TAPHONOMY OF MARINE REPTILES AND DINOSAURS OF THE UPPER CRETACEOUS MORENO FORMATION, CALIFORNIA

The Moreno Formation in California provides well-preserved fossils of marine reptiles and dinosaurs. This study examines the preservation quality of 97 mosasaurs, plesiosaurs, and hadrosaurs of the Upper Cretaceous portion of the Moreno Formation. Seventy-seven mosasaur, 15 plesiosaur, and 5 hadrosaur specimens are analyzed at the University of California Museum of Paleontology in Berkeley and the Natural History Museum of Los Angeles County. The specimens’ average skeletal completeness, skeletal abrasion, weathering, fragmentation, compression, and bone damage marks are researched between three vertebrate groups and three sedimentary members. The obtained results show that (1) the average skeletal completeness of mosasaur, plesiosaur, and hadrosaur specimens of the Moreno Formation is higher than that of these taxa in other fossil sites in North America and abroad, (2) the preservation of the plesiosaurs is the most remarkable, followed by that of the mosasaurs and hadrosaurs, and (3) fossil preservation is varied among different sedimentary members of the Moreno Formation. The exceptional preservation of the Moreno Formation specimens has important implications for the study of the functional morphology, systematics, phylogenetic reconstruction, paleogeography, and regional stratigraphy of mosasaurs, plesiosaurs, and hadrosaurs in the Upper Cretaceous Pacific Coast of North America.