Allometric Analysis of Relative Humerus Width and Olecranon Length in Some Unspecialized Burrowing Mammals

Abstract

Regression and allometric analysis show that ground squirrels and other unspecialized burrowers have relatively greater humerus widths and olecranon process lengths as compared to scansorial and relatively unspecialized ambulatory rodents of similar size. If the increase in relative width due to the need for support is similar in all three groups, then the greater humerus width (16 per cent greater) seen in burrowers is due to the need for extra strength to resist environmental loads occurring while digging. Proof for this statement is derived from accurate predictions of humerus widths and olecranon process lengths for mammals of similar size that are distantly related, but with burrowing habits. The increase in relative widths of humeri due to size was considerably less than theoretical considerations would require. Possible reasons for this discrepancy are discussed.