before the knob, is strongly rounded. The front three side osteoderm pairs are covered by a black film that could be the remnant of their original keratin sheaths. If so, these added to their length. The sheaths show clear grooves and ridges directed towards the point. At the left osteoderm of the third pair, a layered structure is visible at its base, resembling the construction of horn bases in bovids. At the rear osteoderms, the film covering is incomplete, showing that the underlying bone structure does not conform to the sheath riles as it is much smoother. The knob is relatively large with a length of , a width of , and a vertical height of . The bulk of the knob is formed by a pair of large osteoderms, each positioned at the side. In the holotype individual, the left side osteoderm is distinctively longer than the right one, giving the knob as whole a rather asymmetrical profile. This osteoderm also overlaps the last left triangular spike. The general profile of the knob is oval as spikes or keels are lacking. The side osteoderms almost touch each other at the top surface; at the underside a midline hiatus is present. At the rear of the knob, a cluster of small osteoderms is positioned. The outer corners of this cluster are formed by two trapezium-shaped elements. The very rear is formed by a covering triangular midline osteoderm. As a whole, the rear cluster has a straight posterior edge in top view. The bone tissue of the knob has a sponge-like texture with many pits. Apart from these bony structures, the tail also preserves non-bony scales. These are not skin impressions but remains of the keratin skin tissue itself. Such fossil scale remains are exceedingly rare. In between the third pair of tail osteoderms a transverse row of five large scales is present. Behind it a further row is visible, running more to below, and containing two scales. The scales are relatively large with a diameter of between . In cross-section, they have the form of a truncated cone with a rounded top pointing somewhat to behind. More dispersed scales are visible at the base of the fourth osteoderm pair and the front base of the fifth pair. Classification In 2017, Arbour and Evans placed Zuul within the Ankylosauridae, based on a phylogenetic analysis. More specifically, they identified it as an