What Was the Sabre-Toothed Cat? Smilodon and the Teeth That Were Not for Biting Bone

The sabre-toothed cats were a subfamily of the cat family, the Machairodontinae, that split from the ancestors of living cats about twenty million years ago and produced sabre-toothed forms repeatedly, on every continent but Australia and Antarctica; sabre teeth also evolved independently in a marsupial of South America and in an extinct group older than the cats. Smilodon was the last and best-known, living in the Americas from about 2.5 million years ago until 10,000 years ago in three species, of which the largest, Smilodon populator of South America, weighed up to 400 kilograms, heavier than any living cat. It was built like a bear as much as a lion: short-legged, deep-chested, with forelimbs of enormous strength, a short tail, and a skull adapted to open its jaws to 120 degrees, twice a lion's gape, to clear the canines.

The upper canines of Smilodon fatalis, the North American species, were about 18 centimetres long, and those of populator reached 28, flattened from side to side like blades and finely serrated. They were also thin, and biomechanical models show that a bite on struggling prey, or a bite that struck bone, would have snapped them; broken sabres are found in the tar pits, but far fewer than would be expected if the animal bit as a lion does. The current understanding, supported by the skull's shape and the neck's muscles, is that Smilodon used its forelimbs to wrestle prey to the ground and hold it still, then drove the canines into the throat or belly with a downward stroke of the whole head and neck, cutting the great vessels, and let go. The killing bite was quick and the teeth never met bone. What the rest of the body shows:

• •Forelimbs thicker and stronger than any living cat's, for pinning prey
• •A short back and short legs, built for strength rather than speed; Smilodon was an ambusher, not a chaser
• •Neck muscles anchored to a skull with a reduced crest, for the downward stab
• •Small incisors and a weak bite at the front, which suited a killer that did not need to grip
• •Wear on the teeth that suggests it ate the soft parts of a carcass and left the bones, and did not crack them as hyenas do

The prey was large: bison, camels, horses, ground sloths and young mammoths and mastodons, the giants of the American ice age, and the tar-pit bones of those animals carry the marks. Whether Smilodon hunted alone or socially is argued from the pits themselves. Predators there outnumber prey nine to one, as if many came to each trapped animal, and the number of healed injuries, broken hips, crushed vertebrae and diseased limbs on cats that had clearly lived for months afterwards, suggests animals that were fed or tolerated at kills while they could not hunt, which lions do and solitary cats do not. The counter-argument is that the pits drew every predator within smelling distance and that the injured cats may have lived on carrion. The isotopes in Smilodon bone from the pits show a diet of grazing and browsing animals from open and wooded country alike, and a hyoid bone like a lion's that would have let it roar.

Smilodon disappeared around 10,000 years ago with the rest of the American megafauna, in the extinction that took the mammoths, mastodons, horses, camels, ground sloths and the dire wolf, some 70 percent of the continent's large mammals in a few thousand years. A specialist in killing very large prey dies when the prey does, and the causes of the prey's disappearance are the usual two: the end of the ice age, which reshaped the grasslands, and the arrival of humans across the Bering land bridge, whose spear points appear in the same layers as the last of the giants. The last Smilodon teeth from La Brea are dated to about 13,000 years ago, and its South American relative may have lasted a little longer.

The sabre-tooth has been drawn since the 1840s as a tiger with fangs, and it was not striped, not a tiger, and probably not spotted either, since large cats of open country are plain; its coat is unknown. It is the state fossil of California, the most abundant carnivore in the world's richest ice-age deposit, and the case that made palaeontologists cautious about reading a weapon from its shape: a tooth that looks made for biting bone was made for avoiding it, and the animal that carried it was a wrestler with a knife, not a biter.

Smilodon was a bear-built cat of the American ice age, in a lineage separate from living cats, with blade-like canines up to 28 centimetres long that were too fragile to bite bone and were used instead to stab the throat of prey already pinned by its massive forelimbs. It ate the giants of the Pleistocene, may have lived and fed socially, and died out with them about 10,000 years ago when climate change and human hunters removed its prey.