To gain an overview of over 50 million years of horse evolution, examine Figure 25.29, the branched evolution of horses (cladogenesis). At one time, horse evolution was often depicted as a straight line€” implying that an accumulation of changes gradually transformed one species into a species with different characteristics (anagenesis). (See the following figure) How does the shape of the more modern phylogenetic tree contradict the impression that one equid taxon died out as the next taxon emerged?

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Mesohippus (Oligocene) Pliohippus (Pliocene) Equus Hyracotherium (Eocene) Merychippus (Miocene) (Recent)