Open Paleo

Ankylosaurus

Brown, 1908 ANG-kuh-loh-SOR-uhs /ˌæŋkəloʊˈsɔːrəs/

From Greek 'ankylos' (fused, bent) and 'sauros' (lizard), referring to the coossified plates of the skull and the fused vertebral elements.

72.2–66.0 million years ago Maastrichtian, Late Cretaceous
Late Cretaceous stages

Ankylosaurus is the type genus of Ankylosauridae and the monospecific containing Ankylosaurus magniventris, an iconic North American ankylosaurid known from the latest-Maastrichtian Hell Creek (Montana), Scollard (Alberta), and Lance (Wyoming) Formations. Erected by Barnum Brown in 1908 on a partial skeleton (AMNH 5895) collected by Peter Kaisen near Gilbert Creek, Montana, the genus has since been treated in several descriptive works — Carpenter (2004) and Arbour and Mallon (2017) both redescribing its anatomy, and Arbour and Currie (2015) erecting the tribe Ankylosaurini with Ankylosaurus as its name-bearer. Despite a 100+ year history of armor-arrangement debates and only a handful of partial specimens, Ankylosaurus is among the largest and most-derived ankylosaurids, with a heavily coossified cranial roof, a fully fused tail club, and dental proportions (high tooth count, premaxillary-sinus-driven naris displacement) that distinguish it from coeval Edmontonia. Stratigraphic and sedimentary data indicate a preference for upland facies, in contrast to the coastal lowland setting that yielded most Edmontonia material.

Diagnosis

  1. Nasal vestibule roofed entirely by the loreal caputegulum (rather than by the supranarial caputegulum as in Anodontosaurus, Euoplocephalus, Scolosaurus, Ziapelta, and Zuul); external nares open ventrolaterally and are not visible in anterior view.
  2. Loreal caputegulum laterally expanded and bulbous, expanding onto the anterior surface of the premaxillary beak and overhanging the lateral surface of the maxilla.
  3. 34-36 proportionally small maxillary teeth, crown height less than 2% of basal skull length — a greater tooth count than in Anodontosaurus or Euoplocephalus.
  4. Keel of the anterior and posterior supraorbital caputegulae continuous with the keel of the squamosal horn (discontinuous in Anodontosaurus, Euoplocephalus, and Scolosaurus).
  5. Tail-club handle vertebrae with U-shaped neural spines in dorsal view (V-shaped in most other ankylosaurids); neural arch of the handle vertebrae at least twice as wide as in Anodontosaurus and Euoplocephalus of equivalent length.
  6. Substantially larger body size than all other known Laramidian ankylosaurines, with skull width across the supraorbitals 35-70% greater than the largest known skulls of contemporaneous relatives.

Species

Ankylosaurus magniventris Brown, 1908

Type species

From Latin 'magnus' (great) and 'venter' (belly), referring to the unusually wide body cavity.

Holotype
AMNH 5895 , American Museum of Natural History
Material
Partial skull — including a newly identified otic capsule, maxilla fragment, both jugals, and the quadratojugal — two teeth, five cervical and eleven dorsal vertebrae, three caudal vertebrae, two sacral centra, the right scapulocoracoid (coossified), ribs, and numerous osteoderms including portions of both cervical half-rings.
Horizon
Hell Creek Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
Gilbert Creek, Montana, United States

Notable specimens

  • AMNH 5214

    American Museum of Natural History Found 1910 by Barnum Brown exceptional preservation

    Found in the Scollard Formation by the Red Deer River, Alberta. Includes a complete skull, the only mandibles and the first and only tail club known for the genus, plus ribs, vertebrae, and limb bones, making it the most informative Ankylosaurus specimen.

    Carpenter (2004)

  • CMN 8880

    Canadian Museum of Nature Found 1947 by Charles M. Sternberg and T. Potter Chamney largest individual

    Represents the largest known individual of the genus: its skull, at 64.5 cm long, is the largest known for Ankylosaurus and underpins the maximum body-size estimates, though it is damaged in places. Collected near the Red Deer River, Alberta.

    Carpenter (2004)

References

  1. Brown, B. (1908). The Ankylosauridae, a new family of armored dinosaurs from the Upper Cretaceous. Bulletin of the American Museum of Natural History 24: 187-201. American Museum of Natural History.

    Erects both the genus Ankylosaurus and the family Ankylosauridae on AMNH 5895 from the Hell Creek beds of Montana.

    brown1908a
  2. Carpenter, K. (2004). Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. Canadian Journal of Earth Sciences 41(8): 961-986. NRC Research Press. doi:10.1139/e04-043

    Modern redescription of all then-known specimens (AMNH 5895, AMNH 5214, AMNH 5866, CCM V03, CMN 8880); demonstrates lateral naris displacement is pneumatic, not dermal.

    carpenter2004a
  3. Arbour, V. M.; Currie, P. J. (2015). Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs. Journal of Systematic Palaeontology 14(5): 385-444. Informa UK Limited. doi:10.1080/14772019.2015.1059985

    Comprehensive revision of Ankylosauridae; provides the current revised diagnosis of Ankylosaurus and erects the tribe Ankylosaurini with Ankylosaurus as the name-bearer.

    arbour2015a
  4. Arbour, V. M.; Mallon, J. C. (2017). Unusual cranial and postcranial anatomy in the archetypal ankylosaur Ankylosaurus magniventris. FACETS 2(2): 764-794. Canadian Science Publishing. doi:10.1139/facets-2017-0063

    Redescription of Ankylosaurus; newly identifies elements of the holotype AMNH 5895 and of CMN 8880, revises the diagnosis and osteoderm arrangement, and provides updated body-size estimates.

    arbour2017b
  5. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the mass estimate.

    paul2024a
  6. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the appearance features.

    jones2026a