Dryosaurus altus

Dryosaurus altus was a small-bodied dryosaurid ornithopod from the Late Jurassic Morrison Formation of western North America. Its long lower legs and compact torso produced a much lighter build than the contemporary Camptosaurus, while a deep tail helped balance the body during bipedal movement. The front of the mouth formed a toothless beak and the cheek teeth processed vegetation. The holotype includes a partial skeleton and important cranial material, and later discoveries have expanded knowledge of the genus. Some of the most famous skeletons historically displayed as D. altus, however, were separated as Dryosaurus elderae in 2018, so older books and museum labels can combine material that is no longer assigned to the same species.

Its fossils occur between approximately 155 and 145 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The head was small with a beak at the front, leaf-shaped cheek teeth and large eye openings. Short forelimbs ended in five-fingered hands, while the much longer hind limbs had powerful upper segments and elongated feet. Ossified tendons stiffened parts of the back and tail, helping the tail act as a dynamic counterbalance. Unlike hadrosaurs, Dryosaurus lacked a deep dental battery and did not have forelimbs specialized into weight-bearing columns.

• Small beaked skull with leaf-shaped cheek teeth
• Five-fingered hands on short forelimbs
• Long and slender weight-bearing hind limbs
• Elongated feet suited to efficient bipedal movement
• Deep balancing tail reinforced by ossified tendons
• Lightly built torso compared with larger iguanodontians

Samuel Wendell Williston found the holotype at Reed's Quarry 5 near Como Bluff, Wyoming, in 1876 during the early years of the Bone Wars. Othniel Charles Marsh described it in 1878 as Laosaurus altus and created the separate genus Dryosaurus in 1894. The holotype, YPM VP 001876, remains in the Yale Peabody Museum. Carnegie Museum expeditions later collected excellent dryosaur material at Dinosaur National Monument, but a 2018 revision distinguished those Utah skeletons as D. elderae rather than D. altus.

Discovery credit: Samuel Wendell Williston.

Naming authors: Othniel Charles Marsh.

Dryosaurus inhabited the river channels, floodplains and seasonally dry woodland mosaics of the Morrison Formation. It lived among much larger herbivores including sauropods, stegosaurs and Camptosaurus, as well as predators such as Allosaurus and Ceratosaurus. Its small body likely gave it access to low vegetation and ecological space different from the giant browsers. The map point represents the broad Como Bluff quarry region, not a publicly released excavation coordinate.

Dryosaurus cropped low vegetation with its beak and sliced it with cheek teeth. Long hind limbs and a counterbalancing tail support agile bipedal locomotion, but fossils cannot provide a reliable maximum running speed. Speed was probably useful when avoiding predators, although direct chase evidence is absent. No nest, trackway or mass accumulation securely demonstrates its group size, parental care or migratory behaviour.

• Its name means tree or oak lizard, referring to a presumed woodland habitat rather than oak-shaped teeth.
• The type skeleton was discovered near Como Bluff during the Bone Wars era.
• Dryosaurus had five fingers even though its forelimbs were much shorter than its legs.
• Ossified tendons helped stiffen the back and tail.
• Famous Utah fossils once called D. altus are now often classified as Dryosaurus elderae.

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

1. 01
   A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA

   Kenneth Carpenter, Peter M. Galton · Geology of the Intermountain West 5, 167-207 · 2018

   Open source
2. 02
   Dryosaurus altus holotype YPM VP 001876

   Yale Peabody Museum Vertebrate Paleontology Collection

   Open source
3. 03
   Dryosaurus altus

   Dinosaur National Monument, U.S. National Park Service

   Open source
4. 04
   Dryosaurus dinosaur directory entry

   Natural History Museum, London

   Open source