Smilodon

***Smilodon*** is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous cenozoic mammals, and the best known saber-toothed cat. Although commonly known as the **saber-toothed tiger**, it was not closely related to the tiger or other modern cats. *Smilodon* lived in the Americas during the Pleistocene epoch (2.5 mya – 10,000 years ago). The genus was named in 1842, based on fossils from Brazil. Three species are recognized today: ***S. gracilis***, ***S. fatalis***, and ***S. populator***. The two latter species were probably descended from *S. gracilis*, which itself probably evolved from *Megantereon*. The hundreds of individuals obtained from the La Brea Tar Pits in Los Angeles constitute the largest collection of *Smilodon* fossils.

Diego

Overall, *Smilodon* was more robustly built than any extant cat, with particularly well-developed forelimbs and exceptionally long upper canine teeth. Its jaw had a bigger gape than that of modern cats, and its upper canines were slender and fragile, being adapted for precision killing. *S. gracilis* was the smallest species at 55 to 100 kg (120 to 220 lb) in weight. *S. fatalis* had a weight of 160 to 280 kg (350 to 620 lb) and height of 100 cm (39 in). Both of these species are mainly known from North America, but remains from South America have also been attributed to them. *S. populator* from South America was the largest species, at 220 to 400 kg (490 to 880 lb) in weight and 120 cm (47 in) in height, and was among the largest known felids. The coat pattern of *Smilodon* is unknown, but it has been artistically restored with plain or spotted patterns.

In North America, *Smilodon* hunted large herbivores such as bison and camels, and it remained successful even when encountering new prey species in South America. *Smilodon* is thought to have killed its prey by holding it still with its forelimbs and biting it, but it is unclear in what manner the bite itself was delivered. Scientists debate whether *Smilodon* had a social or a solitary lifestyle; analysis of modern predator behavior as well as of *Smilodon*'s fossil remains could be construed to lend support to either view. *Smilodon* probably lived in closed habitats such as forests and bush, which would have provided cover for ambushing prey. *Smilodon* died out at the same time that most North and South American megafauna disappeared, about 10,000 years ago. Its reliance on large animals has been proposed as the cause of its extinction, along with climate change and competition with other species, but the exact cause is unknown. *Smilodon* was around the size of modern big cats, but was more robustly built. It had a reduced lumbar region, high scapula, short tail, and broad limbs with relatively short feet.[23][24] *Smilodon* is most famous for its relatively long canine teeth, which are the longest found in the saber-toothed cats, at about 28 cm (11 in) long in the largest species, *S. populator*.[23] The canines were slender and had fine serrations on the front and back side.[25] The skull was robustly proportioned and the muzzle was short and broad. The cheek bones (zygomata) were deep and widely arched, the sagittal crest was prominent, and the frontal region was slightly convex. The mandible had a flange on each side of the front. The upper incisors were large, sharp, and slanted forwards. There was a diastema (gap) between the incisors and molars of the mandible. The lower incisors were broad, recurved, and placed in a straight line across. The p3 premolar tooth of the mandible was present in most early specimens, but lost in later specimens; it was only present in 6% of the La Brea sample.[3] There is some dispute over whether *Smilodon* was sexually dimorphic. Some studies of *S. fatalis* fossils have found little difference between the sexes.[26][27] Conversely, a 2012 study found that, while fossils of *S. fatalis* show less variation in size among individuals than modern *Panthera*, they do appear to show the same difference between the sexes in some traits.[28]

*S. populator* restored with plain coat, Charles R. Knight, 1903

*S. gracilis* was the smallest species, estimated at 55 to 100 kg (120 to 220 lb) in weight, about the size of a jaguar. It was similar to its predecessor *Megantereon* of the same size, but its dentition and skull were more advanced, approaching *S. fatalis*.[29][4] *S. fatalis* was intermediate in size between *S. gracilis* and *S. populator*.[23] It ranged from 160 to 280 kg (350 to 620 lb).[29] and reached a shoulder height of 100 cm (39 in) and body length of 175 cm (69 in).[30] It was similar to a lion in dimensions, but was more robust and muscular, and therefore had a larger body mass. Its skull was also similar to that of *Megantereon*, though more massive and with larger canines.[4] *S. populator* was among the largest known felids, with a body mass range of 220 to 400 kg (490 to 880 lb),[29] and one estimate suggesting up to 470 kg (1,040 lb).[31] It stood at a shoulder height of 120 cm (47 in).[23] Compared to *S. fatalis*, *S. populator* was more robust and had a more elongated and narrow skull with a straighter upper profile, higher positioned nasal bones, a more vertical occiput, more massive metapodials and slightly longer forelimbs relative to hindlimbs.[4][8] Large tracks from Argentina (for which the ichnotaxon name *Smilodonichium* has been proposed) have been attributed to *S. populator*, and measure 17.6 cm (6.9 in) by 19.2 cm (7.6 in).[32] This is larger than tracks of the Bengal tiger, to which the footprints have been compared.[33]

*S. fatalis* restored with spotted coat

Traditionally, saber-toothed cats have been artistically restored with external features similar to those of extant felids, by artists such as Charles R. Knight in collaboration with various paleontologists in the early 20th century.[34] In 1969, paleontologist G. J. Miller instead proposed that *Smilodon* would have looked very different from a typical cat and similar to a bulldog, with a lower lip line (to allow its mouth to open wide without tearing the facial tissues), a more retracted nose and lower-placed ears.[35] Paleoartist Mauricio Antón and coauthors disputed this in 1998 and maintained that the facial features of *Smilodon* were overall not very different from those of other cats. Antón noted that modern animals like the hippopotamus are able to achieve a wide gap without tearing tissue by the moderate folding of the orbicularis oris muscle, and such a muscle configuration exists in modern large felids.[36] Antón stated that extant phylogenetic bracketing (where the features of the closest extant relatives of a fossil taxon are used as reference) is the most reliable way of restoring the life-appearance of prehistoric animals, and the cat-like *Smilodon* restorations by Knight are therefore still accurate.[34]

*Smilodon* and other saber-toothed cats have been reconstructed with both plain-colored coats and with spotted patterns (which appears to be the ancestral condition for feliforms), both of which are considered possible.[34] Studies of modern cat species have found that species that live in the open tend to have uniform coats while those that live in more vegetated habitats have more markings, with some exceptions.[37] Some coat features, such as the manes of male lions or the stripes of the tiger, are too unusual to predict from fossils.[34]