A new paper:
Free pdf:
https://www.pnas.org/doi/epub/10.1073/pnas.2423019122MacLennan et al. report new radiometric dates and sedimentological context for the exceptionally preserved dinosaurs in the lower Yixian Formation. However, the sedimentology and provenance analysis provided do not support the authors’ interpretation of preservation exclusively via burrow collapses.
The authors conclude that the sediment gradient between the body cavity and its exterior suggests a sieving effect as the bodies rotted. Yet as described, this sieving is the result of a fresh body being covered in sediment, which is not exclusive to burrows. It requires a recent death prior to a geologic event, which would also be accounted for by lahars or flood events as suggested by previous work.
The authors found older detrital zircons in both Psittacosaurus specimens, most likely from posteruptive mixing with material on the landscape. This is evidence of mobilization of the volcaniclastic material, which does not exclude a flood or lahar origin. Lahars often incorporate sediment along their pathway, particularly when associated with large-scale mass wasting events.
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