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Lesson Plans: A Closer Look at the Burgess Shale Fauna

Overview:

Twelve fossil animals from the famous Burgess Shale (an UNESCO World Heritage Site located in Yoho National Park ) are studied and compared to modern animals. This is a biological classification exercise, requiring “thinking outside of the box”!

Learning Expectations:

  • to gain experience classifying (fossil) animals on the basis of their distinctive features
  • to compare fossil animals of the Burgess Shale to those of modern animals
  • to appreciate the scientific importance of the Burgess Shale fossils

Duration of the lesson:

60 – 120 minutes

Required Materials/Preparation:

For each group of students:

  • illustrations (and perhaps photographs) of the 12 Burgess shale fossil animals from Table 1 (see suggested resources)
  • copies of Table 1 (one per student)
  • copies of Discussion Questions
  • copies of the Background Information (guide to classification) included here
  • *computer, with Internet access (optional)

Teacher Background:

The Burgess Shale fossils have been called “the world’s most important fossil discovery”, and are located in Yoho National Park . The fossils are the well-preserved remains of a marine community that lived in a tropical sea in the Cambrian time period, 505 million years ago. The fossil quarry where they are found contains over 170 different species of plants and animals, and is an UNESCO World Heritage Site. The Burgess Shale animals lived shortly after an extraordinary, evolutionary “Big Bang” event, called the Cambrian Explosion. Within a very short time (geologically speaking), a wide range of complex animals (many with hard shells) suddenly appeared in the fossil record.

Modern classification systems recognise 7 basic levels of organisation: species, genera, family, order, class, phyla, and kingdom. Phyla represent the fundamental ground plans of anatomy. In classifying different species, biologists look for distinctive characteristics of the organism. There are about 32 different phyla in the Kingdom Animalia, and the Burgess Shale contains fossil organisms representing all of them, although many of the Burgess Shale animals were in the phylum Anthropoda.

Below is a summary of the main defining characteristics of some of the animal phyla that you’ll need to do this exercise:

Phylum Arthropoda

Arthropods make up 80% of all modern and fossil animals! Arthropods have external skeletons, or exoskeletons, formed of chitin, which may be further strengthened by calcium carbonate. Arthropods have segmented bodies, with different patterns of segment fusion to form integrated units (i.e. head, thorax, rear). They have characteristic jointed appendages, and arthropod means “jointed foot”. Chelicerates, crustaceans, and trilobites typically have biramous appendages (2 branches), with the outer branch usually being a flattened gill, and the inner branch being a walking leg, or otherwise modified for grasping, chewing or reproduction. To classify these animals, scientists examine the structure, number and location of their appendages. Based on these criteria, arthropods can be classified into 4 main classes, which are:

Class Uniramia: Uniramians are the largest class of arthropods, and modern uniramians are terrestrial, including insects, millipedes, centipedes, and their relatives. There is a three-part division of their body into head, thorax, and abdomen. Uniramians have uniramous appendages (single branch), usually in the form of a walking leg. Most modern insects have 3 pairs of walking limbs on their bodies. Uniramians don’t have gills, but breath with tracheae, or perforations on their external body surface.

Class Chelicerata: This class includes spiders and scorpions, mites and ticks, horseshoe crabs, and daddy-longleg spiders. They are aquatic, and are most have a body divided into two main divisions, the prosoma and the opisthosoma. The prosoma has six pairs of appendages, with the first pair of appendages typically forming claws, or chelicerae. Chelicerates lack antennae, the only major group of arthropods without them.

Class Crustacea: Crabs, lobsters, and shrimp are modern crustaceans. There is a three-part division of their body, into head, thorax, and abdomen. They are also aquatic, and have a bivalved carapace (shell with 2 divisions). They have five pairs of appendages on the head. Two pairs are antennae, and the other three pairs are usually used in feeding, as mouthparts.

Class Trilobita (extinct): Trilobites thrived for nearly 300 million years, before the last family of them went extinct 225 million years ago. In trilobites, there is a three-part division of the body, into head (cephalon), middle (thorax), and rear (pygidium). Trilobites had 4 pairs of appendages on their head (the first pair were antennae, the remaining 3 pairs were behind the animal’s mouth). Trilobites had a segmented body, with each segment bearing a pair of walking legs with gills, and most had a hard exoskeleton.

Recently, Dr. Desmond Collins from the Royal Ontario Museum in Toronto, defined another (extinct) class of arthropods which were predators (based on some Burgess Shale animals). This is the Class Dinocarida, meaning “terrible crab”. Dinocarids were bilaterally symmetrical, had 1 or more (pre-oral) claws, had 1 pair or more of prominent eyes, and a mouth on the underside of their head. The trunk was divided into 13 or more segments, each bearing swimming lobes and gills, some organisms had a 3-part tail.

Phylum Onychophora

Onychophorans are close relatives of arthropods. The only living onychophorans are velvet worms, which live in forest regions of South America, Africa, the Caribbean, and Oceania. They have a mixture of characteristics similar to arthropods and annelids (worms).

Phylum Annelida

This phylum includes earthworms, leeches, and a large number of mostly marine worms known as polychaetes. All have characteristic segmented bodies. Polychaetes (meaning “many bristles”) have many bristles on their body, while earthworms and leeches have fewer bristles.

Phylum Porifera

Includes marine sponges. They have a unique feeding system, and don’t have mouths, but have tiny pores in their outer walls through which water is drawn.

Phylum Cnidaria

Includes jellyfish, corals, and sea anemones. They are essentially bag-shaped organisms, with a mouth, but no anus, and usually tentacles around the mouth. They may be either attached to the sea bottom, or free-floating.

Phylum Echinodermata

Includes starfish, sand dollars, and sea urchins. Most modern echinoderms are pentameral, that is, they have rays or arms in fives or multiples of five. However, a number of fossil echinoderms were not pentameral at all, and had bizarre shapes. Echinoderms have a system of internal water-filled canals, which may form suckered “tube feet”, with which the animal may move or grip objects. Echinoderm skeletons are made up of interlocking calcium carbonate plates and spines, enclosed by the epidermis, and forming an endoskeleton.

Phylum Chordata

Includes humans, and other vertebrates. However, not all chordates are vertebrates. Chordates are in part defined by the presence of a notochord, which is a stiffened dorsal rod (in humans, this has evolved into a spinal column).

Procedure:

  1. Students (working individually or in small groups) are given copies of Table 1, as well as either illustrations or photographs of actual fossils (or both) for each of the Burgess Shale animals. (Alternatively, students could be directed to the website, http://paleobiology.si.edu/burgess/, to find the illustrations and photos themselves.) Students make observations about characteristics of each of the animals, including the animal’s shape, morphology, number and arrangement of appendages, and their similarity to modern animals, and record these observations in Table 1.
  2. Students separate animals into groups that are similar in some way. If possible each group is broken into sub-groups with more specific similarities.
  3. Students attempt to classify each fossil animal into one of the major Phyla, given either a standard biological key or the Background Information included here. For any of the animals that were classified as belonging to Phylum Arthropoda, students try to classify them in one of the different classes of arthropods.
  4. Students fill in as much of Table 1 as possible.
  5. Students attempt to answer the Discussion Questions on their own, or the teacher could initiate a class discussion using the questions.

Discussion Questions:

  1. Examine any animals that you thought belonged to Phylum Arthropoda. Name three characteristics that these arthropods have in common.
  2. Which animals were difficult to classify? Why?
  3. Can you think of a reason why our modern classification system does not take into account the morphology of these fossil animals (in question 2 above)? What role do you think extinction has played in evolution?
  4. What can be said about disparity in the Cambrian time period versus diversity today?
  5. Give three reasons why the Burgess Shale fossils are so important to scientists that they were designated an UNESCO World Heritage Site.
  6. Does the Burgess Shale provide evidence for the Gradual Change model of evolution, or the Punctuated Equilibrium model of evolution? Explain your answer.
  7. What morphological feature do all of the Burgess Shale animals studied here have in common?
  8. Write a story describing the lifestyle of one of the fossil creatures and its environment, including a plausible explanation for how it came to be fossilised. Be creative!

Table 1: Some Burgess Shale Animals

Animal Characteristics Resembles PhylaClass
Yohoia        
Marrella        
Sanctacaris        
Pikaia        
Canadaspis         
Aysheaia        
Amiskwia        
Hallucigenia        
Olenoides        
Opabinia        
Wiwaxia        
Anomalocaris        

Evaluation:

The teacher could assess students using any or all of the following criteria:

  • Table 1 completed, with accurate and complete observations, correct classification.
  • Discussion Questions answered satisfactorily.
  • Full participation in the activity and any ensuing class discussion.

Extension of the lesson:

  • Students (working in small groups) define their own specific criteria for use in categorising the organisms. Criteria must be based on visible characteristics of the fossil animals. They should consider the animal’s shape, morphology, number and arrangement of appendages, and similarity to modern animals when they do this.
  • Students create their own biological classification key, then use this to classify additional fossil specimens and revise their key as necessary.
  • Students compare their own classification key with a standard biological key. Any similarities and/or differences are noted.

References (Suggested Related Resources):

For information, illustrations and pictures of Burgess Shale fossils try:

  • The Smithsonian Institute’s National Museum of Natural History website: http://paleobiology.si.edu/burgess/  (Burgess Shale fossil index).
  • The Burgess Shale Geoscience Foundation, http://www.burgess-shale.bc.ca 
  • University of California, Berkeley, Museum of Paleontology website: www.ucmp.berkeley.edu  (For biological classification and evolution information).
  • Briggs, Derek, E.G., et.al., The Fossils of the Burgess Shale, 1994.
  • Gould, Stephen Jay, Wonderful Life, 1989.
  • Coppold, Murray, and Powell, Wayne, A Geoscience Guide to The Burgess Shale, 2000.
  • Yoho National Park website

Acknowledgements:

Created by teacher Lisa Holmstrom, 2005 (modified from similar exercises created by Dr. Mel Reasoner, and another by Donna Cook)

Table 1: Burgess Shale Fossils

Animal Characteristics Resembles PhylaClass
Yohoia 1 large pair of grasping appendages, segmented trunk, head shield, flat tail, 3 sets of walking legs near front, lobe-like appendages along body with gills (?)   Arthropoda (other)
Marrella 2 pairs of appendages (antennae), head shield with 2 sets curved spines, segmented body, each segment with a pair of walking legs and gills   Arthropoda (primitive)
Sanctacaris 6 pairs of spiny appendages on head, wide head shield, segmented trunk with flat tail, lobe-like appendages with gills   Arthropoda Chelicerata
Pikaia elongate body with sigmoidal muscle blocks, flattened tail fin, stiff rod along back (notochord), 1 pair short tentacles   Chordata  
Canadaspis 5 appendages on head, biramous appendages along body (walking leg and gill) , segmented tail, bivalved carapace   Arthropoda Crustacea
Aysheaia Annulated, cylindrical body with lobe-like, spiny appendages with claws, grasping arms near front, mouth at end   Onychophora  
Amiskwia Flattened body, unsegmented trunk, pair of side fins, tail, 2 tentacles   unknown  
Hallucigenia elongate body, lobe-like appendages with claws, spines along back, no distinct head   Onychophora  
Olenoides 3-part body, carapace with segmented thorax, 1 pair of antennae, biramous limbs each with walking leg and gill   Arthropoda Trilobita
Opabinia Elongate, segmented body with lobe-like appendages with gills, trunk-like appendage with claw, 5 eyes   Arthropoda Dinocarida
Wiwaxia Roundish body covered with scales, 2 sets of elongate spines   unknown  
Anomalocaris segmented body with lobe-like appendages and gills, protruding eyes, circular jaw, 1 pair of large grasping claws   Arthropoda Dinocarida

Answers to Discussion Questions:

  1. The arthropods all have exoskeletons, segmented bodies, and frontal appendages (either antennae, or claws).
  2. Wiwaxia and Amiskwia are difficult to classify at the Phylum level, and their affinities to modern animals remain unknown. They have characteristics which do not match the criteria for any of the animal phyla known today. Wiwaxia is sluglike, however its armoured plates make it unlike other molluscs. Yohoia, although an arthropod, is difficult to fit into one of the arthropod classes, since it has just one great appendage.
  3. These animals can’t be classified today because their lineages went extinct a long time ago. Their anatomical designs are unlike those of any modern animal. Extinction is extremely important in terms of shaping evolution, and over 99% of species that have ever lived have gone extinct. Extinctions are always occurring, but sometimes extinction rates rise suddenly for a short period of time (usually due to some environmental crisis), resulting in a mass extinction. Many species are lost forever as a result of mass extinction, however the empty niches caused by a mass extinction may present opportunities for other lineages to adapt to fill these niches, thereby fuelling the diversification of life on Earth.
  4. The Cambrian was a time when there seems to have been more disparity in animal design than there is today (i.e. a greater number of anatomical designs amongst animals). However, today there is more diversity in species, but only within a limited number of basic anatomical designs.
  5. The Burgess Shale fossils are so important to scientists because:
    1. they are very old (505 million years, making them some of the earliest complex animals on Earth)
    2. they are extremely well preserved, so that even soft tissues and internal organs are visible today
    3. the fossil deposit is very rich with about 170 different species of plants and animals, representating each of the animal phyla recognised today
  6. The Burgess Shale supports the Punctuated Equilibrium theory of evolution, because it displays the results of the Cambrian Explosion, in which there was a great diversification of life in a relatively short time, geologically. Prior to the Cambrian explosion, there were nearly 4 billion years during which there were only the simplest life forms inhabiting the planet.
  7. All of the animals presumably have a gill branch, or a means to breathe underwater, since all life was marine at that time in Earth’s history.
  8. (Refer to http://paleobiology.si.edu/burgess/ (see fossil index) for ideas, answers)

 


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