It has long be questioned about cats being social, or not. One thing was for sure, sabre tooth cats, had more developed forelimbs and teeth (long upper canines) than some.

There are 3 species of sabre tooth cats in North and South America, two derived from one:

Mostly N/ America:
Smilodon gracilis, 20-220lb
Smilodon fatales, 350-620lb; (replaced s gracilis)

In South America
Smilodon popular 485 to 961lbs; and up to 48 inches in height.

Thee spot patterns are unknown, but has been artistically reported with plain or spotted patterns.

A lot more is unknown:

-Social or solitary lifestyle;

-What it mainly hunted;

-How it killed: It is thought to have killed prey by holding it still with forelimbs and biting it, but a number of different methods could have been used.

Discovery:

In 1830s, Danish archeologist Peter Wilhem-Lund, while collecting fossils in Calcareous Caves, near lager Santa, Minas Gerais, Brazil. Discovered a S. Popular skull.

He originally thought the sabre tooth cats were transitional to hyenas but found the genus name he wanted was already take by another prehistoric predator. He eventually decided on ‘scalpel’, or ‘two edged knife’, and ‘tooth’, or Smilodon which was closer related to the cat family.

S. populator existed 1 million– around 11,000 years ago; it occurred in the eastern parts of South America.

S. fatalis existed 1.6 million– around 11,000 years ago, in North America. (It is believed both replaced/evolved from s. gracilis).

The smilodon disappeared around the same time most of the North/South American megafauna did. About 11,700 years ago, during the neolithic event, though 2 or 3 theories are widely still attributed, its up for debate.

Description:
Robustly built. The cats had a reduced lumbar region, high scapula, short tail, and broad limbs with relatively short feet. At 28 cm, or (11 in), the long canine teeth in the largest species, S.populator are iconiciy known.

A particularly large S.populator skull from Uruguay measuring 39 cm (15 in) in length even indicates this individual may have weighed as much as 436 kg (961 lb).

Diet:
In addition, s. gracilis specimens from Florida show that this species fed on the peccary platygonus and the llama-like hemiauchenia. Where as studies of s. fatalis show its diet overlap with dire wolf (aenocyon dirus) and american lion (panthera atrox). Who would have known some cats were so competitive.

As smilodon migrated to South America, its diet changed; bison were absent, the horses and proboscideans were different, and native ungulates (hoofed animals), such as toxodonts and litopterns, were completely unfamiliar. Yet s. populator thrived there. Isotopic analysis for smilodon populator has suggested that its prey species even included the larger sized toxodon (similar to hippos).

Hunted both in open and forested habitats:

Traditionally, the most popular theory is with its teeth the cat delivered deep stabbing bite or open-jawed stabbing thrusts to the throat. Another theory was the belly of its prey.

Did you know? 166,000 smilodon fatalis specimens have been found in Los Angeles La Brae tar pits?
The Talara Tar Seeps in Peru represent a similar scenario.

Social or on own ?
Scientists still debate whether the large cats were social. Since S. fatalis fossils were so common at La Brea and Talara, it was likely they were attracted to distress calls of other stuck cats and prey, meaning they were social but unique in its own kinda way.

Bibliography: Cope, E. D. (December 1880). “On the extinct cats of America”. The American Naturalist. 14 (12): 833–858. doi:10.1086/272672. JSTOR2449549.

Berta, A. (1985). “The status of Smilodon in North and South America” (PDF). Contributions in Science, Natural History Museum of Los Angeles County. 370: 1–15. Archived from the original (PDF) on 28 May 2014.

Kurtén, B.; Anderson, E. (1980). Pleistocene Mammals of North America. New York: Columbia University Press. pp. 186–188. ISBN978-0-231-03733-4.