The occurrence of metatarsal splint bones in ruminants and their potential use in establishing phylogenetic relationships

The occurrence of metatarsal splint bones was examined in 21 ruminant species. Lateral metatarsal splint bones were found in 75% of metatarsal specimens from mature moose (Alces alces) on Isle Royale, MI, USA, and 95% of specimens from Alaska and other North American locations. Lateral splints were found in 94% of fossil specimens of A. alces from Alaska and in 100% of fossil specimens of Cervalces scotti. Thus, it is common feature in the Alceini. Medial metatarsal splints were also found commonly in A. alces (69%). Lateral splints are also common in the extant Capreolinae examined (84% of specimens from five species) and Cervinae (88% of specimens from two species). Medial metatarsal splints are less common in the Cervidae (Capreolinae, 23%; Cervinae, 19%). The occurrence of metatarsal splints was examined in nine species from family Bovidae. Only 70% of the specimens had lateral splints, fewer than in the Cervidae (P=0.14). The occurrence of medial splints (51%) tended to be greater than in the Cervidae (22%, P=0.09). The occurrence of lateral splints in the two extant species of Giraffidae (Giraffa camelopardalis, 0%; Okapia johnstoni, 40%) was low. In contrast, the occurrence of medial splints in the giraffids was high (G. c., 89%; O. j., 100%). Neither lateral (40%) nor medial splints (0%) were common in Antilocapra americana. Overall, there is considerable variation among species in the percent occurrence of metatarsal splint bones. Detailed comparison of splint bone occurrence may provide information that is useful in resolving some phylogenetic relationships among ruminant species. While there appear to be general patterns of occurrence of metatarsal splint bones that typify and distinguish Cervidae and Bovidae, the Giraffidae and Antilocapridae do not follow either of these patterns. We conclude that each ruminant family has followed an independent pathway in the reduction of metatarsi II and V, resulting in different patterns of occurrence of metatarsal splint bones. Thus, the usefulness of these as characteristics for resolving phylogenetic relationships among families is questionable.