page_title: Akainacephalus
section_title: Description
hierarchical_section_title: Akainacephalus / Description
caption_attribution_description: English: Photographs of the sacrum, presacral rod, and caudosacral vertebrae of Akainacephalus johnsoni (UMNH VP 20202) in (A), ventral; (B), dorsal; (C), right lateral; (D), left lateral; (E), posterior; and (F), anterior views. Study sites: c, centrum; cs, caudosacral vertebra; csr, caudosacral ribs; ds, dorsosacral vertebrae; dsr, dorsosacral ribs; ns, neural spine; sr, sacral ribs.
context_page_description: Akainacephalus is a genus of herbivorous ankylosaurid dinosaur from the Campanian age Kaiparowits Formation of southern Utah. The type and only species is Akainacephalus johnsoni, known from the most complete ankylosaur specimen ever discovered from southern Laramidia, including a complete skull, tail club, a number of osteoderms, limb elements and part of its pelvis, among other remains.
context_section_description: The describing authors indicated several distinguishing traits. Some of these are autapomorphies, unique derived characters. The supraorbital bosses are massive in side view, forming a high back-swept ridge, also extending sideways over the eye socket, while encompassing the front top corner and the rear edge of the eye socket. The cheek horns are triangular, pointing almost vertically to below. On the frontal bones, a central large flat hexagonal osteoderm is present. The zone spanning the frontal bones and nasal bones is covered by symmetrically positioned, closely packed, pyramid-shaped and conical caputegulae. 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 head armour of Akainacephalus is strikingly similar to that of Nodocephalosaurus, a related form also found in southern Laramidia, in New Mexico. The description therefore closely compared the two genera in order to prove that Akainacephalus was a valid taxon. Akainacephalus and Nodocephalosaurus share certain traits such as pyramid-shaped osteoderms on the snout and flaring armour above the nostrils. There are, however, also differences. With Akainacephalus, the osteoderms of the front and rear supraorbitals form a single back-swept high structure. In N. kirtlandensis, these remain separate elements of far smaller size. Akainacephalus has a much smaller squamosal horn. Its cheek horn points straight to below as an enormous triangle, while that of Nodocephalosaurus curves to behind like a smaller curved fin. A comparison is complicated by the fact that the skull of Nodocephalosaurus is only partly known. Besides, with the holotype of Akainacephalus the squamosal horns have broken off, making it impossible to determine their exact shape, and the skull as a whole has been compressed from front to rear, creating a kink from which snout and rear are appending, and narrowing and raising the area around the eye socket. However, Nodocephalosaurus was found in the Kirtland Formation, in layers that are three million years younger, which precludes the taxa from being identical.
  The front snout bones, the premaxillae, form a wide, U-shaped, upper beak, wider than long. The sides of the snout are not covered by armour. The number of maxillary teeth, per side, has been estimated at a minimum of sixteen. The bony nostrils are oriented to the side of the snout. The nostril is rather small and not clearly subdivided into smaller openings. The quadrate bone is strongly inclined, causing the jaw joint to be positioned, visible in side view, in front of the cheek horn point, which has not been reported in other ankylosaurids.
caption: Sacrum and caudosacral vertebrae
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