Latest news with #Megatherium
Yahoo
4 days ago
- General
- Yahoo
Sloths The Size of Elephants Roamed America, Before Abruptly Vanishing
Massive Megatherium sloths once stood as large as Asian elephants, ripping foliage off treetops with prehensile tongues like today's giraffes. "They looked like grizzly bears but five times larger," says paleontologist Rachel Narducci from the Florida Museum of Natural History. Megatherium were among a dazzling assortment of more than a hundred different sloth species that once roamed the Americas. Their ancient DNA now tells the likely story of why only six sloth species remain. Analyzing the DNA of 403 sloth fossils from museum collections, alongside weight estimates and environmental information, a new study has created a detailed sloth family tree. This 35 million years of evolutionary history revealed these once-diverse animals' sizes matched up neatly with the environmental conditions they experienced. The endearingly dopey mammals we know and love today are so suited to their arboreal environment that they've developed an incredibly strong upper body, have guts designed to hang upside-down, and risk their lives when they descend to poop. "Living sloths are extremely slow and that's because they have a very low metabolic rate," University of Buenos Aires paleontologist Alberto Boscaini told Helen Briggs from the BBC. "This is their strategy to survive." But many ancient species were too heavy for tree branches to bear, and stuck to the ground, like Megatherium and Lestodon. Unlike today's sloths, these species were well suited to moving with agility over the earth and had much faster metabolisms. "Some ground sloths also had little pebble-like osteoderms embedded in their skin," notes Narducci, explaining these rocky bumps were a ground-defense trait they shared with one of their closest relatives, armadillos. There was even an aquatic sloth, Thalassocnus, that survived life on the arid strip between the Andes and Pacific by foraging in the ocean. "They developed adaptations similar to those of manatees," says Narducci. "They had dense ribs to help with buoyancy and longer snouts for eating seagrass." Gigantism evolved several times in sloths and likely contributed to their survival into the Pleistocene ice ages, when they reached their greatest sizes. But about 15,000 years ago many of these species abruptly vanished. "[This] does not track with shifts in palaeotemperature, reinforcing the idea that human impacts played a more prominent role in the extinction of ground sloths than climatic change," the researchers conclude. The bulk that kept giant sloths warm and saved them from local predators made them a target of Earth's most voracious predator: us. Their numbers dropped off massively once humans arrived in North America. In contrast, the sluggish tree-climbers we know today seemed to have had more luck staying out of our reach, at least until more recently. Two of the six species still alive today are now on the IUCN endangered species lists. Boscaini and team's findings echo an increasingly recognized global story: the rapid extinction of megafauna following the arrival of humans – a scenario that's still continuing today. This research was published in Science. This Giant Snail Lays Eggs Out of Its Neck… Yes, Seriously Cephalopods Passed a Cognitive Test Designed For Human Children Study Reveals How Your Cat Remembers Who You Are
Yahoo
23-05-2025
- Science
- Yahoo
8,000-pound sloths once roamed North America. Where'd they go?
Giant sloths used to roam all over North America. Over 10 times bigger than today's sloths, many lived on the ground instead of in the trees and their closest living relatives are actually armadillos and anteaters. The largest of these ancient animals were those in the genus Megatherium–roughly the size of a modern Asian bull elephant and weighed about 8,000 pounds. But how did they grow so large–and why did they shrink down? A new analysis of over 400 fossils found that these sloths evolved three times and that climate changes and increased pressure by early humans wiped out the enormous mammals. The findings are detailed in a study published May 22 in the journal Science. In the new study, the team analyzed ancient DNA samples and compared more than 400 fossils from 17 natural history museums to try and figure out how they grew so large. 'They looked like grizzly bears, but five times larger,' said Rachel Narducci, a study co-author and the collection manager of vertebrate paleontology at the Florida Museum of Natural History. Ground sloths greatly varied in size. The fairly squat and chunky Shasta fed on cacti in the deserts of North America, while the mighty Megatherium could use a long tongue like a giraffe's to rip leaves off of tree tops. Those that developed an affinity for tree climbing much like today's bear-faced slowpokes lived entirely in the tree canopy. Tree-dwelling sloths weighed in at about 14 pounds, compared to 174 pounds for the ground sloths. It's obvious that life in trees requires a weight limit. Branches break when there is too much weight on them and tree sloths have reportedly survived 100 foot falls. Since even a moderate drop can cause severe damage, it makes evolutionary sense for a body to be as small as possible. What is less obvious to paleontologists is why ground sloths grew to such enormous sizes in the first place. The size may have been helpful for finding food or avoiding predators. Ground sloths appear to have had an affinity for cave dwelling and their size likely played a role in finding and making shelter. The more moderately sized Shasta ground sloth favored the smaller natural caves embedded into the cliffsides of the Grand Canyon. These little caves were also convenient places to poop. In 1936, paleontologists found a mound of fossilized sloth poop, bat guano, and packrat middens over 20 feet thick in a cave near Lake Mead. The larger sloths were not just restricted to lives in pre-existing caves. Their claws were among the largest of any known mammal, and they could use them to carve their own caves from rock and earth. Several of the caves that they left behind are still adorned with claw marks along the interior walls. The scientists combined the data on the shape of fossils with DNA from both living and extinct species to build out a sloth tree of life. It traced sloth lineage all the way back to their origin over 35 million years ago. They then added what decades of research has found about where sloths lived, their diets, and whether they were climbers or walkers. Since sloth size was a major question, they measured museum fossils to estimate the sloth weight. 'We [the Florida Museum] have the largest collection of North American and Caribbean-island sloths in the world,' said Narducci, who took several measurements of 117 limb bones. With all of this data in tow, the team imported it into an analysis software and got their answer. Habitat type has primarily influenced size differences among sloths–and climate change by extension. 'Including all of these factors and running them through evolutionary models with multiple different scenarios was a major undertaking that had not been done before,' Narducci said. [ Related: Our bravest ancestors may have hunted giant sloths. ] The sloth dynasty coincided with some life-altering changes in Earth's climate. About 20 million years ago, a large rift opened up between present day Washington state and Idaho, south through parts of Oregon and Nevada. Magma boiled out of this hole, leaving a nearly 600,000 cubic mile scab that is still visible in some places along the Columbia River. These rock pillars have a distinct hexagonal shape, which was caused by the way in which the magma hardened and cracked as it cooled. This volcanic event lasted roughly 750,000 years and aligned with the Mid-Miocene Climatic Optimum–a period of global warming. The warming was likely caused by all of the greenhouse gasses emitted by the volcanic eruption. Sloths responded to this slow-burn chaos by getting smaller. This might be because the warmer temperatures brought increased precipitation, which allowed forests to expand–creating more habitat for the smaller sloths. Additionally, size reduction is a common way for animals to deal with heat stress and has been seen in the fossil record on several different occasions. For about one million years after the volcanic activity calmed down, the world remained warm. Then, a longstanding pattern of cooling that continued in fits and starts up to the present. The sloths also changed with the temperatures. The more temperatures dropped, the bigger they grew. They eventually branched out into the Andes mountains, open savannas, deserts, and the forests of North America. One called Thalassocnus lived in the arid strip of land between the Andes and the Pacific and it foraged for food in the ocean. 'They developed adaptations similar to those of manatees,' Narducci said. 'They had dense ribs to help with buoyancy and longer snouts for eating seagrass.' Ground sloths met the challenges of these diverse environments by bulking up. 'This would've allowed them to conserve energy and water and travel more efficiently across habitats with limited resources,' Narducci said. 'And if you're in an open grassland, you need protection, and being bigger provides some of that. Some ground sloths also had little pebble-like osteoderms embedded in their skin,' Narducci said, in reference to the bony plating that sloths had in common with their armadillo relatives. The larger bodies helped sloths contend with cooling climates. They reached their greatest stature during the Pleistocene ice ages, shortly before they largely disappeared about 15,000 years ago. What really led to the giant sloths' demise is still debated, but hunting and pressure by early humans cannot be ruled out. The sloths were not fast or well-defended 15,000 years ago, and would have likely been an easy target for early humans. After all of the ground-dwelling relatives had gone extinct everywhere else, two species of tree sloth in the Caribbean held on until 4,500 years ago.
New York Post
23-05-2025
- Science
- New York Post
Texas road construction unearths ‘colossal' prehistoric remains of ‘big ol' animals'
A recent excavation in Texas yielded some 'colossal creatures,' according to local officials – and archaeologists are hopeful more will be uncovered soon. The Texas Department of Transportation (TxDOT) announced the discovery in a recent press release. Advertisement In a statement, officials said the excavation took place in Lubbock during the environmental review for Loop 88, a proposed state highway. During the archaeological survey, diggers uncovered ancient bones dating back to prehistoric times. The remains belonged to megafauna, which are large mammals. Chris Ringstaff, a project planner with TxDOT's environmental affairs division, said that megafauna bones '[are] not unusual in the region.' Advertisement Ringstaff also noted that at least one giant ground sloth was identified, thanks to its distinctive tooth. 'Whether all the bones are giant ground sloth or there are different animals such as mammoth or mastodon, we're not sure,' he said. 3 Workers conduct a dig in the excavation site on the side of Loop 88 in Lubbock, Texas. Texas Department of Transportation 'Paleontologists will give us positive identification.' Advertisement 'We're here to get the road built, but who doesn't love digging up big ol' animals?' Ringstaff added. TxDOT noted that the Lone Star State is home to many dried-out lakes called playas, which date back to the Ice Age. 'In prehistoric times, animals and humans used playas as water sources and these sites can sometimes contain evidence of human activity,' the press release noted. 3 Officials begin to extract the remains of the megafauna in the site. Texas Department of Transportation Advertisement Archaeologists are still searching for small artifacts. They're also using dating techniques to determine the age of the remains. If any proof of human settlement is found, the project will be temporarily halted. 'Should the site reveal human activity with megafauna from the Ice Age, it would be [the] first of its kind for a TxDOT project,' the statement said. Several prehistoric bones are found in the US every year. 3 The fossil skeleton of the giant ground sloth, Megatherium. Florilegius/Universal Images Gro Last summer, archaeologists in Iowa unearthed a 13,000-year-old mastodon skull. Later in 2024, a New York homeowner found a complete mastodon jaw in his Scotchtown backyard.
New York Times
03-04-2025
- Science
- New York Times
Scientists Reveal the Hairy Truth About Giant Ground Sloths
Ground sloths emerged in South America tens of million years ago, eventually ranging as far north as Canada. While their modern relatives dwell in trees and top out at the size of a dog, ground sloths also occupied land and seashores and, at their largest, rivaled today's elephants. We know from preserved pelts that some ground sloths had lots of fur. But did other sloths evolve to be nearly hairless? Research published earlier this year in The Journal of Mammalian Evolution offers new insights into what the extinct sloths may have looked like, and how furry they really were. Developing a more accurate picture of ground sloths is not simple. Their habitats varied from tropical to cold climates across the Americas. And they came in a variety of sizes. The megatheres, known as Eremotherium and Megatherium, were among the biggest terrestrial mammals of their time. The team started by determining sloth body temperature. They employed an analysis that two authors involved in the study, Robert Eagle and Aradhna Tripati of the University of California, Los Angeles, pioneered in earlier research that sampled fossilized teeth. Using three megathere teeth and two teeth from relatively smaller ground sloths, they measured the abundance of certain isotopes within minerals inside the sloth teeth, Dr. Eagle explained. 'Isotopes are transformative to be able to illuminate the body temperature of extinct species,' Dr. Tripati said. Remarkably, they found that, at 84 to 89 degrees Fahrenheit, these ground sloths had a lower core body temperature than most large land mammals today. Randon Flores, another study co-author and a Ph.D. student at U.C.L.A., said that low body temperature 'allows us to make inferences about things like metabolic rate,' and from that, he added, 'we can draw comparisons' between the physiology of today's smaller sloths and their much larger extinct relatives. Three-dimensional computer models created by paleoartists were used to estimate the surface area and body volume of the megatheres and the somewhat smaller species, Mylodon and Nothrotheriops. Further analysis allowed the team to adjust for factors like wind speed, humidity and the amount of sunshine in various habitats. The goal, said Michael Deak, the paper's lead author, who is currently at Penn State Shenango, was to determine 'a thermal comfort zone' for each species, in which the animal is neither too hot nor too cold. Megatherium produced the most surprising results. Regardless of the environment, each model indicated a preference for what Mr. Deak described as 'a fairly thick, dense, furry pelt.' Modeling it with sparse elephant-like hair, he continued, indicated the animal would 'be constantly cold-stressed.' Eremotherium, which was slightly smaller than Megatherium, was the only sloth whose fur coverage might have changed depending on its habitat — without at least a centimeter of dense fur, it would have been too cold in the Andes Mountains and some northern habitats. But in tropical climates, sparse fur might have sufficed. The team suggests that Eremotherium may have had either varied fur coverage depending upon region or it may have shed its coat during warmer seasons. Smaller Mylodon and Nothrotheriops would have needed one to five centimeters of denser fur year-round, an amount that matches mummified fur from those animals. But even with thick fur, the authors note, these species inhabited areas in South America where it wouldn't have been enough to combat the cold. That dovetails with fossil evidence suggesting the species sheltered in caves, or even hibernated. The lifestyle of modern tree sloths, said Michael Butcher, a study author and a professor at Youngstown State University, 'is built around conservation of energy.' So he said it makes sense that extinct ground sloths were doing something similar, even 'at much larger body sizes.' Mariana Di Giacomo, a natural history conservator at the Yale Peabody Museum who was not involved in the research, described its models as fun and necessary. But she wishes the team had sampled more than five teeth, and teeth from more varied regions. 'I think they could have been able to say these things with a lot more authority if there had been more data,' Dr. Di Giacomo explained, particularly if they had sampled more fossils, for example, from colder and more southern regions in Argentina or Chile. Greg McDonald, a paleontologist formerly with the federal Bureau of Land Management who was also not involved in the research, said the results of this paper were achieved by synthesizing lots of information from various sources 'to see how well it fit together.' 'The isotope data is really a solid foundation,' he said. Obtaining the same results from disparate sources in the models indicates that this is 'probably a valid underlying explanation' about the amount of sloth fur.
