Posted on 08/11/2005 11:02:22 AM PDT by ZULU
Humans are likely responsible for the extinction of Ice Age megafauna—large mammals like giant sloths, short-faced bears, mammoths, and saber-toothed cats—that occurred in the Americas around 11,000 years ago, a new study says.
Scientists have long debated whether giant pre-historic mammals disappeared because of climate change or because humans hunted them to extinction.
The mass extinctions coincided with both the end of the last Ice Age and the arrival of humans in the Americas around 11,000 years ago. This timing has made it difficult for scientists to isolate the cause of the species' disappearance.
But a study comparing the extinction of giant ground sloths in North and South America with the disappearance of their smaller relatives in West Indian islands has helped clear up the picture, scientists say.
The researchers say archaeological and fossil evidence strongly suggests that ancient hunters pushed the animals to extinction.
Giant ground sloths "cruised through" at least 22 major climate cycles as the continental ice sheets in North America advanced and retreated over the last two million years, said David Steadman, a paleobiologist at the University of Florida.
Steadman is a co-author of the new study published in the Proceedings of the National Academy of Sciences.
"The only thing that's different [at the end of the Ice Age] is the arrival of people," he said.
Giant Sloth: A Case Study
Until about 11,000 years ago, at least 19 different sloth species lived in North and South America in a variety of ecosystems. Only a few small, tree-dwelling sloth species survive today.
Steadman and his colleagues argue that if ecosystem shifts resulting from climate change caused the sloths' demise, then all extinctions—on both islands and the mainland—should have taken place at the same time, as the last Ice Age ended between 15,000 to 9,000 years ago.
Radiocarbon dates of bones, dung, and other tissue of extinct sloths place their last appearance in North America at around 11,000 years ago and at about 10,500 years ago in South America, Steadman says.
But on the islands of Cuba and Hispaniola—shared today by modern-day Haiti and the Dominican Republic—sloths survived until about 4,400 years ago.
Their subsequent extinction coincided exactly with the arrival of the first humans on the islands, Steadman says.
"What [this study] shows us is that there's this great big suggestive pattern that we find: Wherever human beings first appear all around the world, these large mammals pretty quickly become extinct," said Gary Haynes, an archaeologist at the University of Nevada at Reno, who was not involved in the study.
"[Some] people will say that you have to [establish the cause of extinction] species by species, and I think they're probably right," Haynes added. "But the study does create a good model that might make us think that if it worked for one big animal it's probably what we'll find for other big animals."
Overkill Vs. Climate Change
Steadman and his colleagues argue that megafauna species on the American continents, having evolved in an environment without humans, may have been particularly vulnerable to the sudden appearance of big game hunters.
The 5,000-pound (2,300-kilogram) giant ground sloth is a case in point. In addition to having no fear of humans, it was the size of a modern-day elephant, it couldn't hide, and as it name implies, it moved very slowly.
"Walking up to a ground sloth and trying to spear it to death probably wasn't one of the most macho things they [early hunters] did," Steadman said. "Any hunter could outrun one."
But other scientists maintain that climate change was the driving force in Ice Age extinctions. They argue that the retreat of ice sheets from North America caused a major change in habitat that the giant mammals couldn't adapt to.
At the peak of the Ice Age around 20,000 years ago, the ice covered much of North America.
As the sheets melted between 18,000 and 8,000 years ago, warmer temperatures and shifting rainfall patterns forced plants and animals to move out of old habitats and into new ones.
Proponents of the climate-change theory add that there's little evidence that humans hunted anything other than mammoths. Yet species like wild horses, camels, and saber-toothed cats all went extinct at about the same time.
"There are no archaeological sites for species other than mammoths, and perhaps mastodons, where you find a spear sticking out of an animal, and everyone agrees that there is evidence of human hunting," Nevada's Haynes said.
"So the lack of kill sites doesn't bother me," he added. "There's a real lack of a 'smoking gun' implicating either climate change or human hunting, but that's true for every theory."
Climate change may have been a factor in pushing the animals to extinction, Steadman says, but it took humans to push them over the edge.
"Animals like the ground sloth, which had a poor ability to regulate body temperature, should have thrived in a warmer climate," he said.
If humans did kill them off they had good reason too and if the idiots that abound today can't see that they also would have been either throwing spears or being eaten then they are even dumber than they act!
I doubt that humans had much to do with killing off the big predators, however, as the american indians had a hard time with grizzlies let alone the huge meat gulping critters of the ice age.
The fact is, after the ice the water of the plains eventurally went away, as rain fall wasn't that great, the prey annimals died and then the big predators died from lack of food. This is known to many people but apparently facts don't stand in the way of a good story blaming humans for everything. Pretty soon we will have somehow made the dinos die off.
"So, not just any "humans", but Native Americans"
I'll second this one.
Chalk this one up to the "No Duh" category of anthropology.
Humans have a major impact on their environments, and always have.
Who, us????
This is all Bushfault!
Amen. Reparations! Reparations!
Amazing what they accept as good 'science'. They make pronouncements on theories they pull out of their @sses and call it good science, but let someone suggest that there could be a higher power involved in creating the universe and they insist that is 'not scientific' and thus not worth teaching against their other holy theory of 'evolution'. I guess 'good science' is whatever they pronounce it to be.
Now I can't find buffalo jerky anywhere. Accordingly, reparations are in order.
Would it also explain why their favorite position was doggy style?
I must remind myself to not visualize Helen Thomas of any age so soon after ingesting food.
LOL!!!
Danged SUV's!
A frozen mammoth dug up from the Siberian tundra was unveiled in central Japan in a preview of the six-month World Exposition that is expected to draw millions of tourists.
The beast, believed to have lived 18,000 years ago and preserved in a giant refrigerator, is a key exhibit of the Expo, which will open to the public one week later and will largely feature more modern wonders such as robots. Full-bodied mammoths have been found in the ground in the past, but the exhibit at the World Expo is billed as the most successful attempt yet to excavate and display almost the full animal.
The extinct mammoth on display has a nearly intact soil-coloured head covered with muscle tissue and some woolly hair, along with tusks and a front leg. “This is not a mere pavilion, but a laboratory as we will do scientific research here,” Toshio Nakamura, secretary-general of the exposition, told the opening ceremony of the “Mammoth Lab.” “This mammoth has been really well preserved,” Nakamura said, adding that the head has already been monitored through computerised technology. “We would like as many people as possible to take a look at this mammoth and think about the past and the future of human beings.” A group of Russian and Japanese scientists are also hoping to clone mammoths from remains of the animal by using elephant eggs.
Visitors can view the mammoth, which was excavated in 2002, from windows at the lab, where the temperature and humidity are controlled by computers. afp
Hold on there. The Indians caused mass exstinction? Now explain the NCAA silly ruling on Indian names, hmmmm?
Basically, there's no real evidence to support their theory, it's merely a theory.
The evidence doesn't really conform to their theory, but it doesn't disprove it either.
It's mainly people starting with a conclusion, and looking for evidence to support it, and trying to ignore or minimize evidence that contradicts it.
In the end there's nothing useful to learn from their theory, other than that they have an agenda.
Mmmmmmmm. BBQ Sloth! Mmmmmmmmmmmmmmmm
ROFL.
These folks need to be institutionalized, IMHO.
LOL!
Yep. And there is an unbelievable amount of theories that people can take their pick from. I choose to pick truthful intelligent design which is not a theory.
Guilty!
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