Bossies and Blowholes 327gradual change between horse species, one example being Phil Gingerich (1980, 1989), with
his excellent detailed record of early Eocene horses from the Bighorn Basin of Wyoming.
Similarly, when Neil Shubin and I (Prothero and Shubin 1989) looked closely at the horses
from the Eocene and Oligocene deposits in the Big Badlands and related areas, we found
that what had been interpreted as a gradual transformation from Mesohippus to Miohippus
made more sense as a bushy pattern of evolution. Nonetheless, the transformation from
one species to another is very subtle. MacFadden (1984, 1992) has documented the subtle
FIGURE 14.3. A modern view of horse evolution, emphasizing the bushy branching nature of their history, as
many more fossils have been found and new species named. However, the overall trends toward higher-
crowned teeth (shown by the symbols for browsing leaves or grazing grasses), larger size, longer limbs, and
reduction of side toes are still true. (Drawing by C. R. Prothero; after Prothero 1994b)