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About 40 million years ago another group of plant eaters, the cow family, evolved a special stomach in which bacteria grew. The bacteria broke down the hard cell walls of plants, letting the animal eat the cell juice. So the cow family could get much more goodness out of their food than the horse family and replaced them as the most common plant eating group. Pigs, hippopotamuses, camels, lamas, deer, giraffe, cows, sheep and goats all belong to this very successful group of mammals. They are known as the even-toed ungulates (Artiodactyls) because they usually have two or four toes. Contrast this with the horse family. |
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