They’re probably one of the most recognizable animals of the ice age, and with their stocky shoulders and huge dagger-like teeth, they were certainly formidable predators. But it seems these animals were not natural-born killers, as new research shows that it took them quite a few years to fully develop their toothy weapons.
“For predators such as big cats, an important determinant of an individual's full hunting ability is the time required to grow their weapons – their teeth,” said Z. Jack Tseng, who co-authored the new paper published in PLoS One. “This is especially crucial for understanding saber-toothed predators such as Smilodon.”
Smilodon fatalis, one of three recognized saber-toothed cat species, lived on the North American grasslands about 10,000 years ago, where it spent its time ambushing the wild horses, camels and ground sloths with which it shared the landscape. The cat was about the size of a modern-day lion or tiger, but much more heavily built. It also had a stubby little tail and massive 18-centimeter-long (7-inch-long) canines. These teeth were surprisingly fragile and therefore were probably not used in taking down prey due to their risk of breaking – only when the animal was totally subdued would the cat have slashed its throat with them.
The new research gives us a better insight into the big cats' biology and ecology. After taking saber-toothed cat skulls found preserved in the La Brea Tar Pits near Los Angeles, researchers from Clemson University used stable oxygen isotope analysis and X-ray imaging on the cats' tooth enamel to determine their rate of growth. They discovered that they grew at an astonishing 6 millimeters (a quarter inch) per month, but because of their gargantuan size, they were still not fully developed until the cat was 3 years old.
Jaw from a baby Smilodon fatalis, showing one of its adult canines erupting alongside the baby canine. Credit: © AMNH/J. Tseng
“Timing of development is critical for many aspects of vertebrate ecology and evolution,” explains Robert Feranec, who also co-authored the paper. “Changes in the timing of life-history events can have major effects on an organism's adult features and final appearance. For extinct species, we can usually only determine the relative sequence of developmental events. This technique will permit the determination of absolute developmental age not only for Smilodon, but other extinct species.”
Like most mammals, the cubs had baby teeth that were replaced with a permanent set as they got older. This was true even of their large canines, and meant that for a period of about 11 months, the young animals had two sets of dagger-like teeth erupting from their gums. Even though they did not get their trademark teeth until late in life, the researchers were able to show that the cats could still pack a powerful bite even below the age of two, with fully developed jaws appearing around this age.
The team hopes that this new work could be applied to looking at how other extinct animals grew and matured, giving us a greater understanding of how different creatures lived.