Abstract
Hadrosaurid dinosaur diversity in the San Juan Basin of New Mexico has been difficult to determine due, in part, to poor preservation of specimens compared to those found in northern North America. A reexamination of a collection of hadrosaurid material from the Hunter Wash Member of the Kirtland Formation in San Juan County, New Mexico, excavated in 1922 by Charles H. Sternberg, has revealed some well‐preserved specimens. Among these specimens is a large hadrosaurid humerus that is 860 millimeters in length, with a humeral shaft diameter of 176 millimeters. The proportional size of the deltopectoral crest in relation to the humeral shaft indicates that the humerus comes from a saurolophine hadrosaur.Previously recognized hadrosaurid diversity in the lower Kirtland Formation has been restricted to the lambeosaurine, Parasaurolophus cyrtocristatus, and the saurolophine, Kritosaurus navajovius. Recent studies of hadrosaurid elements in this Sternberg collection have indicated that there are additional, as yet unnamed, saurolophine taxa in the San Juan Basin with strong affinities to the Kritosaurini, but distinct from K. navajovius. The large humerus is significantly larger than that of any of the previously known hadrosaurid taxa from the lower Kirtland Formation, including the newly described kritosaurine material. Morphometric analysis of the humerus suggests an element with proportions similar to those of Shantungosaurus, one of the largest hadrosaurs, and dissimilar to any of the previously known San Juan Basin hadrosaurid taxa. The robust construction of the humeral shaft is reflected by a shaft volume to humeral length ratio that greatly exceeds most other hadrosaurid taxa, resulting in a humerus with greater loading capacity. Though it is an isolated element, this humerus provides evidence that there were large hadrosaurids, potentially from a new species, living in the San Juan Basin, expanding the diversity of the San Juan Basin hadrosaurid dinosaur fauna.
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