Journal of Mammalian Evolution

, Volume 23, Issue 1, pp 43–47 | Cite as

Are Hypsodonty and Occlusal Enamel Complexity Evolutionarily Correlated in Ungulates?

  • Nicholas A. FamosoEmail author
  • Edward Byrd Davis
  • Robert S. Feranec
  • Samantha S. B. Hopkins
  • Samantha A. Price
Original Paper


The spread of grasslands and cooling climate in the Miocene contributed to an increasingly abrasive diet for ungulates. This increase in abrasiveness is proposed to select for both hypsodonty and increasing complexity of occlusal enamel bands. If these traits evolved in response to strong selection to resist tooth wear while feeding in grassland habitats, we might expect them to have evolved in a correlated fashion. If, on the other hand, there was a developmental or physiological constraint, or if selection was not strong on total enamel production, we would expect species to have evolved one or the other of these traits at a time, producing an uncorrelated, or even inversely correlated, pattern of trait evolution. To test these hypotheses, we examined the Occlusal Enamel Index (OEI) and Hypsodonty Index (HI) of 773 ungulate teeth. We tested the dependence of OEI on HI for the orders Artiodactyla and Perissodactyla using phylogenetic generalized least squares regression (PGLS). The two traits are not significantly correlated in the PGLS, for Artiodactyla and Perissodactyla. Despite their physical proximity, close functional utility, and conventional correlation, our results reject the hypothesis that HI and OEI are evolutionarily linked in these lineages, suggesting that selection to resist tooth wear was not so strong as to drive the overall evolutionary trajectory of both these traits at the same time.


Hypsodonty Occlusal enamel complexity Artiodactyla Phylogenetic generalized least squares regression Equini Hipparionini 



We would like to thank the UO Paleontology Group and the UO Department of Geological Sciences for feedback and support related to this project. We would like to thank the University of California Museums of Vertebrate Zoology and Paleontology, Florida Museum of Natural History, Burke Museum of Natural History and Culture, John Day Fossil Beds National Monument, American Museum of Natural History, the Smithsonian’s U.S. Museum of Natural History, and University of Nebraska State Museum for access to collections. We would also like to thank John Wible and two anonymous reviewers for their constructive reviews of this manuscript. This paper was partly funded by NSF DEB-1256894-0.

Supplementary material

10914_2015_9296_MOESM1_ESM.pdf (16 kb)
Online Resource 1 R code used to execute analyses. Both the code for the artiodactyl and perissodactyl PGLSs are included (PDF 16 kb)
10914_2015_9296_MOESM2_ESM.pdf (547 kb)
Online Resource 2 File for 101 dated artiodactyl phylogenies. This is a .nex file class = “multiphylo” when used for analysis in R (PDF 547 kb)
10914_2015_9296_MOESM3_ESM.pdf (45 kb)
Online Resource 3 File for the perissodactyl phylogeny. This is a .nex file class = “phylo” when used for analysis in R (PDF 44 kb)
10914_2015_9296_MOESM4_ESM.pdf (105 kb)
Online Resource 4 First and last occurance dates for the perissodactyls phylogeney. This file should be .csv when used for analysis in R (PDF 104 kb)
10914_2015_9296_MOESM5_ESM.pdf (107 kb)
Online Resource 5 OEI and HI data for the artiodactyl PGLSs. This file should be .csv when used for analysis in R (PDF 106 kb)
10914_2015_9296_MOESM6_ESM.pdf (105 kb)
Online Resource 6 OEI and HI data for the perissodactyl PGLS. This file should be .csv when used for analysis in R (PDF 104 kb)


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • Nicholas A. Famoso
    • 1
    • 2
    Email author
  • Edward Byrd Davis
    • 1
    • 2
  • Robert S. Feranec
    • 3
  • Samantha S. B. Hopkins
    • 1
    • 4
  • Samantha A. Price
    • 5
  1. 1.Department of Geological Sciences1272 University of OregonEugeneUSA
  2. 2.University of Oregon Museum of Natural and Cultural HistoryEugeneUSA
  3. 3.Research and Collections DivisionNew York State Museum, 3140 Cultural Education CenterAlbanyUSA
  4. 4.Clark Honors College1293 University of OregonEugeneUSA
  5. 5.Department of Evolution and EcologyUniversity of CaliforniaDavisUSA

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