Description of Acheronauta gen. nov., a possible mandibulate from the Silurian Waukesha Lagerstätte, Wisconsin, USA

Abstract

The Silurian Waukesha Lagerstätte of Wisconsin, USA, hosts a fauna of distinctive soft-bodied organisms, including a range of graptolites, worms, trilobites and uncommon arthropods, but otherwise lacks most of the shelly fauna typical of contemporaneous deposits. While several species have been described, much of the Waukesha biota remains understudied. Here, we examine numerous specimens of a previously unnamed and undescribed vermiform arthropod that bears a cephalic carapace, a suite of specialized head appendages, a long, segmented trunk, and a battery of small swimming appendages. The taxonomic and phylogenetic evaluations presented herein establish this taxon as a novel genus and species, Acheronauta stimulapis gen. et sp. nov., plausibly positioned within the basal mandibulates. Our phylogenetic analyses suggest that a new arthropod clade may be warranted, comprising Acheronauta gen. nov., Captopodus, and the thylacocephalans.

https://zoobank.org/urn:lsid:zoobank.org:pub:B572831B-1A8A-4E4E-9258-34D91AA22A74nk

Keywords:

• Silurian
• Waukesha Lagerstätte
• Wisconsin
• Euarthropoda
• vermiform
• taphonomy

Acknowledgements

The authors thank the Waukesha Lime & Stone Co. and Franklin Aggregate Inc. quarries in Waukesha, Wisconsin, for providing tours to see the Brandon Bridge Formation; C. Eaton at the University of Wisconsin–Madison Geology Museum for accessing and loaning specimens; S. Turpin Cheavens at the University of Missouri School of Medicine for professional illustration (Fig. 11); and S. Jacquet and W. Leibach for GIGAmacro imaging of holotypes. We additionally thank K. Sebert for keeping our interests engaged in the project. J. T. Haug and C. Aria are thanked for their constructive feedback and thorough reviews.

Supplemental material

Supplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772019.2022.2109216.

Author contributions

MAP photographed fossil specimens. MAP and EPA conducted phylogenetic analyses. MAP and JDS produced figures; EPA edited figures. MAP, EPA and JDS wrote and edited the manuscript with input from DGM. JDS conducted SEM and EDS analyses. LSW stacked and traced images of fossil specimens. DGM and JK collected fossil specimens. This work was supported by the University of Missouri Department of Geological Sciences to MAP (John and Betty Marshall Opportunities for Excellence Fund); the Paleontological Society (James M. & Thomas J. M. Schopf Student Research Award) to MAP; the Association of Women Geoscientists (Winifred Goldring award) to MAP; and the National Science Foundation to JDS (EAR CAREER #1652351 and EAR IF #1636643) and EPA (EAR-PF #1725762).

Associate Editor: Greg Edgecombe