In days of old, the cats were gold, and their teeth were used for stabbing: that’s the picture paleontologists once painted of Smilodon fatalis, the saber-toothed cat that roamed North America until its extinction 11,000 years ago. Hunting alone, the tan-colored cat raced its hapless prey across grassy plains and then plunged its vicious, daggerlike fangs into the neck of its quarry.
These days, though, paleontologists paint a very different picture of Smilodon (whose name means saber tooth and has nothing to do with smiling). The new view is based largely on fossils that collections manager Christopher Shaw tends in a back room of the George C. Page Museum in Los Angeles. These fossils were pulled out of the museum’s accompanying Rancho La Brea tar pits, shallow ponds of sticky asphalt that trapped late Ice Age mammals like flypaper. Over a 25,000-year period, from the time of the first deposits in the tar pits 36,000 years ago, at least 2,500 saber- toothed cats were trapped. From this collection of 166,000 Smilodon bones, the largest such collection in the world, paleontologists are slowly piecing together a picture of the life and times of the ferocious feline.
They know, for instance, that Smilodon could roar like a lion, because its throat bones--the hyoids--are shaped like those of a roarer. And they’re now pretty sure the cat did not have the dry-grass coloration of a lion, as earlier paintings of Smilodon depict, but was spotted like a leopard, as the Page Museum mural now presents it. The evidence for the spots is indirect, because no one has yet unearthed a fossilized flap of saber-tooth skin. But pieces of leaves found in the tar or stuck to the teeth of fossilized herbivores suggest that the Pleistocene Los Angeles basin was a plain dotted with sagebrush, buckwheat, and clumps of oak and pine. In short, it was a place where spotty camouflage would be just the ticket for a lurking predator.
And lurk it did, if Smilodon’s bones are being interpreted correctly. Overall, its skeleton is closer to a lion’s than to any other cat’s, but it differed from the lion in size and bulk. At three feet high, Smilodon was a foot shorter than the lion. Nor was it as long, measuring about five and a half feet from snout to rump, compared with the lion’s seven feet. But it was almost twice as heavy: recent estimates put it at 750 pounds. The saber-toothed cat also sported a bobtail, in marked contrast to the long tails that help provide balance for such distance runners as cheetahs, leopards, and lions. Short legs, bulky body, puny tail--all these add up to an animal that didn’t run far while hunting. That same bulk means the cat could topple large, lumbering prey that didn’t run far either, like a juvenile mastodon or mammoth. So it’s most likely that Smilodon waited for its prey to draw near and then launched a surprise assault.
This much about Smilodon’s life was pieced together from the best, near-perfect bones of the museum’s cat collection. But perfection isn’t always a plus in paleontology. Shaw actually prefers the bad bones-- the mangled, misshapen specimens that are housed in a special set of shelves draped with protective plastic. This is the paleopathology collection: more than 5,000 bones, every one a mess in one way or another. There are dislocated hips, their sockets burnished smooth by the incessant scraping of bone on bone. There are bite wounds, some suspiciously saber- toothed in shape, others hideously bubbly from infections that persisted for months. There are femurs, tibias, and fibulas that are blemished by lumpy, bony projections--evidence of the body’s attempts to reinforce overexerted muscles that just kept on ripping. And each bone has something to tell Shaw and company about the way the long-dead cat lived its life.
Many of the injuries, for instance, were so dramatic that the cat would surely have dragged its limbs or limped badly, yet the amount of infection or scraping means that the animal was around for a while after it ran into trouble. How could it have survived its injury if it couldn’t hunt? A solitary hunter, as most cats are, would have been a goner. This suggests that Smilodon was a social creature, like the lion. This is just an awesome injury, mutters Shaw, showing off a mashed-up pelvis with a thighbone to match. Now, this animal was so crippled that it could not have gotten enough food if it were a lone hunter. So this and other examples suggest that these animals had a social structure that actually encouraged the nurturing of injured individuals. Perhaps their families brought them food, or at least protected them from other carnivores. At the very least, injured animals may have been allowed to hang around the site of a kill and eat after everyone else was done.
Of course, you could argue--and paleontologists used to--that the tar pits, with their writhing masses of trapped ground sloths, dire wolves, and mastodons, were a year-round smorgasbord of captive treats. Injured animals, no longer able to fend for themselves, could limp over and dig in. But that popular picture is wrong. Sure, the museum houses more than a million bones, but that’s a million bones piled up over 25,000 years. It wasn’t a giant orgy of death here, says Shaw. There wasn’t a lot of carrion for crippled animals to come in and make a livelihood out of. We’re talking one large herbivore per decade: that’s not very good on the pickings.
Another specimen, a femur with a nasty, knobby growth on it--the telltale mark of a repeated muscle injury--provides additional indirect information about Smilodon’s habits. Obviously the cats won’t be stressing their muscles when they’re sleeping, Shaw says. They’re going to be stressing their muscles when they’re using the most violent and jerking motions--like attacking. He and fellow paleontologist Fred Heald used that starting point--simply tallying which muscles were most commonly injured-- to figure out which muscles the cat used most when grappling with prey. The collection is littered with such injuries. The particular femur Shaw is holding is knobbed at the place where an adductor muscle joined the thighbone to the pelvis, pulling the thigh forward and sideways when flexed. A few trays down, there’s a foreleg bone with a hummock where the deltoid muscle attached from the shoulder blade, elevating the leg on demand.
Overall, we found that the most common position for these animals to be stressed in was with their forelegs out, forward, and slightly bent and their front paws in a grasping position, says Shaw. Their hind legs would be crouched in a pushing or pulling stance. So it seems that these animals were most often injured trying to acquire prey either by pushing animals, bowling them over, or pulling them back toward themselves. Smilodon’s traumatic injuries--fractured lower limbs, dislocated hips, crushed chests--fit the pushing-pulling scenario, too, because these are injuries you’d expect from an animal wrestling bulky prey and occasionally ending up underneath it. (The larger, less-studied dire wolf paleopathology collection has many more hoof-dented skulls, as befits a hunter who goes in headfirst for the hamstring or the throat.)
This fits with another Smilodon theory, put forward by William Akersten, former curator at Rancho La Brea and now curator at the Idaho Museum of Natural History. Instead of going for the neck as a lion does, Akersten’s Smilodon would have bitten a chunk out of its upended victim’s belly. (That’s more like the method of the modern-day Komodo dragon. These reptiles are also saber-toothed, suggesting that a saber would be just the tool for belly-biting.) The saber teeth are very strong in the forward- backward direction but not nearly as strong side-to-side, explains Shaw. If these things were going into the neck of a living animal, where there are lots of big bones and everything’s dynamic, everything’s moving, it’s more likely we would have found more broken teeth in these animals. But out of 700 skulls, we have only two specimens with broken canines that have wear on them, meaning ones that were broken during the animal’s lifetime.
What’s more, Akersten argues that the ten-inch-long saber teeth were actually blunter than butter knives and that the animal’s lower jaw would have gotten in the way of any stabbing stroke. Akersten thinks Smilodon bit its victims, driving its sabers deep into the belly with powerful head-depressing muscles and gripping a chunk of flesh with its other, interlocking teeth. It ripped out the chunk, then hung around until the animal bled to death.
Akersten’s idea is not universally accepted, though. All of us crazy paleontologist, saber-toothed-cat types get together once in a while to argue about the new stuff and the old stuff, says Shaw. And it’s kind of neat, because as it’s an extinct animal we’ll never really answer all the questions. So you can be forever right--or forever wrong. Some of the arguments might be settled if we ever find a saber-toothed cat frozen in a glacier someplace. I’d sure love to find a frozen saber-toothed kitty so I could dissect the little guy.