[N] 2006 Allosaurus and other theropods of the Dry Mesa Quarry
Dangerfield, A., Britt, B. & Scheetz, R. (2006) Allosaurus and other theropods of the Dry Mesa Quarry (Upper Jurassic, Morrison Formation) Colorado. JVP 26(3) Abstracts pp.54
In addition to an array of sauropod and ornithischian dinosaurs, the Dry Mesa (DM) assemblage includes 1203 theropod elements pertaining to Allosaurus (MNI 13, 62% of the theropod fauna), Ceratosaurus (MNI 3, 14%), and Torvosaurus (MNI 2, 10%), with Coelurus, Stokesosaurus and Marshosaurus (MNI 1) each comprising 5% of the theropod fauna.
Two species of Allosaurus are recognized in the Morrison Fm., A. fragilis and A. jimmadseni. Based on skull morphology, the only allosaur present at DM is A. jimmadseni, with femora ranging in size from ~120 to 960 mm (average length = 702 mm). By contrast, the Allosaurus femora at the Cleveland Lloyd Dinosaur Quarry (CLDQ) average 502 mm. At DM, the theropod bones are loosely associated, with substantial overlap of individual scatters, making it difficult to assign bones to a specific individual. The most complete associated skeleton pertains to a very large Allosaurus consisting of a cranium, caudal vertebrae, scapcoracoid, and hind limbs (femur length = 960 mm).
The dominant taphonomic features of the theropod elements are insect foraging traces, which occur on 11% of the bones and consist of circular shallow pits 0.5-13mm wide and 5mm deep. The pits occur in small groups, massive clusters, and lineations, and are most common on limb, ventral pelvic, and elongate bones such as ribs and metapodials. The traces show no affinity for specific taxa. No other quarry preserves such a wide range of Allosaurus ontogenetic stages.
It is noteworthy that only one species, A. jimmadseni, is present at DM, and A. fragilis is the only identified species at CLDQ. Although these two quarries represent an impressive Allosaurus sample, neither quarry contains both species, suggesting an ecological or temporal separation.