ALLOMETRIC TRENDS IN GROWTH AND DWARFING IN THE DWARF PRONGHORN CAPROMERYX: DOES DWARFING FOLLOW THE SAME TRENDS AS GROWTH?

Phyletic dwarfing in the fossil record is quite common, and numerous studies of allometric size reduction after dwarfing are documented. Studies of ontogenetic growth in the fossil record are also popular, but with a different set of expectations. But only rarely has anyone compared the trends of ontogenetic growth in a fossil organism with the slope of reduction in size with specific attention given to dwarfing. Do animals get smaller the same way they grow up? We compared the postnatal ontogenetic trend (i.e., slope) in each of the four main limb bones of the late Pleistocene dwarf pronghorn, Capromeryx minor, to the slope for its larger early Pleistocene ancestor C. arizonensis to determine how ontogenetic slopes compare to the slope of dwarfing. We compared the large sample sizes of C. minor (both juveniles and adults) with the adult limb bones of C. arizonensis from the early Pleistocene Inglis locality in Florida. Capromeryx decreased by 14-30% in size from the early to late Pleistocene species, but almost all the dwarfing slopes were isometric, with a slope very close to 1.0. Growth of the juvenile C. minor from the La Brea sample shows isometric slopes in the humerus, femur, and tibia, with a radius growth slope that is just slightly more gracile than isometric. Thus, the overall trend in growth in most limbs is isometric, and so is the trend in dwarfing, so these pronghorns do not show allometric size changes in either process.