Letter | Published:

Initial radiation of jaws demonstrated stability despite faunal and environmental change

Nature volume 476, pages 206209 (11 August 2011) | Download Citation


More than 99 per cent of the roughly 58,000 living vertebrate species have jaws1. This major clade, whose members are collectively known as gnathostomes (‘jawed mouths’), made its earliest definitive appearance in the Silurian period, 444–416 million years (Myr) ago, with both the origin of the modern (crown-group) radiation and the presumptive invasion of land occurring by the end of the Devonian period2 (359 Myr ago). These events coincided with a major faunal shift that remains apparent today: the transition from Silurian ecosystems dominated by jawless fishes (agnathans) to younger assemblages composed almost exclusively of gnathostomes2,3. This pattern has inspired several qualitative descriptions of the trophic radiation and ecological ascendance of the earliest jawed vertebrates3,4,5,6,7. Here we present a quantitative analysis of functional variation in early gnathostome mandibular elements, placing constraints on our understanding of evolutionary patterns during this critical interval. We document an initial increase in functional disparity in the Silurian that stabilized by the first stage of the Devonian, before the occurrence of an Emsian (400 Myr ago) oxygenation event implicated in the trophic radiation of vertebrates8. Subsequent taxonomic diversification during the Devonian did not result in increased functional variation; instead, new taxa revisited and elaborated on established mandibular designs. Devonian functional space is dominated by lobe-finned fishes and ‘placoderms’; high disparity within the latter implies considerable trophic innovation among jaw-bearing stem gnathostomes. By contrast, the major groups of living vertebrates—ray-finned fishes and tetrapods—show surprisingly conservative mandibular morphologies with little indication of functional diversification or innovation. Devonian gnathostomes reached a point where they ceased to accrue further mandibular functional disparity before becoming taxonomic dominants relative to ‘ostracoderm’-grade jawless fishes, providing a new perspective on classic adaptive hypotheses concerning this fundamental shift in vertebrate biodiversity.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    Fishes of the World 4th edn (Wiley, 2006)

  2. 2.

    Early Vertebrates (Clarendon, 1996)

  3. 3.

    & in Palaeozoic Vertebrate Biostratigraphy and Biogeography (ed. ) 67–86 (Johns Hopkins Univ. Press, 1993)

  4. 4.

    The Pattern of Vertebrate Evolution 26 (Oliver & Boyd, 1969)

  5. 5.

    Evolution of the Vertebrates 28 (Wiley, 1991)

  6. 6.

    Vertebrate Paleontology and Evolution 44 (Freeman, 1988)

  7. 7.

    , & Vertebrate Life 8th edn (Pearson Benjamin Cummings, 2009)

  8. 8.

    et al. Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish. Proc. Natl Acad. Sci. USA 107, 17911–17915 (2010)

  9. 9.

    Morphological disparity in Ordovician-Devonian crinoids and the early saturation of morphological space. Paleobiology 20, 320–344 (1994)

  10. 10.

    , & Evolutionary dynamics of complex biomechanical systems: an example using the four-bar mechanism. Evolution 58, 495–503 (2004)

  11. 11.

    , & Evolutionary consequences of many-to-one mapping of jaw morphology to mechanics in labrid fishes. Am. Nat. 165, E140–E154 (2005)

  12. 12.

    Functional versus morphological diversity in macroevolution. Annu. Rev. Ecol. Evol. Syst. 38, 381–401 (2007)

  13. 13.

    & Projecting mechanics into morphospace: disparity in the feeding system of labrid fishes. Proc. R. Soc. Lond. B 269, 317–326 (2002)

  14. 14.

    Biomechanics, functional patterns, and disparity in Late Devonian arthrodires. Paleobiology 35, 321–342 (2009)

  15. 15.

    Evolution of levers and linkages in the feeding mechanisms of fishes. Integr. Comp. Biol. 44, 378–389 (2004)

  16. 16.

    , & Detecting changes in morphospace occupation patterns in the fossil record: characterization and analysis of measures of disparity. Paleobiology 27, 695–715 (2001)

  17. 17.

    Statistical Evidence: A Likelihood Paradigm (Chapman & Hall, 1997)

  18. 18.

    The Fossil Record 2 (Chapman & Hall, 1993)

  19. 19.

    Contributions of individual taxa to overall morphological disparity. Paleobiology 19, 403–419 (1993)

  20. 20.

    & Terrestrial-style feeding in a very early aquatic tetrapod is supported by evidence from experimental analysis of suture morphology. Proc. Natl Acad. Sci. USA 104, 7134–7138 (2007)

  21. 21.

    & Siluro-Devonian vertebrate biostratigraphy and biogeography of China. Palaeoworld 19, 4–26 (2010)

  22. 22.

    & End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates. Proc. Natl Acad. Sci. USA 99, 8139–8144 (2010)

  23. 23.

    , & Handbook of Paleoichthyology Vol. 3D: Chondrichthyes Paleozoic Elasmobranchii (Pfeil, 2010)

  24. 24.

    et al. The Devonian nekton revolution. Lethaia 43, 465–477 (2010)

  25. 25.

    et al. Devonian climate and reef evolution: insights from oxygen isotopes in apatite. Earth Planet. Sci. Lett. 284, 599–609 (2009)

  26. 26.

    et al. Carbon, oxygen and strontium isotope records of Devonian brachiopod shell calcite. Palaeogeogr. Palaeoclimatol. Palaeoecol. 240, 47–67 (2006)

  27. 27.

    & Mass extinctions in the marine fossil record. Science 215, 1501–1503 (1982)

  28. 28.

    , & Silurian atmospheric O2 changes and the early radiation of gnathostomes. Palaeoworld 19, 146–159 (2010)

  29. 29.

    Reef development at the Frasnian/Famennian mass extinction boundary. Palaeogeogr. Palaeoclimatol. Palaeoecol. 181, 27–65 (2002)

Download references


We thank P. Donoghue, M. Rücklin and M. Ruta for discussions. This work was supported by Royal Society and Marie-Curie Actions fellowships, awarded to P.S.L.A.; a Fell Fund award to M.F.; NERC grant NE/G016623/1, awarded in part to E.J.R.; and a FQRNT postdoctoral fellowship, to M.D.B.

Author information

Author notes

    • Martin D. Brazeau

    Present address: NCB Naturalis, 2300 RA Leiden, The Netherlands.


  1. Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK

    • Philip S. L. Anderson
    •  & Emily J. Rayfield
  2. Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK

    • Matt Friedman
  3. Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity at the Humboldt University in Berlin, 10115 Berlin, Germany

    • Martin D. Brazeau


  1. Search for Philip S. L. Anderson in:

  2. Search for Matt Friedman in:

  3. Search for Martin D. Brazeau in:

  4. Search for Emily J. Rayfield in:


P.S.L.A. designed and led the study, developed the biomechanical traits, collected data, performed the disparity and multivariate analyses, and wrote the paper. M.F. gathered data, wrote analytical code, performed the faunal analyses, drafted figures and wrote the paper. M.D.B. gathered data and produced illustrations. E.J.R. gave advice on biomechanical theory. All authors contributed to interpretation of the results and edited the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Philip S. L. Anderson.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    The file contains Supplementary Text, Supplementary Figures 1-13 with legends, Supplementary Tables 1-12 and additional references.

Excel files

  1. 1.

    Supplementary Data

    This file contains raw data analyzed in this study. These include: averaged biomechanical metrics for each genus, multivariate coordinate scores for each genus taken from the NMDS, faunal composition data used for the intrafaunal comparisons.

About this article

Publication history






Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.