1. Evolution and Development Unit, Institute of Biotechnology, PO Box 56 (Viikinkaari 9), FIN-00014 University of Helsinki, Finland
2. Department of Earth Sciences, Denver Museum of Nature and Science, 2001 Colorado Boulevard, Denver, Colorado 80205, USA
3. Department of Geology, PO Box 64 (Gustaf Hällströmin katu 2a), FIN-00014 University of Helsinki, Finland

Correspondence to: Alistair R. Evans¹ Correspondence and requests for materials should be addressed to A.R.E. (Email: arevans@fastmail.fm). Data deposition: the three-dimensional scans for this study are deposited in the MorphoBrowser database (http://morphobrowser.biocenter.helsinki.fi/).

Abstract

The study of mammalian evolution depends greatly on understanding the evolution of teeth and the relationship of tooth shape to diet. Links between gross tooth shape, function and diet have been proposed since antiquity, stretching from Aristotle¹ to Cuvier², Owen³ and Osborn⁴. So far, however, the possibilities for exhaustive, quantitative comparisons between greatly different tooth shapes have been limited. Cat teeth and mouse teeth, for example, are fundamentally distinct in shape and structure as a result of independent evolutionary change over tens of millions of years⁵. There is difficulty in establishing homology between their tooth components or in summarizing their tooth shapes, yet both carnivorans and rodents possess a comparable spectrum of dietary specializations from animals to plants. Here we introduce homology-free techniques^{6, 7, 8} to measure the phenotypic complexity of the three-dimensional shape of tooth crowns. In our geographic information systems (GIS) analysis of 441 teeth from 81 species of carnivorans and rodents, we show that the surface complexity of tooth crowns directly reflects the foods they consume. Moreover, the absolute values of dental complexity for individual dietary classes correspond between carnivorans and rodents, illustrating a high-level similarity between overall tooth shapes despite a lack of low-level similarity of specific tooth components. These results suggest that scale-independent forces have determined the high-level dental shape in lineages that are widely divergent in size, ecology and life history. This link between diet and phenotype will be useful for inferring the ecology of extinct species and illustrates the potential of fast-throughput, high-level analysis of the phenotype.

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