ALLOMETRIC GROWTH IN THE LIMBS OF THE PLEISTOCENE “MOUNTAIN DEER” NAVAHOCEROS FRICKI

Navahoceros fricki was described by Kurtén in 1975 as a late Pleistocene deer with distinctively robust limb bones compared to other deer like Odocoileus (white-tailed deer and mule deer) and Cervus elaphus (elk). It is known from huge samples of juvenile limb bones from San Josecito Cave in Nuevo Leon, Mexico. Using a flexible metric measuring tape, we measured all the unbroken juvenile and adult humeri, radii, femora, and tibiae in the sample, focusing on the diaphyseal shaft length (minus the epiphyses) vs. the midshaft diameter, following the conventions of Kilbourne and Makovicky (2012). Data were then plotted and reduced major axis (RMA) slopes of the data were calculated using PAST software. Since the adults have robust limbs, we wanted to see if they grew up in a significantly more robust pattern than isometric growth (i.e., slope significantly <1.0). The humerus slope was 0.788 (r² = 0.816), significantly more robust than isometry. The radius slope was 1.054 (r² = 0.928) but it was not significantly different from isometry. The femur slope was 0.788 (r² = 0.816), also significantly more robust than the isometric slope. The tibia, however, gave a slope of 1.087 (r² = 0.927), on the gracile side of isometry, but this was not significant at the 95% confidence level. Thus, in proximal limb elements (humerus, femur), Navahoceros did indeed exhibit negative allometry (growing more robust as it grew larger), consistent with the expectation based on the adult robustness. Surprisingly, the distal limb elements (radius and tibia) shows no significant difference from isometry. This contrasts with previous studies of growth in the white-tailed deer (Odocoileus virginianus), which was isometric in the humerus and radius, but gracile in the femur and robust in the tibia.