Evolution in the test size of deep-sea benthic foraminifera during the past 120 m.y.

Evidence is presented for stratigraphic variations in test size of the largest deep-water (> 1500 m water depth) calcareous trochospiral benthic foraminifera for eight dominant lineages composed of ten genera over the past 120 m.y. Variations in test size show (1) a general trend of increasing test size during the past 120 m.y. and (2) fluctuations, highlighted by six minima and six maxima, that are synchronized among genera. The long-term increase in size corresponds to an increase in the δ¹⁸O of deep-water benthic foraminifera. The minimum and maximum sizes correspond to minima and maxima in the δ¹⁸O, respectively. In addition, three major minima in test size correspond to distinct low dissolved oxygen events. These latter synchronisms indicate that oceanic climate and dissolved oxygen or related factors likely controlled evolution in test size of deep-water calcareous trochospiral benthic foraminiferal genera.