ALLOMETRIC GROWTH IN LIMBS OF THE PLEISTOCENE LAMINE CAMELS PALAEOLAMA MIRIFICA AND HEMIAUCHENIA MACROCEPHALA

Until recently, there were not many comprehensive studies of limb allometry in mammals as they grow from tiny juveniles to adults. However, Kilbourne and Makovicky (2012) provided a large data set of the allometric growth in mammalian limbs. Htun et al. (2018) studied the limb growth in the common La Brea tar pits camel Camelops hesternus. We examined large samples of juvenile and adult limb bones of two late Pleistocene lamine camels from the collections from Leisey Shell Pit in the Florida State Museum and from the Camelot locality in the South Carolina State Museum: Palaeolama mirifica and Hemiauchenia macrocephala. Using a flexible metric tape, we measured the diaphyseal length (minus the epiphyseal caps) of the shaft, and midshaft circumference, of the humerus, radius-ulna, femur, and tibia. The data were collected in Excel spreadsheets, and then the reduced major axis (RMA) and their 95% bootstrap confidence intervals were calculated in PAST software, since neither variable was a dependent variable (an assumption of least-squares regression). We found that in Palaeolama, the humerus was significantly more gracile than isometry, and the femur was significantly more robust than isometry, but the radius-ulna and tibia were both isometric. In Hemiauchenia, the humerus and radius-ulna were isometric, but the tibia was significantly more gracile than isometry; not enough femora were available for study. By contrast, Camelops hesternus had a robust humerus but the femur was isometric, and it had a gracile radius-ulna and tibia. Thus, there is no consistent pattern of isometry or allometry among the different segments of the limb of these three lamine camels. This is consistent with what Kilbourne and Makovicky (2012) found across the cursorial artiodactyls, including pronghorns, deer, wildebeest, okapis, and bison.