A novel feeding mechanism of diplodocid sauropods revealed in an Apatosaurine skull from the Upper Jurassic Nail Quarry (Morrison Formation) at Como Bluff, Wyoming, USA

Dental complexes of sauropod dinosaurs have been studied in members of Diplodocoidea and Macronaria. However, the disparity among the number of replacement teeth between the premaxilla, maxilla, and dentary of apatosaurine sauropods has yet to be fully investigated. TATE-099, a nearly complete and associated apatosaurine skull and dental complexes from the upper Morrison Formation (Upper Jurassic) at Como Bluff, Wyoming, contains cranial characters consistent with Apatosaurus sp. Unerupted dental complexes of the right premaxilla, maxilla, and dentary were imaged and digitally reconstructed using computed tomography (CT). Results indicate four premaxillary alveolar positions each with 5–7 unerupted replacement teeth, 10 maxillary alveolar positions each with 3–5 unerupted replacement teeth, and 10 dentary alveolar positions each with only 1–2 unerupted replacement teeth. The capacity of replacement teeth in TATE-099 is higher than reported in the genus Diplodocus and consistent with data from previous studies on niche partitioning among coeval Morrison Formation sauropods. Disparity among the capacity of dental complexes of TATE-099 further suggests novel feeding mechanics in apatosaurines. CT data also support a new hypothesis of tooth replacement in diplodocids, where entire rows of teeth are replaced as a single unit, rather than individually. The high-capacity of replacement teeth in the premaxilla is only known to be succeeded by one taxon (Nigersaurus) and suggests frequent wear of the premaxillary teeth. However, considerably fewer replacement teeth in the dentary of TATE-099 suggests less-frequent. These results offer insight into the feeding mechanisms and disparity of sauropods within Flagellicaudata. Joseph E. Peterson. University of Wisconsin-Oshkosh, Department of Geology, 800 Algoma Boulevard, Oshkosh, Wisconsin 54901, USA. petersoj@uwosh.edu (corresponding author) David Lovelace. University of Wisconsin-Madison, Geology Museum, Madison Wisconsin 53706, USA. dlovelace@wisc.edu PETERSON ET AL.: APATOSAURINE FEEDING MECHANISM 2 Melissa Connely. Stratigraphic rex LLC, Casper, Wyoming 82604, USA. melconn45@gmail.com Julia B. McHugh. Museums of Western Colorado, Grand Junction, Colorado, 81502, USA and Colorado Mesa University, Department of Physical and Environmental Sciences, Grand Junction, Colorado, 81502, USA. jmchugh@westcomuseum.org