Smilodon

Smilodon /ˈsmaɪlədɒn/, is an extinct genus of machairodont felid. It is perhaps the best known saber-toothed cat and lived in North America during the Pleistocene epoch (2.5 mya–10,000 years ago). Several fossils have been found, with one of the largest collections taken from the La Brea Tar Pits. Three species of the genus are known; they vary in size and build.

Overall, Smilodon was more robustly built than any modern cat, with particularly well-developed forelimbs and exceptionally long upper canines. Its jaw had a bigger gape than modern cats and its upper canines were slender and fragile, being adapted for precision killing. These attributes made Smilodon a specialized hunter of large herbivores, such as bison and camels.

Smilodon likely lived in closed habitats, such as forests and bush, which would have provided cover for ambushing prey. Its reliance on large animals may have been the cause of its extinction. Scientists debate over whether Smilodon was a social animal. Comparison of predator responses to distress calls and the prevalence of healed injuries suggest that it was social, while its small brain size and vegetated habitat suggest it was more solitary. Some fossils show signs of ankylosing spondylitis, trauma and arthritis. Smilodon went extinct 10,000 years ago.

Etymology
The nickname "saber-tooth" refers to the extreme length of their maxillary canines. Despite the colloquial name "saber-toothed tiger", Smilodon is not closely related to the tiger (or any other living felid); the latter belongs to the subfamily Pantherinae, whereas Smilodon belongs to the subfamily Machairodontinae. The name Smilodon comes from Greek: σμίλη, (smilē), "carving knife"[1] + ὀδoύς (odoús), "tooth" (whose stem is odont-, as seen in the genitive case form ὀδόντος, odóntos).

Classification
The genus Smilodon was named and described by the Danish naturalist and palaeontologist Peter Wilhelm Lund in 1842. He found the fossils of Smilodon populator in caves near the small town of Lagoa Santa, in Minas Gerais, Brazil.[3] It is grouped with several species of saber-toothed cats in the subfamily Machairodontinae within the family Felidae. An early ancient DNA analysis suggested that Smilodon should be grouped with modern cats (subfamily Felinae)[4] However, a 2005 study found that Smilodon belonged to a separate lineage.[5] Another study published a year later confirmed this, showing that the Machairodontinae diverged early from the ancestors of modern cats and were not closely related to any living feline species.[6] The skull and mandible morphology of the earliest saber-toothed cats were similar to that of clouded leopards. The lineage further adapted to the precision killing of large animals by developing elongated canine teeth and wider gapes, in the process sacrificing high bite force.[7] Smilodon belongs to the tribe Smilodontini, which is known as "dirk-toothed cats". These cats were defined by their long slender canines with fine serrations.

Species
While a number of Smilodon species have been described, today usually only three are recognized.[9]
 * Smilodon gracilis, 2.5 million–500,000 years ago; the smallest and earliest species, estimated at 55 to 100 kg (120 to 220 lb) in weight[10] was the successor of Megantereon in North America, from which it probably evolved. This species reached the north of South America in the early Pleistocene, along with Homotherium, as part of the Great American Interchange.[11] The other Smilodon species probably derived from this species. As its specific name suggests, this species is the most lightly built of the genus.[3]
 * Smilodon fatalis, 1.6 million–10,000 years ago, replaced S. gracilis in North America and invaded western South America.[12] It was intermediate in size between S. gracilis and S. populator.[9] It ranged from 160 to 280 kg (350 to 620 lb).[10] and reached a shoulder height of 100 cm (39 in) and body length of 175 cm (69 in).[13] Sometimes two additional species are recognized, S. californicus and S. floridanus, but usually they are considered to be junior synonyms of S. fatalis.[14]
 * Smilodon populator, 1 million–10,000 years ago; occurred in the eastern parts of South America and was larger than the North American species.[15] It is perhaps the largest known felid, with a body mass range of 220 to 400 kg (490 to 880 lb).[10][16] It stood at a shoulder height of 120 cm (47 in).[9] Compared to S. fatalis, S. populator had a more elongated and narrow skull, higher positioned nasals, more massive metapodials and slightly longer forelimbs relative to hindlimbs.