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Dyoplosaurus

Parks, 1924 DIE-o-plo-SAWR-us

From Greek dyoplos (double-armored) + sauros (lizard): 'double-armored lizard'.

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

Dyoplosaurus is a monospecific genus of ankylosaurid dinosaur from Alberta that lived during the Late Cretaceous (middle Campanian, ~76.5-75 Ma) in what is now the Dinosaur Park Formation. Dyoplosaurus represents a close relative of Scolosaurus and Anodontosaurus, two ankylosaurids known from the Horseshoe Canyon and Dinosaur Park Formation.

Diagnosis

  1. Transverse processes of the third sacral vertebra projecting anterolaterally from the centrum and anteroventrally inclined (~25° from horizontal) — unique among ankylosaurids, giving a distinctive sacral-fenestra pattern.
  2. Pedal unguals triangular in dorsal view, lacking the proximal constriction seen in Euoplocephalus.
  3. Handle (tail-club) vertebrae with sharply pointed neural spines in dorsal view, unlike the broad, tongue-like spines of Ankylosaurus.
  4. Free caudal centra subcircular in anterior and posterior view, with transverse processes directed anterolaterally and present on all free caudal vertebrae (unlike their loss on distal caudals in Pinacosaurus and Tarchia).
  5. Transverse processes meeting the free caudal centrum at a sharp angle in anterior or posterior view, unlike the rounded, obtuse-angled condition in Nodocephalosaurus.

Species

Dyoplosaurus acutosquameus Parks, 1924

Type species

From Latin 'acutus' meaning 'sharp' and 'squama' meaning 'scale', referring to the sharp scale-like osteoderms of the holotype.

Holotype
ROM 784 , Royal Ontario Museum
Material
Partial skull roof, four mandible fragments with two teeth in situ, portions of postcranial armor (some in situ), skin impressions, articulated post-thoracic vertebrae, ten partial thoracic ribs, a partial left ilium, both ischia, the complete tail club, a right radius, left metacarpal IV, and a nearly complete left hind limb (femur, tibia, fibula, pes).
Horizon
lower Dinosaur Park Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Royal Tyrrell Museum Quarry Q002, Alberta, Canada

References

  1. Parks, W. A. (1924). Dyoplosaurus acutosquameus, a new genus and species of armoured dinosaur; and notes on a skeleton of Prosaurolophus maximus. University of Toronto Studies, Geological Series 18: 1-35. parks1924a
  2. Arbour, V. M.; Burns, M. E.; Sissons, R. L. (2009). A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus. Journal of Vertebrate Paleontology 29(4): 1117-1135. Informa UK Limited. doi:10.1671/039.029.0405

    Redescription of the holotype ROM 784; rejects synonymy with Euoplocephalus, resurrects Dyoplosaurus as valid, and provides a revised diagnosis based on sacral and caudal characters.

    arbour2009a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

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

    jones2026a
  4. Penkalski, P. (2018). Revised systematics of the armoured dinosaur Euoplocephalus and its allies. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 287(3): 261-306. Schweizerbart. doi:10.1127/njgpa/2018/0717

    Places the holotype about 8 m above the base of the Dinosaur Park Formation.

    penkalski2018a