File:Dinosaur bone in sandstone (Morrison Formation, Upper Jurassic; western side of Dinosaur Ridge, Colorado, USA) 20.jpg

English: Dinosaur bone in sandstone in the Jurassic of Colorado, USA.

Dinosaur Ridge is a fossil-rich section of the Dakota Hogback in north-central Colorado. It is a north-south trending ridge of eastward-dipping Mesozoic sedimentary rocks. The western side of Dinosaur Ridge has exposures of the Morrison Formation, an Upper Jurassic succession consisting of fluvial (river/floodplain) and lacustrine (lake) deposits, plus reddish-colored paleosol horizons. Dinosaur bones and dinosaur tracks are relatively common in the unit.

The dark structure in the photo is a large pubis bone from a sauropod dinosaur (probably Atlantosaurus) in a fluvial sandstone (= river channel deposit). Paleocurrent indicators show that the river system was flowing to the southeast.

Sauropods were the largest and most massive group of dinosaurs - they had huge bodies, walked on four legs, and possessed very long tails and necks. Fossil bones of several different sauropod dinosaur species have been recovered from the Morrison Formation at Dinosaur Ridge, including (not counting junior synonyms) Atlantosaurus immanis, Apatosaurus ajax, and Camarasaurus sp. (see Mossbrucker & Bakker, 2010, pp. 10, 19, 22).

Dinosaurologist Bob Bakker interprets the long pubis bones of sauropods as having had a pubic mounting function. Pubic mounting is a type of behavior used to assert dominance over other animals.

This bone is radioactive - all of the dinosaur bones at this site are radioactive. They have been partially permineralized by one or more uranium-bearing minerals (e.g., carnotite). A scintillometer reading on a dinosaur bone at this locality was 422 counts per minute, compared with a background reading of 140 cpm.

Stratigraphy: Morrison Formation, Kimmeridgian Stage, middle Upper Jurassic, ~150 to 156 Ma

Locality: "Quarry 5" (= one of Arthur Lakes' dinosaur excavation sites during the Cope-Marsh Bone Wars of the late 1800s), western side of Dinosaur Ridge, between Interstate 70 and the town of Morrison, west of Denver, north-central Colorado, USA

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Reference cited:

Mossbrucker, M.T. & R.T. Bakker. 2010. A guide to the paleontology of the Upper Jurassic Morrison Formation of Morrison, Colorado: new interpretations and discoveries. Bulletin of the Morrison Natural History Museum 1. 35 pp.