Comparing the Latitudinal Ranges of Genera of Mollusca and Arthropoda
Before and After the End-Permian Extinction
Abstract
The end-Permian mass extinction event resulted in the loss of
approximately 80% to 90% of marine animal species due to drastic
changes in climate. Because warming was a major factor in the
extinction, it has been theorized the organisms that did survive were
able to do so because they moved to higher latitudes and this hypothesis
is consistent with tetrapod data. We hypothesized that this relationship
holds true for marine mollusks and arthropods as well. Using
Changhsingian (Late Permian) and Induan (Early Triassic) data from the
Paleobiology Database, we extracted occurrences of classes Bivalvia,
Cephalopoda, Gastropoda, and Ostracoda, which had 2433, 395, 379, and
1717 genus occurrences, respectively. Then, we used the paleolatitude
data for each genus occurrence to characterize the latitude distribution
of each class before and after the Permian/Triassic transition. We
compared the paleolatitude medians before and after the mass extinction
for each class to quantify the latitude shift for each class: 23.18° for
Bivalvia, 37.45° for Cephalopoda, 29.82° for Gastropoda, and 6.29° for
Ostracoda. This finding indicates that each individual class had a
different latitudinal shift, with all classes exhibiting a poleward
shift north. We also conducted Welch t-tests to compare the differences
in latitudinal ranges and found that they were significant (Bivalvia: p
< 2.2e-16, Cephalopoda: p = 3.83e-6, Gastropoda: p <
2.2e-16, Ostracoda: p = 0.0030). In addition, we ran multiple randomized
models to compare them with our original results and found a significant
difference between them via the Kolmogorov-Smirnov test, which means
that the northward migration could be a biological response. Moreover,
the results of our study show that the overall latitudinal range of most
classes contracted after the extinction event, with the exception of the
Cephalopoda class.