No evidence for fungal infection of Upper Jurassic horseshoe crabs: A comment on Błażejowski et al. (2019)

Błażejowski et al. (2019) intended to provide evidence for fungal infection of Upper Jurassic horseshoe crabs from Poland based on the presence of boring traces preserved on their carapaces and assigned to the ichnogenus Mycelites. However, the borings are in fact burrows which can be assigned to the ichnogenus Arachnostega. Thus, their hypothesis about the fungal infection is rejected on the basis of erroneous identification of the ichnofossils preserved. There is also no compelling evidence for environmental deterioration causing the “infection”. Rather, the bottom waters were oxygenated and thus hospitable for benthic organisms.