December 20 , 2016:

The Cleveland-Lloyd Dinosaur Quarry (CLDQ) is the densest deposit of Jurassic theropod dinosaurs discovered to date. Unlike typical Jurassic bone deposits, it is dominated by the presence of Allosaurus fragilis. Since excavation began in the 1920’s numerous hypotheses have been put forward to explain the taphonomy of CLDQ, including a predator trap, a drought assemblage, and a poison spring. In an effort to reconcile the various interpretations of the quarry and reach a consensus on the depositional history of CLDQ, new data is required to develop a robust taphonomic framework congruent with all available data. Here we present two new data sets which aid in the development of such a robust taphonomic framework for CLDQ. First, x-ray fluorescence of CLDQ sediments indicate elevated barite and sulfide minerals relative to other sediments from the Morrison Formation, suggesting an ephemeral environment dominated by periods of hypereutrophic conditions during bone accumulation. Second, the degree of weathering and hydraulic equivalency of small bone fragments dispersed throughout the matrix were analyzed from CLDQ. Results of these analyses suggest that bone fragments are autochthonous or parautochthonous and are derived from bones deposited in the assemblage. The variability in abrasion exhibited by the fragments is most parsimoniously explained by periodic reworking and redeposition during seasonal fluctuations throughout the duration of the quarry assemblage. Collectively, these data support some previous interpretations that the CLDQ represents an attritional assemblage in a poorly-drained overbank deposit where vertebrate remains were introduced post-mortem to an ephemeral pond during flood conditions. Furthermore, elevated heavy metals and rare earth elements detected at the quarry are likely a diagenetic signal, potentially produced in part from an abundance of vertebrate remains, and not the primary driver for the accumulation of carcasses. These new data help to explain the specific depositional environment of the quarry, and represent a significant step in understanding the taphonomy of the bone bed and late Jurassic paleoecology.

Joseph E. Peterson, Jonathan P. Warnock, Shawn L. Eberhart, Steven R. Clawson & Christopher R. Noto (2016)
New data towards the development of a comprehensive taphonomic framework for the Cleveland-Lloyd Dinosaur Quarry.
PeerJ Preprints 4:e2600v1
doi: https://doi.org/10.7287/peerj.preprints.2600v1