Palaeocampa

Palaeocampa (Greek for 'ancient caterpillar') is a genus of aysheaiid lobopodian panarthropods known from the Carboniferous-age Mazon Creek fossil beds and Montceau-les-Mines lagerstätte. The genus contains a single species, Palaeocampa anthrax, which takes its specific name from anthrax (ἄνθραξ), the Greek word for coal, as its fossils were found near coal deposits in Illinois. This genus was first described as a caterpillar, before being redescribed as a fireworm in 2004, and then redescribed again as a lobopodian in 2025. Palaeocampa is extremely unusual for a lobopodian in a variety of ways, being the first and currently only known freshwater lobopodian outside of tardigrades, the first venomous lobopodian, alongside being the only known aysheaiid to possess sclerite armature.

History

Palaeocampa anthrax was first reported from the Mazon Creek deposits of Illinois in 1865 by American paleontologists Fielding Bradford Meek and Amos Henry Worthen. At this point, it was known from only a single specimen discovered by local fossil collector Joseph Evans, which did not preserve the head or legs. The apparent similarity between it and some modern caterpillars led to it being interpreted first as a kind of caterpillar, although this claim was only tentative, as it was not known at the time if lepidopterans existed this far back in the fossil record. Samuel Hubbard Scudder, an entomologist and paleontologist, agreed that there was a resemblance, but not enough to warrant this classification; instead, he assigned it generically to "the class of worms". In 1882, Scudder published a study based on new specimens of Palaeocampa, as the original holotype had been lost in a fire soon after it was described. One specimen preserved the limbs, which allowed Scudder to say confidently that it could not be a caterpillar, which possess three thoracic limbs, a few legless segments, and a number of prolegs, while Palaeocampa possess identical limbs on every segment.