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Microevolution and Macroevolution

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Life Without Legs
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Life Without Legs

Image courtesy of SD Biju


Legless amphibians

Student Exploration

You're Looking For What?

Many people have heard about the worldwide decline in amphibians. Scientists have studied this phenomenon for years, identifying causes and trying to determine if the worldwide environment is changing too rapidly for amphibians to adjust to new conditions through natural selection. But far fewer people know that we have not even identified all the amphibians on the planet; that there are more to amphibians than frogs and salamanders. Find out about a third group of amphibians, a group without legs!

As you may have guessed, due to their cryptic nature, caecillians are not easy to find or study. As a result, much remains to be learned about these animals. In fact, in India they have identified a whole phylogenetic family of caecillians that was previously unknown.

Extension Investigation

Use the resources below to answer the following questions:

  1. What are the three major groups of amphibians?
  2. What physical characteristics make it easy to mistake caecillians for earthworms (Phylum: Annelida)?
  3. If you were to look inside a caecillian and an earthworm how would their internal anatomies compare? What characteristics would allow you to distinguish between them?
  4. What do baby caecillians feed on? How does this help explain their rapid growth?
  5. Given that these animals spend most of their time underground, what do you think this suggests about how animals first moved on to land. Could the first animals on land really have been the first animals "in" land. Do you think it would be easier for animals to adjust from living in water to living underground or above ground? Be specific and thorough in your reasoning.
  6. Where do the closest relatives to the new family of caecillians from Northern India live? What is this relationship taken as evidence of?

Resources Cited

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