Original paper

First fossil horseshoe crab (Xiphosurida) from the Triassic of North America

Lerner, Allan J; Lucas, Spencer G.; Lockley, Martin


The fossil record of horseshoe crabs (Xiphosurida) from the Mesozoic of North America consists of only three name-bearing specimens from the Cretaceous. We add to this depauperate record the first report of a horseshoe crab body fossil from the Triassic of North America. It comes from a locality in the Olenekian (Spathian) Thaynes Group, near Paris, Idaho, USA. This mostly complete and moderately well preserved specimen is assigned to the family Austrolimulidae Riek, 1955 as Vaderlimulus tricki, n. gen., n. sp.Vaderlimulus is the second austrolimulid taxon to be reported from the Mesozoic of North America. Its discovery adds a fourth austrolimulid genus to the global Triassic fossil record. Vaderlimulus had large genal spines that are most comparable to the Early to late Middle Triassic austrolimulid genera Psammolimulus (Spathian) and Austrolimulus (Ladinian). Heightened enlargement and proportional reduction of body elements, sometimes resulting in bizarre forms, is seen throughout the biostratigraphic range (Serpukhovian-Maastrichtian) of the Austrolimulidae. The discovery of Vaderlimulus provides additional fossil evidence of this evolutionary process. Vaderlimulus likely inhabited a shallow, possibly transitional freshwater coastal setting in the Moenkopi depositional basin along the western Pangean coastal margin.


thaynes grouphorseshoe crabvaderlimulusidahoolenekiantriassicxiphosuridaaustrolimulusspathianaustrolimulidaepsammolimulus