LOCOMOTOR PERFORMANCE OF BIPEDAL AND QUADRUPEDAL HETEROMYID RODENTS

1. Running endurance and running direction changes of both bipedal (Dipodomys, Microdipodops) and quadrupedal (Chaetotipus, Heteromys, Liomys, Perognathus) heteromyid rodents were measured to determine if locomotor performance is enhanced in bipedal species. 2. Running endurance was significantly higher in bipedal Dipodomys species (kangaroo rats) compared to quadrupedal species of similar size. Bipedal Microdipodops (kangaroo mouse) had even lower endurance than the quadrupedal species as a group. 3. Both running speed and body mass were found to influence running direction changes. The effects of body mass and speed accounted for more running direction changes in Dipodomys species than the quadrupedal species and the bipedal Microdipodops. 4. Bipedal locomotion in general does not enhance running endurance or the ability to change running direction. However, bipedal Dipodomys had higher running endurance than quadrupedal species of comparable size and, given their size and speed, change running direction as often as a small quadrupedal species. 5. These enhancements of locomotor performance in Dipodomys should improve the predator-escape capabilities of these species relative to quadrupedal species.