TAXONOMIC VERSUS PHYLOGENETIC ESTIMATES OF EXTINCTION SEVERITY IN DEVONIAN TEREBRATULIDE BRACHIOPOD GENERA

What can phylogenetic analysis contribute to studies of extinction dynamics that taxon counting alone cannot? At the P/T boundary, terebratulide brachiopod genera suffer 100% generic extinction, yet, some lineages clearly survived because this clade is extant. In this case, taxonomic and stratigraphic information alone provides no information concerning lineage survival, and the biases in fossil preservation, taxon sampling, or taxonomic inconsistencies prevent us from answering even the most fundamental questions concerning the extinction event. Furthermore, this obvious case of fossil bias casts the estimates of diversity and extinction at other temporal intervals into doubt. Phylogenetic analysis, however, has been shown to provide alternative estimates of lineage diversity and survivorship by identifying post-boundary taxa that form sister-taxa relationships to pre-boundary taxa, as well as potential gaps in the fossil record. I demonstrate this by performing phylogenetic analysis on all 40 well-preserved Devonian terebratulide genera, and comparing extinction severity in terebratulide lineages to extinction severity using taxon names across Early Devonian stage boundaries. Using a list of 67 morphological characters, phylogenetic analysis was performed using PAUP 4.0b10. Eight atrypide and athyridide genera were used as outgroups. At all stage boundaries, taxon counting methods either equal or underestimate generic diversity, and equal or overestimate extinction severity when compared to extinction severity derived from phylogenetic hypotheses.