Comparative architectural properties of limb muscles in Crocodylidae and Alligatoridae and their relevance to divergent use of asymmetrical gaits in extant Crocodylia

Authors

  • Vivian Allen,

    Corresponding author
    1. Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK
    • Correspondence

      Vivian Allen, Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Hatfield AL9 7TA, UK. E: vallen@rvc.ac.uk

    Search for more papers by this author
  • Julia Molnar,

    1. Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK
    Search for more papers by this author
  • William Parker,

    1. Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK
    Search for more papers by this author
  • Andrea Pollard,

    1. Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK
    Search for more papers by this author
  • Grant Nolan,

    1. Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK
    Search for more papers by this author
  • John R. Hutchinson

    1. Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK
    Search for more papers by this author

Errata

This article is corrected by:

  1. Errata: Erratum Volume 227, Issue 6, 790, Article first published online: 11 November 2015

  • The copyright line for this article was changed on 16 November 2015 after original publication.

Abstract

Crocodiles and their kin (Crocodylidae) use asymmetrical (bounding and galloping) gaits when moving rapidly. Despite being morphologically and ecologically similar, it seems alligators and their kin (Alligatoridae) do not. To investigate a possible anatomical basis for this apparent major difference in locomotor capabilities, we measured relative masses and internal architecture (fascicle lengths and physiological cross-sectional areas) of muscles of the pectoral and pelvic limbs of 40 individuals from six representative species of Crocodylidae and Alligatoridae. We found that, relative to body mass, Crocodylidae have significantly longer muscle fascicles (increased working range), particularly in the pectoral limb, and generally smaller muscle physiological cross-sectional areas (decreased force-exerting capability) than Alligatoridae. We therefore hypothesise that the ability of some crocodylians to use asymmetrical gaits may be limited more by the ability to make large, rapid limb motions (especially in the pectoral limb) than the ability to exert large limb forces. Furthermore, analysis of scaling patterns in muscle properties shows that limb anatomy in the two clades becomes more divergent during ontogeny. Limb muscle masses, fascicle lengths and physiological cross-sectional areas scale with significantly larger coefficients in Crocodylidae than Alligatoridae. This combination of factors suggests that inter-clade disparity in maximal limb power is highest in adult animals. Therefore, despite their apparent morphological similarities, both mean values and scaling patterns suggest that considerable diversity exists in the locomotor apparatus of extant Crocodylia.

Ancillary