ScienceShot: Curves Are Tough on the Bones

Brassey et al., Journal of the Royal Society Interface

Simple engineering analyses that estimate bone strength may yield overly optimistic results, a new study suggests. Leg bones must withstand the compressive stresses imposed by an animal's weight. But if the bones are curved—as leg bones often are, even if only slightly—they also sustain bending stresses that result when weight isn't precisely centered on the bone's cross section. To see how bone curvature might affect bone strength estimates, researchers analyzed the leg bones of eight species, from the 220-gram Senegal bushbaby to the 1.2-metric-ton giraffe. They relied on the same sort of high-tech computer models that aerospace engineers use to analyze stresses induced in aircraft parts during flight. (Shown here is the model of a femur of Erinaceus europaeus, the European hedgehog, alongside a version that shows stresses induced by bending; red areas denote high stresses.) Incorporating stresses from bone curves put the bone under about 1.4 times more stress than it would experience if the bones were considered to be simple straight beams, the researchers report online today in the Journal of the Royal Society Interface. The strategy might be especially useful in reconstructing animals that are extinct, such as dinosaurs. Overestimating the strength of a dinosaur's leg bones by ignoring the effects of bone curvature may, in turn, mean overestimating how much weight those bones could have supported. Turns out, large dinos like Tyrannosaurus rex and the lumbering sauropods might have been somewhat slimmer than previously believed.

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