Earth surface processes in the evolution of mammalian tooth shape (Meeting)

Much of the evolution of mammalian tooth shape involves the acquisition of structures to prolong functional longevity, and particularly structural features to confront abrasive tooth wear. Hypsodonty (high-crowned teeth) is the most widespread and conspicuous of these adaptations. Long associated with the consumption of grasses and the grazing habitus, hypsodonty is widely thought in paleontology to indicate open or grassland ecosystems. However, the distribution of hypsodonty among living mammals seems more closely associated with earth surface processes than with grassland ecosystems. That is, variation in tooth wear rates in herbivores is mostly a consequence of soil ingestion, and where studied in actively eroding settings, wear rates show a strong positive correlation with sediment particle flux through the animal’s environment. Among living mammals in South America, high-crowned teeth are associated with herbivorous diets and mountain and volcanic settings exert a positive influence on the prevalence of hypsodonty. This prevalence is coincident with surface processes that entrain and transport mineral particles. In the fossil record of western North America and southern South America, the evolution of hypsodonty is coincident with volcanic activity and the erosion of pyroclastic sediments. In the tectonically and volcanically active Rift System of East Africa, directional evolution of increasing enamel volume, crown complexity, and hypsodonty appears to be triggered above threshold levels of erosion and mineral particle flux. Thus, it now appears that much of mammalian tooth shape evolution resides at the interface between the earth and life sciences, and geomorphology needs to be introduced into the study of evolutionary morphology. This has never been done. Resolution of the complexities, plausibility and universality of the interaction between morphological evolution and geomorphology, will require contributions from a wide variety of specialties, including volcaniclastic sedimentology, geomorphology, paleoceanography, mammalian functional morphology and paleontology, environmental paleobotany, radioecology and isotope geochemistry. The universal currency should be mineral particle flux.

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