COMPARATIVE ANATOMY AND MORPHOMETRIC ANALYSIS OF THE MOST COMPLETE DINOSAUR IN MISSISSIPPI: A CF. SAUROLOPHINAE (HADROSAURIDAE) FROM AN EARLY TO MIDDLE CAMPANIAN LOCALITY IN THE COFFEE FORMATION, PRENTISS COUNTY, MS

The dinosaur fossil record of Mississippi comprises nearly 90 specimens, mostly isolated bones with poor preservation. Hadrosauroids are the most common dinosaurs in the state, although none display diagnostic features allowing referral to the species, genus, or subfamily level. Here, we describe MMNS VP-12239, informally known as the Booneville Dinosaur, the most complete dinosaur found thus far in Mississippi—a potential saurolophine hadrosaurid. This specimen was found in ca. 2011 at the Booneville Dinosaur Site (BDS), an early to mid-Campanian Coffee Formation outcrop in northeastern Mississippi, interpreted as a tidally influenced estuarine to deltaic environment. Other southeastern hadrosauroids including Lophorhothon atopus and Eotrachodon orientalis are described from the Mooreville Chalk, a deepwater marine environment. Notably, the Booneville Dinosaur represents the first taxonomically significant southeastern Hadrosaurian dinosaur to be discovered in a paralic depositional environment. The site has yielded two individuals: a nestling consisting of a toothless dentary, and an adult represented by various postcranial bones. Due to extensive modification of their cranium, phylogenetic hypotheses of hadrosauroid relationships have been influenced by the greater proportion of cranial characters present in the datasets. This is problematic for identifying the adult specimen (MMNS VP-12239) because it only preserves postcranial elements. This challenge is compounded by a paucity of southeastern hadrosauroid specimens for comparison.

Here, we describe the osteology of MMNS VP-12239 aiming at the identification of taxonomically and phylogenetically informative characters, thus facilitating comparisons with other hadrosauroids and character scoring in phylogenetic datasets. The most diagnostic elements include a left humerus and both pubes. The proportions of the humerus of MMNS VP-12239 are consistent with the proximodistally long and craniocaudally narrow humeri of saurolophine hadrosaurids and non-hadrosaurid hadrosauroids, unlike lambeosaurines, in which the opposite is typically observed. Additionally, a Procrustes superimposition geometric morphometric analysis of the pubis of MMNS VP-12239 suggests a morphology similar to that of saurolophines.