Smilodon

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).^[4]

A fully-grown Smilodon weighed approximately 55 to 470 kg (120 to 1,000 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 built for speed.

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 hyena, 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.

[edit]Limbs

S. populator skeleton

Smilodon had relatively shorter and more massive limbs than other felines. It had well developed flexors and extensors in its forepaws,^{[citation needed]} which enabled it to pull down large prey.^[7] 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.

[edit]Teeth and jaws

Skull and neck at the AMNH

Smilodon is most famous for its relatively long canines, which are the longest found in the sabre-toothed cats, at about 28 cm (11 in) long in the largest species Smilodon populator.

These canine teeth were fragile and could not have bitten into bone; thus, these cats did not use their long teeth while taking down prey, due to the risk of breaking them. Only when their prey was totally subdued did they use their teeth to simultaneously sever the blood supply and strangle the windpipe, instantly killing the prey.^{[citation needed]}

Despite being more powerfully built than other large cats, Smilodon actually had a weaker bite. Modern big cats have more pronouncedzygomatic 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.^[8] There seems to a be a general rule that the sabre-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 sabre-toothed cats' teeth were stronger relative to the bite force than those of modern "big cats".^[9] In addition, Smilodon could open its jaws 120 degrees, whereas the lion's gape is limited to 60 degrees.^[10]

It has been suggested that Smilodon's smaller temporalis muscles (controlling much of the bite force) were not used in the killing of prey; rather, Smilodon stretched its jaws around the throat and pressed its canines into the prey with the use of its immense neck and forelimb muscles. The penetration was the result of the neck flexors instead of the jaw muscles, according to this hypothesis.