| Parioscorpio | |
|---|---|
 | |
| Reconstruction as a non-scorpion, enigmatic arthropod | |
 | |
| Fossil specimen ofP. venator | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Genus: | †Parioscorpio Wendruffet al,2020 |
| Type species | |
| †Parioscorpio venator Wendruffet al, 2020 | |
Parioscorpio is an extinct genus ofarthropod containing the speciesP. venator known from theSilurian-agedWaukesha Biota of theBrandon Bridge Formation nearWaukesha, Wisconsin. This animal has gone through a confusing taxonomic history, being called anarachnid,crustacean, and anartiopodan arthropod at various points.[1][2][3] This animal is one of the more famous fossil finds from Wisconsin, due to the media coverage it received based on its original description in 2020 as a basalscorpion.[4][5][6]
The fossils were originally discovered in 1985, tentatively identified as abranchiopod orremipedecrustacean[1][7] but were neglected for decades.[8] In 2016, some of the fossils now assigned toParioscorpio were given the nameLatromirus and were assigned to an extinct group of earlyPaleozoic arthropods known ascheloniellids 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 theInternational Code of Zoological Nomenclature. The fossils known as “Latromirus” were also mistakenly named “Xus yus” in a preprint of a separate paper.[10] Upon initial publication in 2020,Parioscorpio was considered the world's oldest and most primitive knownscorpion, older thanDolichophonus from Scotland by several million years.[3] In 2021, the fossils were reanalysed, andParioscorpio was found not to be a scorpion, but an arthropod of uncertain placement, outside ofMandibulata,Chelicerata and all other groups of extinct arthropods (e.g.Megacheira,Fuxianhuiida,Artiopoda and so on).[8]
In 2021 another paper stated thatParioscorpio venator, including the fossils previously calledLatromirus, might be acheloniellid.[2] If this is correct, it means thatP. venator is related totrilobites,nektaspids,aglaspidids, xenopods, and xandarellids.[11] However in 2022, its affinity as cheloniellid is questioned, and firmly rejected from that clade.[12] Currently the most resolved tree in the paper consideredP. venator as an enigmaticstem-group arthropod.[8][12]
In 2022 a study was published describingAcheronauta stimulapis, a new species of possible mandibulate arthropod from the biota.[13] While coding the phylogenetic trees for this arthropod, the authors of the paper also includedParioscorpio, and all of the trees preformed presented this creature as abasal taxon of arthropod that sat in between the groups Artiopoda and Mandibulata.[13] This discovery actually is consistent with the rejection ofP. venator as a cheloniellid.[12] As of 2023,P. venator is regarded as a basaleuarthropod.[14]
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'sclawedpedipalps),[3] as well as another pair of small appendages.[8] Central to the head was a mouth-coveringhypostome 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 oftergite) 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]
Parioscorpio may had been a marine or brackish waterpredator, using an ambush prey-capture method similar to extant waterbugs (Nepomorpha).[8] It would have lived alongside many other bizarre organisms like theConodontPanderodus, the enigmaticButterfly Animal, theThylacocephalanThylacares, earlysynziphosurans, andTrilobites.[15]