Microwear–mesowear congruence and mortality bias in rhinoceros mass-death assemblages

Abstract

Although we do not know the cause of death of most fossil animals, mortality is often associated with ecological stress due to seasonality and other stochastic events (droughts, storms, volcanism) that may have caused shifts in feeding ecology preceding death. In these instances, dental microwear, which reflects feeding ecology in a narrow window of time, may provide a biased view of diet. Mesowear, another dental-wear proxy based on the morphology of worn cusps, requires macroscopic amounts of dental wear and reflects diet for a longer interval and may be less prone to bias from near-death ecological stress. We compared congruence between microwear and mesowear of North American, fossil rhinocerotid mass-death assemblages and collections of hunted modern rhinocerotids to test the hypothesis that fossil assemblages yield more incongruous microwear and mesowear data as a result of near-death ecological disturbances. In extant rhinos, both mesowear and microwear are associated with diet and height of the feeding environment. Mesowear and microwear in the modern rhinocerotid collections are statistically correlated, with strong relationships between average mesowear scores and labially distributed dental microwear. In contrast, a relationship between mesowear and microwear was not observed among the fossil rhinocerotid assemblages. Mesowear suggests that the fossil rhinos had low-abrasion diets, suggesting that they fed from clean, possibly tall vegetation. Some, but not all, mass-death assemblages produce microwear data with excessive scratches and/or pits compared with expectations based on mesowear results, suggesting that dental microwear was altered shortly before death in some but not all of the fossil assemblages. The dental-wear proxies available to paleoecologists provide a mosaic of dietary evidence reflecting diet over long (mesowear) and more abbreviated (microwear) periods of time that, together, provide a richer understanding of feeding ecology and its relationship to environment, seasonal change, and other ecological disturbances.

Mesowear Analysis of the Tapirus polkensis population from the Gray Fossil Site, Tennessee, USA

“…These results may indicate the population was able to sustain itself and there was survival of older individuals. Taphonomic studies of individual deaths in the level of the species or population are a useful tool to better understand the ecology of the area, what the population demographics mean, why the species were there, and what eventually led to their death (Lyman, 1994;Rogers et al, 2007;Mihlbachler et al, 2018). Mihlbachler et al (2018) recently examined microwear and mesowear in mass death assemblages demonstrating how ecological stress can be documented in dental morphology.…”

“…Taphonomic studies of individual deaths in the level of the species or population are a useful tool to better understand the ecology of the area, what the population demographics mean, why the species were there, and what eventually led to their death (Lyman, 1994;Rogers et al, 2007;Mihlbachler et al, 2018). Mihlbachler et al (2018) recently examined microwear and mesowear in mass death assemblages demonstrating how ecological stress can be documented in dental morphology. A taphonomic examination of the Gray Fossil Site suggests the tapir specimens built up from attrition, rather than a die-off event leading to mass mortality (Hulbert et al, 2009).…”

Paleoecology of the Rhinocerotidae (Mammalia, Perissodactyla) from Béon 1, Montréal-du-Gers (late early Miocene, SW France): Insights from dental microwear texture analysis, mesowear, and enamel hypoplasia

“…ScoreA points toward a more abrasive diet than ScoreB and Ruler, but still coherent with browsing or mixed-feeding (Figure 8). Previous studies reported mesowear scores for extant rhinoceroses using different approaches (Fortelius and Solounias, 2000;Taylor et al, 2013;Mihlbachler et al, 2018;Rivals et al, 2020). The mean values reported by Rivals et al (2020) for extant rhinos using Ruler are under 0.5 for all extant species but C. simum (4.67).…”

Dietary response of early Pleistocene ungulate communities to the climate oscillations of the Gelasian/Calabrian transition in Central Italy

“…Contrary a recent study based on the dental microwear texture analysis reported a greater diversity of feeding behaviours (from browser to grazer) for the large bush-antlered deer E. ctenoides, suggesting a significant dietary plasticity for this early Pleistocene cervid (Berlioz et al, 2017). Dental microwear however records information about the last few meals (hours and days) of an animal before its death (whereas dental mesowear reflects dietary preferences over a longer period; weeks and months) (Sánchez-Hernández et al, 2016;Mihlbachler et al 2018), thus the observed discrepancy could reflect seasonal differences. A more abrasive diet is also recorded for the Olivola…”