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| Parioscorpio venator Wendruff, Babcock, Wirkner, Kluessendorf & Mikulic, 2020 in Anderson, Schiffbauer, Jacquet, ... et Mikulic, 2021. DOI: 10.1111/pala.12534 2020. DOI: 10.1038/s41598-019-56010-z |
Abstract
A relatively uncommon arthropod of the Waukesha lagerstätte, Parioscorpio venator, is redescribed as an arthropod bearing a combination of characters that defy ready classification. Diagnostic features include sub‐chelate ‘great appendages’, a lack of antennae, multiramous anterior trunk appendages, filamentous fan‐like rear trunk appendages, and apparently thin and poorly preserved pleural fields. Phylogenetic analysis resolves this organism as basal to crown‐group Mandibulata and Chelicerata, but its exact placement is inconclusive. Thus, we compare its morphology to several stem groups of arthropods in a discussion of its plausible taxonomic affinities. The examined specimens are probably carcasses and preserve a variety of soft‐tissue details, including muscle blocks in the head, eyes and eye facets, likely ventral nerve cords, a central gut tract and trunk legs with multiple filamentous elements organized into stiff bundles. The preservation habits of P. venator are characterized and compared to previous assessments of Waukesha lagerstätte taxa. Four preservation habits are observed: a phosphatized habit showing flattened to partly three‐dimensional mineralization in francolite; a mouldic habit largely left behind by removed francolite that shows no carbon enrichment despite a darkened colour; sheet‐like or speckled carbonaceous compressions; and scattered pyrite crystals. This redescription highlights both the palaeobiological value of ‘small’ lagerstätten typical of the middle Palaeozoic and the caution that must be taken when interpreting their more enigmatic constituents.
Keywords: stem‐group Arthropoda, taphonomy, phosphatization, nerve cord, appendage, morphology, tagma
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| Specimens upon which the rediagnosis and redescription of Parioscorpio venator Wendruff et al., 2020 are primarily based. A, UWGM2793, a nearly complete specimen with an entire left great appendage. B, UWGM2785, a specimen with all cephalic appendages intact, including both great appendages, which are nearly complete; note that the posterior portion of the body is still buried beneath the matrix. C, UWGM2764, paratype and counterpart to UWGM2163, preserved as a thin film with the right great appendage barely visible on the upper right; no trunk appendages are preserved, which makes the posterior constriction of the axial trunk easy to see compared to other specimens. D–E, part and counterpart of UWGM2857, a nearly complete specimen with numerous head and trunk details. F–G, part and counterpart of UWGM2854, which preserves many three‐dimensional limbs, but whose head is cut off by the border of the matrix. H, UWGM2798, a largely mouldic specimen showing excellent preservation of the cephalic appendages, including two complete great appendages. I–J, part and counterpart of UWGM2885, a nearly complete specimen which shows limited three‐dimensional preservation, but preserves many walking legs as dark compressions. All scale bars represent 5 mm. |
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| Reconstructions of the morphology of Parioscorpio venator. A, whole body, from a three‐quarters dorsal view; note that the limbs can be seen through the thin, translucent tergopleural cuticle; the tentative preservation of the tergopleurae in most specimens raises this possibility. B, focus on the great appendage and second cephalic appendage and their attachment to the head; the reconstruction shows slight lateral displacement of the limbs to better envision their bases; note that the sclerotized portion of the first article of the great appendage is contained within a translucent membrane. C, illustration showing our reconstruction of a standard trunk limb; limb rami are labelled in roman (with alternative interpretations in smaller font), while individual filamentous bundles on the endopod and endopodal exite/exopod are labelled in italics; the exact proportions of the limb components vary based on the limb's placement on the body; this illustrated limb, with the racemose filamentous bundle considerably longer than the exopod/epipod or the walking portion of the endopod, is from the middle of the trunk. © 2021 The Curators of the University of Missouri, a public corporation. |
Evan P. Anderson, James D. Schiffbauer, Sarah M. Jacquet, James C. Lamsdell, Joanne Kluessendorf and Donald G. Mikulic. 2021. Stranger than A Scorpion: A Reassessment of Parioscorpio venator, A problematic Arthropod from the Llandoverian Waukesha Lagerstätte. Palaeontology. DOI: 10.1111/pala.12534
Genus Parioscorpio gen. nov.
Etymology. From Latin, pario, progenitor, and scorpio, scorpion.
Parioscorpio venator gen. et sp. nov.
Etymology. From Latin, venator, hunter.
Types. Holotype, University of Wisconsin Geology Museum, Madison, Wisconsin, UWGM 2162. Paratype,
UWGM 2163.
Location. Waukesha Lime and Stone Company west quarry, north of State Highway 164, Waukesha, Wisconsin,
USA.
Horizon. Lower part of the Brandon Bridge Formation (Silurian: Llandovery, Telychian).
Andrew J. Wendruff, Loren E. Babcock, Christian S. Wirkner, Joanne Kluessendorf and Donald G. Mikulic. 2020. A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation. Scientific Reports. 10: 14. DOI: 10.1038/s41598-019-56010-z
