Supplementary data for: Another worm bites the dust

Based on a dataset of most mid-Paleozoic scolecodonts photographed in the
literature, the Carnegie Museum of Natural History, and newly presented
data from the Appalachian Basin, we find that scolecodonts (polychaete jaw
elements) decrease in size across the Late Devonian boundary, then
increase again to baseline in the Carboniferous. The majority of the data
representing small scolecodonts during the extinction event are newly
presented data in this study. These individuals were sampled from black
shales in a small geographic range at high stratigraphic resolution. Even
when excluding these new data, scolecodonts after the Frasnian-Famennian
boundary are smaller than scolecodonts before the boundary. Lithology or
water depth has a relationship with scolecodont size, but those factors
alone cannot explain the size reduction observed across the extinction
(i.e., we also find big scolecodonts in black shales). This represents a
novel, previously-unreported pattern in scolecodont size occurring across
the Late Devonian mass extinction. We interpret this as an oxygen
stress-driven occurrence of the Lilliput Effect. The biological mechanism
driving the change appears to be adaptation within taxa–either
evolutionary or epigenetic–not a dying off of large clades. Although
oxygen stress is known to reduce biomass of modern communities of
polychaetes, this is new evidence of size reduction due to oxygen stress.