Open Paleo

Hesperosaurus

Carpenter et al., 2001 hes-per-oh-sore-us

Western lizard; from Ancient Greek hésperos (western) and saûros (lizard)

161.5–137.1 million years ago Oxfordian–Berriasian, Late Jurassic–Early Cretaceous
Late Jurassic and Early Cretaceous stages

Hesperosaurus is a herbivorous stegosaurian dinosaur from the Kimmeridgian age of the Jurassic period, approximately 156 million years ago.

Diagnosis

  1. Frontoparietal domed, flat in all other stegosaurs
  2. Cervical plates low and oval versus tall triangular in Stegosaurus
  3. Neural spines of posterior dorsals very tall with teardrop-shaped top in anterior view
  4. Caudal neural spines with uniquely teardrop-shaped apex, intermediate between unexpanded and expanded conditions in other stegosaurs
  5. Ilia strongly divergent anteriorly unlike straight condition in Stegosaurus
  6. Distal end of pubis expanded as in Huayangosaurus, nonexpanding in Stegosaurus

Species

Hesperosaurus mjosi Carpenter et al., 2001

Type species

Named for Ronald G. Mjos, who assisted in collecting and preparing the holotype and had a cast of it made for display.

Holotype
FPDM-V9674 , Fukui Prefectural Dinosaur Museum
Material
Nearly complete disarticulated skull, 13 cervical, 13 dorsal, 3 sacral, 44+ caudal vertebrae, ribs, chevrons, 10 dermal plates, pelvic elements, partial left scapula, ossified tendons
Notes
Originally cataloged HMNH 001 (Carpenter and colleagues, 2001); acquired by the Hayashibara Museum of Natural Sciences as HMNS 14, then transferred in 2015 to the Fukui Prefectural Dinosaur Museum and renumbered FPDM-V9674.
Horizon
lower Morrison Formation, Oxfordian–Berriasian, Late Jurassic–Early Cretaceous , 161.5–137.1 million years ago The age of the containing rock unit; no finer age has been published.
Locality
S. B. Smith Ranch, Wyoming, United States Carpenter and colleagues (2001) give the holotype locality as "Five meters above base (Weege, personal communication), Morrison Formation, S. B. Smith Ranch, Johnson County, Wyoming". No finer age is published, so the stages are the formation's.

Notable specimens

  • “Victoria”

    SMA 0018 University of Zurich Paleontology Museum Found 1996 exceptional preservation

    Rather complete skeleton with skull from the Howe-Stephens Quarry, Wyoming, preserving skin impressions and an impression of a back plate's underside interpreted as a horn sheath, the first direct evidence of such a sheath in any stegosaurian.

    Christiansen & Tschopp (2010)

References

  1. Carpenter, K.; Miles, C. A.; Cloward, K. (2001). New primitive stegosaur from the Morrison Formation, Wyoming. The Armored Dinosaurs 55-75. Indiana University Press, Bloomington. carpenter2001b
  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. Christiansen, N. A.; Tschopp, E. (2010). Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming. Swiss Journal of Geosciences 103(2): 163-171. doi:10.1007/s00015-010-0026-0 christiansen2010a