EVOLUTIONARY CONSEQUENCES OF THE RADIATION OF THE RUMINANTIA (MAMMALIA: ARTIODACTYLA)
Data for this study consist of nearly 200 discrete osteological and dental characters for 135 genera spanning 13 ruminant families. Evolutionary changes were reconstructed on a genus-level phylogeny of the clade, and per branch rates of change were estimated by dividing the number of changes along individual branches by their temporal durations.
The branches of the phylogeny were divided into two a priori categories: those that diverged during the window of time thought to include the radiation (regardless of phylogenetic position), and those that diverged at other times in the clades history. In general, there was no significant difference in the number of changes or rate of evolution between these two sets of branches. In a subsequent analysis, I compared branches that immediately led to the families involved in the radiation to branches from elsewhere in the phylogeny. The data suggest that branches marking the origin of the component families show significantly higher frequencies of character change than do other branches, and thus reject the idea of homogenous rates of character evolution.