Pruemopterus is a genus of eurypterid, an extinct group of aquatic arthropods. The type and only species of Pruemopterus, P. salgadoi, is known only from a single fossil specimen, discovered in deposits of Early Devonian age in Germany. The generic name is derived from the Prüm river and the surrounding Prüm valley, which contains the finding place of the fossil, and the Greek πτερόν (pteron, "wing"), referring to the eurypterid swimming paddles, and the species name honors the Brazilian photographer and photojournalist Sebastião Salgado.
Pruemopterus was a very small adelophthalmid eurypterid, with the type and only known specimen only measuring about 2.5 centimeters (0.98 in) in length. Although superficially similar to the related genus Parahughmilleria, Pruemopterus can be distinguished from other adelophthalmids by several features, most notably its wide and vaguely rectangular carapace (head plate) and its rounded, rather than elongated, eyes. Pruemopterus lived alongside other Early Devonian animals, including several other eurypterid genera, in a shallow brackish to fresh water environment.
Description
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.
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.
History of research
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.
