Meeting Abstract
Size matters: the bones of small animals support less weight than those of large animals. Scientists have argued that larger animals should have thicker bones to support their larger mass. To keep the load on the bones the same across sizes, animals need to scale elastically: larger animals need to have relatively thicker and shorter bones. In contrast, when larger and smaller animals differ only in size but not shape, their size is said to scale geometrically. Previous studies found a wide range of scaling exponents. In this project, we measured the long bones from more than 50 mammal, marsupial, and bird species in the vertebrate collection of the Fresno State Biology Department as part of a course in Comparative Vertebrate Morphology. The objective of this study is to quantify how the bones scales in the arms and legs of walkers and flyers. To determine how length and diameter scale with mass, we measured the humeri, femurs, tibias, and ulnas. Consistent with previous findings on quadrupeds, we expected that the back legs of the quadrupeds and legs of the bipeds would scale geometrically since they serve the same purpose. For the arm, we expected the quadrupeds to scale geometrically and the bipeds to scale elastically due to the different purpose of each limb. Our data on quadrupeds agree with past research. However, quadrupeds and non-flying bipeds appear to scale differently, and birds differ from quadrupeds. Also, upper and lower limb bones scale differently in both quadrupeds and bipeds. Many of the explanations put forward in the literature about the scaling of long bones do not integrate well across all the available data and they do not explain the differences between scaling coefficients for bones within the same limb or for how length versus diameter scales with mass.
