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CrocodilesCrocodiles

  • Subject:
  • |
  • Grade(s): 6-8
  • |
  • Duration: Two class periods

Lesson Plan Sections

Objectives


Students will understand the following:
1. Changes in the environment have important effects on the way many types of animals evolve over long periods of time.
2. Crocodiles have survived and changed very little in the hundreds of millions of years they have survived on earth, in spite of the global catastrophe that caused the mass extinction of the dinosaurs and many other animal species 65 million years ago.
3. Crocodiles have specific characteristics that make them a highly successful animal, able to survive harsh conditions and radical environmental changes.

Materials


For this lesson, you will need:
• Research materials on crocodiles
• Computer with Internet access
• Art materials

Procedures


1. Make sure students realize that the crocodile is one of the oldest animals on Earth; that crocodiles survived even the global environmental changes that caused the extinction of the dinosaurs.
2. Let students know that they will be discussing why crocodiles were able to survive conditions that killed of so many other animal species, and that, to prepare for their discussion, they will be doing research on crocodiles.
3. Allow time for students to use the research materials you have provided, go to the library, or use the Internet to become crocodile experts. Tell them to concentrate on discovering the physical and behavioral attributes that allowed the crocodile to survive for so long.
4. Invite students to share what they already know and what they have found out about crocodiles from their research. Keep a list on the chalkboard of physical and behavioral attributes that make the crocodile such a successful animal. Just a few examples are:
  • Crocodiles can live for a century.
  • They can wait a year between meals.
  • They can float just beneath the surface of the water, where they are almost invisible to other animals, making them highly successful predators.
  • Their eyes, ears, and nostrils remain just above the surface of the water so that they can sense their surroundings at all times.
  • Their hearts are equipped to slow down and to divert blood away from the lungs while the animal is underwater.
5. Briefly discuss with the class how environmental changes can affect the way life on Earth evolves over long periods of time. You can cite as an example that the change from forest to grasslands in Africa (caused by the rise of mountains) made animals that could walk upright more successful than those that lived mainly in trees, possibly altering the course of human evolution.
6. Continue the discussion by asking why crocodiles have not changed over hundreds of millions of years.
7. Challenge students to speculate about how future environmental changes, such as increased water pollution, global warming, and a growing human population, might affect how crocodiles adapt and survive in the next 200 million years. (You might point out that the overhunting of crocodiles in Australia has actually increased the crocodile population, as the primary predator of the baby crocodile is the adult crocodile!)
8. When the discussion is complete, ask each student to write and illustrate a description of how he or she thinks crocodiles might look after 200 million more years of evolution. Will they change at all? If so, what will they look like? What are the reasons for the student's predictions?

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Adaptations


Adaptations for Older Students:
Have each student research at least one animal that did become extinct in prehistoric times and, in a brief essay, explain why the conditions that caused the extinction of that animal did not affect the crocodile's survival.

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Discussion Questions


1. Compare the basic qualities of mammals and reptiles. How are each suited to live in certain environments? What advantages and disadvantages does each type of animal have?
2. Approximately 65 million years ago, dinosaurs became extinct. The most widely accepted theory as to what caused this mass extinction suggests that a giant asteroid struck the earth and caused long-term global cooling and darkness. This climate change killed off many plants, which then starved the herbivores, which in turn starved animals higher up in the food chain. Speculate about how crocodiles survived this global catastrophe. What do we know about modern crocodiles that might explain their ability to survive such harsh conditions?
3. Crocodiles have a very complicated heart that is capable of bypassing the lungs and sending oxygenated blood directly to the brain and other vital organs when the animal is underwater. This ability is being studied by cardiologists and medical researchers, who want to be able to use this ability to help humans. Debate whether animals should be studied—and often killed—in order to further our knowledge of psychology, medicine, animal behavior, and the safety and usefulness of certain products, foods, chemicals, and drugs. Should animal research be limited to "vital" scientific knowledge? If so what qualifies as "vital?"
4. Explain why different types of animals produce such varying numbers of young. Why, under normal circumstances, don't animals that produce a great number of young overpopulate their environment? Why don't animals that produce very few young die out? Consider the following factors: whether the young are born live or as eggs; the gestation period of the young; the parenting tactics of the adults; the readiness of the young to survive on their own; the predators and hardships facing the young; and the age at which the young reach sexual maturity.
5. Throughout the world, crocodiles kill hundreds of humans annually. Considering this threat, should countries, especially those with the greatest crocodile problems, try to eradicate their crocodile populations?
6. In ancient Egypt, crocodiles were respected and even worshipped. Discuss how people across the planet view animals today. Do some societies still elevate some animals to the status of spirits or gods? Which animals are highly prized and revered in our society? Which are looked upon as merely food animals, laboratory animals, or pests? How do you explain this varied view toward different animals?

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Evaluation


You can evaluate your students on their sketches and descriptions using the following three-point rubric:
  • Three points: description well-written, reasons for prediction convincing and based on facts, sketch accurately reflects all details of written description
     
  • Two points: adequate description, some reasons for prediction, sketch adequately reflects written description
     
  • One point: description poorly written, reasons for prediction lacking, sketch vaguely reflects written description
You can ask your students to contribute to the assessment rubric by determining criteria for a well-written description and identifying several key facts that should be included as backups for predictions.

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Extensions


Crocodilians All Over the World
Crocodilians are divided into three subfamilies: Alligatorinae, Crocodylinae, and Gavialinae, which each contain 23 species. These species live all around the world. Divide your students into three groups, and have each group research one of the subfamilies of crocodilians to locate where each species lives. On an index card, they should record the name, habitat, diet, size, and notable facts of each species and post a picture, if available. Use a world map and pushpins to identify the area in which each species lives; you can use pins of different colors for each subfamily. Post the index cards around the map, connecting each card to a pushpin with thin pieces of ribbon or coordinating numbers.

Saving Endangered Crocodilians
Though humans have not yet caused the extinction of any crocodilian species, many of them are (or have been) endangered due to human activities. Have students contact the education department of a local zoo or animal conservation organization to learn what activities are most harmful to crocodiles, both within the United States and around the world. What actions are being taken to help preserve and restore crocodile populations? Two Internet sites that will be helpful in this research are the Crocodile Specialist Group's site and the University of Bristol's Crocodiles: Natural History and Conservation. When their research is complete, students should create a public service campaign designed to increase awareness about these endangered species. Their campaigns might include posters, advertisements, videos, and editorials.

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Suggested Readings


The World's Most Spectacular Reptiles & Amphibians
William W. Lamar. World Publications, 1997.
Read this overview of 400 colorful creatures, which was created by an ace photographer who also happens to be a herpetologist. His appreciation of these spectacular creatures can't help but rub off on you.

Alligators: Prehistoric Presence in the American Landscape
Martha A. Strawn. Johns Hopkins University Press, 1997.
Cousins to the crocodile, alligators have a continuing presence in southern states. This compelling volume contains a wide variety of alligator facts combined with essays, poems, song lyrics, vignettes, and thirty-two photographic sequences. It's a real feast for the eyes and the mind.

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Links


Crocodilians: Natural History and Conservation
Natural history of crocodiles.

Crocodiles, Alligators, and More on the Internet
Bibliography of crocodile and alligator sites.

The Crocodile Files
Crocodile information.

The Electronic Zoo
Links to a variety of resources.

Los Angeles Zoo
Zoo animal features include facts, stories, movie clips, research tips on a wide variety of animals.

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Vocabulary


Click on any of the vocabulary words below to hear them pronounced and used in a sentence.
speaker    caiman
Definition: Any of several Central and South American reptiles that are similar to alligators but that often resemble crocodiles in their appearance.
Context: Alligators abound in the United States, while their close cousins, the caimans, reach south as far as Argentina.
speaker    cold-blooded
Definition: Having a body temperature not internally regulated but approximating that of the environment.
Context: It's a misnomer to call them cold-blooded. Crocodilians, as we now know, are adept at keeping warm.
speaker    gharial
Definition: A large crocodilian native to India.
Context: Neither croc nor alligator, the gharial basks on the banks of an Indian river.
speaker    periscope
Definition: An optical instrument that allows an observer to obtain an otherwise obstructed view, usually above the level of the observer's eyes.
Context: A vanishing act leaves only a highly sensitive periscope—the crocodile's eyes—above the surface.
speaker    predator
Definition: An animal that depends on the killing of other animals for its food.
Context: Dinosuchus, the ancestor of the crocodile, was seven tons of pure predator.
speaker    Sobek
Definition: An ancient Egyptian crocodile god.
Context: The ancient Egyptians bowed down before Sobek.

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Standards


This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
 
Grade level: 6-8, 9-12
Subject area: science
Standard:
Knows about the diversity and unity that characterize life.
Benchmarks:
Benchmark 6-8:
Knows ways in which living things can be classified (e.g., taxonomic groups of plants, animals, and fungi; groups based on the details of organisms' internal and external features; groups based on functions served within an ecosystem, such as producers, consumers, and decomposers).

Benchmark 6-8:
Knows that animals and plants have a great variety of body plans and internal structures that serve specific functions for survival (e.g., digestive structures in vertebrates, invertebrates, unicellular organisms, and plants).

Benchmark 9-12:
Knows how organisms are classified into a hierarchy of groups and subgroups based on similarities that reflect their evolutionary relationships (e.g., shared derived characteristics inherited from a common ancestor; degree of kinship estimated from the similarity of DNA sequences).

Grade level: 6-8, 9-12
Subject area: science
Standard:
Understands how species depend on one another and on the environment for survival.
Benchmarks:
Benchmark 6-8:
Knows how an organism's ability to regulate its internal environment enables the organism to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.

Benchmark 6-8:
Knows ways in which species interact and depend on one another in an ecosystem (e.g., producer/consumer, predator/prey, parasite/host, relationships that are mutually beneficial or competitive).

Benchmark 6-8:
Knows factors that affect the number and types of organisms an ecosystem can support (e.g., available resources; abiotic factors such as quantity of light and water, range of temperatures, and soil composition; disease; competition from other organisms within the ecosystem; predation).

Benchmark 6-8:
Knows relationships that exist among organisms in food chains and food webs.

Benchmark 9-12:
Knows ways in which humans can modify ecosystems and cause irreversible effects (e.g., human population growth, technology, and consumption; human destruction of habitats through direct harvesting, pollution, and atmospheric changes).

Grade level: 6-8, 9-12
Subject area: science
Standard:
Understands the basic concepts of the evolution of species.
Benchmarks:
Benchmark 6-8:
Knows that the fossil record, through geologic evidence, documents the appearance, diversification, and extinction of many life forms.

Benchmark 6-8:
Understands the concept of extinction and its importance in biological evolution (e.g., when the environment changes, the adaptive characteristics of some species are insufficient to allow their survival; extinction is common; most of the species that have lived on Earth no longer exist).

Benchmark 9-12:
Knows that heritable characteristics, which can be biochemical and anatomical, largely determine what capabilities an organism will have, how it will behave, and how likely it is to survive and reproduce.

Benchmark 9-12:
Knows that natural selection leads to organisms that are well suited for survival in particular environments, so that when an environment changes, some inherited characteristics become more or less advantageous or neutral, and chance alone can result in characteristics having no survival or reproductive value.

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Credit


Kirsten Rooks, former biology and geography teacher and current freelance educator.

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