Paleolimulus, an early limuline (Xiphosurida), from Pennsylvanian-Permian Lagerstatten of Kansas and taphonomic comparison with modern Limulus

The Pennsylvanian-Permian horseshoe crab Paleolimulus signatus (Beecher), i ncorporating as a junior synonym P. avitus Dunbar, is one of the earliest s pecies of the Limulina (Xiphosurida). Some specimens from Kansas, USA, are exceptionally well preserved, retaining intact book gills and appendages. I ndistinct, bilobed burrowing traces of variable width occur in association with some examples of P. signatus and may have been produced by that animal . Based on actualistic taphonomic experiments on Limulus polyphemns, ancien t horseshoe crabs and other arthropods having non-mineralized exoskeletons are inferred to have become pliable soon after death or moulting, and to ha ve disarticulated slowly prior to burial. Extreme compression, wrinkling, a nd loose folding of sclerites are attributed to burial of a pliable exoskel eton. Slow preburial disarticulation partly accounts for the exceptional pr eservation of Paleolimulus remains. Also relevant for the exceptional prese rvation of these arthropods was burial in estuarine, tidal flat, or lacustr ine environments. Because of fluctuating salinity and possibly dessicating conditions, these settings were limiting to scavengers, burrowers, and some microbes that could potentially disarticulate or decompose xiphosurid rema ins.