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.
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.
The 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.
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.
In 1990, noted palaeontologist Stephen Jay Gould spoke at the Royal Ontario Museum about the fossils of the Burgess Shale. While many of Gould’s interpretations have been challenged, his talk provides a snapshot of how the organisms were viewed then. (6:20)
So this is Marrella. I should say that arthropods are classified primarily by numbers of segments and patterns in their various body parts.
And here’s Marrella, it’s an arthropod that doesn’t fit into any group. It has these two sets of spines… there it is. It doesn’t have any allegiance.
So Whittington was puzzled when he first published on Marrella in 1971 but he went on and the next creature he studied was Yohoia.
Looked like a shrimp, had been called one by Walcott, and again, as Whittington studied it with care, it just didn’t fit into any modern group. It looks like a shrimp superficially, but when you start counting the segments you don’t have anything like the crustacean body plan.
For instance, up in the head you have this unique set of frontal appendages which have no homologue anywhere else in the arthropods. Whittington ended up calling them simply “the great appendages” because he didn’t know what to do with them.
This is Odaraia, a creature that swims on its back and has a tail fluke that looks more like a whale than an arthropod, but again, not allied to anything.
Looked vaguely like a swimming crustacean, but isn’t when you look at the segments and their patterns of the tail.
This is Sidneyia, which was described by Walcott as a chelicerate, that is a member of the horseshoe crab, eventually the spider-scorpion group. And in some superficial sense that’s what it looks like. But in detail it isn’t.
All chelicerates have six pairs of appendages on their head. Sidneyia has one pair. It’s not like anything… just these antennae… it’s not like anything else… it is just is what it is.
This is Habelia, an odd creature…
… with tubercules all over its body.
This is Leanchoilia, my personal favourite for elegance, but not among the survivors.
Again, these odd great appendages, as Whittington calls them, with their whiplash endings.
This is Aysheaia.
Now, this creature is probably an onychophore, that is it is a member of a modern group symbolized by the genus with the wonderful name Peripatus, which is a not very well known group, but it’s thought to be possibly intermediary between annelids and arthropods and may be the ancestor of the insect group. So here we may have a creature that is truly related to one of the surviving groups of arthropods.
And here is a form that Des Collins found and initially gave a field name, following paleontological tradition…
… he called it “Santa Claws”. And eventually named it Sanctacaris, which means much the same thing. Now again, does it look any different than the ones I just showed you?
Would you have picked out this creature for success? Could you have predicted that this, by virtue of superiority would go on? Yet it looks as though Sanctacaris really is a chelicerate.
There are six pairs of appendages in the right place on the head so this animal may be at least a cousin to one of the successful lineages. Again, would you have known? Could anyone have known?
This is Opabinia. Opabinia, I think, should stand as one of the great moments in the history of human knowledge.
Because Opabinia, which was described as an arthropod, a shrimp-like creature, by Walcott, who shoehorned it into modern groups as he always did. Opabinia was the first creature re-studied by Whittington that broke the conceptual dam, so to speak, and gave insights into this new world.
Because Whittington began his studies in the early 1970s on Opabinia thinking it would be an arthropod. He realizes, as Walcott did not, that there was some three-dimensionality in these creatures, that they were not just films on the rock.
That he could therefore dissect through and find structures underneath. So he said “Now I can resolve this, I’ll dissect through the body and find the appendages underneath which will prove its arthropod nature. He dissected through and he found nothing. There are no appendages.
And as he reconstructed Opabinia, he came to understand it is not an arthropod, it is some bizarre creature of its own unique anatomy. And in publishing a monograph on Opabinia in 1975 I think you have the breakthrough point in the new interpretation of the Burgess Shale.
Here is Marianne’s picture of Opabinia, a bizarre creature with five-count them, five-eyes, this vacuum-cleaner like nozzle with a food-collecting device in front, this bellows-like apparatus behind, followed by a tail. I don’t know what it is. It’s just weird.
This is Nectocaris, a peculiar creature that looks like a chordate behind, combined with a fin ray…
… and more like an octopod in the front. Who knows?
This is Dinomischus, a peculiar, stalked, stemmed creature…
… with no known affinity to anything else.
This is Odontogriphus, literally meaning “the toothed mystery” a good name.
A flat, gelatinous, annulated creature with a row of tooth-like structures surrounding a mouth and a pair of sensory palps.
Walcott described three separate genera which he allocated, as was his wont, according to the shoehorn, into three conventional groups.
This animal he called a jellyfish and called Peytoia.
This creature he called a sea cucumber and called Laggania.
And this, which had been described before and looks like the body of an arthropod, he called (it had been named before) Anomalocaris, meaning “the odd shrimp”. Well I think that you’ve guessed it already.
It turns out that all three go together. They form a single creature which is one of the weirdest of all the odd animals of the Burgess.
It’s also the largest Cambrian organism. Some specimens are almost a metre in length.
The so-called jellyfish is the mouth of this creature, working on a circular, nutcracker principle rather than the jaw of vertebrates principle.
The Anomalocaris itself turns out to be one of a pair of feeding appendages, and the so-called sea cucumber is the body of the whole animal.