The Burgess Shale: Insights into Middle Cambrian Life

6.5. The Burgess Shale - A Window into the Middle Cambrian Biosphere The Burgess Shale records a period just following the Cambrian explosion. This time would see the emergence of some new forms but not to the same dramatic degree or rapidity of the Early Cambrian. In effect, life was starting to evolve within the body plan "rules." Even so, this time sees the evolution of articulate brachiopods (brachiopods with calcareous shells with valves fastened together by teeth and sockets) and an important early chordate, the conodonts ( not to be confused with the earlier conodontomorphs). Figure - The Burgess Shale Quarry, Yoho National Park, B.C. Photo from the International Subcommission On Cambrian Stratigraphy (http://www.palaeontologie.uni-wuerzburg.de/) . The Burgess Shale outcrops in a quarry in Yoho National Park in B.C. (http://www.pc.gc.ca/pn- np/bc/yoho/natcul/natcul15_E.asp) , just next to the border with Alberta. Land Acknowledgement The Burgess Shale site is located within the traditional territory of the Ktunaxa people which extends from south-eastern BC to western Alberta and into Idaho, USA. The Ktunaxa people are also known at the Kootenay, Kootenai, and Kutenai. Interesting fact: Yawunik kootenayi , a species of early arthropod found within the Burgess Shale, is named after the Ktunaxa Nation, hence the inclusion of “kootenayi”. “Yawunik” is a legendary sea monster central to Ktunaxa’s creation story, which describes the origin of humanity. You can read more about Yawunik kootenayi here: https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12161 (https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12161) and you can read about the Ktunaxa story on which the name was based here: https://www.ktunaxa.org/who-we-are/creation-

story/ (https://www.ktunaxa.org/who-we-are/creation-story/) . These extra resources are just for interest and will not be examined. Discovery of the Fossils The fossils here were discovered by Charles Walcott in 1909 who collected more than 65,000 specimens from the quarry between 1911 and 1914. Walcott's specimens were deposited at the Smithsonian Institute in Washington, D.C. but further collections have been housed at the Royal Ontario Museum (http://www.rom.on.ca/) . It wasn't until the late 1960s that the Burgess Shale fauna was recognized for its significant diversity and uniqueness. This special status was due to the work by Harry Whittington, Derek Briggs, and Simon Conway Morris of the Cambridge project. The Burgess Shale is an important fossil find due to the preservation of creatures that lacked significant hard parts. Such softer-bodied creatures very rarely survive the processes of fossilization. Until recently, it was thought that most of the Burgess Shale organisms lived in shallow warm waters on top of a large submarine cliff called the Cathedral Escarpment. It was believed that they were periodically transported off the escarpment by underwater avalanches, called turbidity flows, that were triggered by earthquakes. However, more recent work has suggested most of the Burgess Shale organisms actually lived at the base of the Escarpment rather than on the top. Evidence indicates that this part of B.C. (and all the other areas where Burgess Shale fossils have been found) was close to the equator at this time.

Figure - "Cambrian Sea Mural" at the Field Museum in Chicago. Reconstruction of marine life in the Burgess Shale Reef, 510 million years ago. Anomalocaris sails over a Pikaia and a trilobite. Illustration by Karen Carr (http://www.karencarr.com/) copyright by the Field Museum (http://www.fieldmuseum.org/) . Current Scenario for How This Deposit Happened The Cathedral Escarpment was about 200 meters high. Usually the environment at its base was calm and safe with many animals living either on or in the sea floor or swimming just above it. Fossilized algae suggest sunlight probably penetrated right to the sea floor. Occasionally, there were mudflows which buried the organisms living there in a disorganized jumble. Gradually, over several hundered thousand years, these successive mud flows and other sediments filled in the basin. Figure - A reconstruction of the Burgess Shale site and its surroundings as it were 510 Ma. Image from the Smithsonian National Museum of Natural History (http://paleobiology.si.edu/burgess/) . Several conditions may have contributed to slowing decay and protecting the organisms trapped in the sediment from predators, thereby enhancing the preservation of their soft body parts: 1. The water was relatively under-saturated in oxygen. 2. A layer of sediment rapidly covered the animals. 3. Clay minerals in the surrounding sediment inhibited bacterial activity. Finally, the carbonate rock that made up the escarpment may have protected the animals from the full force of later metamorphic processes. Course Recording of Your Instructor (Louise Longridge) talking about Hiking to the Burgess Shale In this Course Recording I give insights into what it was like to hike up and visit the famous Walcott Quarry of the Burgess Shale, where I went as part of a fieldtrip organized for the Canadian Paleontology Conference in 2003.

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Now that you have watched this recording, you should proceed to learn more about the amazing animals found at this quarry and the other quarries that form part of the Burgess Shale! These hypothesized circumstances resulted in the preservation of a complete record of the creatures that lived on top of that algal reef in the warm shallow Cambrian ocean. This included the soft-bodied forms that are not usually preserved. Of the 140 species recovered, around 60-70% are forms that are not usually preserved in the fossil record. This allows us to appreciate that the fossil record is generally biased to those creatures that possess significant external or internal hard parts. Significant Specimens in the Burgess Shale Some of the significant specimens from the Burgess Shale are described below. See more images and several wonderful animations at the Burgess Shale website hosted by the Royal Ontario Museum. Start here (http://burgess-shale.rom.on.ca/en/sea-odyssey/) , or explore further by going to the home page (http://burgess-shale.rom.on.ca/) of that web resource. (Videos may take a minute or so to load; be patient, it's worth it! ) When seeing these images and animations you should ask yourself "How much of this image is based on evidence, how much is well-founded conjecture (i.e. based on observations but not certain) and how much is almost certainly imagination?". Ponder these three questions by yourself, or discuss on- line & with friends if you like. Pikaia : Early Chordate It is from the chordates that vertebrates and ultimately humans will evolve. Pikaia is one of our earliest ancestors but was only a very minor component of the Burgess shale fauna. If you were an alien observing the Burgess shale creatures back in the Cambrian, it's unlikely that you would bet on the vertebrates as being the group that would eventually be manipulating their environment and creating technologies that would permit them to venture outside of their planet of origin. Figure - Reconstruction of Pikaia , a detail from Cambrian Sea Mural. Illustration by Karen Carr (http://www.karencarr.com/) copyright by the Field Museum (http://www.fieldmuseum.org/) .    0:00 / 7:27 1x 1x 

(https://burgess-shale.rom.on.ca/fossils/pikaia-gracilens/) Check out this 3D Model of Pikaia as well as the Animation of How Pikaia Moved, created by the Royal Ontario Museum as part of their work on the Burgess Shale! (https://burgess-shale.rom.on.ca/fossils/pikaia-gracilens/) Opabinia Opabinia is a soft-bodied animal of modest size. It had a segmented body with lobes on its sides and a fan- shaped tail, 5 eyes, and a grasping trunk. It has no modern analogues today. Figure - Opabinia . Drawing downloaded from Paleoimagery (http://paleoimagery.blogspot.com/) . Check out this 3D Model of Opabinia and the Animation for How Opabinia Moved, created by the Royal Ontario Museum as part of their work on the Burgess Shale! (https://burgess- shale.rom.on.ca/fossils/opabinia-regalis/) Hallucigenia Hallucigenia is of uncertain biological affinities. It was so unusual that the original reconstructions of this creature placed it upside down.

Figure - (left) Reconstruction of Hallucigenia and (right) Simon Conway Morris' original reconstruction of Hallucigenia showing it upside down. Illustration (left) copyright by Karen Carr (http://www.karencarr.com/) . Image (right) from the Geological Survey of Canada (http://www.nrcan.gc.ca/com/) . For a well-informed artist's impression of how this creature moved and lived on sponges, see an animation of Hallucigenia (http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=60&ref=a&) at the Burgess Shale web resource mentioned above. Remember - ask yourself how much of this image is based on evidence, how much is well-founded conjecture and how much is almost certainly imagination? Check out this 3D Model of Hallucigenia as well as the Animation of How Hallucigenia Moved, created by the Royal Ontario Museum as part of their work on the Burgess Shale! (https://burgess- shale.rom.on.ca/fossils/hallucigenia-sparsa/) Anomalocaris The structure and position of Anomalocaris has evolved significantly since the animal was first discovered. In early reconstructions, the two powerful manipulating mandibles on the front of the creature were mistaken for shrimp and the circular mouth was shown as a kind of "pineapple ring" jellyfish. Subsequently, once the true morphology of Anomalocaris was unraveled, it was believed to be the top predator in the Middle Cambrian oceans. It was thought to have swum around gobbling up all sorts of different creatures including trilobites. However, more recent work has suggested that the shape and composition of the animals mouth may have prevented it from consuming its neighbors with mineralized exoskeletons. At this time, the role of Anomalocaris in the Middle Cambrian ecosystem remains uncertain.

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Figure - "Cambrian Sea Mural" at the Field Museum in Chicago. Reconstruction of marine life in the Burgess Shale Reef, 510 million years ago. Anomalocaris sails over a Pikaia and a trilobite. Illustration by Karen Carr (http://www.karencarr.com/) copyright by the Field Museum (http://www.fieldmuseum.org/) . Check out this 3D Model of Anomalocaris as well as the Animation for How Anomalocaris Moved, created by the Royal Ontario Museum as part of their work on the Burgess Shale! (https://burgess- shale.rom.on.ca/fossils/anomalocaris-canadensis/) Arthropods in the Burgess Shale Over 40% of the Burgess Shale fauna are arthropods. Of that fauna only 3 will survive the Cambrian. These 3 species possessed the body plans that we see in all the arthropods to follow. Note how familiar they look. Canadaspis Ancestor of the crustaceans, Canadaspis was a bivalved arthropod and among the earliest animals with a hard shell casing.

Figure - Canadaspis ("Shield of Canada"). Image from Insectos de Chile (http://www.insectos.cl/) . Check out this 3D Model of Canadaspis as well as the Animation of How Canadaspis Moved, created by the Royal Ontario Museum as part of their work on the Burgess Shale! (https://burgess- shale.rom.on.ca/fossils/canadaspis-perfecta/) Aysheaia Aysheaia is an ancestor of the insects. Also known as the velvet worm, this animal has an unusual assembly of spines and grasping arms at the head end. Figure - Aysheaia . Image from the Smithsonian National Museum of Natural History (http://paleobiology.si.edu/burgess/) . Sanctacaris Sanctacaris , an ancestor of scorpions and spiders probably made its living swimming around and seizing prey with its spiny mouth appendages. Figure - Sanctacaris . Image from Palaeos (http://www.palaeos.com/) . Most of the Burgess Shale creatures were extinct by the end of the Cambrian. This could have been in part due to the rise of more effective predators in the Ordovician such as the nautiloids to which soft-bodied creatures would have been particularly vulnerable to attack.

Figure - Artist's conception of an Ordovician marine environment showing a nautiloid grabbing a trilobite. Illustration copyright by Karen Carr (http://www.karencarr.com/) . Required Movie - Origins: Battle for the Planet View the following movie. The study/review questions that follow should be used as a guide/self- assessment tool to help you gauge your understanding of the material presented in the video. Discovery Channel Video, 2004 Half a billion years ago, 300 million years before the first dinosaur, our earliest ancestors fought a battle for survival in the watery cradle of evolution. Journey back to the origin of advanced life on Earth, when life existed only in the sea, the land was barren, devoid of plants or animals. But in shallow water around prehistoric coastlines, strange and wonderful creatures thrived. Join Paleontologist Des Collins, a world authority on these primitive animals, as he leads an expedition to some of the best-preserved fossil specimens at the Burgess Shale, high in Canada's Rocky Mountains. State-of-the-art computer graphics recreate an ancient world filled with a host of strange creatures like the vicious, predatory Anomalocaris and the bizarre and aptly named Hallucigenia . Total Viewing Time: 50 minutes 1of6--Origins-Battle For The Planet (https://www.youtube.com/watch? v=eHTWRYwO1Lo&list=PLD7E7E7CB357E47C1&index=1)

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(https://www.youtube.com/watch?v=eHTWRYwO1Lo&list=PLD7E7E7CB357E47C1&index=1) 2of6--Origins-Battle For The Planet (https://www.youtube.com/watch? v=X8jgze57RCA&list=PLD7E7E7CB357E47C1&index=2) (https://www.youtube.com/watch?v=X8jgze57RCA&list=PLD7E7E7CB357E47C1&index=2) 3of6--Origins-Battle For The Planet (https://www.youtube.com/watch? v=AECUW6kMhp8&list=PLD7E7E7CB357E47C1&index=3) (https://www.youtube.com/watch?v=AECUW6kMhp8&list=PLD7E7E7CB357E47C1&index=3) 4of6--Origins-Battle For The Planet (https://www.youtube.com/watch? v=0FtpS_6qgkM&index=4&list=PLD7E7E7CB357E47C1) (https://www.youtube.com/watch?v=0FtpS_6qgkM&index=4&list=PLD7E7E7CB357E47C1) 5of6--Origins-Battle For The Planet (https://www.youtube.com/watch? v=3DSx02owjC8&list=PLD7E7E7CB357E47C1&index=5) (https://www.youtube.com/watch?v=3DSx02owjC8&list=PLD7E7E7CB357E47C1&index=5) 6of6--Origins-Battle For The Planet (https://www.youtube.com/watch? v=0uuGIuRIeaI&list=PLD7E7E7CB357E47C1&index=6) (https://www.youtube.com/watch?v=0uuGIuRIeaI&list=PLD7E7E7CB357E47C1&index=6) Video Study/Review Questions 1. What did Dr. Simon Braddy believe was the cause of the Cambrian Explosion? 2. What broad biological group do we (humans) belong to? 3. What was the top predator in the Cambrian Ocean? 4. Which group of animals dominated the Oceans of the Cambrian? 5. What strategies could Pikaia have used to escape predators?

6. What was Pikaia's descendent in the Soom shale? 7. How did this creature "make a living"? 8. What was the top predator in the Soom shale? 9. What catastrophe occurred 440 million years ago? 10. Which are more likely to survive such an event, generalists or specialists? 11. What advantages do vertebrates have over arthropods on land? Optional Video View the following episode of PBS Eons to hear more about some of the Burgess Shale fauna! Title: The Extinction That Never Happened Duration: 8:30 minutes (Burgess Shale starts at about 1:30 minutes) Source: PBS Eons, Season 1, Episode 10, 2017. Host: Hank Green The Extinction That Never Happened The Extinction That Never Happened

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