Open Paleo

Galeamopus

Tschopp et al., 2015 GAY-lee-uh-MOH-pus

From Latin 'galeam' (accusative of 'galea', 'helmet') and 'opus' meaning 'need'; intended as a translation of 'Wil-helm' ('want helmet'), honoring the first names of Utterback and Holland, and alluding to the brittle braincase of the type specimen being in need of a helmet.

154.8–143.1 million years ago Kimmeridgian–Tithonian, Late Jurassic
Late Jurassic stages

Galeamopus is a genus of herbivorous diplodocid sauropod dinosaurs. It contains two known species — Galeamopus hayi, known from the Late Jurassic lower Morrison Formation (Kimmeridgian age, about 155 million years ago) of Wyoming, United States, and Galeamopus pabsti, known from Wyoming and Colorado. The type species is known from one of the well-preserved diplodocid fossils, a nearly complete skeleton with an associated skull.

Diagnosis

  1. Dorsoventral height of parietal occipital process low, subequal to less than diameter of foramen magnum (unique among Diplodocinae)
  2. Basipterygoid processes widely diverging (>60°; unique among Diplodocinae)
  3. Ulna to humerus length ratio of more than 0.76 (unique within Diplodocoidea)
  4. Distal articular surface for the ulna on the radius reduced and relatively smooth (unique within Diplodocidae)
  5. Distal condyle of the radius beveled at least 15° to the long axis of the shaft (unique within Diplodocinae)
  6. Lateral edge of proximal end of tibia forms a pinched out projection posterior to the cnemial crest (unique among Diplodocidae)

Species (2)

Galeamopus hayi Tschopp et al., 2015

Type species

Named for Oliver Perry Hay, in recognition of paleontological work.

Holotype
HMNS 175 (=CM 662) , Houston Museum of Nature and Science
Material
Cranial material, cervical/dorsal/sacral/caudal vertebrae, nearly complete forelimb and hindlimb.
Horizon
lower Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Quarry A, Red Fork of the Powder River, Wyoming, United States

Galeamopus pabsti Tschopp & Mateus, 2017

Honors Dr. Ben Pabst, who discovered the holotype and led its preparation and mounting at the Sauriermuseum Aathal.

Holotype
SMA 0011 , Sauriermuseum Aathal
Material
Partial skull; 13 cervical and 8 dorsal vertebrae; partial sacrum; ribs; both scapulae, coracoids, and humeri; left forearm and manus; right ilium and pubis; left ischium and hind limb with pes
Horizon
Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Howe-Scott Quarry, Wyoming, United States
Diagnosis
  1. Horizontal canal on the maxilla connecting the posterior margin of the preantorbital fossa and the ventral margin of the antorbital fenestra
  2. Sagittal nuchal crest on the supraoccipital marked by a vertical midline groove
  3. Anterior cervical vertebrae much taller than wide, with a height-to-width ratio greater than 1.2
  4. Mid- and posterior cervical vertebrae with a large foramen connecting the postzygapophyseal centrodiapophyseal fossa and the spinopostzygapophyseal fossa
  5. Very robust humerus (robusticity index over 0.33) bearing a laterally displaced, rugose tubercle on the concave proximal portion of the anterior surface
  6. Ascending process of the astragalus with a concave posteroventral margin, producing two distinct, rounded posterior processes in ventral view

Notable specimens

  • AMNH 969

    American Museum of Natural History Found 1903 by Peter Kaisen complementary

    Referred specimen of G. hayi preserving a nearly complete skull and the atlas-axis complex in articulation, cranial anatomy largely absent in the type-species holotype, which is composed mainly of a braincase and partial postcranial skeleton.

    Tschopp et al. (2015)

References

  1. Tschopp, E.; Mateus, O.; Benson, R. B. J. (2015). A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3: e857. PeerJ. doi:10.7717/peerj.857 tschopp2015a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the body length, mass, and hip height estimates, and the appearance features.

    jones2026b
  3. Tschopp, E.; Mateus, O. (2017). Osteology of Galeamopus pabsti sp. nov. (Sauropoda: Diplodocidae), with implications for neurocentral closure timing, and the cervico-dorsal transition in diplodocids. PeerJ 5: e3179. PeerJ. doi:10.7717/peerj.3179 tschopp2017a