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Overview:
Crocodilians, including crocodiles and alligators, are ancient animals that survived the period of mass extinction at the Cretaceous/Tertiary boundary about 65 million years ago. While scientists are not sure why crocodilians are so hardy, they have plenty of evidence from modern and prehistoric crocodilians like SuperCroc (Sarcosuchus imperator) to develop hypotheses on this question. Students will investigate this evidence and write reports on their findings.
Connections to the Curriculum:
Geography, life sciences
Connections to the National Geography Standards:
Standard 8: "The characteristics and spatial distribution of ecosystems on Earth's surface"
Time:
Two to three hours
Materials Required:
- Computer with Internet access
Objectives:
Students will
- brainstorm and list reasons why crocodilians might have survived so long;
- research and take notes on questions about modern and prehistoric crocodilians; and
- write papers providing their opinions of why crocodilians have survived so long, including evidence from their research.
Geographic Skills:
Asking Geographic Questions
Acquiring Geographic Information
Organizing Geographic Information
Answering Geographic Questions
Analyzing Geographic Information
S u g g e s t e d P r o c e d u r e
Opening:
Have students name animal species that have become extinct. Discuss the possible reasons for these extinctions, such as a catastrophic meteor collision with Earth or a gradual change in the Earth's climate.
Are students aware of any types of animals that have been able to survive great challenges to their existence? What characteristics do they think an animal species would need to survive for hundreds of millions of years, even as other species are dying off?
Development:
Have students read the first page of the SuperCroc site. They should notice that SuperCroc (Sarcosuchus imperator) lived approximately 110 million years ago. As they may know, many crocodilians (i.e., crocodiles, alligators, caimans, and gharials) continue to exist into the present day.
(If students have studied taxonomy, have them look at the Classification of Crocodilians, and discuss the taxonomy shown here. They should notice that all crocodilians are part of the class Reptilia and order Crocodylia. Alligators and caimans are classified in the family Alligatoridae, while crocodiles are in the family Crocodylidae. Gharials belong to the family Gavialidae.)
Write this question on the board: "Why have crocodilians survived so long?" Inform the class that their goal will be to collect evidence to develop answers to this question.
Ask students to brainstorm the reasons they think crocodilians have been able to survive for so many millions of years when many other animals, such as dinosaurs, became extinct. List their ideas on the board.
Divide the class into small groups. Ask each group to write these questions on their own paper, leaving at least 1/3 of a page between each question.
- What are some of the crocodilians' unique physical characteristics (e.g., body shape, size, or structure)?
- What did SuperCroc eat? What do modern crocodilians eat?
- What types of habitat do crocodilians prefer? Can they adapt to other habitat types?
- How biodiverse does crocodilians' habitat tend to be? In other words, does this type of habitat tend to have many other plant and animals species, or does it tend to have only a few species?
- What types of climate do crocodilians prefer? Do they adapt well to changes in climate?
- How do crocodilians generally react to competition from other species for food or habitat?
Have students use these Web sites to find their answers:
National Geographic: SuperCroc
National Geographic: Wild World
Crocodilians: Natural History and Conservation
PBS: NOVA Online—Crocodiles!
Closing:
Discuss the groups' findings about crocodilians as a class. What do they think are the most likely reasons that crocodilians have survived so long?
Suggested Student Assessment:
Have students write two- to three-page papers addressing the following questions:
- Why have crocodilians survived so long?
- Why do you think crocodilians were able to survive into the present day when dinosaurs were not?
Students' papers should provide specific examples from the research they conducted during the lesson. Remind them that their answers should stay on the topic of crocodilians' long term survival.
Extending the Lesson:
Ask students to use the Web sites listed above to find out about threats to two or three modern crocodilian species (e.g., habitat destruction or water pollution). Have students write paragraphs predicting how these species might fare in the face of these threats, assuming the threats increase in the future. They should base their ideas on what they have learned about crocodilians' previous adaptations.
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