The Softer Side of Sabercats

Science
سه شنبه 11 خرداد 1400 ساعت 19:17
271
Smith sonian mag
Sabertoothed cats have a fearsome reputation. In museum halls and in b-movies, the fanged cats are often shown driving their impressive canines into hapless sloths and mammoths as part of a messy, traumatic hunting strategy. But there’s far more to the prehistoric lives of Smilodon , Homotherium , and other sabercats than how they carved out their meals. Fossils from around the world are helping to highlight the social lives of sabercats.
Two new studies published this year have underscored the fact that sabercats required some of the same family ties that today’s big cats rely upon. Some young sabercats may have stayed with their parents for two years or more as they waited for their impressive fangs to come in. Those parents likely played an essential role in teaching their saberkittens how to catch and eat food, including dragging mammoth legs home to chew on. Together, these studies help highlight how sabercat behavior evolved to cope with a world in which many carnivorous species—from dire wolves to giant bears—competed for prey.
Of all the sabertoothed cats that have ever lived through their 16-million-year history, one of the largest and last was Smilodon fatalis . Hundreds of individuals found in California’s La Brea asphalt seeps have made Smilodon the most iconic of its toothy family—effectively the Ice Age equivalent of Tyrannosaurus when it comes to paleo popularity. But Smilodon didn’t just inhabit prehistoric Los Angeles. Remains of Smilodon fatalis have been found from Alberta through much of South America, and a trio of cats found in Ecuador represents a very rare find, indeed— a Smilodon family.
Fossils of the three cats, described by University of Toronto paleontologist Ashley Reynolds and colleagues in the journal iScience in January , were entombed within a thin lens of sandstone permeated with natural asphalt. This was no ordinary collection of bones.
Among the collection of 56 Smilodon bones recovered from the site were two left lower jaws of similar size. Since no animal has two left mandibles, these bones clearly represented two individuals —relatively young Smilodon that had only recently gotten their adult teeth. More than that, both of these young cats had an extra tooth. Both jaws had a third premolar, or cheek tooth, that’s only present in 2 to 6 percent of all Smilodon specimens. This sort of variation is often caused by inherited genes, a strong indication that these Smilodon were siblings. The third cat in the jumble of bones was bigger. While it’s difficult to confirm based on the available evidence, Reynolds and coauthors hypothesize that this bigger Smilodon was the adult parent of the youngsters. And if that’s correct, the connection indicates that sabercats relied on their parents for a very long time.
Smilodon were not born with their impressive fangs. Saberkittens, like most mammals, had milk teeth that they eventually lost as their adult teeth came in. In this case of Smilodon , this took at least 14 months. But the Smilodon siblings from Ecuador were even older than that, likely about two years old at the time they died. “What was surprising wasn’t so much that there were siblings with a parent,” Reynolds says, “but that these siblings seemed to be quite old while still being with a parent.”
Modern tigers are usually independent of their mothers at this age, yet, Reynolds and coauthors point out, young lions are often still with their mothers at this time. Given how long it took for young Smilodon to grow their fangs, the cubs may have stuck with their mothers for another year or two as they learned to hunt and put that cutlery to work.
The connection offers more evidence that Smilodon was a social cat, an idea proposed based on the sheer number of Smilodon bones found at La Brea. “Living big cats that are highly social stay with the pride they were born in much longer,” Reynolds notes. A social setting allows cats to spend a longer time growing up, learning from the adults and playing with other cats their own age. More research is needed on the idea, Reynolds says, but the fact that Smilodon took so long to grow up might mean that these hunters were not solitary stalkers, but rather social predators that relied on each other.
And Smilodon was not the only attentive sabercat parent. Thousands of miles from Ecuador, in San Antonio, Texas, scientists examined a cave full of Ice Age bones left behind by Homotherium , a different sort of sabercat that prowled the Northern Hemisphere. Homotherium was a lankier cat than Smilodon , with shorter scimitar teeth. “ Smilodon and Homotherium co-occurred,” says Vanderbilt University paleontologist Larisa DeSantis, “and were likely able to do so by doing very different things, having very different ecological niches.” Part of that story is held in Friesenhahn Cave.
DeSantis and colleagues examined what the Friesenhahn Cave Homotherium were eating and published their findings in Current Biology in April. Paleontologists long suspected that the cats were munching on juvenile mammoths on the basis of fossil bones found at the site, but the idea hadn’t been directly investigated. DeSantis and coauthors found that the hypothesis was correct, but with a twist. When Homotherium brought home the Ice Age bacon, so to speak, they only ate the soft parts of their meals.
The table manners of sabercats have been a long-running source of debate among paleontologists and paleoanthropologists. Experts once assumed that the large teeth of sabercats would have prevented them from scraping much off carcasses, and so they would have left plenty of meat around—a boon to early humans who often inhabited the same landscapes. But subsequent research found that Smilodon was capable of stripping down skeletons and even crunching bones. The evidence in the teeth and gnawed pieces of prey changed the image. Yet instead of taking studies of Smilodon as the rule for all sabercats, paleontologists have been striving to understand how different cats carved out varied roles on the landscape just as modern zoologists study how lions, leopards and cheetahs are able to live alongside each other by hunting different prey.
Finding direct, specific evidence of what prehistoric creatures ate is a difficult task. While the cutting canine teeth and slicing cheek teeth of Homotherium left no doubt that this cat ate meat, paleontologists required more specific, detailed evidence to understand how this cat hunted and what role it played on the ancient ecosystem. Whether a cat only eats the soft parts of a carcass or can crunch bones to splinters is important for discerning how the sabercat got its nutrition, how often it had to hunt and even the prey it preferred.
DeSantis and coauthors found that the teeth of Homotherium showed patterns of microscopic damage similar to modern cheetahs, cats that dine on tough flesh and soft tissues but usually eschew bone. More than that, DeSantis notes, the cave has “a high abundance of meaty upper limb bones of juvenile mammoths,” indicating that the cats preferred to bring home parts of the carcass that had a great deal of skin and muscle. The dental clues matched the damage on the mammoth bones found at the site, indicating that Homotherium was able to get much of the flesh off their kills but generally didn’t bother with the bones.
The ancient scimitar cats might have brought mammoth take-out back to their secluded underground den to dine in peace. That might seem strange for a svelte cat with the proportions of a runner, the sort of cat that chased down prey on the open ground. But against the context of the competitive nature of Ice Age ecology, the fact that Homotherium made an underground den is cunning carnivoran strategy.
Homotherium was not the only carnivore on the Pleistocene landscape, and the gracile cats might have faced competition from Ice Age hyenas, bears and other cats. But there may have been another reason, too. “There were juvenile Homotherium specimens found in Friesenhahn Cave, causing one to wonder if the juvenile baby mammoth limbs were a good source of meat provided to the young,” DeSantis says. The possibility offers a tantalizing window into a sweet Ice Age scene. In some moments, Homotherium was a beast of terrible power and grace, able to fell young mammoths and cut off parts to carry off. But at least some of those cats carried those meaty limb bones to the calm and cool of the underground, where mewls of hungry Homotherium kittens awaited the adults. In order to become such powerful predators, saberkittens required an attentive parent while the little fuzzballs cut their teeth on the Pleistocene’s big game.
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