. Following the Earth’s formation 4.5 billion years ago, there was little more than simple blue-green algae for 4 billion years. Then about 541 million years ago, magically, complex life began to develop. Just how it started, where or why are subject to debate. From the fossil record, as the Cambrian period dawned, life suddenly exploded in the sea.
There were few competitors. Every environmental niche was waiting to be exploited. And they quickly were. Within an astonishingly short period of time, the fossil record shows that life went effectively from “zero” to “extremely diverse.
The Burgess Shale fossil beds are a record taken at precisely the right moment when everything was evolving – in the mid-Cambrian, 508 MYa. These early life forms were all soft-bodied. Evolution had not progressed to where hard-bodied species (like clams and snails) were abundant. Instead, worms, jellyfish and other soft fauna were populating the world’s shallow oceans. Soft bodied animals don’t make good fossils and seldom make fossils at all. At the Burgess Shales, a sudden landslide buried many species at the right moment, but also they were buried beneath a layer of very fine anoxic silt, which preserved their most delicate and intricate soft details.
Charles Doolittle Walcott was born in 1850. With no formal scientific training, he apprenticed to a geologist and showed rapid aptitude, making a name for himself initially studying trilobites. When he discovered the Burgess Shale in 1907, he was the head of the US Geological Survey and secretary of the Smithsonian Institution, and friend to financial moguls and presidents but with little time to study fossils. He didn’t relegate the research and didn’t study them until the last years of his life in 1925-27 when he was an old man with old ideas. Even if he had studied them, he would have missed their significance.
In the late 19th century, it was believed that evolutionary life was “cone shaped” – that this huge diversity had evolved in a gradually increasing cone of diversity from a single genus back at the start of the Cambrian. A diagram of this would look like an upside-down cone gradually expanding into a greater variety of species. Walcott thought that everything he found in the fossil record at the Burgess Shale had to be the forerunner of things that came later. He made the mistake of placing the bizarre creatures in existing classifications. As nobody challenged Wolcott’s, all research for the next 50 years was based in this theory.
In 1966, a Cambridge trained academic named Harry Whittington chose the species marrella to study. By the 1970s, he started to believe that the specimens were too different, too anatomically radical to fit into existing boxes and indeed were completely new phyla.
Taxonomy is the science of classification with seven basic levels. At the bottom of the pyramid are about 8.7 million species, many still unknown to science, 1-2 million are animals. Grouped above them come genus, then families, orders, classes, phylum and finally six kingdoms at the very top (animals, plants, fungi, protists, archaebacteria and eubacteria). As you move up the ladder of classification, living things share more and more in common and diversity reduces. There are only 36 animal phyla that encompass 2 million species. Examples include worms and leeches, calms, snails and squid (mollusks), all the vertebrates (chordates) and so on. Phyla include an enormous variety of species all with common traits. There are big differences at the species level (diversity), but little variety at the phylum level (divergence).
Harry Whittington found between 15-20 creatures so different form one another and from existing phyla, that each had to be ranked in its own unique phylum. This turned science’s concepts of evolution upside down. There was no first one species of worm that led to many variations following some lazy evolutionary path through eons of time. Instead, he found that entire phyla had vanished, not just classes, orders, families, genera or species – many creatures found at the Burgess Shale had no descendants. Life did not start as a few, simple creatures that gradually diversified into each and every nook and cranny of our planet, but instead, when life started, it began with an explosion of diversity. The Burgess record showed that Earth has been subject to bursts of diverstiy, followed by cataclysmic die outs and extinctions. Whittington destroyed the Victorian expectation of slow progressive evolution.
“Civilization exists by geological consent, subject to change without notice.” Will Durant.
HOW DO I SEE THE FOSSILS? Since the fossils are a valuable resource and are prone to theft, the site can only be visited accompanied by a guide from the Burgess Shale Geoscience Foundation , located in Field BC.
It is locatedaat an elevation of almost 2,300 metres. Summers are short, and it can snow any day of the year. It is a strenuous 22-kilometre round trip hike with an elevation gain of 830 metres. Physical fitness and foul weather gear are a must. Tours are limited to the summer months of June through September and fill up early – burgessshale.bc.ca
- you can call or book online here. https://www.pc.gc.ca/en/pn-np/bc/kootenay/activ
- tours vary between 7.5 – 11 hours depending on the location, and the cost is between $35 – 70
- hikes are limited to 12 people per group
- a standby policy exists if you are unable to reserve a spot
WHY ARE the FOSSILS SO WELL PRESERVED?
Burgess Shale is famous for the exquisite and uncommon detail in its fossilized soft-bodied organisms. Here’s the science behind the phenomenon.
By preserving delicate structures and tissues unlikely to fossilize under normal circumstances, deposits such as British Columbia’s Burgess Shale provide a startling record of the rapid diversification of early complex life — the so-called Cambrian Explosion. How this occurred has remained enigmatic. Bob Gaines, a geology professor from California’s Pomona College, however, believes he has unlocked the mystery.
Gaines and an international team collected physical and chemical evidence from the Burgess Shale and six similar-aged deposits in China and North America, pegging their extraordinary preservation to severe restriction of microbial activity after burial, due to a lack of oxygen and sulfate normally respired by microbes during decomposition. Furthermore, the mechanism of this restriction appeared to be successive formation of thin carpets of calcium carbonate on the sea floor — mineral barriers that prevented exchange of seawater with fossil-bearing sediments below. With the Burgess Shale itself, formed below the geologic structure known as the Cathedral Escarpment, each critter-entombing mud flow off the scarp was followed by formation of a corresponding carbonate layer. But why, researchers wondered, were Cambrian seas characterized by high calcium carbonate and low oxygen and sulfate levels?
Here, geochemical forensics led researchers to the Great Unconformity, a long-acknowledged global geologic phenomenon in which igneous and metamorphic basement rocks of the Precambrian are overlain by a several-kilometre thick layer of Cambrian sediment. While life flowered in the oceans but had yet to occupy land, these continental rocks underwent unprecedented erosion. Gaines and company hypothesized that the accompanying high rates of chemical weathering would have profoundly impacted ocean chemistry.
As falling rain mixes with atmospheric CO2 it becomes more acidic, leaching elements from rock and transporting them in dissolved form. It’s an important part of the geologic carbon cycle: during chemical weathering, atmospheric CO2 is transformed to bicarbonate (HCO3–) and delivered to the oceans, combining there with calcium (Ca2+) to produce calcium carbonate (CaCO3). Many marine organisms — both micro- and macroscopic — use this compound to produce mineralized shells and skeletons that are subsequently fossilized.
Thus, high concentrations of calcium carbonate may not only have restricted the decomposition of organic matter that led to Burgess Shale-type preservation, but helped spur the Cambrian Explosion by promoting early acquisition of skeletons.
THE LOCALITY TODAY
Aerial view showing Wapta Mountain (left) with the main Burgess Shale sites (WQ: Walcott Quarry; RQ: Raymond Quarry; CQ: Collins Quarry).
The Burgess Shale refers to a fossil-rich locality on Fossil Ridge between Wapta Mountain and Mount Field, just a few kilometres north of the small town of Field, British Columbia. Charles Walcott coined the term to describe various fossiliferous rock layers with soft-bodied preservation that he found in 1909 and 1910 and excavated for several years thereafter. The most important excavations were made within a two-metre-thick section representing a series of layers containing the most exquisitely preserved soft-bodied fossils. This section was named the “Phyllopod bed” by Walcott, in reference to the leaf-like structure of the appendages of certain abundant arthropods, including Waptia.
Left, Marrella splendens, (size = 16 mm) a common fossil from the “Phyllopod bed”; right, the limits of the Phyllopod bed are indicated by a double arrow.
Walcott excavated the Phyllopod bed for several years, leaving what is known today as the Walcott Quarry. This quarry has been expanded by subsequent excavations, in particular by the Geological Survey of Canada and the Royal Ontario Museum.
The Walcott Quarry remains the best-known Burgess Shale site, but is far from the only one. Among the 65,000 Burgess Shale specimens collected by Walcott (mostly from the Phyllopod bed) a few came from rocks about 22 metres higher on the slope. These layers were later excavated by Percy Raymond in 1930 and are now referred to as the Raymond Quarry.
New layers were also excavated below the Walcott Quarry and above the Raymond Quarry by the Royal Ontario Museum in the 1980s. The most important new horizon there – about 40 metres above the Raymond Quarry – is now referred to as the Collins Quarry. Additional soft-bodied fossils can be found in various layers between each of these quarries, but have not yet been collected systematically.
In summary, the different quarries of the Burgess Shale on Fossil Ridge represent various fossil assemblages within a body of shale roughly 100 metres thick, marking a history of fossil deposits covering about 200 000 years of the Cambrian Period.
Fossil Ridge with the various Burgess Shale quarries next to the Cathedral EscarpmentThe Trilobite Beds on nearby Mount Stephen also contain fossils of soft-bodied animals (e.g., Anomalocaris, Wiwaxia) that were discovered in the area in 1886, long before Walcott discovered the original Burgess Shale site on Fossil Ridge. Today, scientists refer to the Trilobite Beds as a Burgess Shale-type locality. This site is of a similar age and within the same geological formation as the Burgess Shale quarries on Fossil Ridge. More importantly, its mode of fossil preservation is also comparable – although it is not part of the original Burgess Shale site on Fossil Ridge proper.
Main Burgess Shale-type deposits in the Canadian Rockies.
In addition to the main quarries on Fossil Ridge and the Trilobite Beds, other locations with Burgess Shale-type fossils have been found in the Canadian Rockies, most within the boundaries of National Parks close to a geological feature called the Cathedral Escarpment. Various sites are known in Yoho National Park, including Mount Field, Mount Stephen (Tulip Beds – S7, Collins Quarry on Mount Stephen), Mount Odaray and Park Mountain. Kootenay National Park contains Burgess Shale-type deposits in the Stanley Glacier and The Monarch areas, while Burgess Shale-type fossils have also been found in Jasper National Park and outside the parks near Cranbrook, British Columbia.
These different fossil assemblages differ in species composition and abundance of specimens, but represent elements of a similar biota.
Different Burgess Shale-type deposits on Mount Stephen. CQ: Collins Quarry, TB: Trilobite Beds, S7: Tulip Beds (S7).
General view of Stanley Glacier in Kootenay National Park. This area has yielded Burgess Shale-type fossils.
THE FOSSILS
The Burgess Shale is famous for its exquisite fossils of soft-bodied organisms. It is exceptional to find complete animals preserved, especially ones that had only soft tissues and no mineralized structures. (Typically it is only the hard parts of organisms – shell or bone – that become fossils.) When this happens, palaeontologists can gain a tremendous amount of ecological and biological information about a particular time in Earth’s history. The Burgess Shale is such a site, providing the best window on animal communities during the end of the Cambrian Explosion.
The Walcott Quarry Community
The best-known Burgess Shale site is the Walcott Quarry on Fossil Ridge. About 150 species of animals, algae, and bacteria from here have been described to date. The mammoth collections available to researchers – about 65,000 specimens at the Smithsonian Institution in Washington D.C., 10,000 at the Geological Survey of Canada in Ottawa, and 150,000 specimens at the Royal Ontario Museum in Toronto – form the basis for detailed studies of individual species. These collections allow researchers to study the overall ecosystem using quantitative statistical methods in ways that are not yet possible for other Burgess Shale-type deposits, which lack sufficient fossils.
Checking bags of fossils at the end of the 2000 Royal Ontario Museum Field Expedition in Field, BC.Most of the fossils from the Walcott Quarry represent organisms that probably lived in comparatively deep waters at the foot of the Cathedral Escarpment. It had been thought the organisms came from shallower waters on top of the Escarpment, but recent research has suggested most of the animals lived and died where they were buried, at the Escarpment’s base.
The Walcott Quarry community is representative of a typical Burgess Shale-type community during the Cambrian. It is estimated that up to 98% of the fossils from this locality are entirely soft-bodied and would stand no chance of being preserved through normal taphonomic processes. The remainder (2%) is represented by animals with parts that were originally mineralized (such as trilobites) and thus can usually fossilize more readily. Trilobites and other “shelly” fossils are found in most typical Cambrian marine deposits around the world. The absence of soft-bodied fossils from those deposits reflects the non-preservation of organisms without hard parts, rather than their absence from the original ecosystem.
Reconstruction of the Burgess Shale community (as seen in the Walcott Quarry). The reconstruction below shows how the community would look if only animals with mineralized parts were present.
General Composition
The composition of the Walcott Quarry community has been extensively studied based on fossil counts made from existing collections. The pie-charts below are derived from a subset of 50,282 specimens collected by the most recent Royal Ontario Museum field expeditions in the Walcott Quarry (the relative abundances of specimens provided in the fossil gallery are based on this number). These represent the relative abundance of specimens and the relative abundance of species within main groups of organisms (or taxa).
The relative abundance of specimens is simply the number of fossils of a particular taxon as a percentage of the total number of fossils collected. The relative abundance of species is the number of species of a particular taxon as a percentage of the total number of species combined. A single taxon might have many species, but be represented by very few specimens. Conversely, one taxon might contain just a few species, but many individual fossil specimens. By comparing the two kinds of pie-charts, palaeoecologists can study patterns of species associations.
The exact affinity of many fossils from the Walcott Quarry is still unknown. However, a large number of species can be linked (as primitive or ancestral forms) to broad groups of organisms that are still known today.
In terms of both number of species and number of specimens, animals make up the majority of the community; a few species of green and red algae, as well as some microbial colonies, are also known. The more important groups by far are the moulting animals with jointed limbs (the arthropods) and the sponges (the poriferans). Most other groups are represented by fewer specimens and species.
In order to understand the ecological structure of the Walcott Quarry community, it is important to determine where and how each kind of organism lived.
In the Walcott Quarry, most species represent benthic forms – animals living in or near the sea bed. Benthic animals can be infaunal (living within the sea-floor sediment), epifaunal (living on the sea-floor surface) or nektobenthic (swimming close to the sea floor).
A small minority of animals did not interact with the sea floor, living entirely in the water column as pelagic (swimming) forms.
Burgess Shale animals can also be categorized based on their mobility. Nektobenthic and nektonic organisms were active swimmers. Planktonic creatures mostly drifted passively rather than actively swimming. Some of the infaunal and epifaunal benthic organisms were sessile (fixed in one place) while others were mobile (able to move around).
A cluster of the sessile benthic sponge Choia ridleyi from the Burgess Shale (size = 7.8 cm).Finally,
Burgess Shale animals can be categorized on the basis of how they obtained their food. Suspension feeders filtered particles of food out of the water. Deposit feeders gathered particles of food that settled on or in the sea floor sediment layer. Carnivorous hunters actively captured and devoured other animals, and scavengers took advantage of any dead bodies they came across. Grazers lived by munching on photosynthetic algae or cyanobacteria that grew in the dim sunlight that penetrated to the base of the Escarpment.
Palaeontologists can recreate the proportions of species in the Burgess ecosystem falling into each of these categories. The overwhelming majority of species (64%) were epifaunal, living on the sea bed (most notably the sponges), followed by the infaunal sediment-dwellers (13%) and the low-level swimming nektobenthics (12%). Swimming nektonic species were the least common (11%).
Food Web
A food web reconstructs the feeding relationships between different organisms in a community.
In the Burgess Shale, the ecosystem ultimately relied on photosynthetic algae and bacteria, which used energy absorbed from sunlight in order to grow. Other organisms fed (directly or indirectly) either on algae and bacteria growing on the sea floor or on planktonic forms that sank from the waters above (see reconstruction of the Burgess Shale community above).
Animals living in or on the sea floor could filter food particles out of the water, scrounge for fragments of food on the muddy bottom, or graze directly on the algal or bacterial mats. Comparatively few animals made a living by active hunting or scavenging, but their impact on the food web would have been great.
The structure of the Burgess Shale ecosystem food web is surprisingly similar to what we see in modern marine communities, although the individual species involved are clearly quite different. This suggests that the basic feeding relationships were quickly established during the Cambrian Explosion and have remained relatively unchanged to the present.
Reconstruction of the Burgess Shale food web. Spheres represent taxa. The taxa at the bottom of this network are primary producers and the taxa at the top are predators.
Palaeontologists can use a variety of clues to reconstruct the diets of Burgess Shale animals. Occasionally feces, or even gut contents, are fossilized, the latter providing a direct record of an animal’s final meal.
Gut contents in Burgess Shale animals. Top, detail of the gut of Ottoia prolifica (maximum width of the worm = 1.2 cm) showing shelly, conic elements of Haplophrentis carinatus. Below, a specimen of the arthropod Sidneyia inexpectans (length = 8 cm), showing fragments of small trilobites in the gut suggesting a predatory (or scavenging) lifestyle (see close up of the gut on the right).
Usually, dietary habits have to be inferred from the ecological niche an animal occupied and from specialized body structures used in feeding. Anomalocaris, for example, had large eyes, grasping limbs, swimming lobes, and tooth-like mouthparts. Together with its large size, these features strongly suggest Anomalocaris was a predator.
Front part of Anomalocaris canadensis, a putative predator from the Burgess Shale (size = 16.6 cm).
Evolutionary Significance
The nature of the animals in the Burgess Shale biota, and their evolutionary significance, have been topics of particular interest since the discovery of the first fossils over a hundred years ago. Interpretations have changed over time, but it is clear these fossils are vital to understand how life shaped itself during the Cambrian Explosion. Interest in the evolutionary significance of the biota was revived by the discovery of other Burgess Shale-type deposits in various parts of the world and detailed re-examination of fossils from the Burgess Shale itself.
Charles Walcott originally considered the fossils of the Burgess Shale to belong to extinct categories within animal groups that are still alive today. However, many Burgess Shale animals look bizarre to modern eyes, and subsequent detailed descriptions suggested they could not be quite so easily accommodated within the definitions based on modern groups.
This was evidence for some, most notably Stephen Jay Gould that the Cambrian Explosion was a period of experimentation, with far more body plans in the Cambrian than today (thus representing greater evolutionary disparity). By chance, only some of these body plans survived to represent the phyla that we know today. If Gould was right, and the strange creatures of the Burgess Shale – referred to by Gould as “weird wonders”- truly represent lost phyla, the range of evolutionary innovations during the Cambrian Explosion would be far greater than previously thought.
More recent observations suggest the number of body plans in the Cambrian was probably no greater than in modern environments. Many of Gould’s “weird wonders” have now been re-accommodated within living animal phyla, albeit at some distance from modern groups within those phyla.
A number of bizarre forms remain difficult to classify. Part of the problem is that some of these are still poorly known – i.e., there is not enough well-preserved fossil material to describe the anatomy of the animals with certainty. Other, better-known fossils display only some of the traits associated with known groups, or possess a combination of traits that remains at odds with what we know for any living or extinct organisms. These are now interpreted as primitive animals which evolved along the lineages of established phyla or groups of phyla.
Some of the most recent changes in interpretation are based on new fossil material that provides many more specimens and traits to study. A number of previously “unclassifiable” fossils (for example Odontogriphus and Nectocaris) had been known from single, poorly-preserved specimens. Hundreds of new specimens are helping to explain the nature and evolutionary significance of these animals. The use of computers (i.e., parsimony analysis) to classify organisms, and the use of the stem group and crown-group concepts, also contributed to this change. Evolutionary relationships are identified by recognizing traits that different organisms share by inheritance.
Changing reconstructions of two “weird wonders” from the Burgess Shale, Odontogriphus (left, fossil length = 8 cm) and Nectocaris (right, fossil length = 4 cm, excluding tentacles), both now considered to belong to stem-groups within the molluscs.
Ecological Significance
The Burgess Shale provides direct fossil evidence of the emergence of a number of animal groups in marine environments that had been mostly unoccupied before the Cambrian Explosion. This evolutionary radiation happened at the same time as a sudden increase in ecosystem complexity, marked by the appearance of new types of species interactions driven by ecological innovations – such as novel feeding strategies and modes of locomotion. At the end of the Cambrian Explosion, the fundamental ecological structures of modern marine ecosystems were firmly in place.
Among the various feeding strategies that are known in the Burgess Shale – predation (including scavenging), herbivory, and detritus and suspension feeding – predation is regarded as one of the most significant. Predators play an important role in structuring modern communities by controlling prey populations. Predation was likely an important driving force for the diversification seen in the Cambrian Explosion, as animals evolved new strategies to eat and avoid being eaten.
A number of possible Burgess Shale predators have been identified based on direct morphological characters (the mouth parts of Anomalocaris) and on gut contents. Indirect evidence such as potential bite marks and defensive features (such as spines in Hallucigenia or plate-like elements in Wiwaxia) have also been identified. The development of mineralized skeletons at the start of the Cambrian Explosion is also thought to have been a response to increased pressure from predators.
The lobopod animal Hallucigenia (top, size = 2 cm) and the armoured slug-like animal Wiwaxia (bottom, size = 3 cm). Hallucigenia possesses rows of spines on the back of its body while Wiwaxia developed a body armour of small, overlapping scales and blades. Both traits may have evolved as a defensive mechanism against predators.
Fossils from the Walcott Quarry
Some groups have more species and specimens than others. Below is a detailed breakdown of the species from the Walcott Quarry belonging to these main groups. Species with mineralized parts are emphasized in bold – these are the only ones that could have been fossilized under normal conditions, rather than the special conditions leading to Burgess Shale-type preservation. Details and illustrations of most species listed below are illustrated in the Fossil Gallery.
Algae and bacteria
Algae: This group consists of eukaryotic organisms that usually depend on light as their source of energy. In the Walcott Quarry, both green and red algae have been identified, but many species are probably just preservational or morphological variants of a small number of taxa. Most have yet to be studied in any detail.
12 species: Bosworthia gyges, Bosworthia simulans, Dalyia nitens, Dalyia racemata, Dictyophycus gracilis, Margaretia dorus, Sphaerocodium? cambria, Sphaerocodium? praecursor, Wahpia mimica, Wahpia virgata, Waputikia ramosa, Yuknessia simplex.
Margaretia dorus..
Cyanobacteria: This is a group of prokaryotic microorganisms that depend on light for their source of energy. In the Walcott Quarry, there are at least two different species, one forming tufts (Marpolia), the other forming sheet-like structures at the sea bottom (Morania). Walcott briefly described 8 species of Morania, but as is the case with the algae, many of these are probably just preservational variants and have yet to be restudied in detail.
9 species: Marpolia spissa, Morania confluens, Morania elongata, Morania fragmenta, Morania? frondosa, Morania? globosa, Morania parasitica, Morania? reticulata.
Marpolia spissa.
Animals
Annelida: These elongated, many-segmented animals are represented today by the common terrestrial earthworms and leeches, marine-swimming animals (“polychaetes”) including bristle worms, and several smaller groups. The annelid body is covered by a thin flexible cuticle that is not moulted during growth. Each major group has a characteristic segment construction; in annelid bristle worms, segments bear a prominent pair of lateral flap-like structures called parapodia that are mainly used for locomotion. Various numbers of “bristles” (chaetae) are organized in bundles along the parapodia and help with movement. Many fossil annelids from the Burgess Shale show exquisite preservation of parapodia and bristles. Based on the morphology of these elements, some were interpreted as active swimmers (e.g., Canadia), while others probably lived in or on the mud at the bottom of the sea (e.g., Peronochaeta). These Burgess Shale taxa are not currently thought to belong to the modern forms of bristle worms, and have most recently been reinterpreted as stem group annelids.
5 species: Burgessochaeta setigera, Canadia spinosa, Insolicorypha psygma, Peronochaeta dubia, Stephenoscolex argutus.
Canadia spinosa.
Arthropoda: Today, arthropods are the most diverse of all animal groups, a distinction they have probably held since the Cambrian. Characterized by a segmented body, a rigid external cuticular covering (the exoskeleton), and jointed limbs, this group is represented by the modern spiders, shrimps, insects, and millipedes. It also includes the now-extinct trilobites. Arthropods grow by shedding their exoskeleton (a process called moulting), which can harden or even mineralize in some cases (such as in crabs and trilobites). The Burgess Shale contains a wide range of fossil arthropod morphologies, many representing various stem groups of particular subgroups within the arthropods. Others, for example Opabinia and Anomalocaris, are considered more primitive and cannot be considered true arthropods (Euarthropoda). These species might represent early stem groups along the lineage leading to true arthropods. Fossil arthropods found in the Walcott Quarry show adaptation to a wide range of habitats and ecologies; they include carnivores and deposit feeders, swimmers, walkers, and probably burrowers.
53 species: Alalcomenaeus cambricus, Anomalocaris canadensis, Branchiocaris pretiosa, Burgessia bella, Canadaspis perfecta, Caryosyntrips serratus, Chancia palliseri, Ehmaniella burgessensis, Ehmaniella waptaensis, Elrathia permulta, Elrathina cordillerae, Emeraldella brocki, Habelia brevicauda, Habelia optata, Hanburia gloriosa, Helmetia expansa, Houghtonites gracilis, Hurdia victoria, Isoxys acutangulus, Isoxys longissimus, Kootenia burgessensis, Laggania cambrica, Leanchoilia persephone, Leanchoilia protogonia, Leanchoilia superlata, Liangshanella burgessensis, Marrella splendens, Molaria spinifera, Mollisonia rara, Mollisonia symmetrica, Naraoia compacta, Naraoia spinifer, Odaraia alata, Olenoides serratus, Opabinia regalis, Oryctocephalus burgessensis, Oryctocephalus matthewi, Pagetia bootes, Perspicaris dictynna, Perspicaris recondita, Plenocaris plena, Priscansermarinus barnetti, Ptychagnostus praecurrens, Sarotrocercus oblita, Sidneyia inexpectans, Skania fragilis, Tegopelte gigas, Thelxiope palaeothallasia, Tuzoia retifera, Tuzoia burgessensis, Waptia fieldensis, Worthenenella crepidulus, Yohoia tenuis.
Naraoia compacta.
Brachiopoda: Brachiopods are bottom-dwelling (benthic) marine suspension-feeding animals enclosed in a two-part shell. Most forms attach to a surface – the sea floor or other organisms – via a flexible cylindrical organ called a pedicle. Brachiopods first appeared in the Early Cambrian and were very important constituents of the sea-floor ecosystem throughout the Palaeozoic Era. Although some species still survive, the phylum was hit hard by the Late Permian mass extinction (about 250 million years ago). Most brachiopod shells are well-mineralized, and they consequently have a good fossil record. In the Burgess Shale, some stem group forms are preserved with soft-tissues, including their pedicles, setae (long, needle-like structures) and traces of the internal body organs. One Burgess Shale species (Acanthrotretella spinosa) has non-mineralized valves.
7 species: Acanthrotretella spinosa, Acrothyra gregaria, Diraphora bellicostata, Lingulella waptaensis, Micromitra burgessensis, Nisusia burgessensis, Paterina zenobia.
Micromitra burgessensis.
Chordata: Chordates are a group of animals united by the possession of a notochord and a dorsal nerve cord. In addition to the vertebrates (including humans) with their defining backbone and spinal column, chordate subgroups also include a number of minor taxa. Some chordates are attached to a surface – usually the sea floor – for at least part of their life, but most are mobile organisms. Pikaia gracilens from the Burgess Shale probably represents a very primitive (stem-group) form of chordates. Well-preserved fossils indicate it was an active swimmer. A second Burgess Shale stem-group chordate species is known only from two poorly preserved specimens.
2 species: Metaspriggina walcotti, Pikaia gracilens.
Pikaia gracilens.
Cnidaria: These radially-symmetrical animals have a simple body organization and two basic life modes: the swimming, jellyfish-like medusae, and sessile, polyp-like forms. The group includes modern corals and jellyfish. Various tubular fossils from the Walcott Quarry have been attributed to primitive sessile cnidarians, but until better details of their soft-tissue structures are found, such conclusions will remain provisional. Mackenzia is the only form not to have inhabited a tube; this soft-bodied, seabed-dwelling animal has been compared to living sea anemones.
4 species: Cambrorhytium fragilis, Cambrorhytium major, Mackenzia costalis, Tubullela flagellum.
Cambrorhytium fragilis.
Ctenophora: Ctenophores are radially organized animals with a simple body plan superficially resembling that of cnidarian jellyfish. Living representatives of this group are termed “comb jellies” because they have 8 comb-like rows of cilia (cilia are small elongated extensions of cells which can reach up to 2 millimetres in modern ctenophores) to propel them through the water. The fossil species from the Walcott Quarry have more comb rows than modern ctenophores and probably represent very primitive (stem-group) forms.
2 species: Ctenorhabdotus capulus, Fasciculus vesanus.
Ctenorhabdotus capulus.
Echinodermata: The echinoderms form a distinctive group of mostly benthic animals (living in, on or just above the sea floor). They are characterized by a multi-element mineralized skeleton with a peculiar microstructure (stereom). Almost all adult echinoderms exhibit fivefold (pentameral) symmetry (i.e., the body is organized into five radially similar sections). Living subgroups include the sea stars, sea urchins, and sea lilies (crinoids). Only stem-group echinoderms are found in the Burgess Shale, where they are relatively rare.
4 species: Echmatocrinus brachiatus, Gogia stephenensis, Walcottidiscus typicalis, Lyracystis reesei.
Echmatocrinus brachiatus.
Hemichordata: Hemichordates are a group of elongate animals with bodies composed of three main parts: a proboscis (mouthpart), collar, and trunk. Two major sub-groups are known, the worm-like enteropneusts and the diminutive and colonial pterobranchs. Primitive members of both groups are probably represented in the Walcott Quarry, but these species have not yet been described in detail.
3 species: Chaunograptus scandens, Oesia disjuncta, “Ottoia tenuis”.
Chaunograptus scandens.
Mollusca: A large group of animals, today characterized by a cavity-forming mantle. Modern molluscs include snails, squids, and clams. Fossils of several swimming and bottom-dwelling soft-bodied forms are known in the Walcott Quarry – these are considered to be basal stem-groups molluscs. Scenella is the only form with a mineralized shell.
5 species: Nectocaris pteryx, Odontogriphus omalus, Orthrozanclus reburrus, Scenella amii, Wiwaxia corrugata.
Odontogriphus omalus.
Onychophora (Lobopoda): Worm-like animals with unspecialized pairs of non-jointed limbs, the modern onychophorans (velvet worms) are all terrestrial. The two fossil species known in the Walcott Quarry are not true onychophorans, but probably belong within the lobopods, a stem-group of organisms more closely related to arthropods.
2 species: Aysheaia pedunculata, Hallucigenia sparsa.
Aysheaia pedunculata.Porifera: The Porifera (or sponges) are among the most primitive animals; their simple body is not organized into true tissues. Sponges are mostly bottom-dwelling suspension feeders, and many forms possess a supporting mesh-work of fine needle-like spicules composed of various minerals. Several different types of fossil sponges are found in the Walcott Quarry, representing all major modern groups as well as potential stem-groups. Many of these have a low preservation potential, but isolated mineralized spicules of some taxa (in bold) are known in other Cambrian fossil deposits that do not preserve soft-tissues.
34 species: Capsospongia undulata, Choia carteri, Choia ridleyi, Crumillospongia biporosa, Crumillospongia frondosa, Diagoniella cyathiformis, Diagoniella hindei, Eiffelia globosa, Falospongia falata, Halicondrites elissa, Hamptonia bowerbanki, Hazelia conferta, Hazelia crateria, Hazelia delicatula, Hazelia dignata, Hazelia lobata, Hazelia luteria, Hazelia nodulifera, Hazelia obscura, Hazelia palmata, Leptomitus lineatus, Leptomitus undulatus, Moleculospina mammilata, Petaloptyon danei, Pirania muricata, Protospongia hicksi, Takakkawia lineata, Vauxia bellula, Vauxia densa, Vauxia irregulara, Vauxia gracilenta, Vauxia venata, Wapkia elongata, Wapkia grandis.
Choia ridleyi.
Priapulida: Predatory marine worms with a large, hook-lined anterior feeding organ called a proboscis, priapulids are relatively rare today. Priapulid-like animals were abundant in Cambrian communities; species found in the Walcott Quarry, including tube-dwelling forms, are probably stem-group priapulids.
5 species: Ancalagon minor, Fieldia lanceolata, Louisella pedunculata, Ottoia prolifica, Selkirkia columbia.
Selkirkia columbia.
Other known animals of uncertain affinities:
10 species: Allonnia sp., Amiskwia sagittiformis, Chancelloria eros, Dinomischus sagittiformis, Eldonia ludwigi, Haplophrentis carinatus, Herpetogaster collinsi, Pollingeria grandis, Portalia mira, Thaumaptilon walcotti.
Portalia mira.