Killing Behavior in Smilodon Fatalis (Mammalia, Carnivora, Felidae) based on Functional Anatomy and Body Proportions of the Front- and Hind Limbs

Abstract

Elongated canines exclusively evolved in carnivores, which are able to stabilize their victims with their anterior extremities. It was shown that power and agility of the front limbs are strongly correlated with the development of sabers. Limb- and skull proportions of the extinct cat Smilodon fatalis were therefore compared with those of six extant species of large felids and those of Canis lupus. Furthermore, differences in hunting behavior and locomotory capabilities were analyzed. Ratios of limb segment lengths have been shown to relate to functional and locomotory differences (e.g., cursoriality) in both extinct and extant felines. S. fatalis is equipped with relatively short and sturdy limbs. Moreover, it possessed a great angle of inclination of the olecranon fossa relative to the long axis of the humerus, in addition to a wide and laterally oriented radial notch. The radial head was more circular than in any other extant cat member. Additionally, the Teres major muscle inserts further away from the shoulder joint and the joints are more powerfully built and demonstrate a great amount of strength and flexibility. It is very likely that Smilodon preyed on the large contemporary megafauna because of its overall more powerful anatomy compared to that of modern felines. Nevertheless, it is still a matter of dispute exactly, which hunting method S. fatalis applied. It is suggested that its massive forelimbs were employed to grasp and hold large prey, which was then pulled down and finally killed or fatally wounded with a canine shear bite applied to the throat or abdomen. In contrast, the lightly built Acinonyx jubatus is found exclusively in low structured habitats, consequently it has the relatively longest limbs of all large felids, the smallest angle of inclination of the olecranon fossa and an insertion of the T. major closer to the joint. Its prey usually weighs less than its own body weight. Bivariate regression analyses on log-transformed limb segment lengths were employed to test overall differences and scaling variations in limb proportions. Multivariate factorial- and discriminant analysis were performed on a number of limb dimensions of all the examined species. Results reveal that cats can accurately be distinguished into three different categories upon these ratios (even across taxonomic boundaries): 1. Highly cursorial felines like the cheetah, 2. Pantherine cats, including the puma, 3. Dirk-toothed cats such S. fatalis, and X. hodsonae (scimitar-toothed felid with the morphology of dirk-toothed cat).