Often, scientists use DNA evidence when anatomical traits alone can't provide clear answers. Giant pandas and red pandas, for example, have given taxonomists a lot of trouble. These two species share anatomical similarities with both bears and raccoons, and both of them have peculiar wrist bones that work like a human thumDNA analysis revealed that the giant panda shares a more recent common ancestor with bears than with raccoons. DNA places red pandas, however, outside the bear clade. So pandas have been reclassified, placed with other bears in the clade Ursidae, as shown in Figure 18–12. What happened to the red panda? It is now placed in a different clade that also includes raccoons and other organisms such as seals and weasels.
MYSTERY CLUE
DNA comparisons show that some populations of brown bears are more closely related to polar bears than they are to other brown bears. What do you think this means for the classification of polar bears?
FIGURE 18–12 Classification of Pandas Biologists used to classify the red panda and the giant panda together. However, cladistic analysis using DNA suggests that the giant panda shares a more recent common ancestor with bears than with either red pandas or raccoons.
18.2 Assessment
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Explain How does evolutionary classification differ from traditional classification?
Apply Concepts To an evolutionary taxonomist, what determines whether two species are in the same genus?
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Explain What is a derived character?
Interpret Diagrams Along any one lineage, what do the locations of derived characters on a cladogram show? In your answer, use examples from Figure 18–9.
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Review How do taxonomists use the DNA sequences of species to determine how closely two species are related?
Relate Cause and Effect Explain why the classification of American vultures has changed.
VISUAL THINKING
Examine the cladogram.
Interpret Diagrams Which groups—X and Y, or X, Y, and Z—have the most recent common ancestor?
Infer Which species—X and Y, or X and Z—share more derived characters?
Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis