16 SEP 2011 by ideonexus

 Atavism In Modern Horses

Modern horses, which descend from smaller, five-toed ancestors, show similar atavisms. The fossil record documents the gradual loss of toes over time, so that in modern horses only the middle one—the hoof—remains. It turns out that horse embryos begin development with three toes, which grow at equal rates. Later, however, the middle toe begins to grow faster than the other two, which at birth are left as thin “splint bones” along either side of the leg. (Splint bones are true vestigia...
Folksonomies: evolution atavism
Folksonomies: evolution atavism
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Modern horses have a common birth defect of growing extra toes from when their ancestors had them.