Pruemopterus

Pruemopterus was a very small adelophthalmid eurypterid, only measuring about 2.5 centimeters (0.98 in) in length. The carapace (head plate) of Pruemopterus was vaguely rectangular in shape, and was about 3.8 millimeters (0.15 in) long and 7.5 millimeters (0.3 in) wide. The compound eyes of Pruemopterus were round and placed in an anterior centrimesial (forward-central) position. Along the seventh to twelfth segments of the opisthosoma (posterior body), Pruemopterus had strong lateral epimera (spines along the edges). The posterior body of Pruemopterus was relatively wide, with the pretelson (the penultimate body segment) being about half as long as it was wide. The telson (the last body segment) itself was lanceolate (lance-shaped) and robust. As in other adelophthalmids, the walking legs of Pruemopterus were spiniferous (having spines). Though they are only preserved fragmentarily, the amount of spinosity (how spiniferous the legs were) appears to have been similar to the related Adelophthalmus.[1]

Pruemopterus differs from other adelophthalmid eurypterids mainly in features of its carapace and its eyes. The short and rectangular carapace of Pruemopterus, and its eyes being rounded rather than elongated, easily distinguishes the genus from the Adelophthalmid genera Eysyslopterus, Pittsfordipterus, Bassipterus and Nanahughmilleria and Adelophthalmus. The same also applies to the genus Parahughmilleria, which co-occurred with Pruemopterus, although the species Parahughmilleria hefteri (possibly a younger growth stage of the species Parahughmilleria major) is superficially similar to Pruemopterus in its streamlined body shape and the lateral epimera along the same segments of the opisthosoma. Pruemopterus can be distinguished from Parahughmilleria hefteri by several features, including its more centrally positioned and rounder eyes, its wider carapace, the epimera being much more prominent and the telson being broader and more robust. Another obvious difference between Pruemopterus and Parahughmilleria is that the opisthosomal segments of Pruemopterus are more or less constant in length, whereas they increase in length posteriorly in Parahughmilleria. The genus Unionopterus, probably an adelophthalmid, is fragmentarily known, which complicates comparisons, but is clearly different from Pruemopterus in its smaller eyes and the wider marginal rim of its carapace.[1]

The only known specimen of Pruemopterus was discovered by the German paleontologist Markus J. Poschmann in the 1980s in an old, now disused, sandstone quarry within the municipality of Hermespand in Weinsheim, Germany, about 800 meters north of the village of Hermespand itself, close to the village of Willwerath. The fossil deposits the specimen was uncovered in belong to the Klerf Formation and are of Early Devonian age, of the uppermost Lower Emsian epoch. Given that the fossil appears to preserve what eurypterid researchers refer to as a type A genital appendage, it appears to have been a female individual.[1]

The specimen is today housed at the Generaldirektion Kulturelles Erbe, Direktion Landesarchäologie/Erdgeschichte in Koblenz, Germany, and is part of the State Collection of Natural History of Rhineland-Palatinate. Originally given the provisional designation 355-D by Poschmann, the specimen has the repository number PWL 2014/5186-LS a,b (a being the part and b being the counterpart of the compression fossil). The fossil was not formally described by Poschmann until 2020, when he determined that the combination of traits displayed suggested that it was an adelophthalmid eurypterid similar to Parahughmilleria, known from the same deposits, but differing in features of its carapace, opisthosoma and telson. Poschmann thus named the new genus and species Pruemopterus salgadoi to accommodate the specimen.[1]

The generic name Pruemopterus is derived from the Prüm river and the surrounding Prüm valley, wherein Hermespand and Willwerath are located, and the suffix '-opterus', derived from the Greek πτερόν (pteron, "wing"), often used in naming eurypterids due to the broad, wing-like swimming appendages of the eurypterine suborder. The species name salgadoi honors the Brazilian photographer and photojournalist Sebastião Salgado.[1]

Poschmann referred Pruemopterus to the eurypterid family Adelophthalmidae, the only family within the superfamily Adelophthalmoidea. In particular, Poschmann noted that morphological comparisons with other adelophthalmid genera suggest that Pruemopterus was most closely related to Parahughmilleria.[1]

Poschmann also noted in his description of the type specimen that there were also close similarities to the Hughmilleriidae in the Pterygotioidea superfamily, though Pruemopterus differed from the genera in that family in having prominent lateral epimera on its opisthosomal segments (a feature for the most part missing among the hughmilleriids) and its eyes not being placed on the margin of the carapace.[1]

The deposits in which the Pruemopterus fossil was discovered are part of the so-called "Fossil-Lagerstätte Willwerath", a "classic" Early Devonian fossil locality that has yielded numerous early land plants, arthropods and vertebrates. Among the chelicerates, to which the eurypterids belong, the Early Devonian deposits have yielded both arachnids and early xiphosurans (genus Willwerathia). Eurypterids are especially diverse in these deposits, accounting for five genera in addition to Pruemopterus: Jaekelopterus, Rhenopterus, Erieopterus, Adelophthalmus and Parahughmilleria.[1] Pruemopterus appears to have lived in non-marine aquatic environments. The Early Devonian eurypterid-yielding fossil sites in the Rhineland have been interpreted as having been part of a shallow aquatic environment with brackish to fresh water.[2]

• List of eurypterid genera
• Timeline of eurypterid research