Arx Fatalis

[Aron Eugine]

Fossilsof Smilodon fatalis are not particularly common in Florida, but there have been many fossils found across the United States, including a prolific collection in Rancho la Brea in Los Angeles, California.

The genus Smilodon contains three widely recognized species: Smilodon populator, Smilodon fatalis, and Smilodon gracilis (Kurten and Werdelin, 1990; Turner, 1996). Two species names widely used in the older scientific and semi-popular literature, Smilodon californicus and Smilodon floridanus, are almost always now regarded as junior synonyms of Smilodon fatalis. Berta (1985) proposed that Smilodon populator and Smilodon fatalis were actually a single species, with the former name having priority. This approach has been followed in a few other studies, but today most experts on extinct felids regard the two species as distinct. Smilodon populator in this scenario is limited to portions of South America east of the Andes.

Although Smilodon fatalis is known from late Irvingtonian (middle Pleistocene) sites in South Carolina, Arkansas, and Nebraska, fossil localities of this age in Florida have not recorded it (although only three such sites are known, so this absence might be an artifact of the sparse record from this time interval). Thus all known Florida records of the species are from the Rancholabrean land mammal age. Fossils of Smilodon fatalis are not particularly common in Florida. Most records are isolated teeth or bones, typically less than five specimens per locality, and most often just one. A partial skeleton of a subadult individual was found at Arredondo 1 in a limestone quarry southwest of Gainesville in the early 1950s (Fig. 2; Kurten, 1965). According to Kurt Auffenberg (pers. comm. to R. Hulbert), his father and former museum curator Walter Auffenberg told him that this skeleton originally included a skull, but that it was retained by the collector. Its whereabouts are unknown. The best skull of Smilodon fatalis from Florida in a museum collection is still the first specimen ever found, in 1888 at a fissure deposit in a limestone quarry near Ocala (Figs. 3-4; Leidy, 1889a, 1889b). According to Leidy (1889b), this skull originally had some teeth, but they were removed by the person who found it. This specimen is the holotype of Smilodon floridanus and is on public display at the Wagner Free Institute of Science in Philadelphia just where Joseph Leidy himself placed it. It has a nearly complete braincase and most of the right maxilla.

Fossils of Smilodon fatalis can easily be distinguished from those of Smilodon gracilis, the only other species in the genus known from Florida, by their much larger size. According to Christiansen and Harris (2005), Smilodon fatalis had a body mass ranging from 350 to 600 pounds (160 to 280 kg), similar in weights observed in the modern Siberian tiger. In contrast, Smilodon gracilis was only about the size of a modern jaguar, weighing between 120 and 220 pounds (55 to 100 kg). There are also morphologic differences. In the teeth, the upper canine of Smilodon fatalis is more curved and has better developed serrations. The lower third premolar of Smilodon fatalis is usually absent, or if present more vestigial than that of Smilodon gracilis. The inner cusp on the upper fourth premolar, the protocone, is very reduced or even absent in Smilodon fatalis. The only felid of similar (or even larger) size present in the late Pleistocene of Florida is the American lion, Panthera atrox. It too is a relatively rare species in Florida. Almost every bone in the skeleton of these two great cats can be distinguished, as detailed in the classic monograph of Merriam and Stock (1932).

Carbone, C., T. Maddox, P. J. Funston, M. G. L. Mills, G. F. Grether and B. Van Valkenburgh. 2009. Parallels between playbacks and Pleistocene tar seeps suggest sociality in an extinct sabretooth cat, Smilodon. Biology Letters 5:81-85.

McHenry, C. R., S. Wroe, P. D. Clausen, K. Moreno, and E. Cunningham. 2007. Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation. Proceedings of the National Academy of Sciences of the United States of America 104:16010-16015.

Van Valkenburgh, B., M. F. Teaford, and A. Walker, A. 1990. Molar microwear and diet in large carnivores: inferences concerning diet in the sabretooth cat, Smilodon fatalis. Journal of Zoology 222:319?340.

This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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. S. fatalis may have been impacted by habitat turnover and loss of prey it specialized on due to possible climatic plus anthropogenic impacts and other factors while the extinction of S. populator remains poorly understood.

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. Among the thousands of fossils found, he recognized a few isolated cheek teeth as belonging to a hyena, which he named Hyaena neogaea in 1839. After more material was found (including canine teeth and foot bones), Lund concluded the fossils instead belonged to a distinct genus of felids, though transitional to the hyenas. He stated it would have matched the largest modern predators in size, and was more robust than any modern cat. Lund originally wanted to name the new genus Hyaenodon, but realizing this had recently become preoccupied by another prehistoric predator, he instead named it Smilodon populator in 1842. He explained the Ancient Greek meaning of Smilodon as σμίλη (smilē), "scalpel" or "two-edged knife", and οδόντος (odóntos), "tooth". This has also been translated as "tooth shaped like double-edged knife". He explained the species name populator as "the destroyer", which has also been translated as "he who brings devastation". By 1846, Lund had acquired nearly every part of the skeleton (from different individuals), and more specimens were found in neighboring countries by other collectors in the following years.[1][2] 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.[3] 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.[4]

Fossils of Smilodon were discovered in North America from the second half of the 19th century onwards.[1] 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.[5] The species name means "deadly".[6] 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.[7] 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.[1] S. fatalis has junior synonyms such as S. mercerii, S. floridanus, and S. californicus.[4] 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.[3] Nordic paleontologists Bjrn Kurtn and Lars Werdelin supported the distinctness of the two species in an article published in 1990.[8] 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.[9]

In his 1880 article about extinct cats, Cope also named a third species of Smilodon, S. gracilis. The species was based on a partial canine, which had been obtained in the Port Kennedy Cave near the Schuylkill River in Pennsylvania. Cope found the canine to be distinct from that of the other Smilodon species due to its smaller size and more compressed base.[7] Its specific name refers to the species' lighter build.[10] This species is known from fewer and less complete remains than the other members of the genus.[11] S. gracilis has at times been considered part of genera such as Megantereon and Ischyrosmilus.[12] S. populator, S. fatalis and S. gracilis are currently considered the only valid species of Smilodon, and features used to define most of their junior synonyms have been dismissed as variation between individuals of the same species (intraspecific variation).[4][3] One of the most famous of prehistoric mammals, Smilodon has often been featured in popular media and is the state fossil of California.[1]

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