Osteohistology of the northern raccoon ( Procyon lotor ) reveals unusual prevalence of cortical compacted coarse cancellous bone

Northern raccoons (Procyon lotor) are common throughout North America and have been introduced into other countries through a variety of means. Intraskeletal surveys of northern raccoon bone microstructure are currently absent in the literature despite the prevalence of the northern raccoon throughout North America. To further explore raccoon bone tissue composition, we describe dentary, forelimb, and hindlimb bone microstructure in a female northern raccoon. General cortical organization consisted of an endosteal layer of lamellar bone followed by a mid-cortex of woven-parallel complex bone (WPC), compacted coarse cancellous bone (CCCB), or both WPC and CCCB. An incomplete incipient external fundamental system is found in the outer cortex of appendicular bones, but not the dentary. All sampled bones contained one or two lines of arrested growth, and all growth lines were near the periosteal surface. Bone microstructure composition deviated from most previous descriptions of carnivore cortices due to the extensive intraskeletal presence of CCCB. CCCB in long bone mid-diaphyses of mammals is reported in only a few of the extant vertebrate taxa thus far studied and the causes of the continued persistence of this tissue type remain unknown. Growth marks and the developing external fundamental system align with northern raccoon life history data and degree of epiphyseal fusion in the current sample. These results therefore support bone microstructure analysis as an accurate tool to evaluate individual life histories in northern raccoons. Detailed osteohistological investigations, such as the present study, also contribute to expanding our understanding of the complexities of mammalian bone formation.