A NODOSAURID SKELETON FROM THE GLENROCK EXPOSURE WITH NOVEL ARMOR MORPHOLOGY AND EVIDENCE OF TYRANNOSAURUS FEEDING

GPM-0018 is an associated ankylosaur skeleton excavated from the Glenrock Exposure of the Lance Formation (Upper Maastrichtian), WY. The specimen consists of over 250 osteoderms and one right ischium. Based on the morphology of the osteoderms, which are generally symmetrical and have slightly concave bases, and the ischium, which is strongly curved, GPM-0018 is identified as a nodosaurid (most probably Denversaurus). The recovered osteoderms range in morphology from small elliptical nodules to larger keeled components of the cervical half-rings. Many of the medium-sized osteoderms are hexagonal in dorsal/ventral view. That these hexagonal osteoderms articulated together in a mosaic fashion is affirmed by multiple fused sections, where the hexagonal osteoderms had grown together. The largest of these fused mosaic sections is over 230 mm long and is similar in general form to a portion of a pelvic shield, as is known in ankylosaurs like Gastonia and Polacanthus, but lacks keels, rosettes, or other prominent surface features. Both the lateral and medial side of the ischium bear large indentations, some with associated pre-burial surface abrasion. Comparisons with bite marks known from other Late Cretaceous dinosaurs indicate that these punctures were left by the bite of a tyrannosaur. The abundance of these feeding marks on the ischium and the absence of other non-osteoderm bones preserved at the site suggest that the GPM-0018 skeleton was extensively picked over by a Tyrannosaurus and that more desirable elements were consumed or carried away.