Fig. 3

Patterns of body size evolution in fossil horses from North America. For the first 30 million years of their history, there was relatively little change in body size, and the growth in average size over the past 25 million years reflects an expansion of diversity within the group as a whole rather than a progressive increase in every component lineage. In fact, several lineages of horses underwent reductions in body size over the same period. This shows how trends may be localized both temporally and taxonomically. From MacFadden (1992), reproduced by permission of Cambridge University Press