The fossils were originally discovered in 1985, tentatively identified as a branchiopod or remipedecrustacean[1][7] but were neglected for decades.[8] In 2016, some of the fossils now assigned to Parioscorpio were given the name Latromirus and were assigned to an extinct group of early Paleozoic arthropods known as cheloniellids in a Ph.D dissertation,[9] but the name was never published in a peer-reviewed journal and is therefore not valid in accordance with the International Code of Zoological Nomenclature. Upon initial publication in 2020, Parioscorpio was considered the world's oldest and most primitive known scorpion, older than Dolichophonus from Scotland by several million years.[3] In 2021, the fossils were reanalysed, and Parioscorpio was found not to be a scorpion, but an arthropod of uncertain placement, outside of Mandibulata, Chelicerata and all other groups of extinct arthropods (e.g. Megacheira, Fuxianhuiida, Artiopoda and so on).[8]
In 2021 another paper stated that Parioscorpio venator, including the fossils previously called Latromirus, might be a cheloniellid.[2] If this is correct, it means that P. venator is related to trilobites, nektaspids, aglaspidids, xenopods, and xandarellids.[10] However in 2022, its affinity as cheloniellid is questioned, and firmly rejected from that clade.[11] Currently the most resolved tree in the paper considered P. venator as an enigmatic stem-group arthropod.[8][11]
In 2022 a study was published describing Acheronauta stimulapis, a new species of possible mandibulate arthropod from the biota.[12] While coding the phylogenetic trees for this arthropod, the authors of the paper also included Parioscorpio, and all of the trees preformed presented this creature as a basal taxon of arthropod that sat in between the groups Artiopoda and Mandibulata.[12] This discovery actually is consistent with the rejection of P. venator as a cheloniellid.[11] As of 2023, P. venator is regarded as a basal euarthropod.[13]
Morphology
Movement of the raptorial appendages of P. venator
The animal is around 1.6–4.5 cm (0.63–1.77 in) long.[8][2] It is characterized by a trapezoidal head with a pair of eyes located antero-medially, a pair of enlarged raptorial appendages (previously thought to be scorpion's clawedpedipalps[3]), as well as another pair of small appendages.[8] Central to the head was a mouth-covering hypostome and a pair of muscular blocks articulated to the raptorial appendages.[8] The trunk is composed of 14 segments, each associated with a pair of thin pleurae (lateral extension of tergite) and appendages.[8] The first segment is covered by the head while the posterior segments may have lateral spines.[8] The anterior 12 pairs of trunk appendages are multiramus (each composed of 4 bundles of setae and a segmented endopod) while the last two pairs are simple fan-like structures.[8] The trunk ends with 3 spines.[8]
^ abcBraddy, S.J.; Dunlop, J.A. (2021). "A sting in the tale of Parioscorpio venator from the Silurian of Wisconsin: is it a cheloniellid arthropod?". Lethaia. 54 (1): 1–7. doi:10.1111/let.12457. S2CID245285654.
^Wendruff, Andrew J. (2016). Paleobiology and Taphonomy of exceptionally preserved organisms from the Brandon Bridge Formation (Silurian), Wisconsin, USA (PhD). The Ohio State University.
^Ortega-Hernández, Javier; Legg, David A.; Braddy, Simon J. (February 2013). "The phylogeny of aglaspidid arthropods and the internal relationships within Artiopoda". Cladistics. 29 (1): 15–45. doi:10.1111/j.1096-0031.2012.00413.x. PMID34814371. S2CID85744103.
^ abPulsipher, M. A.; Anderson, E. P.; Wright, L. S.; Kluessendorf, J.; Mikulic, D. G.; Schiffbauer, J. D. (2022). "Description of Acheronauta gen. nov., a possible mandibulate from the Silurian Waukesha Lagerstätte, Wisconsin, USA". Journal of Systematic Palaeontology. 20 (1). 2109216. doi:10.1080/14772019.2022.2109216. S2CID252839113.
