Notes on the pelvic armor of European ankylosaurs (Dinosauria: Ornithischia)

The pelvic armor elements in the ankylosaurian material from the Upper Cretaceous of Iharkút, Hungary are described here. Among these, a new articulated hip region of a small bodied ankylosaur is referred here to cf. Struthiosaurus sp. It preserves, uniquely among Late Cretaceous European ankylosaurs, an in situ pelvic armor composed of among others four, keeled, oval to circular osteoderms lying centrally and arranged longitudinally above the synsacral neural spines. This is the first indication of this type of pelvic osteoderm arrangement in an ankylosaur, increasing our knowledge on this poorly known part of the ankylosaur skeleton. Some additional pelvic osteoderms are also described that help to reconstruct and distinguish the pelvic armor of the two Late Cretaceous European ankylosaurs Struthiosaurus and Hungarosaurus. Both taxa have some fused parts in the pelvic armor but most probably neither of them had a single, fused pelvic shield as that of the Early Cretaceous Polacanthus. Interwoven texture on the ventral surface of the osteoderms, observed in both European taxa and known in other ankylosaurs (e.g. Polacanthus, Nodosaurus), is suggested here to be a characteristic feature of the non-keeled, fused pelvic armor elements of Ankylosauria.