Osteology, Morphometrics, and Phylogenetic Systematics of the ‘Booneville Dinosaur’ (Ornithopoda: Hadrosauridae) From the Early–Middle Campanian Coffee Formation of Northeastern Mississippi

The non-avian dinosaur fossil record of Mississippi includes members of the clades Hadrosauroidea, Nodosauridae, Tyrannosauroidea, Ornithomimidae, Dromaeosauridae, and Ceratopsia. These members are represented only by non-articulated usually isolated elements, deposited in the marine and terrestrial units of the Mississippi Embayment from the Coniacian through the Maastrichtian of the Late Cretaceous. MMNS VP-12239, also known colloquially as the Booneville Dinosaur, is an iguanodontian ornithopod discovered at the Booneville Dinosaur Site, an outcropping of the Coffee Formation in northeastern Mississippi. This specimen is the most taxonomically significant dinosaur to be discovered in Mississippi and is represented by partially complete postcranial material, including taxonomically informative elements such as the left and right pubes and a left humerus. Morphometric and phylogenetic analyses were utilized to elucidate the taxonomic identity of MMNS VP-12239 among iguanodontian ornithopods. MMNS VP-12239 was recovered as a basal hadrosaurid, an outgroup of the clade containing the more morphologically derived hadrosaurids (Saurolophidae). The morphometric analysis of the humerus supports this hypothesis as the humeral characters of MMNS VP-12339 were found to be very similar to other outgroups of Saurolophidae. The geometric morphometric analysis performed for the pubis, however, conflicted with this hypothesis and suggested a morphology more similar to the clade Saurolophinae than either Lambeosaurinae or any non hadrosaurid hadrosauroids. This suggests that MMNS VP-12239 is likely an outgroup member of the clade Saurolophidae with a pubic morphology more similar to Saurolophinae. MMNS VP-12239 is morphologically and chronologically distinct from other Appalachian hadrosaurids and shares few similarities with hadrosaurids outside of Appalachia.