ONTOGENY AND LIMB BONE SCALING IN 2 NEW-WORLD MARSUPIALS, MONODELPHIS-DOMESTICA AND DIDELPHIS-VIRGINIANA

This study examines the growth of two species of marsupials who share common ancestry and are born at the same neonatal size of a little les s than 1 g. Despite this similarity at birth, adult size of these two species differs by about 50 times, with the smaller species believed t o be the more ancestral. We quantified the growth in the limb bones (h umerus, femur, ulna, tibia, metacarpal, and metatarsal) beginning arou nd 40 days of age until adult size was reached. Results indicate that the larger species grows at a higher rate of growth as well as for a l onger period of time to reach its larger adult size. Despite these dif ferences in growth, there were few differences observed in the scaling over time of length to width in the various limb bones that were meas ured. The two species, although different in their adult size and the patterns of growth, maintain the same length to width proportions in e ach limb bone. The biggest difference between species in scaling was o bserved in the bones of the hands and feet, which may suggest adaptati on to size and/or locomotor performance as body size increases. Despit e variation in size, these heterochronic patterns do not affect the sh ape among adults or over evolutionary time. (C) 1997 Wiley-Liss, Inc.