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Transitional Forms (2 of 2)

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Our understanding of the evolution of horse feet, so often depicted in textbooks, is derived from a scattered sampling of horse fossils within the multi-branched horse evolutionary tree. These fossil organisms represent branches on the tree and not a direct line of descent leading to modern horses.

But, the standard diagram does clearly show transitional stages whereby the four-toed foot of Hyracotherium, otherwise known as Eohippus, became the single-toed foot of Equus. Fossils show that the transitional forms predicted by evolution did indeed exist.

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Left: Each branch tip on the tree of horse evolution indicates a different genus, though the feet of only a few genera are illustrated to show the reduction of toes through time.

Teach this!
Lesson plans for teaching about transitional forms
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Homologies


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Spanish translation of Understanding Evolution For Teachers from the Spanish Society of Evolutionary Biology.