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Hypacrosaurus

Brown, 1913 hi-PAK-ro-SAWR-us

Near the highest lizard; from Ancient Greek hypo- (less or under) and akros (high or topmost), combined with sauros (lizard), because it was almost but not quite as large as Tyrannosaurus

83.6–66.0 million years ago Campanian–Maastrichtian, Late Cretaceous
Late Cretaceous stages

Hypacrosaurus is an extinct genus of duckbill dinosaur similar in appearance to Corythosaurus. Like Corythosaurus, it had a tall, hollow rounded crest, although not as large and straight. It is known from the remains of two species that spanned 75.0 to 69.5 million years ago, in the Late Cretaceous of Alberta, Canada, and Montana, United States, and is the latest hollow-crested duckbill known from good remains in North America. It was an obscure genus until the discovery in the 1990s of nests, eggs, and hatchlings belonging to H. stebingeri.

Diagnosis

  1. Dorsal neural spines extremely high and massive, five to seven times the height of their centra
  2. Radius substantially longer than the humerus
  3. Metatarsals greatly elongated
  4. Ischium with a large, foot-like terminal expansion on a very massive shaft
  5. Dorsal vertebrae with a large perforation through the thin plate descending from the posterior zygapophyses to the neural canal

Species (2)

Hypacrosaurus altispinus Brown, 1913

Type species

From Latin 'altus' ('high' or 'tall') and 'spina' ('spine'), referring to the tall neural spines that are 5 to 7 times the height of their respective vertebral bodies in the back.

Holotype
AMNH 5204 , American Museum of Natural History
Material
Last eight dorsal vertebrae, two anterior caudal vertebrae, both ilia, the right ischium, the right pubis, and several ribs.
Horizon
Horseshoe Canyon Formation, Campanian–Maastrichtian, Late Cretaceous , 83.6–66.0 million years ago
Locality
Four miles above Tolman Ferry, Alberta, Canada Brown (1913) places the holotype fifty feet above the river and names no formation. The Horseshoe Canyon assignment rests on reference works rather than on a source treating this specimen.

Hypacrosaurus stebingeri Horner & Currie, 1994

Honors Eugene Stebinger, who first described the Two Medicine Formation and found the first remains of the species.

Holotype
MOR 549 , Museum of the Rockies
Material
Nearly complete skeleton, including skull, ilium, and dorsal vertebrae
Horizon
upper Two Medicine Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
TM-065, Badger Creek, Montana, United States

Synonyms of the genus

Name Type Reason
Cheneosaurus junior subjective Now generally interpreted as juvenile individuals of Hypacrosaurus, though this has not been formally tested.

References

  1. Brown, B. (1913). A new trachodont dinosaur, Hypacrosaurus, from the Edmonton Cretaceous of Alberta. Bulletin of the American Museum of Natural History 32(20): 395-406. brown1913a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

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

    jones2026a
  3. Horner, J. R.; Currie, P. J. (1994). Embryonic and neonatal morphology and ontogeny of a new species of Hypacrosaurus (Ornithischia, Lambeosauridae) from Montana and Alberta. Dinosaur Eggs and Babies 312-336. Cambridge University Press, Cambridge. horner1994a