Smilodon

Smilodon Temporal range:
Smilodon californicus fossil at the National Museum of Natural History, Washington, DC
Conservation status
Extinct
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Felidae
Subfamily:	Machairodontinae
Genus:	Smilodon Lund, 1842
Species
S. populator Lund, 1842 (type) S. fatalis Leidy, 1869 S. gracilis Cope, 1880

Smilodon (Template:Pron-en), often called sabre-toothed cat or sabre-toothed tiger, is an extinct genus of machairodontine. The saber-toothed cat was endemic to North America and South America, living from the Early Pleistocene through Lujanian stage of the Pleistocene epoch (1.8 mya—10,000 years ago).

Etymology

The nickname "sabre-tooth" refers to the extreme length of their maxillary canines. Despite the colloquial name of "saber-toothed tiger", Smilodon is not a tiger, which belong to the subfamily Pantherinae. The name Smilodon is a bahuvrihi from Greek: Template:Polytonic, smilē, "chisel" and Greek Template:Polytonic (odoús), "tooth", Genitive: Template:Polytonic,odóntos.

Classification and species

The genus Smilodon was described by the Danish naturalist and palaeontologist Peter Wilhelm Lund in 1841. He found the fossils of Smilodon populator in caves near the small town of Lagoa Santa, in the state of Minas Gerais, Brazil.

A number of Smilodon species have been described, but today usually only three are recognized.

Smilodon neogaeus/populator skeleton

• Smilodon gracilis, 2.5 million-500,000 years ago; the smallest and earliest species (estimated to have been only 55 to 100 kg (120 to 220 lb)) was the successor of Megantereon in North America, from which it probably evolved. The other Smilodon species probably derived from this species.
• Smilodon fatalis, 1.6 million-10,000 years ago, replaced Smilodon gracilis in North America and western South America. In size it was between Smilodon gracilis and Smilodon populator, and about the same as the largest surviving cat, the Siberian Tiger. This species was about 1m high at the shoulder and is estimated to have ranged from 160 to 280 kg (350 to 620 lb). Sometimes two additional species are recognized, Smilodon californicus and Smilodon floridanus, but usually they are considered to be subspecies of Smilodon fatalis.
• Smilodon populator ("the devastating Smilodon"), 1 million-10,000 years ago; occurred in the eastern parts of South America and was the largest species of all machairodonts. It was much larger than its cousins, S. fatalis and S. gracilis, possessing a massive chest and front legs, and is the largest known variety of saber-toothed cat, it was more than 1.22 m (48 in) high at the shoulder, 2.6 m (100 in) long on average and had a 30 cm (12 in) tail. With an estimated weight of 360 to 470 kg, and exceptionally large individuals estimated to have exceeded 500 kg, it was among the heaviest known felids. Its upper canines reached 30 cm (12 in) and protruded up to 17 cm (6.7 in) out of the upper jaw. Genetic evidence suggests that Smilodon populator and other members of the genus diverged from the main lineage of modern cats (subfamily Felinae) around 14-18 million years ago.

Smilodon populator is also known form the famous cave site of Ultima Esperanza, with well-preserved remains retaining endogenous DNA

Anatomy

The species of Smilodon were among the largest felids ever to live; the heaviest specimens of the massively built carnivore S. populator may have exceeded 500 kg (1,100 lb).

Smilodon fatalis shown to scale to demonstrate the compact muscular build

A fully-grown Smilodon weighed approximately 55 to 500 kg (120 to 1,100 lb), depending on species. It had a short tail, powerful legs, muscular neck and long canines. Smilodon was more robustly built than any modern cat, comparable to a bear. The lumbar region of the back was proportionally short, and the lower limbs were shortened relative to the upper limbs in comparison with modern pantherine cats, suggesting that Smilodon was not a very fast runner.

The largest species, the South American S. populator, had higher shoulders than hips and a back that sloped downwards, superficially recalling the shape of a hyaena, in contrast to the level-backed appearance of S. fatalis, which was more like that of modern cats. However, while its front limbs were relatively long, their proportions were extremely robust and the forearm was shorter relative to the upper arm bone than in modern big cats, and proportionally even shorter than in S. fatalis. This indicates that these front limbs were designed for power rather than fast running, and S. populator would have had immense strength in its forequarters.

Limbs

Smilodon had relatively shorter and more massive limbs than other felines. It had well developed flexors and extensors in its forepaws, which enabled it to pull down large prey. The back limbs had powerfully built adductor muscles which might have helped the cat's stability when wrestling with prey. Like most cats, its claws were retractable.

Teeth and jaws

Skeleton of Smilodon californicus at La Brea Tar Pits Museum

Smilodon is most famous for its relatively long canines. They are the longest canines of the saber-toothed cats at about 28 cm (11 in) long in the largest species Smilodon populator. They were probably built more for stabbing than slashing. Despite being more powerfully built than other large cats, Smilodon actually had a weaker bite. Modern big cats have more pronounced zygomatic arches, while Smilodon had smaller zygomatic arches which restricted the thickness and therefore power of the temporalis muscles, and thus reduced Smilodon’s bite force. Analysis of its narrow jaws indicates that it could produce a bite only a third as strong as that of a lion. There seems to a be a general rule that the saber-toothed cats with the largest canines had proportionally weaker bites. However, analyses of canine bending strength (the ability of the canine teeth to resist bending forces without breaking) and bite forces indicate that saber-toothed cats' teeth were stronger relative to the bite force than those of modern "big cats". In addition, Smilodon could open its jaws 120 degrees, whereas the lion can only open its jaws to 65 degrees.

It has been suggested that smilodon's smaller temporalis muscles, (controlling much of the bite force) was not used in the killing of prey, but rather, the immense strength of the neck of smilodon allowed it to stretch its jaws around the throat and press its canines into the prey with the usage of such immense neck and forelimb muscles rather than an actual bite: the penetration was the result of the neck flexors instead of the jaw muscles, as according to this hypothesis.

Ecology

Social behavior

Restoration of Smilodon fatalis

The social pattern of this cat is unknown. It has been suggested, based on the abundance of S. fatalis fossils in proportion to prey animals trapped in the La Brea tar-pits, that they were packs of scavengers, lured in by the distress calls of trapped prey. This possibility was tested in 2008 by Chris Carbone (of the Zoological Society of London), who documented the responses of African predators of the Serengeti and Kruger National Park to recorded distress calls of prey species; it was determined that playbacks of prey sounds attract social carnivores, but not solitary hunters. Additionally, some fossils show healed injuries or diseases that would have crippled the animal. Some palaeontologists see this as evidence that saber-toothed cats were social animals, living and hunting in packs that provided food for old and sick members. Living in groups might also allow more effective competition with social lions and wolves. The canine teeth and body size of Smilodon were about the same in both male and female cats. This suggests that one theory about their teeth – that they were used by males to attract mates – is incorrect.

Diet and hunting

Restoration of Smilodon populator

Smilodon probably preyed on a wide variety of large game including bison, deer, American camels, horses and ground sloths. As it is known for the saber-toothed cat Homotherium, Smilodon might have killed also juvenile mastodons and mammoths. The La Brea tar pits in California trapped hundreds of Smilodon in the tar, possibly as they tried to feed on mammoths already trapped. The Natural History Museum of Los Angeles County has many of their complete skeletons.

Modern big cats kill mainly by crushing the windpipe of their victims, which may take a few minutes. Smilodon’s jaw muscles were probably too weak for this and its long canines and fragile skull would have been vulnerable to snapping in a prolonged struggle or when biting a running prey. Research in 2007 concluded that Smilodon more probably used its great upper-body strength to wrestle prey to the ground, where its long canines could deliver a deep stabbing bite to the throat which would generally cut through the jugular vein and / or the trachea and thus kill the prey very quickly. The leaders of this study also commented to scientific journalists that this technique may have made Smilodon a more efficient killer of large prey than modern lions or tigers, but also made it more dependent on the supply of large animals. This highly-specialized hunting style may have contributed to its extinction, as Smilodon’s cumbersome build and over-sized canines would have made it less efficient at killing smaller, faster prey if the ecosystem changed for any reason.

S. fatalis skeleton

Research upon which African carnivores response to playback of animals in distress has been used to analyse the finds of animal species and their numbers at the La Brea Tar Pits. Such playbacks find animal distress calls such as would come from an animal trapped in the tar pit would attract pack hunters such as lions and spotted hyenas, not lone hunters. Given the carnivores found at tar pits were predominately Smilodon and the social dire wolf, this suggests that the former like the latter was also a social animal. One expert, who found the study convincing, further speculated that if that was the case, then Smilodon's exaggerated canine teeth might have been used more for social or sexual signaling than hunting. However, the lack of sexual dimorphism in the canine teeth refutes this proposal.

Extinction

Smilodon became extinct around 10,000 BC, a time which saw the extinction of many other large herbivorous and carnivorous mammals.

Prehistoric humans, who reached North America at the end of the Ice age, are often viewed as responsible for this extinction wave. Others have suggested that the end of the ice age caused the extinction. As the ice age ended there would have been shrinking environments and changing vegetation patterns. Extensive grasslands, with different types of grasses, and isolated forests replaced healthy mixes of forests and grasslands. The summer and winter both became more extreme and North America began to dry out or began to be covered in snow, thus denying food sources for mammoths and in turn Smilodon. However, this hypothesis does not explain how Smilodon and its ancestors successfully survived many previous interglacials.

External links

• Schneider, Jens, Killing behavior in Smilodon fatalis (Mammalia, Carnivora, Felidae) based on functional anatomy and body proportions of the front- and hind limbs Diploma thesis in German language
• Sabre-toothed cats
• Smilodon article at bluelion.org
• Western Center for Archaeology and Paleontology Hemet, CA