Cretaceous–Tertiary extinction event

Radiolaria have left a geological record since at least the Ordovician times, and their mineral fossil skeletons can be tracked across the K-T boundary. There is no evidence of mass extinction of these organisms, and, there is support for high productivity of these species in Southern high latitudes as a result of cooling temperatures in the early Paleocene.[7] Approximately 46% of diatom species survived the transition from the Cretaceous to the Upper Paleocene. This suggests a significant turnover in species, but not a catastrophic extinction of diatoms, across the K–T boundary.[7][17]

The occurrence of Planktonic foraminifera across the K-T boundary has been studied since the 1930s.[18][19] Research spurred by the possibility of an impact event at the K-T boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary.[7] However, there is debate ongoing between groups that believe the evidence indicates substantial extinction of these species at the K-T boundary,[20] and those who believe the evidence supports multiple extinctions and expansions through the boundary.[21][22]