Akainacephalus

Akainacephalus (meaning "thorn head") is a monospecific genus of ankylosaurid dinosaur from southern Utah that lived during the Late Cretaceous (late Campanian, 76.26 Ma) in what is now the Horse Mountain Gryposaur Quarry of the Kaiparowits Formation. The type and only species, Akainacephalus johnsoni, is 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. It was described in 2018 by Jelle P. Wiersma and Randall B. Irmis. It is closely related and shares similar cranial anatomy to Nodocephalosaurus.

==Discovery and naming== thumb|left|upright=1.0|alt=Drawn map showing fossil location|Map of the Grand Staircase–Escalante National Monument. Kaiparowits Formation is in dark green. 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. 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. The age of the layer is 76.26 ± 0.10 million years based on zircon dating. In 2014, the skull was subjected to a CT scan in order to reveal the internal anatomy. The specimen was subsequently described in 2018 by Jelle P. Wiersma and Randall B. Irmis.