Open Paleo

Akainacephalus

Wiersma & Irmis, 2018 ah-KAY-nuh-SEF-uh-lus

From Greek 'akaina' meaning 'thorn' or 'spike' and 'kephale' meaning 'head'; meaning 'thorn head'

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

Akainacephalus 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.

Diagnosis

  1. Massive supraorbital bosses forming a tall backswept flange extending laterally over the orbits and enveloping the anterodorsal and posterior margins of the orbit
  2. Nearly vertical projecting triangular quadratojugal horns
  3. Frontal bears a large, flat, centrally positioned hexagonal-shaped caputegulum
  4. Tightly spaced, symmetrically positioned pyramidal and conical-shaped caputegulae across the frontonasal region
  5. Distinct midline row of conical-shaped caputegulae across the nasal region, symmetrically separating dorsolateral caputegulae
  6. Basioccipital foramen positioned anterior and dorsal to the occipital condyle

Species

Akainacephalus johnsoni Wiersma & Irmis, 2018

Type species

Named for Randy Johnson, the volunteer preparator at the Natural History Museum of Utah who prepared the skull and lower jaws of the holotype.

Holotype
UMNH VP 20202 , Utah Museum of Natural History
Material
Partial skeleton: complete skull, both mandibles, predentary, vertebrae (dorsal, dorsosacral, sacral, caudosacral, caudal), dorsal ribs, complete tail club, both scapulae, left coracoid, right humerus, right ulna, partial left ilium, left femur, left tibia, left fibula, phalanx, two partial cervical osteoderm half rings, 17 osteoderms
Horizon
middle Kaiparowits Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
HMG Quarry, Utah, United States

References

  1. Wiersma, J. P.; Irmis, R. B. (2018). A new southern Laramidian ankylosaurid, Akainacephalus johnsoni gen. et sp. nov., from the upper Campanian Kaiparowits Formation of southern Utah, USA. PeerJ 6: e5016. PeerJ. doi:10.7717/peerj.5016 wiersma2018a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the body length, mass, and hip height estimates, and the appearance features.

    jones2026a