Extinction Buffering and Environmental Contingency in Infaunal Marine Benthos

Infaunal organisms may be less exposed to predation and physical disturbance than epifaunal organisms, potentially affecting lineage survival and diversification. We compare 188,883 fossil occurrences of 4735 marine benthic genera in five classes that include both infaunal and epifaunal forms. Boundary-crosser estimates show lower mean extinction rates for infaunal genera than for epifaunal genera within each of the Ordovician–Permian (O–P) and Triassic–Quaternary (T–Q) intervals. Mean net-diversification contrasts are positive in both intervals, and nominal statistical support is only available for the younger interval. Direct comparison shows no significant between-interval difference in extinction, origination or net-diversification contrasts. Reduced extinction supplies the positive contribution to the mean net-diversification contrast, while lower mean origination partially offsets this benefit. Temperature–extinction and CO2–extinction correlations change from positive in the older period to negative in the younger period; the CO2 pattern is more consistent across temporal aggregations. In the younger interval, a higher CO2 is associated with a weaker relative infaunal extinction advantage at both 5 and 10 Myr resolutions. Lower adjusted infaunal extinction odds also occur during the end-Ordovician, Oceanic Anoxic Event 2 (OAE2) and Cretaceous–Paleogene (K–Pg) crises; no significant differences are detected for the other three focal crises. The protective direction is maintained in all 10 occurrence-age randomisations for these three events and after excluding hard-substrate borers, whereas between-event heterogeneity is more sensitive to age uncertainty. Survival buffering is not significantly associated with changes in origination or net diversification after the six crises. Together, these results identify reduced extinction as the primary demographic advantage of infaunal life in the studied intervals and crises.