The Smilodon or saber-toothed tiger is a genus of extinct carnivorous mammals that belonged to the family Felidae or cats. There were multiple saber wielding fiends in evolutionary history, to the extent that there are “true” and “false” saber tooth cats, but more on that later. For now, consider Smilodon populator, the largest saber-toothed tiger, weighing as much as 400 kg and standing 4 feet at the shoulder, with two long, curved 11-inch canines capable of ripping out your jugular in a bite. Most of us can only wish for such a quick journey to death’s sweet release during finals week, but we have to make do with the lesser cats on campus with their heads in our dustbins.
Now, why are the sabers unlikely? In fact, evidence shows that they are very likely indeed. The saber teeth are an evolutionary success story, with them appearing in multiple evolutionary lines independently of each other (something called convergent evolution). The Smilodon belongs to the line called the true saber tooth cats. Others, like Thylacosmilus, are the fake saber tooth cats. In fact, Thylacosmilus wasn’t even a cat. It was more closely related to marsupials and probably had a pouch. Scientists think we live in an unusual time with no real saber-toothed species around and predict another such species might arise in the next 5 to 15 million years (refer to the Nat Geo article). What’s even more surprising is that we might have our own saber tooth species already, or rather a precursor, in the form of the sunda clouded leopard, which has abnormally large teeth for its size. But the origin of these teeth is not very clear.
Okay, their origin is a mystery, but again why the unlikeliness? Before I give you that answer, revisit the part in the previous article about the hunting techniques of the saber tooths. They hunted by ambushing prey. Modern day big cats use their teeth to grip their prey and suffocate them to death, but the saber tooth didn’t barely had enough bite force required to do so (about one third of the modern day lion), not to mention that the teeth would break under stress of holding onto struggling prey. Rather they dug in deep with their saber teeth and then proceeded to rip off the meat to quickly as they used their developed forelimbs (stronger than modern day cats) to hold down the prey.{: .text-justify}
Now, this certainly suggests a level of specialization required to make use of the saber teeth. The teeth most likely evolved in and from animals that hunted like modern day big cats using suffocating bites. As the teeth get longer, they can’t handle the bending stress of high force biting and need the bite force to be reduced, and the muscle mass to be transferred from the jaws to the neck and forearms. Furthermore, ambush tactics would need to be evolved, or at least improved upon.
Why would any animal choose to evolve a feature that causes it to have significantly different body anatomy than the already working anatomy that it possesses? Evolution is a slow process (regardless of what our politicians might believe) and it would require a significant amount of time as well as re-direction of resources in the body to bring about these changes.
However, evolution isn’t an empirical scale of an animal’s features. It’s a constantly occurring process that happens relative to the environment. It has no grand design in mind as the end product, rather, it’s the accumulation of small changes that may or may not have an effect on the organisms functioning. Since the changes in an organism occur due to random chance mutations, one change is usually too small to have a significant impact. Rather, as the changes accumulate, they have larger and larger impact on the organism and the effect of natural selection on them rises as well. Thus, he ancestors of the sabre tooth had no choice about their anatomy. Random small changes, like slight enlargement of canine teeth, accumulated in some organisms which were either afforded some advantage by these teeth or were not initially affected by them.
Now, as discussed earlier, the teeth needed some extra anatomic changes to help with their use. One of the questions asked by the researchers was about whether the features required to complement the long canines appear together (pleiotropically) or if they occurred at different times and there were species between the saber tooth cats and their ancestors that didn’t have all the features needed with the saber teeth. The similarities between the skulls of saber tooth cats and pantherines, two distant groups on the evolutionary tree, suggested that the features appeared as a mosaic. Hence, the slightly larger teeth might have been used for threatening mating displays and/or didn’t cause much change in the hunting habits in these mosaic forms. Slowly, the changes accumulated, and the selective pressures (pressure on an organism to evolve towards a certain direction due to its environment) moved the organism towards larger teeth in conjunction with a mosaic of other features like forelimb strengthening and neck muscle enlargement. The skull type of the saber tooth cats allowed a wider gape in exchange for bite force, becoming more specialized towards the shear bite. The environment that could cause such a selective pressure is one where the herbivores to be hunted are larger than oneself and need to be taken down quickly, due to competition with other predators. (refer to the article on nimravid’s weblog).
A similar situation exists in the African savannahs today, with multiple carnivores hunting prey larger than themselves. They seem to have adapted to it using pack behavior to protect themselves and their kills, like lions. Others like hyenas can crush bones to get to the marrow the other animals can’t. And others yet, like the cheetah hunt alone, but can climb trees with their kills to avoid other predators. The case of the sunda clouded leopard is interesting, because it might be an organism in which similar changes are accumulating. However, studies also show that the pantherines (the genus Panthera; lions, tigers, African leopards) are more similar to the saber tooth cats in skull shape than the sunda leopard. So, while the sunda clouded leopard may or may not give rise to the next saber tooth, something can and likely will. For all we know, the ancestor to modern saber tooth cat might be yawning away its first morning among the litter of the campus cat (who are becoming a real nuisance out of late and this adds to the list of reasons why they need to be removed.)