DESCRIBING AN ENIGMATIC, MARRELLOMORPH-LIKE ARTHROPOD FROM THE SILURIAN BRANDON BRIDGE FORMATION, WAUKESHA, WI

The Brandon Bridge Formation, Waukesha, WI, USA, hosts a Silurian Konservat-Lagerstätte of unique soft-bodied fossils. This assemblage mostly lacks a typically Paleozoic biomineralizing fauna, but preserves taxa rarely observed elsewhere in the Silurian, marking its importance for investigating the evolution of soft-bodied organisms during this time. Samples come from finely laminated dolomudstone and dolomite in the lower portion of the formation and are preserved through sub-three-dimensional phosphatization, with some kerogenization and limited pyritization. Much of the biota remains understudied or undescribed, despite the quality of the assemblage. Using a combination of light microscopy, SEM-EDS, µCT, and morphological character analysis, we describe what may be the most enigmatic arthropod from the Waukesha assemblage and determine its phylogenetic placement.

Papiliomaris kluessendorfae gen. et sp. nov. (proposed) has five head appendages and nine to eleven trunk segments. The antennules are uniramous with coarse setae on the podomeres, while the antennae bear fine, plumose filaments, either in two ranks on a uniramous limb, or in one rank on a tightly coupled biramous limb. The other head limbs bear two rows of filamentous setae on their exopods. The longest exopods are found on the maxillules, while the mandibles exopods have longer setae. The maxillae are typically smaller than the prior two limbs and poorly preserved. Most trunk segments bear short, pointed pleurites, and trunk limbs are questionably preserved.

Previously, P. klussendorfae has been associated with bivalved arthropods or the Marrellomorpha. Samples used in the study show no evidence of a bivalved carapace, though biomineralized tissues can be poorly preserved in this deposit which may result in the loss of this feature. The limited trunk segments and the form of the trunk appendages suggest P. klussendorfae is not a marrellomorph; however, initial phylogenetic analyses placed Marrella as a sister clade. This may be due to a limited systematic understanding of the Marrellomorpha and/or the grossly similar appearance to P. klussendorfae.