Growing Taxonomic Diversity of the mid-Cretaceous (late Albian-Cenomanian) Wayan Formation Vertebrate Assemblage of Idaho
KRUMENACKER, L. J., Idaho Museum of Natural History and Department of Geosciences, Idaho State University, Pocatello, ID. AVRAHAMI, Haviv, North Carolina Museum of Natural Sciences and Department of Biological Sciences, North Carolina State University, Raleigh, NC. IRMIS, Randall, Natural History Museum of Utah, University of Utah, Salt Lake City, UT. KIRKLAND, James I., Utah Geological Survey, Salt Lake City, UT. WEAVER, Lucas, Biology Department, University of Washington, Seattle, WA. WILSON, Gregory P., Burke Museum, University of Washington, Seattle, WA. ZANNO, Lindsay, North Carolina Museum of Natural Sciences and Department of Biological Sciences, North Carolina State University, Raleigh, NC
Previous sampling of the vertebrate assemblage of the mid-Cretaceous (late Albian-Cenomanian) Wayan Formation of eastern Idaho suggests a low taxonomic diversity, with the majority of fossil remains belonging to either eggshell assignable to Macroelongatoolithus carleylei (representing a giant oviraptorosaurian theropod) or skeletal elements of the burrowing orodromine neornithischian Oryctodromeus cubicularis. Collaborative work has demonstrated the presence of numerous new taxonomic records that are now undergoing preparation and description. A partial skeleton, consisting of dorsal and caudal vertebrae, limb elements, and armor elements represents a small nodosaurid ankylosaurian of as-yet uncertain affinities. A hadrosauroid of indeterminate affinities is known from very fragmentary associated vertebrae and a dentary fragment. A small tyrannosauroid, similar to Moros intrepidus from the Mussentuchit Member of the Cedar Mountain Formation in Utah, is known from a partial femur. Crocodyliforms include the partial skull of a large neosuchian similar to Deltasuchus from the Woodbine Formation in Texas, and a braincase of an as-yet unidentified diminutive taxon. At least four multituberculate mammal taxa are known from isolated teeth, including a new species of Cimolodon, representing the oldest known occurrence of the genus. Dental remains of metatherian and eutriconodont mammals have also been recovered from the Wayan and are currently undergoing description.
Paleobiota of the Wayan is most similar to that of the Cenomanian (98-96 Myr) Mussentuchit Member of the Cedar Mountain Formation. Both assemblages preserve an atypical abundance of eggshell referable to partially buried clutches and fossorial vertebrate remains, which may reflect an ecological signal and/or taphonomic biases operative in the upland monsoonal paleoenvironment. The presence of orodromine, caenagnathid, nodosaurid, tyrannosauroid, and hadrosauroid dinosaurs, neosuchian crocodyliforms, and multituberculate and metatherian mammals reflect the typical faunal components of later Late Cretaceous Laramidian assemblages, making the Wayan specimens integral in documenting the rise of typical Late Cretaceous faunas.