Where were fossils of the Smilodon first discovered?
Smilodon
Fossils of "Smilodon" were discovered in North America from the second half of the 19th century onwards. In 1869, American paleontologist Joseph Leidy described a maxilla fragment with a molar, which had been discovered in a petroleum bed in Hardin County, Texas. He referred the specimen to the genus "Felis" (which was then used for most cats, extant as well as extinct) but found it distinct enough to be part of its own subgenus, as "F." ("Trucifelis") "fatalis". The species name means "fate" or "destiny", but it is thought Leidy intended it to mean "fatal". In an 1880 article about extinct American cats, American paleontologist Edward Drinker Cope pointed out that the "F. fatalis" molar was identical to that of "Smilodon", and he proposed the new combination "S. fatalis". Most North American finds were scanty until excavations began in the La Brea Tar Pits in Los Angeles, where hundreds of individuals of "S. fatalis" have been found since 1875. "S. fatalis" has junior synonyms such as "S. mercerii", "S. floridanus", and "S. californicus". 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". Swedish paleontologists Björn Kurtén and Lars Werdelin supported the distinctness of the two species in 1990.
Smilodon
The earliest felids are known from the Oligocene of Europe, such as "Proailurus", and the earliest one with saber-tooth features is the Miocene genus "Pseudaelurus". The skull and mandible morphology of the earliest saber-toothed cats was similar to that of the modern clouded leopards ("Neofelis"). 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. As their canines became longer, the bodies of the cats became more robust for immobilizing prey. In derived smilodontins and homotherins, the lumbar region of the spine and the tail became shortened, as did the hind limbs. Based on mitochondrial DNA sequences extracted from fossils, the lineages of "Homotherium" and "Smilodon" are estimated to have diverged about 18 Ma ago. 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. "Megantereon" itself had entered North America from Eurasia during the Pliocene, along with "Homotherium". "S. gracilis" reached the northern regions of South America in the Early Pleistocene as part of the Great American Interchange. The younger "Smilodon" species are probably derived from "S. gracilis". "S. fatalis" existed 1.6 million–10,000 years ago (late Irvingtonian to Rancholabrean ages), and replaced "S. gracilis" in North America. "S. populator" existed 1 million–10,000 years ago (Ensenadan to Lujanian ages); it occurred in the eastern parts of South America.