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Dryosaurus

Marsh, 1894 DRY-uh-SOR-uhs /ˌdraɪəˈsɔːrəs/

From Greek drys (δρῦς), 'tree' or 'oak', + Greek sauros, 'lizard'; means 'tree lizard', reflecting the forested habitat rather than the shape of its teeth

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

Dryosaurus meaning 'tree, oak' and σαυρος (sauros) meaning 'lizard' (the name reflects the forested habitat, not a vague oak-leaf shape of its cheek teeth as is sometimes assumed) is an extinct genus of herbivorous ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont (formerly classified as a hypsilophodont). Fossils have been found in the western United States and were first discovered in the late 19th century. Valdosaurus canaliculatus and Dysalotosaurus lettowvorbecki were both formerly considered to represent species of Dryosaurus.

Diagnosis

  1. Cervical vertebrae long and biconcave (not opisthocoeolous as in Camptosaurus)
  2. Six coossified vertebrae in sacrum, without peg-and-notch articulation
  3. Prepubis long and narrow; postpubis elongate and slender
  4. Femur shorter than tibia; posterior limbs very long
  5. Metatarsals long and hollow; fifth metatarsal represented by short splint only
  6. First digit in pes complete; five digits in manus, not nearly parallel (fifth not at right angles)

Species (2)

Dryosaurus altus Marsh, 1894

Type species

From Latin 'altus' meaning 'tall', given because the specimens were larger than those of Laosaurus celer, the species it was originally compared to when named as Laosaurus altus.

Lectotype
YPM 1876 , Yale Peabody Museum of Natural History
Material
Braincase, quadrate, squamosal, posterior parts of both frontals, jugal, the main body of one maxilla, both partial dentaries with maxillary and dentary teeth, pelvis and hind limb
Notes
The tooth Marsh figured in the original description is not part of this specimen. Galton (1983) traces it to Yale accession 1048, a shipment from Cañon City, Colorado, making it a paralectotype from Garden Park rather than lectotype material. It is now lost. YPM 1884, from Quarry 13 1/2 at Como, is a second paralectotype.
Horizon
Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Quarry 5, Como Bluff, Wyoming, United States Galton (1983) locates the quarry at T. 22 N., R. 77 W., Sec. 17, in Albany County, and attributes it to W. H. Reed.

Dryosaurus elderae Carpenter & Galton, 2018

Honors Ann Schaffer Elder (1958-2009) for assistance to Carpenter at the Carnegie Quarry, Dinosaur National Monument.

Holotype
CM 3392 , Carnegie Museum of Natural History
Material
Partial articulated skeleton: skull and lower jaw, six cervicals, thirteen dorsals, sacrum, pelvis, right scapula, coracoid and humerus, partial right hind limb, and an articulated left hind foot
Horizon
middle Brushy Basin Member, Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Carnegie Quarry, Dinosaur National Monument, Utah, United States
Diagnosis
  1. Maxillary teeth with a broad midline ridge bearing up to three fine secondary longitudinal ridges (weak primary ridge with few secondary ridges in D. altus)
  2. Horizontal maxillary ramus of the jugal below the orbit deep (slender in D. altus)
  3. Basal tuberae massive projections separated by a midline sulcus (a posteroventral sheet or wedge with no sulcus in D. altus)
  4. Anterior cervical vertebrae low relative to their length (shorter and taller in D. altus)
  5. Ilium long and low, especially the postacetabular process

Notable specimens

  • CM 11340

    Carnegie Museum of Natural History Found 1922 by Earl Douglass ontogeny

    Front half of a hatchling skeleton from Dinosaur National Monument, Utah. It confirmed that Dryosaurus followed craniofacial growth patterns seen in other vertebrates: proportionally large eyes and a short snout when young, with eyes shrinking and snout lengthening with age.

    Carpenter (1994)

References

  1. Marsh, O. C. (1894). The typical Ornithopoda of the American Jurassic. American Journal of Science s3-48(283): 85-90. American Journal of Science (AJS). doi:10.2475/ajs.s3-48.283.85 marsh1894a
  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. Carpenter, K. (1994). Baby Dryosaurus from the Upper Jurassic Morrison Formation of Dinosaur National Monument. Dinosaur Eggs and Babies 288-297. Cambridge University Press, Cambridge. carpenter1994a
  4. Carpenter, K.; Galton, P. M. (2018). A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA. Geology of the Intermountain West 5: 167-207. doi:10.31711/giw.v5.pp167-207 carpenter2018b
  5. Galton, P. M. (1983). The cranial anatomy of Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and East Africa, with a review of hypsilophodontids from the Upper Jurassic of North America. Geologica et Palaeontologica 17: 207-243.

    Redescribes the cranial material of YPM 1876, lectotype of Laosaurus altus and type of Dryosaurus altus. Identifies the tooth Marsh figured as a paralectotype from Garden Park, not part of YPM 1876.

    galton1983a