A Study of the Sinuous Crouch of Smilodon fatalis

Abstract

Mammalian carnivores generally are considered to belong either to the pursuit or ambush predator categories. Anatomical features for these opposing styles of capturing prey differ, although specific strategies typify familial taxonomic levels. The species of the Canidae tend toward pursuit, while most of the Felidae specialize in ambush. Cats also engage in prey stalking behavior, whether an ambush or pursuit predator. Remaining cryptic for as long as possible is a good strategy to increase the success of a hunt, especially when the quarry sought is fleet of foot, agile, wary and highly capable of evading predation. The extinct sabertooth cat, Smilodon fatalis, has long been considered to be an ambush predator because it was large‐bodied and short‐limbed. Smilodon’s skeleton is robust, and has been reconstructed as heavily muscled because it shows prominent muscle scars. Because of this high degree of robustness, it has also been thought to have had questionable flexibility. No characters showing specific enhancements to Smilodon’s adaptations for clandestine stalking despite its formidable musculoskeletal anatomy have been identified in a search of the published literature. This study describes morphological features that have been newly identified as being able to improve this sabercat’s ability to move sinuously and stealthily during an ambush. These are derived from unique pectoral girdle and forelimb, vertebral column and pelvic girdle and hindlimb features. Specifically, truncated scapular and ilial shapes as well as short limbs give Smilodon a lower crouching profile than can be achieved by other felids. Usually, in sinuously moving cats, even when the animal is seeking to remain as cryptic as possible, the posterodorsal aspect of the scapula and the anterodorsal ilial regions project above the pointed dorsal tips of the elongated vertebral spinous processes. These highest projections may be visible above any vegetation cover, revealing the cat’s presence to potential prey. In contrast, in Smilodon, with fore and hindlimbs equivalently flexed, the shoulder and hip regions fall below the level of the most dorsal tips of the spinous processes, enhancing the cat’s ability to flatten its body to facilitate concealment while stalking. This study interprets the unique morphological limb features in Smilodon as adaptations to enhance the sinuous movements the cat used in getting as close to potential prey animals as possible prior to making a final rush to grapple with them. We also demonstrate how this anatomy leads to the conclusion that Smilodon’s habits fit it to its forested or scrub environment as a solitary ambush predator.