Functional limb morphology of extinct carnivores Smilodon fatalis, Panthera atrox, and Canis dirus based on comparisons with four extant felids and one extant canid
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Adaptations for hunting and locomotor functions of animals are related to the limb functional characteristics of limb muscles, muscle attachment sites on bones, and joint articular surface shapes. This dissertation includes study of extant Felis catus, Neofelis nebulosa, Panthera leo, and Acinonyx jubatus and extinct Smilodon fatalis, Panthera atrox, and Canis dirus. The extant species exhibit different locomotor modes. The functional characteristics of extinct species are predicted based on limb bone morphology.N. nebulosa, F. catus, and V. vulpes forelimb musculature was described, muscle maps were generated, and muscle fiber analysis was completed. Muscle attachment sizes were also compared in these species to explore the relationship between the size of a muscle and its attachment area. In addition to the bones of these three species, limb bones of extant Acinonyx jubatus, Panthera leo, Vulpes vulpes and extinct Smilodon fatalis, Panthera atrox, and Canis dirus were analyzed using geometric morphometric techniques to examine muscle attachment sites and joint articular surfaces. This was performed to infer the degree of muscle mechanical advantage and joint mobility in the extinct species and to suggest functional capabilities and behavior, such as different hunting and locomotion modes.When compared to felids, V. vulpes has larger muscles crossing the shoulder joint. Consequently, felids displayed larger ratios for muscles used for scapular and antebrachium rotation. In the geometric morphometric analysis of the forelimb, the cursorial carnivores differed from non-cursorial felids in glenoid fossa shape, humeral greater and lesser tubercles and radial tuberosity positioning, and distal radioulnar joint articular facet shape. P. atrox often clustered with P. leo. S. fatalis showed large attachment sites for scapular retraction muscles. Glenoid and distal radioulnar articular facet shapes in S. fatalis suggest increased shoulder joint and anteroposterior humerus rotation ability. In addition, shapes of elbow joint articulation and distal radioulnar articular facets in S. fatalis point to increased antebrachium rotation ability. These characters together may have aided S. fatalis during grappling with large prey. However, S. fatalis clustered with canids in the analyses of the scapula and ilium, suggesting the need for high endurance muscles needed during prey wrestling.