The taphonomic clock in fish otoliths

Abstract

Paleobiological and paleoecological interpretations rely on constraining the temporal resolution of the fossil record. The taphonomic clock, that is, a correlation between the alteration of skeletal material and its age, is an approach for quantifying time-averaging scales. We test the taphonomic clock hypothesis for marine demersal and pelagic fish otoliths from a 10–40 m depth transect on the Mediterranean siliciclastic Israeli shelf by radiocarbon dating and taphonomic scoring. Otolith ages span the last ~8000 yr, with considerable variation in median and range along the transect. Severely altered otoliths, contrary to pristine otoliths, are likely to be older than 1000 yr. For pelagic fish otoliths, at 30 m depth, taphonomic degradation correlates positively with postmortem age. In contrast, no correlation occurs for demersal fishes at 10 and 30 m depth, mostly because of the paucity of very young pristine (<150 yr) otoliths, possibly due to a drop in production over the last few centuries. Contrary to molluscan and brachiopod shells, young otoliths at these depths are little affected and do not show a broad spectrum of taphonomic damage, because those that derive from predation are excreted in calcium- and phosphate-rich feces forming an insoluble crystallic matrix that increases their preservation potential. At 40 m depth, all dated otoliths are very young but rather damaged because of locally chemically aggressive sediments, thus showing no correlation between taphonomic grade and postmortem age. Our results show that local conditions and the target species population dynamics must be considered when testing the taphonomic clock hypothesis.

How long does a brachiopod shell last on a seafloor? Modern mid‐bathyal environments as taphonomic analogues of continental shelves prior to the Mesozoic Marine Revolution

“…The taphonomic clock is thus typically accelerated in shallow marine environments; most destructive alteration occurs early, and age cohorts that are decades or centuries old may not differ in alteration (Agiadi et al . 2021; Tomašových et al . 2022 c ).…”

Palaeontological evidence for community-level decrease in mesopelagic fish size during Pleistocene climate warming in the eastern Mediterranean

“…In order to test whether any differences in the body size of the fishes between the glacials and the interglacial were statistically significant, we used a non-parametric Kruskal–Wallis test, followed by a pairwise Wilcoxon test with a-posteriori Bonferroni correction to compare median weight between the three assemblages and estimate 95% confidence intervals around this parameter using a bootstrap procedure with 10 000 iterations. To test for differences in otolith preservation that could affect the interpretation of our results, we quantified and statistically compared the otolith preservation state following a previously presented approach [66]. Specimens that could not be identified at least to family level were included in the otolith preservation analysis, but excluded from size calculations.…”

Palaeontological evidence for community-level decrease in mesopelagic fish size during Pleistocene climate warming in the eastern Mediterranean

“…We used a non-parametric Kruskal-Wallis test, followed by a pairwise Wilcoxon test with a-posteriori Bonferroni correction to compare median weight between the three assemblages and estimate 95% confidence intervals around this parameter using a bootstrap procedure with 10,000 iterations. To test for differences in otolith preservation that could affect the interpretation of our results, we quantified and statistically compared the otolith preservation state following a previously presented approach (62). Specimens that could not be identified at least to family level were included in the otolith preservation analysis, but excluded from size calculations.…”