Unit 4 Study Guide: Impacts of Environmental Change on Horses

Use this guide to help you test your knowledge by quizzing yourself on the terms with the definitions hidden and answering the concept questions.

New Vocabulary or Terminology

• adaptive radiation
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  The process in which a lineage diversifies into several new forms with new adaptations.
• brachyodont
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  Short-crowned teeth with a cap of enamel that extends to the gum line, and one or more well-developed roots. The chewing surfaces are usually pointed and tend to be good for tearing or shredding.
• browser
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  Feeding strategy in which most of diet consists of leaves, shoots, twigs, and fruits
• biome
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  Large ecological communities often defined by the dominant vegetation type and climate.
• clade
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  A group that includes a common ancestor and all of its descendants. A group based on evolutionary history.
• grazer
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  Feeding strategy in which most of diet consists of grass.
• hypsodont
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  High-crowned teeth with enamel that extends below the gum line, and a hard, protective coating of cementum. They tend to have flat chewing surfaces that are good for grinding.
• lineage
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  Sequence of ancestors and descendants.

Conceptual Questions

1. What is the difference between a browser and a grazer?
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   Browsers have a diet mostly composed of tree leaves, shoots, twigs, and fruit. Grazers have a diet mostly composed of grass.
2. Which feeding strategy would be most advantageous in forested environments and why?
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   Browsing because forests are dominated by trees and other woody vegetation.
3. A grazing diet tends to cause a lot of tooth wear due to the high content of abrasive silica in grasses and the ingestion of grit and soil when feeding on low-lying vegetation. Which type of teeth would be better adapted to eating grasses?
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   Hypsodont (high-crowned) teeth.
4. As grasslands expanded, what general trends were seen in the Equidae?
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   General trends included a change from brachyodont to hypsodont teeth, an increase body size, and a reduction in toes until horses stood on a single, bony hoof.
5. As additional fossil horse taxa were discovered, what happened to scientific ideas about horse evolution?
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   Horse evolution was originally thought to be essentially linear, with changes in a single direction. Scientists have revised this idea in light of new data and now understand that the horse family tree has many branches and that there were exceptions to the trends in some lineages.