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.