title: Abrasive, silica phytoliths and the evolution of thick molar enamel in primates, with implications for the diet of Paranthropus boisei.
abstract: BACKGROUND
  Primates--including fossil species of apes and hominins--show variation in their degree of molar enamel thickness, a trait long thought to reflect a diet of hard or tough foods. The early hominins demonstrated molar enamel thickness of moderate to extreme degrees, which suggested to most researchers that they ate hard foods obtained on or near the ground, such as nuts, seeds, tubers, and roots. We propose an alternative hypothesis--that the amount of phytoliths in foods correlates with the evolution of thick molar enamel in primates, although this effect is constrained by a species' degree of folivory.
  
  
  RESULTS
  From a combination of dietary data and evidence for the levels of phytoliths in plant families in the literature, we calculated the percentage of plant foods rich in phytoliths in the diets of twelve extant primates with wide variation in their molar enamel thickness. Additional dietary data from the literature provided the percentage of each primate's diet made up of plants and of leaves. A statistical analysis of these variables showed that the amount of abrasive silica phytoliths in the diets of our sample primates correlated positively with the thickness of their molar enamel, constrained by the amount of leaves in their diet (R(2) = 0.875; p<.0006).
  
  
  CONCLUSIONS
  The need to resist abrasion from phytoliths appears to be a key selective force behind the evolution of thick molar enamel in primates. The extreme molar enamel thickness of the teeth of the East African hominin Paranthropus boisei, long thought to suggest a diet comprising predominantly hard objects, instead appears to indicate a diet with plants high in abrasive silica phytoliths.
authors.affiliation: Department of Anthropology, University of New Mexico, Albuquerque, New Mexico, United States of America. drabenol@unm.edu
authors.forename: Diana
authors.initials: D
authors.lastname: Rabenold
authors.forename: Osbjorn M
authors.initials: OM
authors.lastname: Pearson
mesh_terms: D000349:Africa; D000818:Animals; D003743:Dental Enamel / Q000737:chemistry / Q000502:physiology*; D004032:Diet; D006244:Hardness; D015186:Hominidae; D015233:Models, Statistical; D008962:Models, Theoretical; D008963:Molar / Q000502:physiology; D010161:Paleodontology / Q000379:methods; D010802:Phylogeny; D010944:Plants / Q000378:metabolism; D011323:Primates; D012044:Regression Analysis; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D012822:Silicon Dioxide