Abstract
BackgroundThe sabertooth cat, Smilodon fatalis, was an enigmatic predator without a true living analog. Their elongate canine teeth were more vulnerable to fracture than those of modern felids, making it imperative for them to immobilize prey with their forelimbs when making a kill. As a result, their need for heavily muscled forelimbs likely exceeded that of modern felids and thus should be reflected in their skeletons. Previous studies on forelimb bones of S. fatalis found them to be relatively robust but did not quantify their ability to withstand loading.Methodology/Principal FindingsUsing radiographs of the sabertooth cat, Smilodon fatalis, 28 extant felid species, and the larger, extinct American lion Panthera atrox, we measured cross-sectional properties of the humerus and femur to provide the first estimates of limb bone strength in bending and torsion. We found that the humeri of Smilodon were reinforced by cortical thickening to a greater degree than those observed in any living felid, or the much larger P. atrox. The femur of Smilodon also was thickened but not beyond the normal variation found in any other felid measured.Conclusions/SignificanceBased on the cross-sectional properties of its humerus, we interpret that Smilodon was a powerful predator that differed from extant felids in its greater ability to subdue prey using the forelimbs. This enhanced forelimb strength was part of an adaptive complex driven by the need to minimize the struggles of prey in order to protect the elongate canines from fracture and position the bite for a quick kill.
Highlights
Few extinct predators are as well-known as the saber tooth cats, which are touted for their prowess as ultimate mammalian predators [1,2]
When Smilodon fatalis was compared with all extant felids and the larger, extinct lion, Panthera atrox, it had humeri that were more resistant to non-axial bending (J/2) and more resistant to bending in both the mediolateral and craniocaudal planes relative to bone length (Table 1, Fig. 1a–c)
Large felids tend to have a minor advantage over smaller felids, with slightly more resistance to bending in the proximal forelimbs [28,29], for its size, S. fatalis had exceptional resistance to bending in the humerus
Summary
Few extinct predators are as well-known as the saber tooth cats, which are touted for their prowess as ultimate mammalian predators [1,2]. From external measurements of the forelimb bones, it appears that they were relatively thick for their length [2,12,13] and probably more resistant to bending and compressive loads; more accurate estimates of strength require data on both external diameters and cortical bone thickness. It might be expected that the humeri of cats that are arboreal or take prey larger than themselves would exhibit greater cortical thickening than expected based on body mass alone This does not appear to be the case, as a recent study found that humeral cross-sectional properties were better predictors of body mass than prey size or locomotor habits in extant felids [30]. We provide the first quantitative analysis of the ability to resist bending stresses in the forelimbs of S. fatalis using radiographic images, and compare it to living cats; and because Smilodon was as large, or larger than the largest extant felids, we included the extinct American lion (Panthera atrox) in our sample as a much larger species with forelimb morphology that is similar to its extant sister group, Panthera leo [31], and unlike Smilodon
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