2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): STONE, Dwayne D., Dept. of Geology, Marietta College, Marietta, OH 45750; CRISP, Edward L., Geology Dept., West Virginia University at Parkersburg, Parkersburg, WV 26101, ecrisp@alpha.wvup.wvnet.edu; BISHOP, John R., Rt. 2 Box 137, Ravenswood, WV 26164
Keywords: Coprolite, Jurassic, Morrison Formation, Allosaurus
A theropod dinosaur coprolite has been excavated in Emery County, Utah from a red-brown mudstone of the Upper Jurassic Brushy Basin Member of the Morrison Formation. The coprolite is nearly complete and is divisible into two parts, the main mass and a dribbling zone. The well-indurated main mass, which tapers at both ends, is 1.52 m in length, 0.457 m in maximum width, and 10.2 cm thick. The 1.52 m long dribbling zone consists of small isolated coprolites that curve towards the end of the dribbles. The coprolite geometry is interpreted to indicate that the main mass was defecated first, then the animal walked forward to release smaller amounts of feces. The coprolite consists of dark gray bone fragments, ranging from pebble to sand size, in a red-brown matrix. Bone fragments represent about 50% of the mass and have broken, jagged ends, possibly indicating breakage by the biting action of a carnivore. XRD analysis of the bone fragments and matrix reveal that both are primarily composed of carbonate fluorapatite. The large size of the coprolite and its geometry and stratigraphic location indicate that it represents fecal droppings from a large Allosaurus. Further support for this hypothesis is the fact that a broken distal end of an Allosaurus tooth was found within the coprolite, indicating that during mastication a tooth was broken and ingested. The carnivore did not grab a portion of flesh and bone from a prey animal and then swallow it whole. Instead the eater masticated its meal and broke the bones into smaller portions. This is the largest and oldest theropod dinosaur coprolite known. Work is continuing on a second theropod coprolite higher in the section at this location and pieces of theropod coprolites from two additional localities have been identified. Morrison Formation theropod coprolites are no longer considered to be absent or scarce and future searching should reveal additional large specimens.
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