Punctuated EquilibriumThe theory of punctuated equilibrium is an inference about the process of macroevolution from the pattern of species documented in the fossil record. In the fossil record, transition from one species to another is usually abrupt in most geographic locales -- no transitional forms are found. In short, it appears that species remain unchanged for long stretches of time and then are quickly replaced by new species. However, if wide ranges are searched, transitional forms that bridge the gap between the two species are sometimes found in small, localized areas. For example, in Jurassic brachiopods of the genus Kutchithyris, K. acutiplicataappears below another species, K. euryptycha. Both species were common and covered a wide geographical area. They differ enough that some have argued they should be in a different genera. In just one small locality an approximately 1.25m sedimentary layer with these fossils is found. In the narrow (10 cm) layer that separates the two species, both species are found along with transitional forms. In other
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