And then there were none: decrease of origination and the decline of Conulariida

Abstract

Although the evolutionary history of conulariids has been widely studied, previous works have focused mostly on limited time intervals. In this paper, we examine the diversity dynamics of the group throughout its entire history, using various mathematical approaches. An updated occurrences database was compiled to estimate the genus-level richness throughout the fossil record and to calculate diversity and evolutionary rate. For a better understanding of the group’s macroevolutionary dynamics, two additional analyses were applied to check for age dependency on extinction and to infer whether any environmental factors may explain the variations in origination and extinction rates. The analyses show that Conulariida diversity behaviour is characteristic of the Palaeozoic evolutionary fauna. The decline after the Late Ordovician and subsequent disappearance of the group throughout the Palaeozoic and Triassic is due not so much to an increase in extinction rate, but to a significant decrease in origination rate. The analysis of potential influences from environmental factors, such as sea level, continental breakup, continental scatter, global average temperatures, deep ocean temperatures and atmospheric oxygen level, resulted in no clear correlation. Higher extinction risk was associated with genera having a shorter evolutionary history. The genera Conularia and Paraconularia, often used as catch-all taxa, require systematic revision to clarify the true diversity of the group. Overall, the main drivers of Conulariida diversityremain uncertain.