Comparative Osteohistological Analysis of Two Mesopredators, Didelphis virginiana and Procyon lotor
Abstract
Examining the bone microstructure of modern vertebrates can reveal information about the biology and environment of extinct animals. Didelphis virginiana, the Virginia opossum, and Procyon lotor, the common raccoon, are both mesopredators that inhabit a wide variety of environments in North America. These two animals are omnivorous, nocturnal, and arboreal, exploiting similar resources in both urban and rural settings. However, the opossum, a marsupial mammal, has a much lower metabolic rate than the raccoon. This study qualitatively analyzes the osteohistology of these two mammals and adds to a growing database of modern vertebrate osteohistological descriptions. The right and left humerus, ulna, radius, femur, tibia, and fibula of an opossum and female raccoon collected from Tulsa County, Oklahoma, were histologically sectioned. The left side of the dentary of both animals was sectioned as well. The epiphyses of both animals were found to be unfused indicating they are both juveniles. The bone microstructure of contralateral elements for each individual was extremely similar. The opossum elements exhibit a high proportion of poorly organized parallel-fibered bone with mostly radial vascularization, which is remarkably scarce. The cortex of the raccoon bones are mainly fibrolamellar tissue with longitudinal vascularization that is much denser than seen in the opossum. No lines of arrested growth (LAGs) were found in the raccoon elements, indicating the animal was less than a year old. One LAG was found in the opossum indicating the animal was at least a year old. These two mesopredators inhabited similar niches and grew to comparable sizes (based on limb length) yet their histology records different growth patterns. The poor vascularization of the opossum bones and abundance of parallel-fibered tissue indicates a slower growth rate, likely due to its lower metabolic rate. Previous paleontological research has hypothesized on the metabolic rates of extinct animals based on osteohistological patterns. This study shows that similarly sized animals may both be homeothermic, yet exhibit different histological patterns.
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