New remains of the ankylosaurian dinosaur Polacanthus from the Lower Cretaceous of Soria, Spain

The Zorralbo locality of the eastern Cameros Basin, near Soria, Spain, has produced a diverse dinosaur assemblage from the Lower Cretaceous Golmayo Formation. Ankylosaurs are represented by dorsal vertebrae and ribs, a fragmentary sacrum and ilium, and several types of dermal armour. Most, if not all, of the material probably belongs to a single medium to large-sized adult individual. The Soria remains are referred to Polacanthus on the basis of the presence of conical, ungrooved presacral spines, a sacropelvic shield composed of irregularly arranged bosses and small tubercles, large spined plates, and hollow-based triangular caudal plates with an extended posterior basal edge and a pointed spine. Polacanthus is well known from the Wealden Group (Barremian-Aptian) of the Isle of Wight and from the Weald Clay Group of West Sussex (England). In addition, isolated remains have been reported from the penicontemporaneous formations of the Iberian Peninsula. The Soria outcrop is currently the most productive Polacanthus site outside England. Moreover, it has yielded the oldest record (late Hauterivian to basal Barremian according to charophyte association) of this ankylosaur known to date in Europe. Minor anatomic differences between the Soria material and the taxa P. foxii (type-species) and P. rudgwickensis suggest the presence of a third species of Polacanthus in the Iberian Peninsula, but additional material is needed to confirm this interpretation.