Parioscorpio | |
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Reconstruction as a non-scorpion, enigmatic arthropod | |
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Fossil specimen of P. venator | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Genus: | † Parioscorpio Wendruff et al, 2020 |
Type species | |
†Parioscorpio venator Wendruff et al, 2020 |
Parioscorpio is an extinct genus of arthropod containing the species P. venator known from the Silurian-aged Waukesha Biota of the Brandon Bridge Formation near Waukesha, Wisconsin. This animal has gone through a confusing taxonomic history, being called an arachnid, crustacean, and an artiopodan 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 basal scorpion. [4] [5] [6]
The fossils were originally discovered in 1985, tentatively identified as a branchiopod or remipede crustacean [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. 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 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. [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 considered P. venator as an enigmatic stem-group arthropod. [8] [12]
In 2022 a study was published describing Acheronauta 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 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. [13] This discovery actually is consistent with the rejection of P. venator as a cheloniellid. [12] As of 2023, P. venator is regarded as a basal euarthropod. [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's clawed pedipalps), [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]
Parioscorpio may had been a marine or brackish water predator, using an ambush prey-capture method similar to extant waterbugs (Nepomorpha). [8] It would have lived alongside many other bizarre organisms like the Conodont Panderodus, the enigmatic Butterfly Animal, the Thylacocephalan Thylacares, early synziphosurans, and Trilobites. [15]