The phylogenetic signal of extinction through the rise and fall of early vertebrates: field of bullets or clustered strike?

We investigate patterns of phylogenetic selectivity of extinction in early aquatic vertebrates from the Silurian to the Carboniferous, an interval punctuated by one of the Big Five mass extinctions and marked by many critical anatomical (e.g. jaws, limbs) and ecological (e.g. macrophagy, terrestrialization) vertebrate evolutionary innovations. Using a new >1300 taxon, formally inferred supertree, we show that phylogenetic extinction clustering in early vertebrates varied through time and between major ecomorphological divisions of the tree. At the end of the Silurian and into the Early Devonian, jawless fishes became marginalized components of vertebrate faunas and show more strongly clustered extinction than jawed fishes, which became ecologically dominant during this interval. Clustered extinction (contemporaneous extinction of close relatives) is typical of most stages of the Devonian, particularly during the Late Devonian extinctions. By contrast, the subsequent early Carboniferous interval of putative recovery is characterized by overdispersed extinction (contemporaneous extinction of distant relatives), consistent with widespread persistence of phylogenetically distinct lineages. This work shows how varying patterns of extinction selectivity pruned the vertebrate tree at the time when the first-order patterns of diversity apparent in modern aquatic vertebrate faunas were first established.