Gavrilets, S. 1998. "Dynamics of clade diversification on the
morphological hypercube" Proceedings of the
Royal Society London B (in press).
ABSTRACT
Understanding the relationship between taxonomic and morphological
changes is important in identifying the reasons for
accelerated morphological diversification early in the history of
animal phyla. Here, a simple general model describing the
joint dynamics of taxonomic diversity and morphological disparity
is presented and applied to the data on the diversification of blastozoans.
I show that the observed patterns of deceleration in clade diversification
can be explicable in terms of the geometric structure of the
morphospace and the effects of extinction and speciation on morphological
disparity without invoking major declines in the size of morphological
transitions or taxonomic turnover rates.
The model allows testing of hypotheses about patterns of diversification
and estimation of rates of morphological evolution. In the case of
blastozoans, I find no evidence that major changes in evolutionary rates
and mechanisms are responsible for the deceleration of morphological
diversification seen during the period of this clade's expansion.
At the same time, there is evidence for a moderate decline in overall rates of
morphological diversification concordant with a major change (from
positive to negative values) in the clade's growth rate.