Rocky Mountain Section - 75th Annual Meeting - 2025

Paper No. 35-5
Presentation Time: 11:20 AM

NEW MONSTERSAUR SPECIMENS FROM THE KAIPAROWITS FORMATION OF UTAH REVEAL UNEXPECTED RICHNESS OF LARGE-BODIED LIZARDS IN LATE CRETACEOUS NORTH AMERICA


WOOLLEY, Charles, Dinosaur Institute, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA 90007; Univeristy of Southern California Department of Earth Sciences, 3651 Trousdale Pkwy, ZHS 119, Los Angeles, CA 90089-0001, SERTICH, Joseph, Department of Geosciences, Colorado State University, Fort Collins, CO 80523, MELSTROM, Keegan M., Department of Biology, University of Central Oklahoma, Edmond, OK 73034; Dinosaur Institute, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA 90007, IRMIS, Randall, Department of Geology and Geophysics, University of Utah, 115 S 1460 E, Salt Lake City, UT 84112; University of Utah, Natural History Museum of Utah, 301 Wakara Way, Salt Lake City, UT 84108 and SMITH, Nathan D., Dinosaur Institute, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA 90007

Monstersauria (Squamata, Anguimorpha) fossils are present in most upper Cretaceous sedimentary basins in western North America, but despite almost a century of collection, their record remains extremely fragmentary. Here, we describe new material belonging to large-bodied monstersaurs, including a new taxon, Bolg amondol gen. et sp. nov., based on a fragmentary associated skeleton and co-occurring specimens from the middle unit of the upper Campanian Kaiparowits Formation of Grand Staircase-Escalante National Monument in southern Utah, USA. Phylogenetic analyses recover B. amondol within Monstersauria, with two unique anatomical features: fused osteoderms on the jugal, and the presence of autotomy septa on the distal caudal vertebrae. Critically, B. amondol is morphologically distinct from the problematic Late Cretaceous North American monstersaur Palaeosaniwa canadensis, whereas co-occurring monstersaur vertebrae and parietals from the Kaiparowits Formation (c.f. P. canadensis) highlight a pressing need for a reassessment of this important taxon. These results offer new evidence that at least three lineages of distinct, large-bodied monstersaurian lizard were present on the paleo-subcontinent of Laramidia during the Campanian Stage. Importantly, B. amondol represents the most complete squamate recovered from late Campanian southern Laramidia and reveals key anatomical characteristics for future identification of isolated lizard fossil elements.