Parioscorpio
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''Parioscorpio'' is an extinct genus of
arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
containing the species ''P. venator'' known from the
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
-aged
Waukesha Biota The Waukesha Biota (also known as Waukesha Lagerstätte, Brandon Bridge Lagerstätte, or Brandon Bridge fauna) is an important fossil site located in Waukesha County and Franklin, Milwaukee County within the state of Wisconsin. This biota is pr ...
of the
Brandon Bridge Formation The Brandon Bridge Formation is a geologic formation in Wisconsin. It preserves fossils dating back to the Silurian period, including those of graptolites, conodonts and '' Parioscorpio.'' See also * List of fossiliferous stratigraphic units ...
near Waukesha, Wisconsin. This animal has gone through a confusing taxonomic history, being called an
arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...
,
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
, and an
artiopoda Artiopoda is a clade of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomor ...
n arthropod at various points. 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 Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...
.


Taxonomy

The fossils were originally discovered in 1985, tentatively identified as a
branchiopod Branchiopoda, from Ancient Greek βράγχια (''bránkhia''), meaning "gill", and πούς (''poús''), meaning "foot", is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Diplostraca (or Cladocera), Notostraca, the Devonian ...
or
remipede Remipedia is a class of blind crustaceans, closely related to hexapods, found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Se ...
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
but were neglected for decades. 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 The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
arthropods known as
cheloniellid Cheloniellida is a taxon (usually referred to as an order) of extinct Paleozoic arthropods. As of 2018,Wendruff, Andrew James, et al. "New cheloniellid arthropod with large raptorial appendages from the Silurian of Wisconsin, USA." BioRxiv (2018) ...
s in a Ph.D dissertation, 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 International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is also informally known as the I ...
. The fossils known as “Latromirus” were also mistakenly named “Xus yus” in a preprint of a separate paper. Upon initial publication in 2020, ''Parioscorpio'' was considered the world's oldest and most primitive known
scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...
, older than '' Dolichophonus'' from Scotland by several million years. In 2021, the fossils were reanalysed, and ''Parioscorpio'' was found not to be a scorpion, but an arthropod of uncertain placement, outside of
Mandibulata The clade Mandibulata constitutes one of the major subdivisions of the phylum Arthropoda, alongside Chelicerata. Mandibulates include the crustaceans, myriapods (centipedes and millipedes, among others), and all true insects. The name "Mandibul ...
,
Chelicerata The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, tic ...
and all other groups of extinct arthropods (e.g.
Megacheira Megacheira ("great hands", also historically great appendage arthropods) is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either consider ...
,
Fuxianhuiida Fuxianhuiida is an extinct clade of arthropods from the Cambrian of China. All currently known species are from Cambrian Series 2 aged deposits in Yunnan, Yunnan Province, including the Maotianshan Shales, Chengjiang biota. Although historically ...
,
Artiopoda Artiopoda is a clade of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomor ...
and so on). In 2021 another paper stated that ''Parioscorpio venator'', including the fossils previously called ''Latromirus'', might be a
cheloniellid Cheloniellida is a taxon (usually referred to as an order) of extinct Paleozoic arthropods. As of 2018,Wendruff, Andrew James, et al. "New cheloniellid arthropod with large raptorial appendages from the Silurian of Wisconsin, USA." BioRxiv (2018) ...
. If this is correct, it means that ''P. venator'' is related to
trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...
s, nektaspids, aglaspidids, xenopods, and xandarellids. However in 2022, its affinity as cheloniellid is questioned, and firmly rejected from that clade. Currently the most resolved tree in the paper considered ''P. venator'' as an enigmatic
stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
arthropod. In 2022 a study was published describing '' Acheronauta stimulapis'', a new species of possible mandibulate arthropod from the biota. 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. This discovery actually is consistent with the rejection of ''P. venator'' as a cheloniellid. As of 2023, ''P. venator'' is regarded as a basal
euarthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
.


Morphology

The animal is around long. 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
pedipalp Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among Chelicerata, chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to ...
s), as well as another pair of small appendages. Central to the head was a mouth-covering hypostome and a pair of muscular blocks articulated to the raptorial appendages. The trunk is composed of 14 segments, each associated with a pair of thin pleurae (lateral extension of
tergite A ''tergum'' (Latin for "the back"; : ''terga'', associated adjective tergal) is the Anatomical terms of location#Dorsal and ventral, dorsal ('upper') portion of an arthropod segment other than the head. The Anatomical terms of location#Anterior ...
) and appendages. The first segment is covered by the head while the posterior segments may have lateral spines. 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. The trunk ends with 3 spines.


Paleoecology

''Parioscorpio'' may had been a marine or brackish water
predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
, using an ambush prey-capture method similar to extant waterbugs (
Nepomorpha Nepomorpha is an infraorder of insects in the "true bug" order (biology), order (Hemiptera). They belong to the "typical" bugs of the suborder Heteroptera. Due to their Aquatic insects, aquatic habits, these animals are known as true Heteroptera# ...
). It would have lived alongside many other bizarre organisms like the
Conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
'' Panderodus,'' the enigmatic Butterfly Animal, the
Thylacocephala The Thylacocephala (from the Greek or ', meaning " pouch", and or ' meaning "head") are group of extinct probable mandibulate arthropods, that have been considered by some researchers as having possible crustacean affinities. As a class they ...
n '' Thylacares,'' early synziphosurans, and Trilobites.


References

{{Taxonbar, from=Q83291300 Silurian life of North America Telychian first appearances Fossil taxa described in 2020 Prehistoric arthropod genera Controversial taxa Silurian arthropods of North America