An almost complete skeleton of an ankylosaurid was excavated during the 2008, 2009, and 2010 field seasons from the Horse Mountain Gryposaur (HMG) Quarry in the Grand Staircase–Escalante National Monument, Kane County, Utah.

[1] The Horse Mountain Gryposaur Quarry represents a multitaxic and multidominant bonebed that has produced a mostly complete, partially articulated skeleton of the hadrosaurid Gryposaurus, the holotype of the baenid turtle Arvinachelys, an articulated skeleton of a small alligatoroid, and a partial skull of a small theropod.

The bonebed is deposited in a fine- to medium-grained sandstone crevasse splay that is located within the lower section of the middle unit of the Kaiparowits Formation.

It represents about 45% of the skeletal elements and is part of the collection of the Natural History Museum of Utah in Salt Lake City.

[2] The generic name, Akainacephalus, is derived from the Greek words "akaina" (thorn or spine) and "kephalè" (head), in reference to the thornlike cranial caputegulae of the holotype skull.

The nasal bones exhibit a distinct central row of conical caputegulae, symmetrically separated from the osteoderms above and to the sides of them.

At the rear of the skull, the part of the foramen magnum formed by the basioccipital is located obliquely above and in front of the occipital condyle.

The external nares are fully obscured in front view, a condition not seen in many Asian and Laramidian ankylosaurids, and are relatively small, tear-shaped openings.

Positioned on the rear margin of the left nares is a small bony fragment as in Pinacosaurus and Minotaurasaurus which suggests the presence of internarial apertures.

The jugals consist of a broad element that touches the front-most part of the quadratojugal and the rear margin of the maxilla.

The jugal forms a shelf that is ornamented towards the sides with a small ridge of rugose co-ossified bone.

[2] The external nares are ornamented with a supranasal caputegulum that is arranged along the premaxillary beak at the back and the sides.

Positioned on the sides of each prefrontal is a subtriangular caputegulum with a keeled apex, which is anterior to the anterior-most supraorbital boss.

The circumorbital complex consists of a supraorbital horn, a lacrimal caputegulum, a jugal osteoderm, and the thickened rim along the posterior margin of the orbital.

The surangular, along with the posterior margin of the dentary, contributes to the tallest portion of the mandible and forms the coronoid process.

Unlike other ankylosaurids, the underside of the posterior surface of the centrum possesses a recurved, hook-like projection, which is followed by a longitudinal keel.

The caudal vertebrae have a short but tall boot and centra that have anterior and posterior articular surfaces that are spool-shaped and are slightly amphicoelous.

The acromion process of the scapula is positioned directly above the glenoid fossa and projects exactly upright to the side surfaces of the scapular blade.

On the side of the deltopectoral crest is large yet round protuberance which forms the articulation surface for the muscle M. latissimus dorsi.

The only remains of the left ulna is the olecranon process and a partial shaft with the radial notch morphology being similar to that of other ankylosaurs.

As with other ankylosaurid tail clubs, the handle is reinforced by elongated prezygapophyses which extend across for nearly half of the length of the next vertebra.

[2] However, Park et al. (2019) found both Akainacephalus and Nodocephalosaurus to be basal to Saichania, Talarurus, Tarchia and Zaraapelta, which suggests that a migration occurred before the Cenomanian stage and that ankylosaurines dispersed at least twice from Asia to Western North America.

[3] Frauenfelder et al. (2022) recovered Akainacephalus as sister taxon to two clades, with one of the clades consisting of Tsagantegia, Nodocephalosaurus and Talarurus while the other consists of more deeply nested taxa such as Saichania, Pinacosaurus, Scolosaurus, Anodontosaurus, Euoplocephalus and Ankylosaurus.

[2] Gobisaurus Zhongyuansaurus Shamosaurus Tsagantegia Crichtonsaurus Pinacosaurus mephistocephalus Zaraapelta Tianzhenosaurus Pinacosaurus grangeri Saichania Tarchia gigantea Nodocephalosaurus Akainacephalus Minotaurasaurus Tarchia kielanae Shanxia Euoplocephalus Oohkotokia Scolosaurus Ziapelta Anodontosaurus Ankylosaurus Dyoplosaurus Akainacephalus is known from the middle unit of the Kaiparowits Formation which has been dated to the upper Campanian stage, 76.26 ± 0.10 Ma.

The Kaiparowits Formation preserves a unique record of Late Cretaceous terrestrial vertebrate ecosystems in the Western Interior of North America as it was deposited in a wet alluvial to coastal plain setting that was dominated by large river channels, ponds, lakes, and wetlands.

The rivers flowed across the wet alluvial to coastal plain setting and were drained into the Western Interior Seaway.