ARE PALEONTOLOGISTS JUDGING BY APPEARANCE? PRESERVATION STATE ARE NOT CORRELATED WITH FOSSIL-AGE IN MARINE ENVIRONMENTS

​Previous studies point out that old shells are not necessarily old-age shells, despite the huge bunch of age-dated shells available today, but this question appears to be sometimes unsolved or partially misregarded by geoscientists, particularly to those dealing with the Quaternary fossils. In order to clarify this noteworthy question, we accessed a large dataset of individually dated shells with their corresponding taphonomic scores. All shells were collected on Southern Brazilian shelf (SBS). A total of 126 shells, belonging to genus _Nuculana_ (86) and _Mactra_ (60) were accessed. The _Mactra_ shells are from shallow waters (seven up to 21 m) while _Nuculana_ samples are gathered from outer shelf waters (100 up to 242 m). Shallow sites show a more heterogeneous (i.e. high dispersion) ensemble of damage properties, whereas outer shelf sites present less variation in taphonomic variables, using interquartile range of taphonomic standardize scores (IQR_{TAPHO_shallow} = 0.21, IQR_{TAPHO_outer shelf} = 0.13). This pattern is also clearly observed in individually dated specimens when considering the counts in total taphonomic grades binned by depth (shallow vs. outer shelf). Contrariwise, counts of individually dated shells (grouped into 500‐year bins) reveal the contradictory pattern; outer shelf sites exhibit high age dispersion, whereas shallow sites display a restricted interquartile range of ages (IQR_shallow = 1.8 kyrs; IQR_{outer shelf} = 4.2 kyrs). The results show that taphonomic variation is not a direct signal of the magnitude of time-averaging. Nevertheless, these results are influenced by depth (stratigraphic context) and by intrinsic proprieties of the shells, for example, microstructure. These findings highlight that picking-up fossils by "appearance" (preservation state) to analytical analyses (e.g., dating, isotopes and so on), may introduce bias on results and, consequently, lead to incorrect conclusions. That is primarily advised for Quaternary studies based on shells (or fossils in a general way), especially those without taphonomy baselines, or those in deep time that assume that variation in the degree of preservation is a direct consequence of the magnitude of time-averaging or temporal mixing of shelly assemblages [CAPES-IODP 091727/2014; CNPq 422766/2018-6]