, Volume 96, Issue 4, pp 423–448 | Cite as

The evolutionary continuum of limb function from early theropods to birds

  • John R. HutchinsonEmail author
  • Vivian Allen


The bipedal stance and gait of theropod dinosaurs evolved gradually along the lineage leading to birds and at some point(s), flight evolved. How and when did these changes occur? We review the evidence from neontology and palaeontology, including pectoral and pelvic limb functional morphology, fossil footprints/trackways and biomechanical models and simulations. We emphasise that many false dichotomies or categories have been applied to theropod form and function, and sometimes, these impede research progress. For example, dichotomisation of locomotor function into ‘non-avian’ and ‘avian’ modes is only a conceptual crutch; the evidence supports a continuous transition. Simplification of pelvic limb function into cursorial/non-cursorial morphologies or flexed/columnar poses has outlived its utility. For the pectoral limbs, even the classic predatory strike vs. flight wing-stroke distinction and separation of theropods into non-flying and flying—or terrestrial and arboreal—categories may be missing important subtleties. Distinguishing locomotor function between taxa, even with quantitative approaches, will always be fraught with ambiguity, making it difficult to find real differences if that ambiguity is properly acknowledged. There must be an ‘interpretive asymptote’ for reconstructing dinosaur limb function that available methods and evidence cannot overcome. We may be close to that limit, but how far can it be stretched with improved methods and evidence, if at all? The way forward is a combination of techniques that emphasises integration of neontological and palaeontological evidence and quantitative assessment of limb function cautiously applied with validated techniques and sensitivity analysis of unknown variables.


Dinosaur Bird Evolution Flight Locomotion Biomechanics Theropod 



Hearty thanks are due to Eric Snively for lending us the phrase ‘interpretive asymptote.’ We thank the Department of Veterinary Basic Sciences at The Royal Veterinary College for supporting this work. Vivian Allen’s research was partly supported by a Sam and Doris Welles award from the University of California Museum of Paleontology. We appreciate the influence of fellow members of the Structure and Motion Laboratory, Stanford University’s Neuromuscular Biomechanics Laboratory, and Padian Lab at Berkeley. Martin Baeker, Charlotte Miller, Heather Paxton and three anonymous reviewers are thanked for their constructive feedback on earlier drafts of this manuscript. Scott Hartman, Jim Robins and Frederik Spindler are thanked for provision of their artwork as noted in the figure captions.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  1. 1.Structure and Motion Laboratory, Department of Veterinary Basic Sciences, The Royal Veterinary CollegeUniversity of LondonHertfordshireUK

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