Giant ground sloths may have been meat-eating scavengers

Modern sloths may be dedicated vegetarians, but at least one of their massive Ice Age cousins chowed down on meat when it had the chance. Darwin’s ground sloth — which could grow to over 3 meters long and weigh as much as about 2,000 kilograms — may have been an opportunistic scavenger, chemical analyses of fossil sloth hair suggest.

Paleontologist Julia Tejada of the University of Montpellier in France and colleagues analyzed the chemical makeup of two amino acids, the building blocks of proteins, within the fossil hair of two giant ground sloth species: Darwin’s ground sloth (Mylodon darwinii) of South America and the Shasta ground sloth (Nothrotheriops shastensis) of North America (SN: 4/25/18). The team compared these with samples from living sloths, anteaters and other modern omnivores.
Nitrogen isotopes, different forms of the element, can vary a lot among different food sources as well as between ecosystems. Those isotope values in one amino acid, glutamine, change significantly with diet, increasing the higher the animal is on the food chain. But diet has little impact on the nitrogen values in another amino acid, phenylalamine. By comparing the nitrogen isotopes in the two amino acids found in the sloths’ hair, the researchers were able to eliminate ecosystem effects and zoom in on diets.

The data reveal that while the diet of the Shasta ground slothwas exclusively plant-based, Darwin’s ground sloth was an omnivore, Tejada and colleagues report October 7 in Scientific Reports.

The findings upend what scientists thought they knew about the ancient animals. Scientists have assumed the ancient creatures were herbivores. That’s in part because all six modern species of sloth are confirmed vegetarians, and in part giant ground sloths’ teeth and jaws weren’t adapted for hunting or powerful chewing and tearing (SN: 6/20/16).

But Darwin’s ground sloth could have managed to ingest already-killed meat, Tejada and colleagues say. And that might help solve a long-standing puzzle: the apparent absence of large carnivorous mammals in South America at the time. Darwin’s ground sloth, the researchers add, may have filled a vacant ecological niche: the scavenger who wouldn’t say no to a meaty meal.

Here’s how ice needles sculpt patterns into cold, rocky landscapes

Neat rings, stripes and swirls embellish many cold, rocky landscapes. Although these beautiful stone patterns look like humanmade artwork, they’re all natural. Scientists have long known that such rocky patterns result from freezing and thawing. But precisely how they develop has been a mystery — until now.

New experiments reveal that so-called “ice needles” can sort and organize rocks into many patterns, Anyuan Li of the University of Tsukuba in Japan and colleagues report the Oct. 5 Proceedings of the National Academy of Sciences.

“The beauty of [our] experiments is that you can actually see direct information on how the patterns form,” says Bernard Hallet of the University of Washington in Seattle, who has studied natural patterns in surface rocks around the world.
The researchers spread pebbles atop a pan holding moist, fine-grained soil, then froze and thawed this mini-landscape over and over. When the moist soil had not yet frozen but the air temperature dropped below freezing, tiny, needlelike columns of ice sprouted up from the soil. These ice needles, each up to a few centimeters high, lifted any stones atop them. When temperatures rose again, the ice collapsed and the stones tumbled off. Because the ice needles curved as they grew, the stones tended to fall off their icy pedestals to one side.

Over many freeze-thaw cycles, the ice needles cleared patches of exposed soil. Since needles could more easily form in spots where there were fewer rocks in the way, they more efficiently cleared out any remaining pebbles. Stones were gradually shuffled into clusters between stone-free areas to form larger patterns. The pattern that builds on a landscape “strongly depends on its [local stone] concentration,” says study coauthor Quan-Xing Liu, a theoretical ecologist at East China Normal University in Shanghai.
In lab experiments, the team “was able to able to get patterns after 30 freeze cycles,” says Hallet. That could equate to 30 cold nights — or 30 years, if each freeze lasted a whole winter. In the real world, Hallet says, some patterns might take “thousands, if not tens of thousands, of years to form.”

Using observations from their soil experiments, the researchers built a computer simulation of ice needle landscaping. This simulation could predict stone movement in the open environment under a range of conditions. The simulation confirmed that the rate of pattern formation depended on how dense the stone cover was, among other factors. The shapes and formation rates of patterns were also related to how moist the soil was, how the ground sloped and how tall the ice needles grew.

“We see identical patterns in different systems, such as fluids,” Hallet says of the rock formations. Materials with different characteristics or sizes often start all mixed together but don’t stay that way (SN: 4/22/21). Phase separation is the process that morphs these mixes into patterns. The new study is among the first to show how phase separation applies to landscapes.

The combination of experiments and computer modelling in this study provides a new way to connect how natural landscapes form and how their materials behave, says Rachel Glade, a geologist at the University of Rochester in New York who was not involved in the work. This approach “is vital for our understanding of complex materials,” she adds, and it could help us understand how landscapes may evolve differently in a changing climate.

A new map shows where carbon needs to stay in nature to avoid climate disaster

Over decades, centuries and millennia, the steady skyward climb of redwoods, the tangled march of mangroves along tropical coasts and the slow submersion of carbon-rich soil in peatlands has locked away billions of tons of carbon.

If these natural vaults get busted open, through deforestation or dredging of swamplands, it would take centuries before those redwoods or mangroves could grow back to their former fullness and reclaim all that carbon. Such carbon is “irrecoverable” on the timescale — decades, not centuries — needed to avoid the worst impacts of climate change, and keeping it locked away is crucial.

Now, through a new mapping project, scientists have estimated how much irrecoverable carbon resides in peatlands, mangroves, forests and elsewhere around the globe — and which areas need protection.

The new estimate puts the total amount of irrecoverable carbon at 139 gigatons, researchers report November 18 in Nature Sustainability. That’s equivalent to about 15 years of human carbon dioxide emissions at current levels. And if all that carbon were released, it’s almost certainly enough to push the planet past 1.5 degrees Celsius of warming above preindustrial levels.
“This is the carbon we must protect to avert climate catastrophe,” says Monica Noon, an environmental data scientist at Conservation International in Arlington, Va. Current efforts to keep global warming below the ambitious target of 1.5 degrees C require that we reach net-zero emissions by 2050, and that carbon stored in nature stays put (SN:12/17/18). But agriculture and other development pressures threaten some of these carbon stores.

To map this at-risk carbon, Noon and her colleagues combined satellite data with estimates of how much total carbon is stored in ecosystems vulnerable to human incursion. The researchers excluded areas like permafrost, which stores lots of carbon but isn’t likely to be developed (although it’s thawing due to warming), as well as tree plantations, which have already been altered (SN: 9/25/19). The researchers then calculated how much carbon would get released from land conversions, such as clearing a forest for farmland.

That land might store varying amounts of carbon, depending on whether it becomes a palm oil plantation or a parking lot. To simplify, the researchers assumed cleared land was left alone, with saplings free to grow where giants once stood. That allowed the researchers to estimate how long it might take for the released carbon to be reintegrated into the land. Much of that carbon would remain in the air by 2050, the team reports, as many of these ecosystems take centuries to return to their former glory, rendering it irrecoverable on a timescale that matters for addressing climate change.
Releasing that 139 gigatons of irrecoverable carbon could have irrevocable consequences. For comparison, the United Nations’ Intergovernmental Panel on Climate Change estimates that humans can emit only 109 more gigatons of carbon to have a two-thirds chance of keeping global warming below 1.5 degrees C. “These are the places we absolutely have to protect,” Noon says.

Approximately half of this irrecoverable carbon sits on just 3.3 percent of Earth’s total land area, equivalent to roughly the area of India and Mexico combined. Key areas are in the Amazon, the Pacific Northwest, and the tropical forests and mangroves of Borneo. “The fact that it’s so concentrated means we can protect it,” Noon says.

Roughly half of irrecoverable carbon already falls within existing protected areas or lands managed by Indigenous peoples. Adding an additional 8 million square kilometers of protected area, which is only about 5.4 percent of the planet’s land surface, would bring 75 percent of this carbon under some form of protection, Noon says.

“It’s really important to have spatially explicit maps of where these irrecoverable carbon stocks are,” says Kate Dooley, a geographer at the University of Melbourne in Australia who wasn’t involved in the study. “It’s a small percentage globally, but it’s still a lot of land.” Many of these dense stores are in places at high risk of development, she says.

“It’s so hard to stop this drive of deforestation,” she says, but these maps will help focus the efforts of governments, civil society groups and academics on the places that matter most for the climate.