Palaeocampa

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. Scudder wrote then, that Palaeocampa must belong to the myriapods. Alanops was later determined to be a freshwater belinurine species, What the 2004 study called a proboscis was determined to be a dorsal structure, a sclerotized headshield similar to those found in some other lobopodians (e.g. Collinsovermis). ==Description==

Palaeocampa anthrax USNM PAL 38032b.png|Specimen of Palaeocampa from the Mazon Creek fossil beds Palaeocampa anthrax MNHN SOT 3657.png|Another specimen of Palaeocampa Palaeocampa anthrax spines 1.png|SEM photograph of the spines of Palaeocampa, seen emerging from the modified basement papillae Palaeocampa anthrax spines 2.png|SEM photograph of the spine apex of Palaeocampa, showing the crenellated, weakly tapering tip of the spine Palaeocampa is a small lobopodian, reaching a maximum of in length, not including spines or frontal appendages. It has a head bearing a ridged dorsal sclerite, a large annulated pair of frontal appendages, and a small, secondary pair of appendages just beneath the head. It lacks eyes, and the morphology of its mouth is unknown. The trunk consists of ten segments, each bearing a pair of broad, annulated, lobopodous appendages, approximately equal in length to the width of the trunk, and lacking claws. The entire body and the limbs, including the frontal appendages, are further lined with small, regularly distributed papillae. Above each leg pair are paired sets of dorsolateral and lateral sclerites, or bristles. The body also terminates with an unpaired set of bristles. Each bundle contains a large number of independent bristles, growing from a complex modified basement papillae, the lateral sets being slightly shorter. These sclerites have an architecture unique in the animal kingdom; each spine is straight, highly elongate, and tapered only slightly at the end before expanding back out into a crenellated apex, which Knecht et al. (2025) compared to a rook chess piece. The spine is divided longitudinally by prominent ridges, and between them three smaller ridges. These ridges are serrated, following a sawtooth-like pattern upwardly towards the apex, similar to roof shingles. Internally, the sclerites are septated and hollow, probably with a spongy filling material and a central pore running through the middle. The dorsum of the trunk was thickened compared with the rest of the cuticle, and further reinforced with hundreds of small sclerotized papillae which gave it a pebbly, armoured appearance. These dorsal armour papillae have a small central pore, which is thought to have originally contained a sensory, hair-like seta, similar to the setae-bearing papillae of Aysheaia. ==Paleobiology==

Palaeocampa is remarkable as the first and currently only known freshwater lobopodian, excluding some tardigrades. Previously, all xenusiid lobopodian fossils have been found in marine deposits, including Palaeocampas closest relative Hadranax augustus, which is found in Cambrian deep sea deposits. The lost holotype of Palaeocampa comes from an inland, Braidwood biota locality of the Mazon Creek, dominated by plants and populated by various terrestrial and freshwater arthropods, as well as freshwater fish and sharks. The Montceau-les-Mines palaeoenvironment is even further inland, as much as 300 kilometres, an intermontane network of rivers, lakes, and deltas. Here, Palaeocampa is found on the same layers as freshwater arthropods like Alanops, and the euthycarcinoids Sottyxerxes and Schramixerxes. It also would have co-existed with freshwater xenacanth sharks, lungfish, temnospondyls, syncarid shrimp, and ostracods. Palaeocampa is the only confirmed venomous lobopodian. The spines of Palaeocampa also differ in the outward direction of their serrations, as opposed to the inwardly facing hooks more commonly found in urticating hairs. == Phylogeny ==

Phylogeny of Panarthropoda after Knecht et al. 2025: }} }}}}}}}}}}}}}}}}}}}}}}}}}} }}}} }} }} }} }}}}}}}}}}}}}}}}|style=font-size:90%}} ==References==