Open Paleo

Thescelosaurus

Gilmore, 1913 THESS-el-oh-sore-us /ˌθɛsɪləˈsɔːrəs/

From Greek 'theskelos' meaning 'marvelous' or 'wondrous' and 'sauros' meaning 'lizard', hence 'marvelous lizard'.

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

Thescelosaurus is a genus of ornithischian dinosaur that lived during the Late Cretaceous period in western North America. It was named and described in 1913 by the paleontologist Charles W. Gilmore; the type species is T. neglectus. Two other species, T. garbanii and T. assiniboiensis, were named in 1976 and 2011, respectively. Additional species have been suggested but are currently not accepted. Thescelosaurus is the eponymous member of its family, the Thescelosauridae. Thescelosaurids are either considered to be basal ("primitive") ornithopods, or are placed outside of this group within the broader group Neornithischia.

Diagnosis

  1. Ventral surfaces of cervical vertebrae flattened and rugosely roughened, unlike rounded or keeled surfaces in other dinosaurs
  2. Posterior thoracic ribs single-headed, fusion to transverse process differs from double-headed ribs anterior
  3. Four phalanges on third digit of fore foot, an unusual number found only in Hypsilophodon among dinosaurs
  4. Projecting lip-like process on outer posterior side of proximal femur, not before observed in orthopodous dinosaurs
  5. Fifth metatarsal vestigial and attached to posterior side of metatarsal IV, partly functional
  6. Pelvic arch sufficiently diagnostic to separate genus at once from all other known dinosaurs

Species (3)

Thescelosaurus neglectus Gilmore, 1913

Type species

From Latin 'neglectus' meaning 'neglected', referring to the holotype specimen having been overlooked and set aside in museum storage for years before being formally described.

Holotype
USNM 7757 , National Museum of Natural History, Smithsonian Institution
Material
Articulated skeleton lacking skull, neck, humeri, scapulae, and coracoids.
Horizon
Lance Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
Doegie Creek, Wyoming, United States

Thescelosaurus assiniboiensis Brown et al., 2011

Named for the District of Assiniboia, a former (1882–1905) administrative unit of the North-West Territories enclosing the Frenchman Formation exposures; itself named after the Assiniboine First Nations People.

Holotype
RSM P 1225.1 , Royal Saskatchewan Museum
Material
A small, relatively complete skeleton preserving a partial skull (including a nearly complete braincase), dorsal, sacral, and caudal vertebral series, dorsal ribs, pelvic girdles, and hindlimbs.
Horizon
Frenchman Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
Frenchman River Valley, near Cambery Coulee, Saskatchewan, Canada
Diagnosis
  1. Supraoccipital bears a distinct median foramen running from the roof of the myelencephalon through to the dorsal surface of the element (autapomorphy).
  2. Dorsal and posterior margins of the squamosal convex (autapomorphy), rather than flat/concave.
  3. Calcaneum not reduced and thus participates in the mesotarsal joint (unlike T. garbanii, in which it is reduced and excluded).

Thescelosaurus garbanii Morris, 1976

Honors Harley Garbani, the fossil collector who discovered the holotype.

Holotype
LACM 33542 , Natural History Museum of Los Angeles County
Material
Five posterior cervical and eleven anterior dorsal vertebrae, plus a left pes, tarsus, tibia, fibula, and distal end of femur
Horizon
Hell Creek Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
LACM V3152, Montana, United States
Diagnosis
  1. Calcaneum excluded from midtarsal joint by a laterally expanded astragalus (calcaneum retains participation in the midtarsal joint in other referred Thescelosaurus specimens)

Synonyms of the genus

Name Type Reason
Bugenasaura junior subjective B. infernalis must be assigned to Thescelosaurus following preparation of the 'Willo' specimen, which revealed a complete skull lower and longer than previously inferred.

Notable specimens

  • “Willo”

    NCSM 15728 North Carolina Museum of Natural Sciences Found 1999 by Michael Hammer iconic

    Famous nicknamed specimen from the upper Hell Creek Formation of Harding County, South Dakota, preserving most of the skeleton and a complete skull. A chest mass once publicized as a fossilized heart is now doubted to be a geologic concretion.

    Boyd et al. (2009)Fisher et al. (2000)Cleland et al. (2011)

  • MOR 979

    Museum of the Rockies complementary

    Specimen from the Hell Creek Formation of Montana preserving a nearly complete skull and skeleton, one of the new finds that combined skull and skeleton material and helped resolve the historic and current species of the genus.

    Boyd et al. (2009)

  • TLAM.BA.2014.027.0001

    Timber Lake and Area Museum complementary

    Specimen from the Hell Creek Formation of Dewey County, South Dakota, including a mostly complete though slightly crushed skull and much of the skeleton. Its overlapping skull material allowed both it and the Willo specimen to be assigned to T. neglectus.

    Boyd (2014)

References

  1. Boyd, C. A.; Brown, C. M.; Scheetz, R. D.; Clarke, J. A. (2009). Taxonomic revision of the basal neornithischian taxa Thescelosaurus and Bugenasaura. Journal of Vertebrate Paleontology 29(3): 758-770. doi:10.1671/039.029.0328

    Taxonomic revision of Thescelosaurus; restricts T. garbanii to holotype LACM 33542 and sinks Bugenasaura into the genus.

    boyd2009a
  2. Fisher, P. E.; Russell, D. A.; Stoskopf, M. K.; Barrick, R. E.; Hammer, M.; Kuzmitz, A. A. (2000). Cardiovascular evidence for an intermediate or higher metabolic rate in an ornithischian dinosaur. Science 288(5465): 503-505. doi:10.1126/science.288.5465.503 fisher2000a
  3. Cleland, T. P.; Stoskopf, M. K.; Schweitzer, M. H. (2011). Histological, chemical, and morphological reexamination of the "heart" of a small Late Cretaceous Thescelosaurus. Naturwissenschaften 98(3): 203-211. doi:10.1007/s00114-010-0760-1 cleland2011a
  4. Boyd, C. A. (2014). The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus. PeerJ 2: e669. doi:10.7717/peerj.669 boyd2014a
  5. Gilmore, C. W. (1913). A new dinosaur from the Lance Formation of Wyoming. Smithsonian Miscellaneous Publications 61(5): 1-5. gilmore1913a
  6. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

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

    jones2026a
  7. Morris, W. J. (1976). Hypsilophodont dinosaurs: a new species and comments on their systematics. Athlon: Essays on Palaeontology in Honour of Loris Shano Russell. Royal Ontario Museum.

    Erects Thescelosaurus garbanii on the partial hindlimb LACM 33542 from the Hell Creek Formation of Montana.

    morris1976a
  8. Brown, C. M.; Boyd, C. A.; Russell, A. P. (2011). A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America. Zoological Journal of the Linnean Society 163(4): 1157-1198. Oxford University Press (OUP). doi:10.1111/j.1096-3642.2011.00735.x

    Erects Thescelosaurus assiniboiensis on skeleton RSM P 1225.1 from the Frenchman Formation of Saskatchewan.

    brown2011a