Paleotribological models using preserved fossil tissue properties reveal functional significance of Eurasian mammoth dental evolution.

Abstract

Eurasian mammoths (Mammuthus) underwent substantial modifications in molar morphology as later-diverging species evolved progressively thinner enamel and increased enamel crest complexity. These features have been hypothesized to reduce whole-tooth wear and extend dental longevity as increasingly graze-dominated diets evolved within the lineage. This hypothesis has yet to be directly tested. Here, we developed an in-silico wear model using experimentally derived wear rates from fossil and extant proboscidean dental tissues. The models revealed that shifts in tissue topology do not affect whole-tooth wear rate, as inverse trends in lamellar frequency and enamel thickness preserve a consistent surface enamel area fraction; the determining factor of wear. Rather, topological shifts produce a wear-emergent secondary occlusal surface with greater numbers of triturating crests that create a regular, low-relief, file-like shearing pavement. These changes in occlusal architecture likely directly impacted the mastication capacity of Mammuthus dentitions, facilitating their dietary expansion to incorporate fibrous, lower-nutrient graze. STATEMENT OF SIGNIFICANCE: Eurasian mammoths evolved progressively thinner enamel and more complex enamel crests which have been hypothesized to reduce whole-tooth wear and extend dental longevity as grazing intensified, but this idea has not yet been directly tested. Here, we test this long-standing hypothesis using mechanical testing and in-silico wear models on fossil Woolly mammoth and modern Indian Elephant molars. We demonstrate that wear relevant material properties can be preserved in fossil dentitions and show that the addition of enamel plates through evolutionary time does not decrease whole-tooth wear rate as previously hypothesized, but rather topological shifts facilitate the emergence of a regular, low-relief, occlusal surface with an increasing number of triturating crests that likely improved mastication capacity of fibrous, lower nutrient graze.