Although some transitions, such as that of Dinohippus to Equus, were indeed gradual progressions, a number of others, such as that of Epihippus to Mesohippus, were relatively abrupt in geologic time, taking place over only a few million years.
Selv om nogle overgange, såsom den fra Dinohippus til Equus, faktisk skete gradvist, var flere andre, såsom den fra Epihippus til Mesohippus, relativt brat ud fra en geologisk tidsskala og fandt sted i løbet af kun et par millioner år.