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Causes & Consequences of Pleistocene Megafaunal Extinctions as Revealed from Rancho L
#1
Saber-tooth surprise: Fossils redraw picture of the fearsome big cat
Hundreds of teeth pulled from the La Brea tar pits in California are revising our image of this icon of the Ice Age.

[Image: intenselooka.jpg]
Dappled by leafy shade, saber-tooth cats feast on a forest herbivore while dire wolves chase bison in the open grassland of Pleistocene California. According to analysis of their teeth, the saber-tooth cats of the American West were most likely forest-dwellers that hunted animals such as tapir and deer. ILLUSTRATION BY MAURICIO ANTÓN

4 MINUTE READ
BY JOHN PICKRELL
PUBLISHED AUGUST 5, 2019

Until about 10,000 years ago, the saber-tooth cat Smilodon fatalis was a fearsome predator in what is now the American West. More than 3,000 fossilized cats have been pulled from the acrid ooze of the La Brea tar pits in California, and researchers studying them have long pictured Smilodon as a lion-like hunter, chasing bison and horses out on open grasslands.

But now, analyses of hundreds of teeth from La Brea are painting a vastly different picture of this prehistoric terror, which could weigh up to 600 pounds and sported seven-inch-long canine teeth.

“The iconic images you see of saber-tooth cats taking down bison, that’s actually not supported at all,” says study leader Larisa DeSantis, a paleontologist at Vanderbilt University in Nashville, Tennessee. The research, published today in the journal Current Biology, provides evidence that Smilodon may instead have been a forest dweller that primarily feasted on leaf-browsing creatures.

“[They] were more likely to be taking things like tapirs and deer, as opposed to horses and bison,” DeSantis says.

Her team’s comprehensive study also helps to explain why smaller predators such as coyotes and grey wolves were able to survive to the modern day, while larger carnivores such as saber-tooth cats, dire wolves, and American lions all went extinct 10,000 to 12,000 years ago. (Also find out about a type of saber-tooth cat that may have encountered the first humans migrating into Europe.)

The key, her team suggests, was dietary flexibility following the disappearance of many of North America’s large prehistoric herbivores, such as giant ground sloths, mammoths, mastodons, and camels. For instance, previous work found that coyotes got 20 percent smaller after the herbivore extinction event, and the new look at their teeth shows that they also adjusted their lifestyles to adapt to their new reality.

“When the large predators and prey go extinct, not only do they shrink, but they fundamentally change their diet and start scavenging to become the opportunists we know today,” DeSantis says.

Handle the tooth

The scientists studied more than 700 fossil teeth collected from La Brea that once belonged to various herbivores as well as saber-tooth cats, American lions, dire wolves, cougars, coyotes, and grey wolves. The team looked at both microscopic patterns of wear, which give an indication of the types of foodstuffs the creatures were chewing on, as well as the proportions of two carbon isotopes within the tooth enamel.

These two slight variants of the carbon atom build up in plants at different rates within forested versus open environments. Herbivores that eat those plants then carry a chemical clue to their preferred habitats within their bodies, something that gets carried over into any carnivores that prey upon them. This means that the remains of carnivores can reveal whether they were eating prey that lived in forested or more open habitats.

"The cats and dogs partition out what they are doing."

Previous studies had looked at the proportion of carbon and nitrogen isotopes in the remains of a protein called collagen found in the bones of predators at La Brea. Those papers came to the conclusion that the largest of the predators—including Smilodon, dire wolves, and American lions—were all likely hunting in open environments.

“All of the data up until this point showed they were competing for similar prey,” DeSantis says. Some experts therefore proposed that this rivalry for resources may have contributed to their extinction. But using tooth enamel is now regarded as the “gold standard” for these kinds of isotope tests, DeSantis says.

“Tooth enamel is more reliable than collagen,” says Julie Meachen, a paleontologist at Des Moines University in Iowa who was not on the study team. That’s because enamel is less likely to be altered during the fossilization process or by spending a long time underground.

And “when we look at the enamel, we get a totally different picture,” DeSantis says. “We find that the saber-tooth cats, American lions, and cougars are actually doing what cats typically do, which is hunting within forested ecosystems and using cover to potentially ambush their prey.”

By contrast, their canine counterparts, including the dire wolves, coyotes, and grey wolves, were the ones hunting in more open environments.

“The cats and dogs partition out what they are doing,” she says.

Optimized to survive

The results suggest there was actually much less competition for prey among the region’s largest Pleistocene carnivores, particularly between the saber-tooth cats and dire wolves.

The new study is significant “because it is the first paper to show that Smilodon and dire wolves were really doing something different in terms of prey choices,” Meachen says. “It makes sense that Smilodon would hunt in a more closed environment, considering they likely did not chase prey for any appreciable distance. They were ambush predators, based on their body morphology.”

The paper “adds to our understanding of who Smilodon fatalis was and where it preferred to hang out,” adds paleontologist Christopher Shaw, an affiliate curator at the Idaho Museum of Natural History and a former collections manager at the La Brea Tar Pits and Museum. Other evidence suggests Smilodon were eating bison some of the time at La Brea, he says, but this may not be as contradictory as it seems.

“At one time, there was a subspecies of bison that was adapted to and lived in woodland habitats and may well have been ideal prey,” Shaw says.

Critically, the study adds to evidence that highly specialized prey preferences is what likely doomed species such as Smilodon and the dire wolves, while coyotes managed to survive the ecological shift by being highly flexible and taking prey as small as rats or rabbits, in addition to scavenging.

Coyotes, Meachen says, “can change their prey and even prey-killing strategy to optimize chances of survival.”

https://www.nationalgeographic.com/scien...XX9lRF3S0U



Intense look at La Brea Tar Pits explains why we have coyotes, not saber-toothed cats

The most detailed study to date of ancient predators trapped in the La Brea Tar Pits is helping Americans understand why today we're dealing with coyotes dumping over garbage cans and not saber-toothed cats ripping our arms off.

Larisa DeSantis, a Vanderbilt University paleontologist, grew up visiting the one-of-a-kind fossil site in Los Angeles, which contains fossils of predators that tried to eat horses, bison and camels stuck in the tar over the past 50,000 years and themselves became trapped, offering the best opportunity to understand Ice Age animals facing climate change. The Pleistocene Epoch spanned 2.6 million years ago to about 10,000 years ago, encompassing multiple glacial and interglacial periods and the arrival of humans, one or both of which forced predators to adapt their diets or die.

DeSantis spent the last decade visiting La Brea, studying the teeth of extinct species such as American lions, saber-toothed cats and dire wolves; and teeth from ancient animals whose offspring are still alive today, such as gray wolves, cougars and coyotes. Her work revealed that competition for prey among carnivores wasn't a likely cause of the Pleistocene megafaunal extinction as formerly believed, because, like dogs and cats of today, one preferred running after herbivores in the open fields, while the other preferred stalking them in forested areas.

"Isotopes from the bones previously suggested that the diets of saber-toothed cats and dire wolves overlapped completely, but the isotopes from their teeth give a very different picture," said DeSantis, an associate professor of biological sciences at Vanderbilt. "The cats, including saber-toothed cats, American lions and cougars, hunted prey that preferred forests, while it was the dire wolves that seemed to specialize on open-country feeders like bison and horses. While there may have been some overlap in what the dominant predators fed on, cats and dogs largely hunted differently from one another."

To study these ancient predators, she employs dentistry—taking molds of the teeth and shaving off tiny bits of enamel for chemical analysis. Information about everything the animal ate lies within the isotopes, she said. Further, the microscopic wear patterns on teeth can clarify who was eating flesh or scavenging on bones.

It's likely that those giant predators went extinct due to climate change, the arrival of humans to their environment or a combination of the two, she said, and her team is working to clarify the cause of the extinction with multiple colleagues across six institutions as part of a separate on-going study.

What they know is predators alive today in the Americas were better able to adapt their diets. Instead of only feeding on large prey, they could effectively hunt small mammals, scavenge what they could from carcasses or do both.

"The other exciting thing about this research is we can actually look at the consequences of this extinction," DeSantis said. "The animals around today that we think of as apex predators in North America—cougars and wolves—were measly during the Pleistocene. So when the big predators went extinct, as did the large prey, these smaller animals were able to take advantage of that extinction and become dominant apex-predators."

An even more detailed picture of ancient life at La Brea is contained in the paper "Causes and consequences of Pleistocene megafaunal extinctions as revealed from Rancho La Brea mammals," published today in the journal Current Biology.

https://phys.org/news/2019-08-intense-la...-pits.html



Journal Reference:
Larisa R.G. DeSantis, Jonathan M. Crites, Robert S. Feranec, Kena Fox-Dobbs, Aisling B. Farrell, John M. Harris, Gary T. Takeuchi, Thure E. Cerling. Causes and Consequences of Pleistocene Megafaunal Extinctions as Revealed from Rancho La Brea Mammals. Current Biology, 2019; 29 (15): 2488 DOI: 10.1016/j.cub.2019.06.059

Summary
The fossils preserved in the Rancho La Brea “tar” seeps in southern California span the past ∼50,000 years and provide a rare opportunity to assess the ecology of predators (e.g., the American lion, sabertooth cats, cougars, dire wolves, gray wolves, and coyotes), including clarifying the causes and consequences of the terminal Pleistocene extinction event. Here, a multi-proxy approach elucidates dietary responses of carnivorans to changing climates and megafaunal extinctions. Using sample sizes that are unavailable anywhere else in the world, including hundreds of carnivoran and herbivore specimens, we clarify the paleobiology of the extinct sabertooth cats and dire wolves—overturning the idea that they heavily competed for similar prey. Canids (especially the dire wolf) consumed prey from more open environments than felids, demonstrating minimal competition for prey throughout the latest Pleistocene and largely irrespective of changing climates, including just prior to their extinction. Coyotes experienced a dramatic shift in dietary behavior toward increased carcass utilization and the consumption of forest resources (prey and/or plant resources) after the terminal Pleistocene megafaunal extinction. Extant predators’ ability to effectively hunt smaller prey and/or utilize carcasses may have been a key to their survival, especially after a significant reduction in megafaunal prey resources. Collectively, these data suggest that dietary niches of carnivorans are not always static and can instead be substantially affected by the removal of top predators and abundant prey resources.

https://www.cell.com/current-biology/ful...19)30786-9
[Image: wildcat10-CougarHuntingDeer.jpg]
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  • Claudiu Constantin Nicolaescu, OldGreenVulture
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#2
^ Yeah, IMO, that report is yet another example of a recent 'bold claim' by scientists, esp' as regards their quite fanciful
idea that social lion species in the Americas, (or elsewhere - then or ever - according to known data) "preferred forests",
since that def' runs counter to the basic grasslands prey-density required to keep them in overtly needful hypercarnivory!
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#3
^ You dont like this part?

The research, published today in the journal Current Biology, provides evidence that Smilodon may instead have been a forest dweller that primarily feasted on leaf-browsing creatures. “[They] were more likely to be taking things like tapirs and deer, as opposed to horses and bison,” DeSantis says.
[Image: wildcat10-CougarHuntingDeer.jpg]
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#4
^ Not so much Smilodon, since other papers discuss the likelihood of them being more akin to tigers, in being forest
dwellers, albeit we'd also have to note that quite large cervids, such as elk/wapiti & moose were likely prey, along with
extinct giant sloths & whatnot, which also then lived there.

However, the other papers noted that P.leo atrox, was comparatively rarely found in the La Brea complex, & was very
likely to have been a grasslands hunter like its cousins elsewhere, in Eurasia & Africa, so preying on large herd beasts.
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#5
I'd also note that recent studies concerning S.populator in South America note evidentially this cat was an open-ground
hunter too, even if it also took glyptodonts & other large prey which primarily ate leafy/forest vegetation, as well...
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#6
It shouldn’t be all that surprising. S. fatalis always seemed more of a woodland/woodland-savanna mosaic living species, in between S. gracilis (woodland) and S. populator (savanna).
Not to mention, given the disproportionate amount of dire wolves and S. fatalis at La Brea compared to literally any other carnivore, it indicates which species were more dominant either all around or in a “specific” area.
[img=0x0]http://i68.tinypic.com/5u3d6w.jpg[/img]
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