Revisiting horseshoe crab fossils from the Middle Triassic (Anisian) Strelovec Formation Konservat-Lagerstätte of Slovenia

Xiphosura are a group of marine euchelicerates with a fossil record spanning the majority of the Phanerozoic. Despite this longevity, horseshoe crab fossils are uncommon. This rarity is a result of their cuticular exoskeleton that limits the preservational potential of xiphosurid specimens. Nonetheless, a xiphosurid evolutionary radiation is recorded in Triassic-aged deposits. This event likely reflects the occupation of vacant niches after the end-Permian extinction. Here, we revisit Sloveniolimulus rudkini Bicknell et al., 2019b-a Middle Triassic horseshoe crab from the Strelovec Formation that was previously known from one specimen-and include newly identified material to explore the validity of the taxon. We demonstrate that unique genal spine morphologies are observed in all specimens, supporting the maintenance of S. rudkini. In documenting this material, we also considered the preservational pathways for horseshoe crabs in limestone and document other metazoan groups from this as-of-yet underexplored Konservat-Lagerstätte.