Controlled feeding trials with ungulates: a new application of in vivo dental molding to assess the abrasive factors of microwear

Abstract

Microwear, the quantification of microscopic scratches and pits on the occlusal surfaces of tooth enamel, is commonly used as a paleodietary proxy. For ungulates (hoofed mammals), scratchdominant microwear distinguishes modern grazers from browsers, presumably as a result of abrasion from grass phytoliths (biogenic silica). However, it is also likely that exogenous grit (i.e. soil, dust) is a contributing factor to these scratch-dominant patterns, which may reflect soil ingestion that varies with feeding height and/or environmental conditions (e.g. dust production in open and/or arid habitats). This study assessed the contribution of exogenous grit to tooth wear by measuring the effects of fine-and medium-grained silica sand on tooth enamel using a novel live-animal tooth-molding technique. It therefore constitutes the first controlled feeding experiment using ungulates and the first in vivo experiment using abrasives of different sizes. Four sheep were fed three diet treatments: (1) a mixture of Garrison and Brome hay (control), (2) hay treated with fine-grained silica sand (180-250 µm) and (3) hay treated with medium-grained silica sand (250-425 µm). We found a significant increase in pit features that was correlated with an increase in grain size of grit, corroborating earlier chewing simulation experiments that produced pits through grit-induced abrasion (i.e. the 'grit effect'). Our results support an interpretation of large silica grains fracturing to create smaller, more abundant angular particles capable of abrasion, with jaw movement defining feature shape (i.e. scratch or pit).

Mechanical modelling of tooth wear

“…The pellet ingredient table [11] shows that the lucerne diet includes pure lignocellulose next to other components that contain acid detergent fibre and acid detergent lignin. Fibres have been suggested previously to be responsible for polishing dental surfaces [13]; our results also raise the possibility that some plant fibres might cause scratches. More comparative and experimental work is needed to explore this possibility.…”

“…Phytoliths have long been considered as a major agent of wear [1,13] and grazing has been considered the main driver of the evolution of hypsodonty [3]. Our grass and grass-rice diets, rich in ADIA levels and known to contain phytoliths, did cause parallel scratches on enamel.…”

“…Exposing rabbits and guinea pigs (Cavia porcellus) to diets designed to reflect different proportions of internal and external abrasives (sand), and measuring the resulting effects manually and by computed tomography, differences in wear and in the responding tooth growth could be demonstrated [11,12]. Most recently, the effects of external grit on the microwear signature were demonstrated in live sheep [13] and angles of approach in chewing were shown to affect microwear [14].…”

Phylogenetic signal in tooth wear dietary niche proxies: What it means for those in the field

“…This manifests as dietary shifts, say from a less gritty diet to a more gritty diet, but should rarely manifest as an intraspecific shift from herbivory to carnivory, for example (Price, Hopkins, Smith, & Roth, ). We further agree with DeSantis et al () that experimental diets can and do change the properties of mammal tooth wear (Hoffman, Fraser, & Clementz, ). However, our study refers only to the natural diet of mammals.…”

Feeding Ecology in Oligocene Mylodontoid Sloths (Mammalia, Xenarthra) as Revealed by Orthodentine Microwear Analysis

“…These wear features are influenced by the properties of ingested food items (e.g., grass, leaves, fruits, insects, meat) or exogenous items (e.g., dust, grit), and have a rapid turnover of several days to one or two weeks (Teaford and Oyen 1989; Hoffmann et al 2015). Several microscopic techniques have been used for microwear analysis: scanning electron microscopy (e.g., Rensberger 1978; Walker et al 1978), stereomicroscopy (e.g., Solounias and Semprebon 2002; Semprebon et al 2004, 2016; Merceron et al 2005; Koenigswald et al 2010; Rivals et al 2010), and confocal microscopy (e.g., Scott et al 2005, 2006; Ungar et al 2008; Schulz et al 2010; Calandra and Merceron 2016).…”