Friday, August 17, 2018

[Paleontology • 2017] Vaderlimulus tricki • First Fossil Horseshoe Crab (Xiphosurida) from the Triassic of North America

 Vaderlimulus tricki 
Lerner, Lucas & Lockley, 2017

  holotype (UCM 140.25) lit from the upper right. Note that the right genal spine extends approximately in-line with the rounded telson boss.  

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.

Keywords: Thaynes group, Horseshoe crab, Vaderlimulus, Idaho, Olenekian, Triassic, xiphosurida, Austrolimulus, spathian, Austrolimulidae, Psammolimulus

 Reconstruction of Vaderlimulus tricki.  

Subphylum Chelicerata Heymons, 1901
Order Xiphosurida Latreille, 1802
Suborder Limulina Richter & Richter , 1929
Family Austrolimulidae Riek, 1955

Genus Vaderlimulus nov. 

Etymology: The generic name Vaderlimulus is suggested by a resemblance of the holotype prosoma to the helmet worn by Darth Vader, a well-known fictional character from the Star Wars film series.

Vaderlimulus tricki sp. nov.
 Etymology: The trivial name tricki was chosen in recognition of Trick Runions of the Dinosaur Trackers Research Group, University of Colorado at Denver, who collected the holotype specimen and made it available for study.

 Allan J. Lerner, Spencer G. Lucas and Martin Lockley. 2017. First Fossil Horseshoe Crab (Xiphosurida) from the Triassic of North America. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 286(3); 289 - 302. DOI: 10.1127/njgpa/2017/0702