Size variations in foraminifers from the Early Permian to the Late Triassic: implications for the Guadalupian-Lopingian and the Permian-Triassic mass extinctions

The final 10 Myr of the Paleozoic saw two of the biggest biologic crises
in Earth history: the Middle Permian extinction (often termed the
Guadalupian-Lopingian extinction, GLE) that was followed 7–8 Myr later by
Earth’s most catastrophic loss of diversity, the Permian-Triassic mass
extinction (PTME). These crises are not only manifest as sharp decreases
in biodiversity and - particularly for the PTME - total ecosystem
collapse, but they also drove major changes in biological morphological
characteristics such as the Lilliput effect. The evolution of test size
among different clades of foraminifera during these two extinction events
has been less studied. We analyzed a global database of foraminiferal test
size (volume) including 20226 specimens in 464 genera, 98 families, and 9
suborders from 632 publications. Our analyses reveal significant
reductions in foraminiferal mean test size across the
Guadalupian-Lopingian boundary (GLB) and the Permian-Triassic boundary
(PTB), from 8.89 to 7.60 log10 μm3 (lg μm3), and from 7.25 to 5.82 lg μm3,
respectively. The decline in test size across the GLB is a function of
preferential extinction of genera exhibiting gigantism such as
fusulinoidean fusulinids. Other clades show little change in size across
the GLB. In contrast, all Lopingian suborders in our analysis (Fusulinina,
Lagenina, Miliolina, and Textulariina) experienced a significant decrease
in test size across the PTB mainly due to size-biased extinction and
within-lineage change. The PTME was clearly a major catastrophe that
affected many groups simultaneously, and the GLE was more selective,
perhaps hinting at a subtler, less extreme driver than the later PTME.