July 21, 1998 Scientists have extracted and amplified DNA from 19,000-year-old sloth dung from Gypsum Cave in Utah, 18 miles east of Las Vegas, Nev. The DNA comes from plants the animal ate and from cells that lined its digestive tract.
The researchers are the first to successfully use what's called the PCR technique to analyze DNA in coprolites, or ancient feces. PCR, or polymerase chain reaction, is a method used to make numerous copies of a specific segment of DNA quickly and accurately. Their new twist on PCR includes chemical pretreatment that removes sugars and unlocks DNA for extraction.
Their modern biotechnological feat could be a boon to those embroiled in the controversy over why great Pleistocene beasts in North America suddenly became extinct at around 11,000 years ago, when humans spread over the continent. Their modified PCR technique will be of special interest to those who suggest a new line of argument in the controversy. The new argument is that prehistoric humans possibly carried disease that contributed to the demise of the large mammals, or "megafauna." Experts say the idea might most feasibly be tested at oceanic islands where populations of large mammals quickly died off.
"What I think this means we can do...is see how much genetic change there is through time in an animal that became extinct and determine if that's why it became extinct," said Paul S. Martin of the Desert Laboratory at The University of Arizona in Tucson and professor emeritus of geosciences at the UA.
Martin is on an international science team reporting the research in the July 17 issue of Science in the article, "Molecular Coproscopy: Dung and Diet of the Extinct Ground Sloth 'Nothrotheriops shastensis.'" Authors of the paper are Hendrick N. Poinar and Michael Hofreiter of the Zoological Institute and Max Planck Institute for Evolutionary Anthropology at the University of Munich, (Martin), W. Geoffrey Spaulding of Dames & Moore in Las Vegas, Nev., Artur Stankiewicz and James F. Carter of the University of Bristol, England, and Goran Possnert and Svanta Paabo of the Angstrom Laboratory, Division of Ion Physics, Uppsala, Sweden.
The researchers have radiocarbon dates on Shasta ground sloth dung from arid caves in the American Southwest that range from 30,000 years ago to 11,000 years ago. The sloths were herbivores that weighed about 400 pounds, about the size of black bears. The living animal they probably most closely resemble is the giant anteater.
"It would really be wonderful to know if there's any way measure genetic change through time, if there was a genetic bottleneck or 'squeeze shoot'" that made sloths especially vulnerable to changing climate or other stresses, or if they were in good shape genetically when they vanished, Martin said.
Martin is a pioneering proponent of the theory that prehistoric human predators swiftly exterminated giant mammals, mostly large herbivores, that roamed what essentially was a prehistoric North American big game park until the end of the last Ice Age. The casualty list of flagship species that disappeared in what he terms a 'blitzkrieg' includes mammoths and gomphotheres, mastodon, horses, camels, ground sloths, giant peccaries, brush and musk oxen, several bison species, four-horned antelope, giant beaver, tapir, glyptodonts and giant armadillo. Among the carnivores and omnivores that simultaneously succumbed were a giant bear, the dire wolf, two types of saber-tooth 'cats,' a lion akin to the African lion and a cheetah.
Growing numbers of scientists agree that the timing of human operations around the world is a factor to be reckoned with in the history of mass extinction of megafauna, Martin noted. It's the proximate details of what happened that can provoke rigorous debate.
Scientists can now analyze plant DNA to discover if the Shasta ground sloth changed its eating habits through time. In the article published today in Science, the authors report one surprise: DNA from the Gypsum Cave dung shows that 43 percent of the plant mass consumed was caper and mustard plants. The authors note that these plants have not been found by traditional macroscopic analysis, done by careful dissection and analysis of coprolite contents under the microscope.
The mustard on which this sloth browsed might be a perennial shrubby mustard that grows five to eight feet tall and flowers in the spring, Martin said. The capers are probably now known as Rocky Mountain bee plant, which grows wild by the side of the road in the Arizona-New Mexico-Utah-Colorado four corners area. These and other plants important in animal diet apparently don't preserve well after they are digested, he added.
Given the new ability to extract plant DNA from coprolites, scientists also will be able to discover more about extinct animals that don't fall in the category of common "bread-and-butter fossils," Martin said. One such extinct creature is the brush ox, an animal smaller than the musk ox. It ranged in rough country high in the Rocky Mountains of the western United States.
Scientists have found bones of the brush ox, but have never been able to identify its dung, the key to its diet. Jim Mead of the Northern Arizona University geology department at Flagstaff may have collected such dung, unidentified pellets that are larger than pellets from Harrington's Extinct Mountain Goat. The new technique might tell him if his samples are from brush ox or the more common elk.
In addition, given the new ability to extract animal DNA from coprolites, scientists will be able to match the different extinct animals with their fossil dung.
The breakthrough in DNA analysis of coprolites also may enable researchers to determine what parasite loads the animals carried, or if they caught anything equivalent to Ebola virus from humans when people came on the scene, Martin said. The idea that humans spread viruses to far bigger mammals is advanced by Ross McPhee, curator of mammals at the American Museum of Natural History. McPhee this week is headed for Wrangel Island in search of more evidence on this story, Martin said.
Russian scientists in 1993 discovered that dwarf woolly mammoths roamed Wrangel Island in the Arctic Ocean as recently as 4,000 years ago. The woolly mammoth had disappeared completely 6,000 years earlier in Europe, North America and continental Siberia. A leading British paleontologist hailed the Wrangel Island discovery as "one of the most extraordinary fossil finds of recent times," a revelation as striking as the 1938 discovery of the living coelacanth, a deep sea fish supposedly extinct for 60 million years.
Remains of the dwarf woolly mammoths from Wrangel Island were radiocarbon dated in Tucson at the UA-National Science Foundation Accelerator Mass Spectrometer facility and reported in the UA-based journal, Radiocarbon, in February 1996. Martin and Anthony J. Stuart of Norfolk Museums, Norwich, England, noted in their article published in the same journal that the Wrangel Island discovery flew in face of the idea that the Younger Dryas cold snap or other major climate upset of 11,000 to 10,000 years ago forced megafaunal extinction. They further argued that grasses and other plants similar to those on which Wrangel Island mammoths grazed must have survived in refugia-size patches in western North America well into the Holocene, the present era that began 10,000 years ago.
"We are going to gain more knowledge about the life and life history of these animals," Martin said. "It is possible to know what these creatures are by their waste, by what they were eating, by what their genetic envelope looks like and maybe what some of their parasites were."
The last nationally famous celebrity who really paid much attention to extinct North American big game was Thomas Jefferson, he added. "Jefferson entertained the romantic view that proboscideans (elephants) might be found alive in the Wild West. The dream vaporized when Lewis and Clark and other explorers with instructions to keep a look out failed to find any."
Later discoveries of dinosaur bones in the American West fired public imagination and enthusiasm for extinct giant reptiles, but extinct giant mammals have yet to ride the same publicity wave.
"Until we really understand that this continent was populated by animals far more glorious than bison, elk and deer, we sell this place short when we sing 'Home on the Range'," Martin said.
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