FIRST NOVEL WYOMING PLIOSAURID LOCALITY IN 120 YEARS

The holotype of pliosaurid Megalneusaurus rex, as first described by Wilbur Knight in 1895, included two limbs, vertebral, and pectoral material. However, of this original material, all skeletal elements except the limbs have been lost. The 1895 excavation site of this specimen was rediscovered in 2008 from which an additional articulated forelimb and vertebral elements have been collected and described. Though other plesiosaurian skeletal remains have been collected from the Sundance formation, the bones collected from Knight’s site represented the only pliosaurid individual known from the Jurassic of Wyoming. New material collected in 2013 and 2014 represents the second distinct pliosaurid specimen from the Sundance formation of Wyoming. These partially articulated post-cranial remains were found in the Redwater Shale near the Red Gulch Dinosaur Trackway. The depositional environment was similar to that of the 1895 excavation site, an offshore mudstone, directly below a bivalve shoal and 20 m below the Windy Hill Sandstone. The newly collected material includes articulated phalanges from digits II-V, a dorsal rib with intact articular surfaces, and associated metapodials and phalanges (including one distal phalanx). The propodial elements closely fit descriptions of the holotype M. rex material, including proximally concave metapodials and laterally interlocking, offset phalanges. Deformation of one associated phalanx may represent a pathology. A comparison of phalangeal dimensions to those of the forelimb recovered in 2008 from the Knight locality suggest that the new specimen was somewhat smaller than the holotype. Although incomplete and damaged by modern pedogenesis, the new material may be used to constrain previous estimates of body size through comparisons to related genera.