Fig. 2. Phylogenetic hypothesis of the taxa used in this study compiled from
Messenger and McGuire (1998)
and Irwin and Arnason (1994).
Species in which head-butting has been observed during male—male
aggression are marked with a filled circle. See text for references. The
numbers at the terminal branches represent the percentage sexual dimorphism in
body length (top) and the percentage of the lateral projected body area made
up by the melon (bottom). Numbers at nodes represent the contrast values for
the node. The contrast value for a given node of the tree was calculated by
taking the average of the descendant nodes along one bifurcation and
subtracting it from the average along the other bifurcation and dividing this
difference by a measure of the variance weighted by the lengths of the
subsequent branches (Felsenstein,
1985).
