Skip to main content
Article
Locomotor loading mechanics in the hindlimbs of tegu lizards (Tupinambis merinae): comparitive and evolutionary implications
Publications
  • K. Megan Sheffield
  • Michael T. Butcher
  • S. Katherine Shugart
  • Jennifer C. Gander
  • Richard W. Blob, Clemson University
Document Type
Article
Publication Date
1-1-2011
Publisher
The Company of Biologists Ltd
Abstract

Skeletal elements are usually able to withstand several times their usual load before they yield, and this ratio is known as the bone's safety factor. Limited studies on amphibians and non-avian reptiles have shown that they have much higher limb bone safety factors than birds and mammals. It has been hypothesized that this difference is related to the difference in posture between upright birds and mammals and sprawling ectotherms; however, limb bone loading data from a wider range of sprawling species are needed in order to determine whether the higher safety factors seen in amphibians and non-avian reptiles are ancestral or derived conditions. Tegus (family Teiidae) are an ideal lineage with which to expand sampling of limb bone loading mechanics for sprawling taxa, particularly for lizards, because they are from a different clade than previously sampled iguanas and exhibit different foraging and locomotor habits (actively foraging carnivore versus burst-activity herbivore). We evaluated the mechanics of locomotor loading for the femur of the Argentine black and white tegu (Tupinambus merianae) using three-dimensional measurements of the ground reaction force and hindlimb kinematics, in vivo bone strains and femoral mechanical properties. Peak bending stresses experienced by the femur were low (tensile: 10.4±1.1 MPa; compressive: –17.4±0.9 MPa) and comparable to those in other reptiles, with moderate shear stresses and strains also present. Analyses of peak femoral stresses and strains led to estimated safety factor ranges of 8.8–18.6 in bending and 7.8–17.5 in torsion, both substantially higher than typical for birds and mammals but similar to other sprawling tetrapods. These results broaden the range of reptilian and amphibian taxa in which high femoral safety factors have been evaluated and further indicate a trend for the independent evolution of lower limb bone safety factors in endothermic taxa.

Comments
This document may be reprinted and distributed for non-commercial and educational purposes only, and not for resale. No resale use may be made of material on this web site at any time. Publisher may require a subscription to access this version. All other rights reserved. The published version may be found here: http://jeb.biologists.org/content/214/15/2616.full.pdf+html?sid=76db34dc-d123-4b73-a4f4-62c3a9ad89ae
Citation Information
Please use publisher's recommended citation.