Prep: 15 mins | Activity: 30-45 mins
Cladograms are diagrams that show phylogenies, the evolutionary relationships between organisms. In this introductory example of cladogram construction, students use observable traits of animals as a line of empirical evidence supporting the common ancestry among the animals. Students employ two graphical techniques, concentric circle diagrams and cladograms, to establish the ancestral connections between animals.
Phenomenon: Hold up or project the picture of a dog, wolf, and bear. Ask students if the animals are related. Let them share their thoughts and jot down ideas to revisit after the activity.
How is empirical evidence of common ancestry and evolutionary relationships identified and represented among several species?
This activity can help you build toward the following dimensions of the NGSS:
HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.
Obtaining, Evaluating,and Communication Information
LS4.A: Evidence of Common Ancestry and Diversity
Patterns
Copy or post student pages. Have the pictures of phenomena ready to show or project. No disposal required.
1. For each animal, list as many characteristics of that animal as you can. If you know something about the physiology of the animal (that it lays eggs, for example), list that too.
2. Across all of the animals, color-code the traits. For example, if each animal has a backbone, color or highlight backbone in the same color. Choose a second color for other traits shared by the animals.
3. Circle the trait that separates each animal from the rest.
Student answers may vary.
B. Identification of common and derived traits
C. Chart
D. Concentric circle diagram
E. Cladogram
Using complete sentences, explain why you put each species where you did on the cladogram. What is the empirical evidence that led to the placement of each animal?
Answers will vary depending on the traits selected, but all empirical evidence should be associated with an anatomical, physiological, or genetic trait of the animal.
According to your cladogram and derived characteristics chart, which species are more closely related and share the most traits? What evidence supports your claim?
Species more closely related will be closer on the limb, and they will share more common traits. In this case, rhinos and owls are more closely related.
According to your cladogram, what is the most distant derived characteristic? What evidence supports your claim?
The oldest derived characteristics are lungs and/or legs. All of the animals have backbones, and the next trait to separate species is the presence of lungs and/or legs.
Use the same procedure and determine the common ancestry between dogs, wolves, and bears.
Answers will vary. Size, hibernation, or pack/solitary lifestyle may be distinguishing factors for students. They should produce a list of very similar traits among the species. All 3 species have a backbone, fur, large canine teeth, and give birth to live young.
Explain if the evidence matches your initial thinking about the common ancestry among dogs, wolves, and bears.
Answers will vary. Most students will not think that bears, dogs, and wolves are related. Most will recognize that dogs and wolves are closely related.
Scientific names
Dog: Canis familiaris
Grey wolf: Canis lupus
Brown bear: Ursus arctos
Bears and wolves split evolutionarily about 40 million years ago. Examination of both families’ teeth suggest how similar the two species are. Bears are larger, have smaller ears, and tend to be solitary. Dogs have smaller bodies and generally are social animals. Their classification is the same through the suborder Caniformia: Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Carnivora, and Suborder Caniformia. The families are different. Dogs and wolves are family Canidae, and bears are family Ursidae.
Are these animals related? What do you think?
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