Xiphosurid from the Upper Permian of Tasmania confirms Palaeozoic origin of Austrolimulidae

Abstract

Representatives of Austrolimulidae exhibit the most extreme morphological variation documented within true horseshoe crabs. Relative to the more standard morphologies of paleolimulids and limulids, austrolimulids have been described as oddball taxa. Despite their unique morphologies, austrolimulid diversity is somewhat understated. A horseshoe crab specimen from the Upper Permian Jackey Shale of Tasmania described in Ewington et al. (1989) is reconsidered here to develop the recent increased interest in the family. The specimen was originally assigned to Paleolimulus sp., but an array of unique features suggests it belongs within Austrolimulidae and Tasmaniolimulus patersoni gen. et sp. nov. is erected herein. Parsimony-based phylogenetic analyses support such a placement of T. patersoni in Xiphosurida and show that the new taxon is located at the base of Austrolimulidae. Furthermore, landmark-based geometric morphometric analyses corroborate the erection of the new taxon and illustrate a more extensive occupation of morphospace by austrolimulids than previously observed. Further studies of the paraphyletic genus Paleolimulus are needed to highlight the true diversity of austrolimulids and paleolimulids.