The Occurrence and Morphology of a Lateral Metatarsal Splint Bone in Moose (Alces alces)

Abstract

Moose (Alces alces) appear to be different from most other cervids in that a well-developed metatarsal splint bone is present. It is found apposed to the plantolateral portion of the cannon bone in over 70 % of adults. It averages 3.3 mm in width and extends about 22% of the total length of the metatarsal. It may be derived through calcification of connective tissue or by elongation of the vestigial metatarsal V. Anat Rec, 294:231-235, 2011. V V C 2010 Wiley-Liss, Inc. Key words: moose; metatarsalMoose (Alces alces) are members of the family Cervidae (deer). The phylogenetic relationships within the Cervidae have been the subject of extensive review (Groves and Grubb, 1987;Gilbert et al., 2006). Cervids are pecoran artiodactyls in which metapoidals III and IV are fused to form a single bone, commonly referred to as the ''cannon'' bone. Metapoidal I is consistently absent. The abaxial metapoidals, II and V, are significantly reduced on both the thoracic and pelvic limbs. The major classification within the Cervidae is based on accessory metacarpal morphology (Brooke, 1878). In telemetacarpal cervids [ex. Roe deer (Capreolus capreolus), whitetailed deer (Odocoileus virginianus)] the distal portion of the regressed metacarpals 2 and 5 remain while in plesiometacarpal cervids [ex. wapiti (Cervus elaphus), Fallow deer (Dama dama)] the proximal portion is retained. This morphologically based, phylogenetic grouping has been substantiated by more recent molecular (Randi et al., 1998;Hassanin and Douzery, 2003;Fernandez and Vrba, 2005;Gilbert et al., 2006) and behavior-based comparisons (Cap et al., 2002). Moose are telemetacarpal cervids (Bubenik, 1998).In contrast to the metacarpals, the accessory metatarsals in most cervids have regressed to such an extent that they are not mentioned in descriptions of their skeletal anatomy (Groves and Grubb, 1987;Bubenik, 1998). We have observed that moose are somewhat different from other cervids in that a robust lateral metatarsal splint bone is frequently present. In this report, we describe the presence and morphology of this splint bone in a very isolated and well-studied population of moose from Isle Royale National Park, MI. MATERIALS AND METHODSDescriptive observations and quantitative measurements of metatarsal morphology of North American moose (Alces alces) were made on 531 metatarsals collected from Isle Royale National Park, MI (Peterson, 1977). All specimens were obtained from animals that died of natural causes. Age was determined by counting the number of layers in the cementum of teeth (Sergeant and Pimlott, 1959;Wolfe, 1969). Sex was determined based on the presence (males) or absence (females) of antler pedicels. The presence or absence of the metatarsal splint bone was recorded. The qualitative description of the splint bone included a description of the proximal and distal ends. Each end was classified as fused to the cannon bone (distinct end not discernable) or distinct (distinct end discernable). If distinct, the end was present in two forms. It cou...