Smilodon
Smilodon | |
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Mounted S. populator skeleton at Tellus Science Museum | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Suborder: | Feliformia |
Family: | Felidae |
Subfamily: | †Machairodontinae |
Tribe: | †Smilodontini |
Genus: | †Smilodon Lund, 1842 |
Type species | |
†Smilodon populator Lund, 1842
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Other species | |
Synonyms | |
Genus synonymy
Species synonymy
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Smilodon is a
Overall, Smilodon was more robustly built than any
In North America, Smilodon
Taxonomy
During the 1830s, Danish
Fossils of Smilodon were discovered in North America from the second half of the 19th century onwards.
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
Evolution
Long the most completely known
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.[4] 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.[15] As their canines became longer, the bodies of the cats became more robust for immobilizing prey.[14] In derived smilodontins and homotherins, the lumbar region of the spine and the tail became shortened, as did the hind limbs.[4] Based on mitochondrial DNA sequences extracted from fossils, the lineages of Homotherium and Smilodon are estimated to have diverged about 18 Ma ago.[16]
The earliest species of Smilodon is S. gracilis, which existed from 2.5
Despite the colloquial name "saber-toothed tiger", Smilodon is not closely related to the modern tiger (which belongs in the subfamily Pantherinae), or any other extant felid.[19] A 1992 ancient DNA analysis suggested that Smilodon should be grouped with modern cats (subfamilies Felinae and Pantherinae).[20] A 2005 study found that Smilodon belonged to a separate lineage.[21] A study published in 2006 confirmed this, showing that the Machairodontinae diverged early from the ancestors of modern cats and were not closely related to any living species.[22] The following cladogram based on fossils and DNA analysis shows the placement of Smilodon among extinct and extant felids, after Rincón and colleagues, 2011:[17]
Felidae |
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Description
Skeleton
Smilodon was around the size of modern
S. gracilis was the smallest species, estimated at 55 to 100 kg (120 to 220 lb) in weight, about the size of a
External features
Smilodon and other saber-toothed cats have been reconstructed with both plain-colored
Traditionally, saber-toothed cats have been
Paleobiology
Diet
An apex predator, Smilodon primarily hunted large mammals. Isotopes preserved in the bones of S. fatalis in the La Brea Tar Pits reveal that ruminants like bison (Bison antiquus, which was much larger than the modern American bison) and camels (Camelops) were most commonly taken by the cats there.[40] Smilodon fatalis may have also occasionally preyed upon Glyptotherium, based on a skull from a juvenile Glyptotherium texanum recovered from Pleistocene deposits in Arizona that bear the distinctive elliptical puncture marks best matching those of Smilodon, indicating that the predator successfully bit into the skull through the glyptodont's armored cephalic shield.[41] In addition, isotopes preserved in the tooth enamel of S. gracilis specimens from Florida show that this species fed on the peccary Platygonus and the llama-like Hemiauchenia.[42] 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.[43] 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.[40] More detailed isotope analysis however, indicates that Smilodon fatalis preferred forest-dwelling prey such as tapirs, deer and forest-dwelling bison as opposed to the dire wolves' preferences for prey inhabiting open areas such as grassland.[44] The availability of prey in the Rancho La Brea area was likely comparable to modern East Africa.[45]
As Smilodon migrated to South America, its diet changed; bison were absent, the
Predatory behavior
The
The
Debate continues as to how Smilodon killed its prey. Traditionally, the most popular theory is that the cat delivered a deep stabbing bite or open-jawed stabbing thrust to the throat, killing the prey very quickly.[56][57] Another hypothesis suggests that Smilodon targeted the belly of its prey. This is disputed, as the curvature of their prey's belly would likely have prevented the cat from getting a good bite or stab.[58] In regard to how Smilodon delivered its bite, the "canine shear-bite" hypothesis has been favored, where flexion of the neck and rotation of the skull assisted in biting the prey, but this may be mechanically impossible. However, evidence from comparisons with Homotherium suggest that Smilodon was fully capable of and utilized the canine shear-bite as its primary means of killing prey, based on the fact that it had a thick skull and relatively little trabecular bone, while Homotherium had both more trabecular bone and a more lion-like clamping bite as its primary means of attacking prey. The discovery, made by Figueirido and Lautenschlager et al., published in 2018 suggests extremely different ecological adaptations in both machairodonts.[59] The mandibular flanges may have helped resist bending forces when the mandible was pulled against the hide of a prey animal.[60]
The protruding incisors were arranged in an arch, and were used to hold the prey still and stabilize it while the canine bite was delivered. The contact surface between the canine crown and the gum was enlarged, which helped stabilize the tooth and helped the cat sense when the tooth had penetrated to its maximum extent. Since saber-toothed cats generally had a relatively large infraorbital foramen (opening) in the skull, which housed nerves associated with the whiskers, it has been suggested the improved senses would have helped the cats' precision when biting outside their field of vision, and thereby prevent breakage of the canines. The blade-like carnassial teeth were used to cut skin to access the meat, and the reduced molars suggest that they were less adapted for crushing bones than modern cats.[51] As the food of modern cats enters the mouth through the side while cutting with the carnassials, not the front incisors between the canines, the animals do not need to gape widely, so the canines of Smilodon would likewise not have been a hindrance when feeding.[38] A study published in 2022 of how machairodonts fed revealed that wear patterns on the teeth of S. fatalis also suggest that it was capable of eating bone to a similar extent as lions. 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.[61]
Despite being more powerfully built than other large cats, Smilodon had a weaker bite. Modern big cats have more pronounced
Natural traps
Many Smilodon specimens have been excavated from
The Talara Tar Seeps in Peru represent a similar scenario, and have also produced fossils of Smilodon. Unlike in La Brea, many of the bones were broken or show signs of weathering. This may have been because the layers were shallower, so the thrashing of trapped animals damaged the bones of previously trapped animals. Many of the carnivores at Talara were juveniles, possibly indicating that inexperienced and less fit animals had a greater chance of being trapped. Though Lund thought accumulations of Smilodon and herbivore fossils in the Lagoa Santa Caves were due to the cats using the caves as dens, these are probably the result of animals dying on the surface, and water currents subsequently dragging their bones to the floor of the cave, but some individuals may also have died after becoming lost in the caves.[69]
Social life
Scientists debate whether Smilodon was
Another argument for sociality is based on the healed injuries in several Smilodon fossils, which would suggest that the animals needed others to provide them food.[73][74] This argument has been questioned, as cats can recover quickly from even severe bone damage and an injured Smilodon could survive if it had access to water.[75] However, a Smilodon suffering hip dysplasia at a young age that survived to adulthood suggests that it could not have survived to adulthood without aid from a social group, as this individual was unable to hunt or defend its territory due to the severity of its congenital issue.[76] The brain of Smilodon was relatively small compared to other cat species. Some researchers have argued that Smilodon's brain would have been too small for it to have been a social animal.[77] An analysis of brain size in living big cats found no correlation between brain size and sociality.[78] Another argument against Smilodon being social is that being an ambush hunter in closed habitat would likely have made group-living unnecessary, as in most modern cats.[75] Yet it has also been proposed that being the largest predator in an environment comparable to the savanna of Africa, Smilodon may have had a social structure similar to modern lions, which possibly live in groups primarily to defend optimal territory from other lions (lions are the only social big cats today).[51]
Whether Smilodon was sexually dimorphic has implications for its reproductive behavior. 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
A set of three associated skeletons of S. fatalis found in Ecuador and described in 2021 by Reynolds, Seymour, and Evans suggests that there was prolonged parental care in Smilodon. 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. The subadult specimens are also hypothesized to have been male and female, respectively, while the adult skeletal remains found at the site are believed to have belonged to their mother. The subadults were estimated to have been around two years of age at the time of their deaths, but were still growing.[81] S. fatalis had proportionally larger hyoid bones than modern felid species and thus likely produced deeper vocalizations. While Smilodon had the same number of hyoid bones as the "roaring" cats, their shape was closer to that of "purring" species.[82]
Development
Smilodon started developing its adult saber-teeth when the animal reached between 12 and 19 months of age, shortly after the completion of the eruption of the cat's
A 2017 study indicates that juveniles were born with a robust build similar to the adults. 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. Felid forelimb development during ontogeny (changes during growth) has remained tightly constrained. The curve is similar to that for modern cats such as tigers and cougars, but shifts more towards the robust direction of the axes than is seen in modern felids.[86] Examinations by Reynolds, Seymour, and Evans (2021) suggest that Smilodon had a unique and fast growth rate similar to a tiger, but that there was a prolonged period of growth in the genus similar to what is seen in lions, and that the cubs were reliant on their parents until this growth period ended.[81]
Paleopathology
Several Smilodon fossils show signs of ankylosing spondylitis, hyperostosis and trauma.[87] One study of 1,000 Smilodon skulls found that 36% of them had eroded parietal bones, which is where the largest jaw muscles attach. 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.[88] 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. Sternum injuries are also common, probably due to collision with prey.[89]
The frequency of trauma in S. fatalis specimens was 4.3%, compared to 2.8% in the dire wolf, which implies the ambush predatory behavior of the former led to greater risk of injury than the pursuit predatory behavior of the latter. Smilodon remains exhibit relatively more shoulder and
Osteomyelitis in the left fourth metacarpal bone has been reported in a S. populator specimen dating back to Marine Isotope Stage 5. This pathology resulted in the machairodont individual becoming incapable of flexing its toe and would have severely diminished its ability to hunt prey.[92]
Distribution and habitat
Smilodon lived during the
S. gracilis entered South America during the early to middle Pleistocene, where it probably gave rise to S. populator, which lived in the eastern part of the continent. S. fatalis also entered western South America in the late Pleistocene, and the two species were thought to be divided by the
S. populator was very successful, while Homotherium never became widespread in South America. The extinction of the thylacosmilids has been attributed to competition with Smilodon, but this is probably incorrect, as they seem to have disappeared before the arrival of the large cats. The
Extinction
Along with most of the New World Pleistocene megafauna, Smilodon became extinct by 10,000 years ago in the
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. It was even proposed that the saber-toothed predators were inferior to modern cats, as the ever-growing canines were thought to inhibit their owners from feeding properly. Since then, however, it has been shown that the diet of machairodontines such as Smilodon and Homotherium was diverse. They do not seem to have been limited to giant animals as prey, as suggested before, but fed on whatever was available, including bovines, equines and camelids.[106][107] Additionally, non-machairodontine felids such as the American lion and Miracinonyx also became extinct during the Late Pleistocene, and saber-toothed and conical toothed felids had formerly coexisted for more than a million years.[108] The fact that saber-teeth evolved many times in unrelated lineages also attests to the success of this feature.[104]
The youngest direct radiocarbon date for S. fatalis differs from that of S. populator by thousands of years, the former just before the Younger Dryas cooling event and the latter by the early Holocene.[109] The latest S. fatalis specimen recovered from the Rancho La Brea tar pits has been dated to 13,025 years ago.[110] A specimen of S. fatalis from Iowa dates to 13,605–13,455 years Before Present (BP).[111] The latest 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.[112] The most recent credible carbon-14 date for S. fatalis has been given as 11,130 BP.[113] However, such radiocarbon dates are likely uncalibrated, meaning that they were not adjusted from calendar years to regular years. As a result, the dates appear younger than they actually are. Therefore, the S. fatalis specimen from Rancho La Brea is the youngest-recorded of the species,[109] suggesting extinction before the Younger Dryas based on its last appearance in California as opposed to other regions where megafauna declined by the Younger Dryas.[105]
See also
- List of largest carnivorans
- List of largest prehistoric carnivorans
- Megafauna
- Late Pleistocene extinctions
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