a definitive pattern of steady change from four toes to three and finally, one toe. Foot and toe evolution in different branches of the family were not revealed as an orthogenetic 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 suggested that parallel and convergent evolution took place simultaneously and that selected quantum shifts involving adaptive relationships also influenced this evolutionary process (Simpson, 1951). Simpson (1951) also argued that the more progressive horses of the middle Oligocene and all the horses of the late Oligocene are placed by convention in a single genus, Miohippus, but that Miohippus and Mesohippus intergrade so perfectly and the differences between them are very slight.
MacFadden (1992) moved forward from the work of Simpson (1951) and dif
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