Open Paleo

Pinacosaurus

Gilmore, 1933 PIN-ak-o-SAWR-us

From Greek 'pinax' meaning 'plank' and 'sauros' meaning 'lizard'; translates as 'plank lizard', named for the small rectangular plank-like scutes covering its head.

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

Pinacosaurus is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous (Campanian, roughly 75 to 71 million years ago), mainly in Mongolia and China.

Diagnosis

  1. Embayment divides each supranarial ossification.
  2. Weakly developed cranial ornamentation, with discrete caputegulae limited to the nasal region.
  3. Sagittal ('ethmoid') ossification(s) on the nasals.
  4. Nasoprefrontal pyramid, lacrimal incisure, relatively flat postfrontal skull roof, and lateral supraorbitals with distinct peaks (shared with Minotaurasaurus).
  5. Multiple paranasal openings and a more horizontal pterygoid body (shared with Minotaurasaurus and Eopinacosaurus).

Species (2)

Pinacosaurus grangeri Gilmore, 1933

Type species

Named for Walter W. Granger, the paleontologist who accompanied the 1923 American Museum of Natural History Central Asiatic Expedition and discovered the original specimens.

Holotype
AMNH 6523 , American Museum of Natural History
Material
Crushed skull and mandibles, atlas, axis, several osteoderms, and fragments
Horizon
Bayn Dzak Member, Djadokhta Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Bayan Zag, Ömnögovi, Mongolia
Diagnosis
  1. Single 'C' paranasal opening leading into the premaxillary sinus, plus a B aperture (P. hilwitnorum has three or more).
  2. Squamosal horns short and drooping ventrolaterally in juveniles, becoming more erect and recurved in adults.
  3. Paired parietals (ambiguous); sagittal nuchal element absent; no postpalatal foramen.
  4. Medial process of the postorbital abuts the frontal; squamosal excluded from the nuchal border by the supranuchal.
  5. Low-relief internarial caputegulae.
  6. Vertical grooves on the teeth divergent; prominent, ridge-like medial brace on the scapula.
  7. Some caudal osteoderms with an unusual cross-hatched groove pattern.

Synonyms

  • Pinacosaurus ninghsiensis junior subjective

    Synonymized with P. grangeri by Penkalski (2026).

Pinacosaurus hilwitnorum Penkalski, 2026

Latinization of the truncated surnames of Robert Hill, Larry Witmer, and Mark Norell, who first described the holotype skull (IGM 100/1014) in 2003 as a referred specimen of P. grangeri.

Holotype
IGM 100/1014 , Paleontological Center, Mongolian Academy of Sciences
Material
Skull with lower jaws.
Horizon
Bayn Dzak Member, Djadokhta Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Ukhaa Tolgod, Ömnögovi, Mongolia
Diagnosis
  1. Three or more 'C' paranasal apertures plus B (P. grangeri has a single 'C' plus B).
  2. More prominent nasal ridges; pointed internarials.
  3. Fused parietals (paired in P. grangeri).
  4. Small triangular sagittal nuchal element (possible postparietal).
  5. Posterior palatal foramen present.
  6. Parallel vertical grooves on teeth (divergent in P. grangeri); reduced scapular medial brace.

Synonyms of the genus

Name Type Reason
Syrmosaurus junior subjective Penkalski (2026) and Hill and colleagues (2003) both list Syrmosaurus viminicaudus as a junior synonym of Pinacosaurus grangeri, the Syrmosaurus holotype being consistent with the Bayan Zag material.

Notable specimens

  • PIN 614

    Paleontological Institute, Russian Academy of Sciences complementary

    A nearly complete postcranial skeleton, originally described as Syrmosaurus viminicaudus by Maleev in 1952 and now considered the same species as P. grangeri.

    Hill et al. (2003)Penkalski (2026)

References

  1. Hill, R. V.; Witmer, L. W.; Norell, M. A. (2003). A new specimen of Pinacosaurus grangeri (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia: ontogeny and phylogeny of ankylosaurs. American Museum Novitates (3395): 1-29. doi:10.1206/0003-0082(2003)395<0001:ANSOPG>2.0.CO;2 hill2003a
  2. Gilmore, C. W. (1933). Two new dinosaurian reptiles from Mongolia with notes on some fragmentary specimens. American Museum Novitates 679: 1-20. gilmore1933b
  3. Penkalski, P. (2026). The morphology and systematics of Pinacosaurus. Historical Biology 1-42. doi:10.1080/08912963.2026.2633178

    Systematic revision of Pinacosaurus; redescribes P. grangeri and erects P. hilwitnorum sp. nov. for the Ukhaa Tolgod skull IGM 100/1014 previously referred to P. grangeri.

    penkalski2026a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026a