During the 1830s, Danish naturalist Peter Wilhelm Lund and his assistants collected fossils in the calcareous caves near the small town of Lagoa Santa, Minas Gerais, Brazil.

After more material was found (including incisor teeth and foot bones), Lund concluded the fossils instead belonged to a distinct genus of felids, though transitional to the hyenas.

[1][2][3] Though some later authors used Lund's original species name neogaea instead of populator, it is now considered an invalid nomen nudum, as it was not accompanied with a proper description and no type specimens were designated.

[4] Some South American specimens have been referred to other genera, subgenera, species, and subspecies, such as Smilodontidion riggii, Smilodon (Prosmilodon) ensenadensis, and S. bonaeriensis, but these are now thought to be junior synonyms of S. populator.

[5] American paleontologist Annalisa Berta considered the holotype of S. fatalis too incomplete to be an adequate type specimen, and the species has at times been proposed to be a junior synonym of S. populator.

[9] A 2018 article by the American paleontologist John P. Babiarz and colleagues concluded that S. californicus, represented by the specimens from the La Brea Tar Pits, was a distinct species from S. fatalis after all and that more research is needed to clarify the taxonomy of the lineage.

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.

[20] The earliest species of Smilodon is S. gracilis, which existed from 2.5 million to 500,000 years ago (early Blancan to Irvingtonian ages) and was the successor in North America of Megantereon, from which it probably evolved.

[26] 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.

[37] 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.

[44] Stable carbon isotope measurements of S. gracilis remains in Florida varied significantly between different sites and show that the species was flexible in its feeding habits.

[45] Isotopic studies of dire wolf (Aenocyon dirus) and American lion (Panthera atrox) bones show an overlap with S. fatalis in prey, which suggests that they were competitors.

[55]The brain of Smilodon had sulcal patterns similar to modern cats, which suggests an increased complexity of the regions that control the sense of hearing, sight, and coordination of the limbs.

[55] Smilodon was likely an ambush predator that concealed itself in dense vegetation, as its limb proportions were similar to modern forest-dwelling cats,[56] and its short tail would not have helped it balance while running.

If correctly identified, the tracks indicate that the animal had fully retractible claws, plantigrade feet, lacked strong supination capabilities in its paws, notably robust forelimbs compared to the hindlimbs, and was probably an ambush predator.

Analysis of the cross-sections of S. fatalis humeri indicated that they were strengthened by cortical thickening to such an extent that they would have been able to sustain greater loading than those of extant big cats, or of the extinct American lion.

This and comparisons with bite marks left by the contemporary machairodont Xenosmilus suggest that Smilodon and its relatives could efficiently de-flesh a carcass of meat when feeding without being hindered by their long canines.

Based on their conclusions that Smilodon fatalis had no sexual dimorphism, Van Valkenburgh and Sacco suggested in 2002 that, if the cats were social, they would likely have lived in monogamous pairs (along with offspring) with no intense competition among males for females.

The two subadult individuals uncovered share a unique inherited trait in their dentaries, suggesting they were siblings; a rare instance of familial relationships being found in the fossil record.

Juvenile and adolescent Smilodon specimens are extremely rare at Rancho La Brea, where the study was performed, indicating that they remained hidden or at denning sites during hunts, and depended on parental care while their canines were developing.

[92][93][94] A 2024 study found evidence that adolescent Smilodon kept their milk sabers for extended periods (estimated at 30 months) to help reinforce their adult canines as they grew in.

Comparison of the bones of juvenile S. fatalis specimens from La Brea with those of the contemporaneous American lion revealed that the two cats shared a similar growth curve.

They also showed signs of microfractures, and the weakening and thinning of bones possibly caused by mechanical stress from the constant need to make stabbing motions with the canines.

[98] Bony growths where the deltoid muscle inserted in the humerus is a common pathology for a La Brea specimen, which was probably due to repeated strain when Smilodon attempted to pull down prey with its forelimbs.

[100] A 2023 study documented a high degree of subchondral defects in limb-joint surfaces of S. fatalis and dire wolf specimens from the La Brea Tar pits that resembled osteochondrosis dissecans.

The mosaic vegetation of woods, shrubs, and grasses in southwestern North America supported large herbivores such as horses, bison, antelope, deer, camels, mammoths, mastodons, and ground sloths.

North America also supported other saber-toothed cats, such as Homotherium and Xenosmilus, as well as other large carnivores including dire wolves, short-faced bear (Arctodus simus) and the American lion.

[109] S. populator preferred large prey from open habitats such as grassland and plains, based on evidence gathered from isotope ratios that determined the animal's diet.

[119] Writers of the first half of the twentieth century theorized that the last saber-toothed cats, Smilodon and Homotherium, became extinct through competition with the faster and more generalized felids that replaced them.

[126] Smilodon populator remains found in the cave of Cueva del Medio, near the town of Soria, northeast Última Esperanza Province, Magallanes Region in southernmost Chile have been dated to 10,935–11,209 years ago.