New data towards the development of a comprehensive taphonomic framework for the Late Jurassic Cleveland-Lloyd Dinosaur Quarry, Central Utah

Abstract

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 1920s, 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 that 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 in the region, suggesting an ephemeral environment dominated by periods of hypereutrophic conditions during bone accumulation. Second, the degree of abrasion 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 rather than transported. The variability in abrasion exhibited by the fragments is most parsimoniously explained by local periodic re-working and re-deposition during seasonal fluctuations throughout the duration of the quarry assemblage. Collectively, these data support 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, while the elevated heavy metals detected at the Cleveland-Lloyd Dinosaur Quarry are not likely the primary driver for the accumulation of carcasses, they are likely the result of multiple sources; some metals may be derived from post-depositional and diagenetic processes, and others are potentially produced from an abundance of decomposing vertebrate carcasses. These new data help to support the inferred depositional environment of the quarry as an ephemeral pond, and represent a significant step in understanding the taphonomy of the bonebed and Late Jurassic paleoecology in this region.

Histology and Geochemistry of Allosaurus (Dinosauria: Theropoda) From the Cleveland-Lloyd Dinosaur Quarry (Late Jurassic, Utah): Paleobiological Implications

“…The mudstones and limestones of the CLDQ have been deposited in a lacustrine environment (Hunt et al, 2006). However, several environmental and taphonomic interpretations have been proposed such as an oxbow (Dodson et al, 1980), a floodplain pond in an anastomosing system (Richmond and Morris, 1996), a spring-fed pond or seep (Bilbey, 1999) and ephemeral pond (Gates, 2005;Peterson et al, 2017). Paleoclimatic reconstructions of the Morrison Formation indicate that the climate was warm and strongly seasonal (e.g., Dodson et al, 1980;Turner and Peterson, 2004;Tanner et al, 2014), i.e., a more or less dry season followed by a humid season characterized by monsoonal conditions.…”

“…Fossil material of the CLDQ is commonly found to be enriched in heavy metals, such as Mo, As, U, Pb, Sr, Mg, Na, and Zn (Peterson et al, 2017). This enrichment may either be through a diagenetic process, or part of a bioaccumulation during the decomposition of numerous dinosaur carcasses (Peterson et al, 2017).…”

“…Fossil material of the CLDQ is commonly found to be enriched in heavy metals, such as Mo, As, U, Pb, Sr, Mg, Na, and Zn (Peterson et al, 2017). This enrichment may either be through a diagenetic process, or part of a bioaccumulation during the decomposition of numerous dinosaur carcasses (Peterson et al, 2017). The water of the depositional environment corresponds to a neutral pH with possible fluvial influence (Suarez M. B., 2004), and was a reducing environment, as suggested by the presence of metal oxides, sulfides and barite (Peterson et al, 2017).…”

“…This enrichment may either be through a diagenetic process, or part of a bioaccumulation during the decomposition of numerous dinosaur carcasses (Peterson et al, 2017). The water of the depositional environment corresponds to a neutral pH with possible fluvial influence (Suarez M. B., 2004), and was a reducing environment, as suggested by the presence of metal oxides, sulfides and barite (Peterson et al, 2017). In our study, only Zn appears to show a signal with a pattern associated to the microstructure of bone tissues.…”

Peer Review #2 of "Notes on the cheek region of the Late Jurassic theropod dinosaur Allosaurus (v0.1)"

“…Manuscript to be reviewed 1976; Gates, 2005;Peterson et al, 2017). The most common dinosaur found at that site is Allosaurus, which is represented by at least 46 individuals (Carpenter, 2010), although the material is generally found disarticulated.…”