Supplemental information for: An early burst in brachiopod evolution corresponding with significant climatic shifts during the great Ordovician biodiversification event

We employ modified tip-dating methods to date divergence times within the
Strophomenoidea, one of the most abundant and species-rich brachiopod
clades to radiate during the Great Ordovician Biodiversification Event
(GOBE), to determine if significant environmental changes at this time
correlate with the diversification of the clade. Models using origination,
extinction and sampling rates to estimate prior probabilities of
divergence times strongly support both high rates of anatomical change per
million-years and rapid divergences shortly before the clade first appears
in the fossil record. These divergence times indicate much higher rates of
cladogenesis than typical of brachiopods during this interval. The
correspondence of high speciation rates and high anatomical disparity
suggests punctuated (speciational) change drove the high frequencies of
early anatomical change, which in turn suggests increased ecological
opportunities rather than shifting developmental constraints account for
high rates of anatomical change. The pulse of rapid evolution began
coincident with cooling temperatures, the start of major oscillations in
sea level, and increased levels of atmospheric oxygen. Our results suggest
that these factors permitted major geographic and ecological expansion of
strophomenoids with intervals of geographic isolation, resulting in
elevated speciation rates and corresponding elevated frequencies of
punctuated change.