Open Paleo

Brontotholus

Woodruff et al., 2025 BRON-toe-thole-luss

From Greek 'brontē' (thunder) and 'tholos' (dome); in homage to the 1985 film Mad Max Beyond Thunderdome and the paratype locality name Beyond Thunder Dome.

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

Brontotholus is an extinct genus of pachycephalosaurid dinosaur known from the Late Cretaceous (Campanian stage) Two Medicine and Oldman formations of Montana, United States, and Alberta, Canada, respectively. The genus contains a single species, Brontotholus harmoni, known from multiple partial domes.

Diagnosis

  1. Frontoparietal dome anteroposteriorly longer than laterally wide throughout ontogeny
  2. In dorsal view, dome is sub-triangular, laterally wider posteriorly and strongly tapering anteriorly
  3. In anterior/posterior view, dome has a low dorsal profile, being over 1.5 times laterally wider than dorsoventrally thick in largest specimens
  4. Peripheral element sutural contacts (posterior supraorbital, postorbital) have vaulted, triangularly peaked dorsal margins
  5. Posterior supraorbital sutural contacts have a prominent dorsoventral concavity
  6. Sutural contacts of posterior supraorbital and postorbital bear several projecting dorsoventral ridges and grooves

Species

Brontotholus harmoni Woodruff et al., 2025

Type species

Honors the late Robert 'Bob' Harmon, former Chief Preparator at the Museum of the Rockies.

Holotype
MOR 480 , Museum of the Rockies
Material
Complete frontoparietal dome.
Horizon
Two Medicine Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Montana, United States

Notable specimens

  • MOR 453

    Museum of the Rockies ontogeny

    Largest specimen referred to Brontotholus, identified as a late subadult based on osteohistological analysis; tentatively referred to the genus as B. sp. Used to infer the ontogenetic stage of the holotype.

    Woodruff et al. (2025)

  • TMP 1989.069.0021

    Royal Tyrrell Museum of Paleontology Found 1989 by Wendy Sloboda range extension

    The only Brontotholus specimen from the Oldman Formation of Alberta, Canada; all other referred material comes from the Two Medicine Formation of Montana. Tentatively referred as B. sp.

    Woodruff et al. (2025)

References

  1. Woodruff, D. C.; Horner, J. R.; Goodwin, M. B.; Evans, D. C. (2025). The first pachycephalosaurid from the Late Cretaceous Two Medicine Formation: effects of the Western Interior Seaway on North American pachycephalosaurid evolution. Zoological Journal of the Linnean Society 205(2). Oxford University Press (OUP). doi:10.1093/zoolinnean/zlaf087 woodruff2025a