Lab 10 – Fossils OEB 51
Lab 10: Fossil diversity from the Ediacaran and Cambrian
20 April 2016
We are extremely lucky to have access to a large assortment of historically important fossils, including many Cambrian specimens from the famous Burgess Shale site. Please handle these fossils with extreme care.
Feel free to place them under the dissecting scope to see any details. Draw and label your figures with suggested structures.
Consider the following questions: What is a fossil? What needs to happen for fossils to form?
Can we know all animals that ever lived by looking at the fossil record? Why or why not?
While you go through the material, think about the following aspects of the animal’s life and take notes. What can you infer about the biology of that animal based on its remains? • Life style (benthic vs. pelagic; sessile vs. mobile etc.) • Feeding habits • Symmetry Do you think it belonged to any of the modern phyla? If yes, what are the reasons?
You can make your own reconstruction of how you think these animals were like when alive.
1 Lab 10 – Fossils OEB 51
Ediacaran (Late Neoproterozoic)
When was the Ediacaran period?
CHOOSE These fossils represent some of the earliest evidence of macroscopic life. Using both the specimens ONE and figures from the available books, try to understand the organization of the organisms.
• Charnia masoni • Dickinsonia elongata
It is tempting to try to assign fossils of the Ediacaran to modern groups of animals. You probably have already done this to a certain degree in your head. What does Charnia resemble? Is this line of reasoning fruitful, or are there reasons to avoid it?
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• Stromatolites are even older and were abundant during the Proterozoic. Although there are modern stromatolites, they are rare. What organisms build these structures? What could have caused the decline of stromatolites in the end of the Precambrian/Cambrian?
Cambrian (Early Phanerozoic)
Trace fossils (Ichnofossils) Ichnofossils are impressions left on the substrates by organisms. They are indirect evidence of ancient life and provide us with a record of the activity of an organism. Ichnofossils include trails, burrows and can also mean the remains of other organic/chemical material produced. CHOOSE ONE • Treptichnus pedum The first 3-dimensional animal traces, piercing through bedding planes of sediment, and also the definition of the lower Cambrian. What kind of organism might have left these traces? What behavior do they record?
• Ruscophycus trilobatum Any guesses as to what type of animal may have left these marks? What anatomical innovations might have been needed?
• Arenicolites woodi (Upper Cambrian) What kind of organism do you think made these burrows?
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Cambrian (continued)
• Archaeocyatha CHOOSE Archaeocyathus profundus • Cambrocyathus profundus ONE These are characteristic members of the early Cambrian fauna, and the whole group was extinct by the end of the Cambrian. They lived in shallow water and are considered to be the first ‘reef- building’ animals. What kind of animals do you think they were and why? What might have been their life style and feeding mode?
• Hyolithida Haplophrentis reesei
Does this fossil resemble any extant group? Which and why?
• Trilobita Paradoxides harlani (Middle Cambrian) • Isotelus gigas (Middle Ordovician)
Draw and label one. Compare the Cambrian and post-Cambrian trilobite fossils. Do you see any major differences? Identify the invertebrate clade in which you would place these animals.
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Burgess Shale (Cambrian) The Burgess Shale fossil bed provides a unique glimpse into animal life shortly after the Cambrian Explosion. It shows exceptional preservation (Lagerstätten) – what geological event must have CHOOSE happened to allow this? Consider the rock matrix in which these fossils occur – how large are the TWO sediment grains? Are animals preserved 3-dimensionally?
• Anomalocaris canadensis Are these the entire animal? If not, what part of the body are they? What was the life style of the animal? Look at illustrations in the textbooks.
• Burgessochaeta setigera Can you see any characteristics that make it similar to the extant polychaete annelids? You might need a dissecting microscope to observe in more details.
• Marrella splendens Marrella is the most abundant genus in the Burgess Shale. In which phylum can we place it?
• Vauxia gracilenta This fossil is thought to be a branching sponge (Porifera). Can you see oscula?
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Burgess Shale (continued)
Look up at the geological time scale to visualize where each of the organisms and moments we studied today are placed in time.
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More recent Phanerozoic invertebrate fossils Some of the following fossils are more similar to their modern counter-parts. Identify the phylum to which they belong. What were the main characters that you used to make this placement?
Saccocoma pectinata Upper Jurassic period
Phylloceras heterophyllum Lower Jurassic
Worm trails Devonian
Eurypterus (sea scorpion) Silurian period (New York)
Lithified block – Upper Ordovician period Examine this fossil assemblage from the Ordovician, well after the Cambrian Explosion. What phyla do you recognize?
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