DOI: 10.5061/dryad.h70rxwdgh
title: Size variations in foraminifers from the Early Permian to the Late Triassic: implications for the Guadalupian-Lopingian and the Permian-Triassic mass extinctions

description: 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.
description: We constructed a global database of foraminifer test sizes from
 the Early Permian to the Late Triassic illustrated in 632 published
 papers. Our database includes 20,226 individual specimens representing 464
 genera, 98 families, and 9 suborders. We applied the timescale and ages
 provided in the IUGS Geological Time Scale (2018)
 (http://www.stratigraphy.org/ICSchart/ChronostratChart2018-08). The
 systematic classification of foraminifers has been controversial, and here
 we follow Tappan and Loeblich (1988), Mikhalevich (2000), Armstrong and
 Brasier (2004), and Groves et al. (2005). We have performed additional
 standardization for some controversial and uncertain species (including
 synonyms) (by Haijun Song). Foraminiferal test
 morphologies are widely variable and include cones, columns, disks,
 spheres, hemispheres, and ellipsoidal shapes. We use test volume as a
 proxy for body size to mitigate against biases caused by shape changes
 over time. Test symmetries were used to calculate test volume from the two
 measurable axes in thin-sectioned specimens. The logarithmic scale with
 base 10 of test volume has been chosen because the rate of biological
 evolution is an inverse power function of time, it is often used for
 statistical comparison of right-skewed distributions (Gingerich 1983). In
 addition, the value is reduced on a linear scale after logarithmization,
 making it easier to compare test sizes across a broad range of sizes
 (Payne 2005). We chose the <i>t</i>-test
 method to compare the differences in the mean test values of foraminifera
 between adjacent stages, and this analysis is mainly performed using the
 Statistical Package for the Social Sciences (SPSS).