CLARIFYING THE TAXONOMIC AFFINITY OF THREE UNDESCRIBED ARTHROPODS FROM THE WAUKESHA LAGERSTÄTTE, WISCONSIN, USA

The Silurian Brandon Bridge Formation, Waukesha, WI, USA, hosts a Konservat-Lagerstätte of unique soft-bodied fossils. Unlike most Silurian deposits, this assemblage lacks most biomineralizing fauna, but preserves taxa not observed elsewhere. Most animal fossils are preserved through sub 3-D phosphatization, with rare kerogenization and limited pyritization. Despite the abundance and quality of the assemblage, much of this biota remains understudied or undescribed. Using a combination of light microscopy, SEM-EDS, µCT, and morphological character analysis, we elucidate the phylogenetic placement of three enigmatic arthropod fossils from the Waukesha Lagerstätte.

Acheronauta ferropugnax gen. et sp. nov. (proposed) is a relatively common, crustacean-like arthropod bearing two or three raptorial head limbs, a head carapace, a long, segmented trunk, and small, posterior swimming appendages. Initial analyses suggested an affinity with either the thylacocephalans or remipedes, both of which have an overall similar morphology to A. ferropugnax. However, thylacocephalans are completely enclosed in a bivalved carapace, while remipedes have only a head shield, suggesting that A. ferropugnax. is a unique taxon bearing affinities with the Remipedia.

Papiliomaris kluessendorfae gen. et sp. nov. (proposed) has five head appendages and ten trunk segments. The uniramous antennules have podomeres with setae, while the other head limbs bear two rows of filamentous setae. The most prominent head appendages, the mandibles, have shorter rami but longer setae than the maxillules. Maxillae are typically small and poorly preserved. Though P. klussendorfae was briefly associated with Marrellamorpha, the limited trunk segments and the form of the trunk appendages suggest an alternative taxonomic placement.

The uncommon Chelulaphora punctanti gen. et sp. nov. (proposed) bears a combination of characters—including 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—that defy ready classification. Phylogenetic analyses resolve this organism as basal to crown-group Mandibulata and Chelicerata, but its exact placement is inconclusive.