most accurate under the principle of Occam's razor: Referred material In 1874, G. M. Dawson excavated specimen USNM 7943 at the Milk River locality of the Frenchman Formation in Alberta. It was collected from terrestrial sediments that are considered to be from the Maastrichtian stage of the Late Cretaceous, approximately 70.6 to 66 million years old. The specimen consisted of a partial first cervical ring, which is part of the dinosaur's neck. In 2013, this material was assigned to Scolosaurus by Arbour and Curry who conducted a detailed phylogenetic analysis of the ankylosauridae. It is currently housed at the Smithsonian Institution in Washington, DC. In 1928, George F. Sternberg, collected specimen USNM 11892, from the Montanazhdarcho holotype locality, high up in the Two Medicine Formation in Glacier County, Montana. The material, a partial skull, was recovered from channel sandstone sediments that were deposited during the Campanian stage, approximately 74 million years ago. This is also housed at the Smithsonian Institution. Other referred specimens include FPDM V-31, NSM PV 20381 and TMP 2001.42.9. FPDM V-31 and TMP 2001.42.9 are both skulls, in various states of preservation. NSM PV 20381 includes a skull, dorsal vertebrae, caudal vertebrae, ribs, both scapulae, both ilia, partial ischia, and both femora, both tibiae and fibulae. Distinguishing anatomical features A differential diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism. According to Arbour and Currie (2013), Scolosaurus (including the Two Medicine material) can be distinguished from other ankylosaurines based on the following characteristics: the squamosal horns are proportionately longer, are backswept, and have distinct apices (unlike Anodontosaurus lambei and Euoplocephalus tutus) the presence of a small circular caputegula at the bases of the squamosal and quadratojugal bones (unlike Euoplocephalus tutus) the postacetabular process of the ilium is proportionately longer (compared to Anodontosaurus lambei, Dyoplosaurus acutosquameus and Euoplocephalus tutus) the presence of proportionately large circular medial osteoderms with low central prominences, and compressed, half-moon shaped lateral/distal osteoderms on the cervical half rings (unlike Anodontosaurus lambei and Euoplocephalus tutus) the sacral ribs are laterally-directed (unlike Dyoplosaurus acutosquameus) the osteoderms are conical, with centrally positioned apices on the lateral sides of the anterior portion of the tail (unlike Dyoplosaurus acutosquameus) the