netic process in the fossil record. Simpson (1951) also rejected the idea that horse evolution was a totally random process. He argued that a distinct process known as transformation leading to specialization can be identified in the fossil record. He also suggests that parallel and convergent evolution took place simultaneously and that selected quantum shifts involving adaptive relationships also influenced this evolutionary process (Simpson, 1951).
MacFadden (1992) moves forward from the work of Simpson (1951) and differentiates between the two major modes of species evolution and the speciation process generally interpreted from the fossil record. He defines "anagenesis" as associated with macroevolution or phyletic transformation from ancestral to descendant species. Cladogenesis, or branching as opposed to phyletic speciation, is the dominant mode of speciation in rapidly evolving clades, particularly during an adaptive radiation (MacFadden, 1992).
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