Comments about the history of this manuscript

I edited the manuscript originally and the main problem was that the conclusions are based on very weak evidence:

Figures. The manuscript consists in a taphonomic study of the Late Jurassic Cleveland-Lloyd Dinosaur Quarry in Central Utah, and when I firstly received this article for edition, I was surprised that any photograph of the outcrops has been provided. The original submission also lacked pictures of the bone bed under study, and the sedimentary facies where it was preserved wasn’t shown either. Thus, the taphonomic study was based almost only on the finding of several minuscule bone fragments obtained by screening of a bulk of apparently consolidated sediment, which was also never shown. Authors interpreted those bone fragments as syndepositional, meaning that they were buried and fossilized at the same time than the other bones of the bone bed. However, no convincing evidence is provided for demonstrate that. On the contrary, they identified different states of abrasion in the bones, suggesting that some were more exposed than others. They stated that more than 1000 bone fragments less than 5 mm in size were collected from “blocks of lithified mudstones”, but the different degree of weathering or the presence of sharp edges corresponding to fresh fractures is not easy to determine from figures. Reviewers were skeptical about that bone conditions (more angular vs. more rounded). Although requested, authors did not provide better figures during the entire editorial process, rather, they tried to improve the original ones, but the results were not satisfactory. After my insistence, photographs of the studied sites were finally provided, but also of poor quality. Authors declared that the tiny bone fragments come from collected sediments taken “following the excavation of a theropod femur and tibia” which are also not figured.

Interpretations: In this paper authors failed to demonstrate that the tiny bone fragments were not disaggregated by recent exposition of large dinosaur bones; for instance the caudal vertebrae figured in Fig. 3F appears to be very much weathered with the superficial bone lost, so, it would be interesting that they also analyze the sedimentary-blocks around that fossil. The hypothesis 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” is plausible and has been previously suggested. The fossilization in such conditions can produce a very hard radial fracturing (mainly micro-fractures) in the bones during diagenesis (see for instance Previtera et al. 2016).Thus, a possible alternative hypothesis for the origin of the small bones could have been that they were incorporated into the sediments once (since) the bone bed was firstly discovered and excavated to collecting the skeletal pieces. Only one sauropod large vertebra as that shown in figure 3 could have produced more than 1000 of these so small bones found scattered through the site. If we investigate the history of the CLDQ, the Morrison Fm. was laid under a river system with extensive level plans where dinosaurs lived. According to some authors dinosaur skeletons were integrated to the deposit along a considerable period of time. Others are more inclined to think that the skeletons at the CLDQ pertained to animals that died suddenly, altogether. Time after, the sediments of the Morrison Fm. were covered by several other formations, as well as also the bone beds, which appear to have been gradually mineralized by groundwater. Posterior and more recent erosion of the uppermost layers leaved exposed the bone bed (Stokes, 1985). According to this last author, bones firstly collected were disarticulated but they were not fractured or weathered. Thus, it is improbable that the small bone fragments were produced before fossilization of the skeletons. The history of the quarry then starts when the man enters in the scene. Stokes (1985) relates that knowing who found the CLDQ for the first time is like asking who discovered America, but he suggests that it may has been discovered by the 1880’s by ranchers in the area, who collected the first bones. In 1928 personal of the Utah University started the hardest collecting. More than 500 well preserved bones were collected in that season, and more than 7000 bones were excavated during annual field works since that date until the late 60’s, when the Cleveland-Lloyd Center was created. Bulldozers were used to avoid souvenirs hunters (small bones) during the construction. A water-flood occurs in the winter of 1978 and the damage to the exposed bones was severe. Additionally, 18 holes were made at the west of the quarry in the frame of a core drilling program by the Bureau of Land Management. This is just a rapid review to show the disturbances that the quarry experimented since its discovery which supports my recommendation to consider more seriously the hypothesis that the small fragments may have been the result of recent disintegration of bones by weathering or fragmentation, buried by floods.

Other concerns related to the history of the quarry is the origin of the increased amounts of heavy metals that authors described to have found associated to sediments and bones in CLDQ. I requested that authors consider the possibility that the origin of these elements can be nearest mining activities because some of them (As, Cr), are very common as the byproducts of core drillings or extractive mining exploitation. Barite is also a very frequently used material in mines. That possibility was considered by authors as a very improbable origin even thought there were mining projects developing in the Morrison Formation since 1900 at least. They refused the possibility because they thought that the protective construction that was made to the quarry would avoid the infiltration of these elements. The problem with this explanation is that contamination could have produced previously to the construction of the protective structure and it could have been produced by several sources (e.g. contaminated groundwater).

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