Zuul is a genus of herbivorous ankylosaurine dinosaur from the Campanian Judith River Formation of Montana.

On 16 May, a skid-steer loader removing a 12 m (39 ft)-high overburden unexpectedly hit upon an ankylosaurian tail club.

The skeleton was largely articulated, but the skull and some neck vertebrae were separated from the main torso, while five ribs and the left ilium had shifted from their original position.

The museum performed a laser scan of the skull, allowing its original form to be determined by the process of retro-deformation, or compensating for compression of the fossil.

[1] In 2017, based on the specimen the type species Zuul crurivastator was named and described by Arbour and Evans.

The generic name was adopted from the demon and demi-god Zuul, the Gatekeeper of Gozer, featured in the 1984 film Ghostbusters.

The epithet, read as "Destroyer of Shins" by the naming authors,[2] refers to a presumed defensive tactic of ankylosaurids, smashing the lower legs of attacking predatory theropods with their tail clubs.

[1][3] The specimen, which is stored as ROM 75860, was found in a sandstone layer of the Judith River Formation, part of the middle Coal Ridge Member with an age of between 76.2 and 75.2 million years.

The caputegulae, armour tiles of the head, that lay on the nasal bones, the frontals and the parietals, are imbricated, overlapping, and pointed on top.

The squamosal horns, on the rear corners of the skull roof, have conspicuous longitudinal grooves on their side surfaces.

The osteoderms on the side of the tail, the knob itself excepted, have a front edge with a strongly hollow profile, while their points are off-set to the rear.

The squamosal horn protrudes to behind the rear edge of the skull roof, just as with Scolosaurus but different from Anodontosaurus, Euoplocephalus or Ziapelta.

The caputegulae behind the eye socket are small and sparsely distributed, again like Scolosaurus but differing from Anodontosaurus, Euoplocephalus or Ziapelta.

The osteoderms on the handle of the tail club are relatively larger and more pointed than those of Asian ankylosaurines of the Nemegt Formation of Mongolia.

Above the eye socket the front and rear supraorbitals form a sharp edge, protruding sideways.

Similar plates in specimens of Euoplocephalus and Dyoplosaurus were reported by Walter Preston Coombs as bony eyelids.

The adductor fossa, the opening through which the muscles closing the jaw entered its hollow inside, is relatively small and shallow.

[1] At the rear underside of the right lower jaw numerous ossicles, small bony scales, are visible.

Even lower, rows of smaller hexagonal or diamond-shaped ossicles are positioned, of about 6 mm (0.24 in) in diameter, grouped in rosettes.

The tail club, including the handle, has a length of 210 centimetres (83 in), a record among North American ankylosaurids.

To increase the chance of a damaging plastic deformation on impact of the knob, the handle is a stiff structure, the lack of flexibility caused by special connections between the vertebrae.

The paired front joint processes, the prezygapophyses, are strongly elongated and overlap half of the preceding vertebra.

[1] The front three side osteoderm pairs are covered by a black film that could be the remnant of their original keratin sheaths.

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.

In the holotype individual, the left side osteoderm is distinctively longer than the right one, giving the knob as whole a rather asymmetrical profile.

[1] Zhejiangosaurus luoyangensis Pinacosaurus grangeri Pinacosaurus mephistocephalus Tsagantegia longicranialis Talarurus plicatospineus Nodocephalosaurus kirtlandensis Saichania chulsanensis Zaraapelta nomadis Tarchia kielanae Ziapelta sanjuanensis Euoplocephalus tutus Ankylosaurus magniventris Anodontosaurus lambei Scolosaurus cutleri Zuul crurivastator Dyoplosaurus acutosquameus