Parioscorpio

The fossils were originally discovered in 1985, tentatively identified as a branchiopod or remipede crustacean[1][2] but were neglected for decades.[3] 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,[4] 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.[5] 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).[3]

In 2021 another paper stated that Parioscorpio venator, including the fossils previously called Latromirus, might be a cheloniellid.[6] If this is correct, it means that P. venator is related to trilobites, nektaspids, aglaspidids, xenopods, and xandarellids.[7]

Movement of the raptorial appendages of P. venator

The animal is around 1.6 to 2.8 centimetres long.[3] 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 clawed pedipalps[5]), as well as another pair of small appendages.[3] Central to the head was a mouth-covering hypostome and a pair of muscular blocks articulated to the raptorial appendages.[3] The trunk is composed of 14 segments, each associated with a pair of thin pleurae (lateral extension of tergite) and appendages.[3] The first segment is covered by the head while the posterior segments may have lateral spines.[3] 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.[3] The trunk ends with 3 spines.[3]

Parioscorpio may had been a marine or brackish water predator, using an ambush prey-capture method similar to extant waterbugs (Nepomorpha).[3] It would have lived alongside many other bizarre organisms like the Conodont Panderodus, the enigmatic Butterfly Animal, the Thylacocephalan Thylacares, early Xiphosurans, and Trilobites.[8]