Scolosaurus

Scolosaurus is an extinct genus of ankylosaurid dinosaurs within the subfamily Ankylosaurinae. It is known from the lower levels of the Late Cretaceous Dinosaur Park Formation (latest middle Campanian stage, about 76.5 Ma ago) of Alberta, Canada. It contains a single species, Scolosaurus cutleri.[1] It is the oldest known North American anklylosaurid.

Discovery
Scolosaurus was named by Franz Nopcsa von Felső-Szilvás in 1928, based on holotype NHMUK R.5161, a nearly complete specimen that preserves the entire skeleton except for the distal end of the tail, the right forelimb, the right hindlimb, and the skull. The rare preservation of osteoderms and skin impression are also present. The fossil skeleton was discovered by William Edmund Cutler of the Royal Tyrrell Museum of Palaeontology in 1914 at Quarry 80 of the Deadlodge Canyon locality.[1][2] It was collected from the bottom of the Dinosaur Park Formation in fine-grained sandstone and fine-grained claystone sediments that were deposited during the Campanian stage of the Late Cretaceous period, approximately 76.5 million years ago. This makes it the oldest known North American ankylosaurid.[3] Original reports indicated that specimen NHMUK R.5161 was excavated from the uppermost layers of the underlying Oldman Formation, but this has proven to be inaccurate. The holotype specimen is housed in the collection of Natural History Museum, London in London, England.

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.[4] 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. Kevin Padian et al. (1995) assigned this material to Scolosaurus, which finally provided the known material with a skull.[5] This is also housed at the Smithsonian Institution.

In 2008, D. K. Zelenitsky and F. Therrien assigned specimens FPDM V-31, NSM PV 20381 and TMP 2001.42.9 to Scolosaurus. 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. These specimens were also recovered at the Two Medicine Formation and were excavated from mudstone and lithified, lenticular sandstone sediments that were also deposited during the Campanian.[6]

In 2013, Arbour and Currie reassigned specimen MOR 433, upon which the genus Oohktokia was based, to Scolosaurus. This specimen consisted of a partial skull, both humeri, a caudal vertebra and several osteoderms. MOR 433 was recovered in the Upper Member of the Two Medicine Formation, in Montana, which radiometric dating has shown to be approximately 74 million years old.[7] The remains were collected in 1986-1987 in grey siltstone that was deposited during the Campanian stage of the Cretaceous period.[3] The specimen is housed in the collection of the Museum of the Rockies in Bozeman, Montana.