Burgess Shale fossils
The Burgess Shale is an exceptional Middle
Cambrian age (about 540 million
years ago) fossil locality located in
Yoho National Park
in the Rocky
Mountains, near Field, British Columbia, Canada. The locality is special
because of the soft-bodied preservation of a wide diversity of fossil
invertebrate animals. The locality has been intensely studied since its
discovery in 1909 by Charles Walcott, and has been declared a World Heritage
Site. A popular introduction to the Burgess Shale can be found in Steven
J. Gould's book, "Wonderful Life".
The Burgess Shale occurs within the Stephen Formation in
Burgess Pass on the southwest side of the saddle between Mount Wapta and
Mount Field. At the time of deposition, this area was near the equator,
and was the continental margin of North America. A 100m high near-vertical
cliff of limestone occurred at the edge of the shelf. These rocks are known
as the Cathedral Formation, and probably represent the escarpment of a large
submarine slump (i.e. landslide) like those observed off the edge of
carbonate platforms in areas like the Bahamas and Honduras today. The
Burgess Shale was deposited at the base of this cliff, probably in anoxic
conditions, as indicated by the lack of bioturbation (burrows, trackways,
etc.) and the abundance of pyrite (often indicating the presence of H2S).
All the organisms within the Burgess Shale have been transported to this
location, probably by small mudflows that flowed over the edge of the cliff.
This accounts for the variable orientation of the fossils and their
superb preservation.
There are two quarries on Mt. Field/Mt. Wapta -- the lower Walcott Quarry
and the upper Raymond Quarry, the latter a few metres stratigraphically higher
in the Stephen Formation. The faunas in the two quarries are similar, but
with differences in the relative abundance of some of the organisms.
Additional localities with soft-bodied preservation, and further differences
in the fauna have been found on Mt. Stephen and further south.
The illustrations presented here are from photographs taken in the Walcott
and Raymond quarries on September 24, 1995 during a hike guided by
Glen DePaoli of the
Yoho-Burgess Shale Research Foundation. No collecting is permitted in the quarries (or anywhere in
Yoho National Park), and all trips to the quarry must be guided. See
Burgess Shale hike information for details. Although collecting is not an option, there
is plenty of material visible in the quarries, so a macro lens offers the
ability to bring back plenty of photographs. It would
not take much to do better than my results (I do not have great equipment
and I did not even use a tripod).
If you try this yourself, you may want to experiment with wetting the
specimens or orienting them to reflect the sunlight.
These pictures are copyright (c) 1995 by
Andrew MacRae, but are freely
distributable for non-commercial use, provided you give credit.
Please contact me for other
arrangements. I have 24-bit versions of these images, if anyone wants
higher quality.
The Walcott Quarry
Looking northwest -- 328Kbytes. Mount Wapta is the peak visible in the distance. The
escarpment in the Cathedral Formation is visible just a few metres beyond the
edge of the quarry on the left. It occurs at the contact between the white
dolomite and the grey slate/shale of the Stephen Formation. If you have
access to older photographs of the Walcott quarry, it is worth comparing
them to this photo -- the quarry has doubled in size as a result of
continued work in the last few years, mainly by Des Collins at the
Royal Ontario Museum.
Bedding in the Walcott quarry -- 144Kbytes. This photo shows details of the bedding within the Burgess
Shale. The bedding occurs a the scale of a few centimetres, and consists
mostly of graded beds. The yellowish bands are slightly calcareous, while
the darker grey bands are more pelitic (clayey). Both lithologies are
very fine grained (silt size grains or smaller). These lithological
differences are obvious only where the weathering of the face of the quarry
has altered the carbonate-rich beds. The graded beds represent individual
sediment-input events, possibly representing storms that disturbed muddy
sediment high on the escarpment, and caused it to rain down into the deeper
water at this location, burying and smothering organisms carried along
for the ride. The scale bar is 30 centimetres.
Anomalocaris sp.
Anomalocaris frontal appendage/claw -- 152Kbytes. This specimen is only a small part of
Anomalocaris, which was a large (up to 60cm or more) arthropod-like
predator. This claw was used to grasp prey. Walcott quarry.
Marrella
Marrella splendens is a
small "arthropod" somewhat reminiscent of a trilobite, but with several
distinctive features. This illustration also shows the dark "blob" produced by
body contents which were squeezed out of the animal after burial. Marrella is one of the most common fossils in the Burgess Shale, and
was probably the first soft-bodied organism noticed by Walcott. Walcott
quarry.
Marrella splendens. The
Burgess Shale fossils are preserved as highly-compressed films on the surface
of the rock, with some 3-dimensional structure preserved. Some organic
material is preserved on the surface, and this produces a highly reflective
surface. This Marrella example uses reflected light, making the fossil
look light-coloured against the dark shale/slate background. Contrast this
appearance with the previous example, which uses diffuse light. Walcott quarry.
Trilobites
Olenoides serratus. This is the largest of several species of trilobites
found in the Burgess Shale, some of which have been preserved with soft
appendages. This specimen is missing its left free cheek (on the head),
but its skeleton is otherwise complete, and I think one of the posterior
antennae is present, but it is not easily visible in the photograph. The
orange colour is produced by iron oxides. This specimen was wetted for
the photograph. Walcott quarry.
Agnostid trilobites are also common in the quarry, but none appear to have
appendages preserved.
Sponges
Vauxia gracilenta has a
branching morphology, and is very common. Walcott quarry.
Tuzoia
Tuzoia is a "bivalved"
crustacean grossly similar to certain types of modern brine shrimp. This
photo shows only the carapace (the two shells), with their distinctive
reticulate surface ornamentation. In early interpretations, the claw
of Anomalocaris was reconstructed as the tail of Tuzoia!
Tuzoia is particulary common in the Raymond quarry, where this
photo was taken.
Ottoia and Leanchoilia
Ottoia, showing muscle bands and gut. Ottoia is a priapulid worm found
commonly in the Burgess Shale. It was carnivorous, and probably lived in
a burrow like modern priapulids. This specimen has been wetted and oriented
to reflect the light, in order to show a delicate irridescent film which
preserves details of muscle bands, the gut, and even the small hooks at
one end of the worm (on the right -- unfortunately out of focus). Walcott
quarry.
Ottoia and Leanchoilia -- 424Kbytes. This
specimen has two individuals of Ottoia and portions of at least three
individuals of Leanchoilia. The specimen on the right has just the head,
and shows the pair of peculiar appendages found on Leanchoilia. The
specimen on the left (with swimming appendages directed upwards -- I am
not sure if this is upside-down or not :-)) is particularly interesting -- it
has some dark-coloured sand-size (shell?) fragments in a linear arrangement
along the back of the animal. I think these are gut contents.
Cool! This specimen is from the Raymond quarry, where Leanchoilia
is particularly common.
Other Links
Selected References
Aitken, J.D., 1989. Birth, growth, and death of the Middle Cambrian
Cathedral carbonate lithosome, Southern Rocky Mountains. Bulletin of
Canadian Petroleum Geology, v.37, no.3, p.316-333.
Aitken, J.D. and McIlreath, I.A., 1990. Comments and Reply on "The Burgess
Shale: Not in the shadow of the Cathedral Escarpment". Comment: In defense
of the escarpment near the Burgess Shale fossil locality. Geoscience Canada,
v.17, no.2, p.111-116.
Briggs, D.E.G.; Erwin, D.H.; Collier, F.J., 1994 The Fossils of the Burgess
Shale. Smithsonian Institution Press: Washington, p.1-238. ISBN 1-56098-364-7
Butterfield, N.J., 1990a. Organic preservation of non-mineralizing organisms
and the taphonomy of the Burgess Shale. Paleobiology, v.16, no.3, p.272-286.
Butterfield, N.J., 1990b. A reassessment of the enigmatic Burgess Shale
fossil Wiwaxia corrugata (Matthew) and its relationship to the
polychaete Canadia spinosa Walcott. Paleobiology, v.16, no.3, p.287-303.
Jun-yuan Chen, Ramskold, L., Gui-qing Zhou, 1994 (May 27). Evidence for
monophyly and arthropod affinity of Cambrian giant predators. Science,
v.264, p.1304-1308. [Also, "News and Views" on p.1283-1284 by D.E.G. Briggs]
Collins, D.H.; Briggs, D.E.G.; and Conway-Morris, S., 1983. New Burgess Shale
fossil sites reveal Middle Cambrian faunal complex. Science, v.222, p.163-167.
Conway-Morris, S. and Whittington, H.B., 1979. The animals of the Burgess
Shale. Scientific American, v.241, p.122-133.
Conway-Morris, S. and Whittington, H.B., 1985. Fossils of the Burgess Shale.
A national treasure in Yoho National Park, British Columbia. Geological
Survey of Canada, Miscellaneous Reports 43, p.1-31.
Fritz, W.H., 1990. Comments and Reply on "The Burgess Shale: Not in the
shadow of the Cathedral Escarpment". Comment: In defense of the escarpment
near the Burgess Shale fossil locality. Geoscience Canada, v.17, no.2,
p.106-110.
Gould, S.J., 1989. Wonderful Life: The Burgess Shale and the nature
of history. W.W.Norton and Company: New York, p.1-347. ISBN 0-393-02705-8
Hine, A.C.; Locker, S.D.; et al., 1992. Megabreccia shedding from modern,
low-relief carbonate platforms, Nicaraguan Rise. Geological Society of
America Bulletin, v.104, p.928-943.
Ludvigson, R., 1989. The Burgess Shale: Not in the shadow of the Cathedral
Escarpment. Geoscience Canada, v.16, no.2, p.51-59.
Ludvigson, R., 1990. Comments and Reply on "The Burgess
Shale: Not in the shadow of the Cathedral Escarpment". Reply: To comments
by Fritz and Aitken and McIlreath. Geoscience Canada, v.17, no.2, p.116-118.
Piper, D.J.W., 1972. Sediments of the Middle Cambrian Burgess Shale, Canada.
Lethaia, v.5, p.169-175.
Ramskold, L., 1992. The second leg row of Hallucigenia discovered.
Lethaia, v.25, p.221-224.
Ramskold, L. and X.-G. Hou, 1991. New early Cambrian animal and onychophoran
affinities of engimatic metozoans. Nature, v.351, p.225-228.
Andrew MacRae
macrae@geo.ucalgary.ca
Looking northwest -- 328Kbytes. Mount Wapta is the peak visible in the distance. The
escarpment in the Cathedral Formation is visible just a few metres beyond the
edge of the quarry on the left. It occurs at the contact between the white
dolomite and the grey slate/shale of the Stephen Formation. If you have
access to older photographs of the Walcott quarry, it is worth comparing
them to this photo -- the quarry has doubled in size as a result of
continued work in the last few years, mainly by Des Collins at the
Royal Ontario Museum.
Bedding in the Walcott quarry -- 144Kbytes. This photo shows details of the bedding within the Burgess
Shale. The bedding occurs a the scale of a few centimetres, and consists
mostly of graded beds. The yellowish bands are slightly calcareous, while
the darker grey bands are more pelitic (clayey). Both lithologies are
very fine grained (silt size grains or smaller). These lithological
differences are obvious only where the weathering of the face of the quarry
has altered the carbonate-rich beds. The graded beds represent individual
sediment-input events, possibly representing storms that disturbed muddy
sediment high on the escarpment, and caused it to rain down into the deeper
water at this location, burying and smothering organisms carried along
for the ride. The scale bar is 30 centimetres.
Anomalocaris frontal appendage/claw -- 152Kbytes. This specimen is only a small part of
Anomalocaris, which was a large (up to 60cm or more) arthropod-like
predator. This claw was used to grasp prey. Walcott quarry.
Marrella splendens is a
small "arthropod" somewhat reminiscent of a trilobite, but with several
distinctive features. This illustration also shows the dark "blob" produced by
body contents which were squeezed out of the animal after burial. Marrella is one of the most common fossils in the Burgess Shale, and
was probably the first soft-bodied organism noticed by Walcott. Walcott
quarry.
Marrella splendens
Olenoides serratus. This is the largest of several species of trilobites
found in the Burgess Shale, some of which have been preserved with soft
appendages. This specimen is missing its left free cheek (on the head),
but its skeleton is otherwise complete, and I think one of the posterior
antennae is present, but it is not easily visible in the photograph. The
orange colour is produced by iron oxides. This specimen was wetted for
the photograph. Walcott quarry.
Vauxia gracilenta has a
branching morphology, and is very common. Walcott quarry.
Tuzoia is a "bivalved"
crustacean grossly similar to certain types of modern brine shrimp. This
photo shows only the carapace (the two shells), with their distinctive
reticulate surface ornamentation. In early interpretations, the claw
of Anomalocaris was reconstructed as the tail of Tuzoia!
Tuzoia is particulary common in the Raymond quarry, where this
photo was taken.
Ottoia, showing muscle bands and gut. Ottoia is a priapulid worm found
commonly in the Burgess Shale. It was carnivorous, and probably lived in
a burrow like modern priapulids. This specimen has been wetted and oriented
to reflect the light, in order to show a delicate irridescent film which
preserves details of muscle bands, the gut, and even the small hooks at
one end of the worm (on the right -- unfortunately out of focus). Walcott
quarry.
Ottoia and Leanchoilia