ays of life. MacFadden (1994) also says that horse diversity increased so dramatically that at some fossil sites from 15 million years ago, as many as a dozen species have been found.
What this suggests, in the view of many professionals, is that a cladogenetic or branching speciation took place during the Eocene and continued into the Oligocene, with rapid diversification becoming characteristic of the early Miocene (Hulbert, 1996). Earlier, MacFadden (1994) and Simpson (1951) agree that an anagenetic macroevolutionary transformation took place, leading to limited diversity and numbers of species. The fossil record, says MacFadden (1992), is an excellent medium for examining both anagenesis and cladogenesis. It is the purpose of this report to draw upon the literature to examine the fossil record from the late Eocene and the Oligocene with specific reference to Miohippus and Mesohippus. Such an examination will demonstrate that from the Oligocene period on, cladogenetic evolution of the horse was occurring - a process that is rooted in the Eocene, but most readily observable in the latter period.
Hulbert (1996) states that paleontologists have been analyzing the equid fossil record for well over 150 years. Between 1973 and 1987, paleontologists named an average of three new species of fossil horses per year. Many palentological interpretations are controversial, with contending and alternative hypotheses and theories coming into vogue and then falling by the wayside as new fossil evidence is uncovered. Throughout the course of the twentieth century, the trail of horse evolution has followed what Hulbert (1996) calls a two-track system. On the one hand, paleontologists including George Gaylord Simpson (1951) argued that the evolution of the horse family was definitely not orthogenetic, or straight and linear in terms of evolutionary pattern. There was, says Simpson (1951), no constant and overall increase in size or ...