RODENTS OF UNUSUAL SIZE: A STUDY OF ALLOMETRIC LIMB SHAPE CHANGE IN THE MAMMALIAN CLADE EUARCHONTOGLIRES

The Euarchontoglires are a diverse and successful clade of mammals that have adapted to a diverse range of habits (richochetal, fossorial, aquatic, terrestrial, arboreal). Body size in this group ranges widely from <10 g for some species of mice to as much as 200 kg in the genus Gorilla. Quantifying their locomotor diversity, therefore, should illuminate long bone characteristics that may signify terrestrial or arboreal habits in their fossil relatives. Moreover, the diverse range of locomotor styles in this clade can provide useful and informative insight into the evolution of arboreality, whether this trait is primitive or derived among the euarchontan mammals, whether it has appeared once or multiple times in multiple lines, and possibly provide insight into the evolution of bipedalism within our own group. Although a host of studies have examined locomotion and limb morphology in primates and other euarchontoglires few have examined primates, rodentia, lagomorpha, scandentia, or dermoptera collectively using a shape analysis such as thin plate splines.

Using linear and geometric morphometrics, I tested two hypotheses: 1) locomotor habit and/or body mass should correlate with long bone shape changes in Euarchontoglires and 2) body mass should affect shape change within certain locomotor regimes (fossorial, arboreal, etc.). Over 100 specimens of left humeri and femora from Euarchontoglire specimens were examined and digitized.

MANOVA of the partial warps reveals significant shape differences between locomotor groups, most notably between terrestrial and arboreal. The greatest amount of shape change related to mass was seen in the forelimb, and relatively little in the hindlimb; however the amount of shape change caused by changes in body mass were not statistically significant. Data supports the correlation of locomotor habit with long bone shape changes within Euarchontoglires, but not a correlation between mass and shape change. The relationship between bone shape and body mass appears to be isometric across all locomotor groups; body mass does not have a significant effect on shape change within these groups. Long bone shape seems to correlate well with specific locomotor styles, and this may prove to be a useful method for accurately predicting locomotor styles within extinct taxa.