Genome of American Clovis skeleton mapped: Ancestor of most present-day Native American populations

They lived in America about 13,000 years ago where they hunted mammoth, mastodons and giant bison with big spears. The Clovis people were not the first humans in America, but they represent the first humans with a wide expansion on the North American continent -- until the culture mysteriously disappeared only a few hundred years after its origin. Who the Clovis people were and which present day humans they are related to has been discussed intensely and the issue has a key role in the discussion about how the Americas were peopled. Today there exists only one human skeleton found in association with Clovis tools and at the same time it is among the oldest human skeletons in the Americas. It is a small boy between 1 and 1.5 years of age -- found in a 12,600 old burial site, called the Anzick Site, in Wilsall, Montana, USA. Now an international team headed by Danish researcher Eske Willerslev has mapped his genome thereby reviving the scientific debate about the colonization of the Americas.

Roughly estimated some 80 % of all present-day Native American populations on the two American continents are direct descendants of the Clovis boy's family. The remaining 20 % are more closely related with the Clovis family than any other people on Earth, says Lundbeck Professor Eske Willerslev from the Centre for GeoGenetics at the Natural History Museum of Denmark, University of Copenhagen. This surprising result has now been published in the scientific journal Nature. The discovery is so decisive that Nature has chosen to send the article to the press at a later time than usual as they fear the media embargo may be broken. A comprehensive international telephone press conference has been arranged and will be held in the Crow tribe's reservation in Montana -- close to where the boy was found. Behind the results are a group of international researchers led by Professor Eske Willerslev from Centre of Excellence in GeoGenetics, Natural History Museum at University of Copenhagen, Denmark.

The missing link

It is almost like finding the 'missing link' to the common ancestor of the Native Americans. The Clovis boy's family is the direct ancestor to roughly estimated 80 % of all present day Native Americans. Although the Clovis culture disappeared its people are living today. Put simply it is a sensation that we succeeded in finding an approximately 12,600 year old boy whose closest relatives can be regarded as the direct ancestor to so many people, Eske Willerslev says and adds: This also means that Clovis did not descend from Europeans, Asians or Melanesians, a theory that a number of scientists have advocated. They were Native Americans -- and the Native American ancestors were the first people in America. This is now a fact.

Shane Doyle, a historian from the Apsaalooke (Crow) tribe, who helped the team with consultations to the Montana tribes agrees: This discovery by Eske and his team proves something that tribal people have never doubted -- we've been here since time immemorial and all the ancient artifacts located within our homelands are remnants from our direct ancestors. But the discovery is only part of the importance of this study. The other part being Eske and his team's respectful commitment to interacting face to face with tribal communities and listening to Native American leaders, which has lead directly to the reburial of this little boy."

Also Sarah Anzick, a molecular biologist in the study and the steward of the remains that were found on private land is excited: After 46 years since the discovery on my family land, we are finally hearing this child's story through his genetic legacy. I find it remarkable that the descendants of the Clovis culture, which seemed to have vanished 12,600 years ago, are still alive and thriving today. Interestingly, the teams find that Native American ancestors coming in from Siberia split into two groups. One group is ancestors to the Native Americans presently living in Canada and the other one -- which is represented by the Clovis boy -- is the ancestor to virtually all Native Americans in South America and Mexico. The US is still a white spot on the map when it comes to genome-wide data from Native Americans. The team members hope to be able to accessing such data in the future to understand the full picture.

The study validates the concept of continuity in the history of Native Americans, and suggests that modern Native Americans are direct descendants of the first people occupying this land, says Rasmus Nielsen, a co-author on the study and a Professor at UC Berkeley, who developed the method used for determining that many modern native Americans are direct descendants of the Clovis boy's family.

An Asian homeland for the First Americans

The first humans came from Siberia via the so-called Beringia Land Bridge, which during the latest ice age connected Siberia with North America and did not bring the Clovis culture with them. The Clovis culture arose after they arrived in America and the boy from Anzick was more a descendant of the first immigrants.

Michael Waters, the key archaeologist connected to the study and who has worked on many Clovis and older sites in North America elaborates: The genetic findings mesh well with the archaeological evidence to confirm the Asian homeland of the First Americans, more clearly define their genetic heritage, and is consistent with occupation of the Americas a few thousand years before Clovis. The findings do not support a western European origin of the First Americans as suggested by the Solutrean hypothesis. The genetic information provided by the Anzick boy is part of the larger story of modern human dispersal across Earth and is shedding new light on the last continent to be explored and settled by our species.

Then who were the first immigrants? We don't know. Yet. Maybe a Native American, maybe an ancestor related to the Mal'ta boy from Siberia and another one who was East Asian. We don't know. But our results eliminate all other theories about the origins of the first people in America. The first people in America were the direct ancestors of Native Americans, says Professor Willerslev and continues:

We can see that the Clovis boy shares about 1/3 of his genes with the 24,000 year old child from Mal'ta at the Siberian Lake Baikal who we have analyzed previously. The same goes for all present day Native Americans. Therefore the encounter between East Asians and the Mal'ta group happened before Clovis. The human remains from the Anzick site will be reburied sometime this year in cooperation with Native American tribes in Montana. Eske Willerslev has in connection with the genome work on the Clovis boy visited several of Montana's Native American tribes with Crow historian Shane Doyle to discuss the findings.
________________
References:

Science Daily. 2014. “Genome of American Clovis skeleton mapped: Ancestor of most present-day Native American populations”. Science Daily. Posted: February 12, 2014. Available online: http://www.sciencedaily.com/releases/2014/02/140212132807.htm

Did a Comet Really Chill and Kill Clovis Culture?

A comet crashing into the Earth some 13,000 years ago was thought to have spelled doom to a group of early North American people, and possibly the extinction of ice age beasts in the region.

But the space rock was wrongly accused, according to a group of 16 scientists in fields ranging from archaeology to crystallography to physics, who have offered counterevidence to the existence of such a collision.

"Despite more than four years of trying by many qualified researchers, no unambiguous evidence has been found [of such an event]," Mark Boslough, a physicist at Sandia National Laboratories in New Mexico, told LiveScience.

"That lack of evidence is therefore evidence of absence."

Changing times

Almost 13,000 years ago, a prehistoric Paleo-Indian group known as the Clovis culture suffered its demise at the same time the region underwent significant climate cooling known as the Younger Dryas. Animals such as ground sloths, camels and mammoths were wiped out in North America around the same period.

In 2007, a team of scientists led by Richard Firestone of the Lawrence Berkeley National Laboratory in California suggested these changes were the result of a collision or explosion of an enormous comet or asteroid, pointing to a carbon-rich black layer at a number of sites across North America. The theory has remained controversial, with no sign of a crater that would have resulted from such an impact.

"If a four-kilometer [2.5-mile] comet had broken up over North America only 12.9 thousand years ago, it is certain that it would have left an unambiguous impact crater or craters, as well as unambiguous shocked materials," Boslough said.

Boslough, who has spent decades studying the effects of comet and asteroid collisions, was part of a team that predicted the visibility of plumes from the impact of the 1994 Shoemaker-Levy 9 comet with Jupiter.

"Comet impacts may be low enough in density not to leave craters," Firestone told LiveScience by email.

He also points to independent research by William Napier at the University of Cardiff in the United Kingdom that indicates such explosions could have come from a debris trail created by Comet Encke, which also would not have left a crater.

A large rock plunging into the Earth's atmosphere may detonate in the air without coming into contact with the ground. Such an explosion occurred in Siberia in the early 20th century; the explosive energy of the so-called Tunguska event was more than 1,000 times more powerful than the atomic bomb dropped on Hiroshima.

"No crater was formed at Tunguska, or the recent Russian impact," Firestone said.

But Boslough said this math doesn't add up. The object responsible for the Tunguska event was very small, about 130 to 160 feet (40 to 50 meters) wide, while the recent explosion over Russia was smaller, about 56 feet (17 meters). The proposed North American space rock linked with the Clovis demise is estimated to have been closer to 2.5 miles (4 kilometers) across.

"The physics doesn't support the idea of something that big exploding in the air," he said, noting that the original research team doesn't provide any explanation or models for how such a breakup might occur.

If such a large object crashed into the Earth, the resulting crater would be too large to miss, particularly when it was only a few thousand years old, Boslough said. He pointed to Meteor Crater in Arizona, which is three times as old and formed by an object "a million times smaller in terms of explosive energy."

"Meteor Crater is an unambiguous impact crater with unambiguous shocked minerals," Boslough said. If a 2.5-mile comet had broken into pieces, it could have made a million Meteor Craters, he added.

Firestone argued that water or ice could have absorbed the impact, possibly leaving behind no crater.

Boslough disagreed. Even if the comet had plunged into the ice sheet covering much of North America, the crater formed beneath it would still be sizable. "We wouldn't be able to miss that right now — it would be obvious," Boslough said.

The arguments and evidence against the impact were published in the December 2012 American Geophysical Union monograph.

Earliest Americans Arrived Even Earlier

"Extraordinary claims require extraordinary evidence"

Powerful impacts are Boslough's field, but the other 15 scientists working on the paper offered up other sources of counterevidence for the existence of a collision.

"We all independently came to the conclusion that the evidence doesn't support a Younger Dryas impact," Boslough said.

"We all came to this based on our own very narrow piece of the puzzle."

For instance, the initial team studying the event announced the discovery of a carbon-rich black layer, colloquially known as a "black mat," at a number of sites in North America. Containing charcoal, soot and nanodiamonds, such material could be formed by a violent collision.

But this isn't the only possible source.

"The things they call impact markers are not necessarily indicators of high-pressure shocks," Boslough said. "There are other processes that potentially could have formed them."

Speaking of the black mat found in central Mexico, Firestone said, "Boslough is correct that there are other black mats, but these are dated to 12,900 years ago at the time of impact." He points to independent research published this fall that located hundreds to thousands of samples.

However, radiocarbon dating of one of the sites in Gainey, Mich., suggested its samples were contaminated.

Melted rock formations and microscopic diamonds found in a lake in Central Mexico last year were also suggested as evidence for the collision, but Boslough's team disagrees with the age of the sediment layer in the region.

Boslough said the standard for indicating a strong shock occurred is pretty high in the impact community, and the findings by the original team don't meet them. Nor do they offer up any physical models that propose how an impact or airburst would have occurred — and the ones Boslough has run just don't pan out.

"It's really a stretch to claim that there was this large impact event with no crater and no unambiguous shock material, because large impacts are such rare events," Boslough said.

"When somebody is making a claim that something extraordinary happened, something out of the ordinary and with a very low probability, and they have ambiguous evidence, then the default is that it didn't happen," he continued.

"Extraordinary claims require extraordinary evidence."

Firestone stands firm.



"All the evidence has now been confirmed by others," he said.

"Boslough has no data supporting his arguments, and ignores the counter arguments of Bill Napier."
__________________________
References:

Livescience. 2013. “Did a Comet Really Chill and Kill Clovis Culture?”. Discovery News. Posted: March 1, 2013. Available online: http://news.discovery.com/human/life/did-a-comet-really-chill-and-kill-clovis-culture-130301.htm

Challengers to Clovis-age impact theory missed key protocols, new study finds

University of Oregon psychologist was on the team, which confirmed the presence of magnetic particles

An interdisciplinary team of scientists from seven U.S. institutions says a disregard of three critical protocols, including sorting samples by size, explains why a group challenging the theory of a North American meteor-impact event some 12,900 years ago failed to find iron- and silica-rich magnetic particles in the sites they investigated.

Not separating samples of the materials into like-sized groupings made for an avoidable layer of difficulty, said co-author Edward K. Vogel, a professor of psychology at the University of Oregon.

The new independent analysis -- published this week in the online Early Edition of the Proceedings of the National Academy of Sciences -- did, in fact, isolate large quantities of the "microspherules" at the involved sites where the challengers previously reported none. Lead author Malcolm A. LeCompte, an astrophysicist at Elizabeth City State University in North Carolina, said the findings support the climate-altering cosmic impact, but his team stopped short of declaring this as proof of the event.

The Clovis-age cosmic-impact theory was proposed in 2007 by a 26-member team led by Richard B. Firestone. That team included University of Oregon archaeologists Douglas J. Kennett and Jon M. Erlandson. While other groups have found corroborating evidence of a potential cosmic event, other groups reported difficulties doing so. One group, led by Todd A Surovell of the University of Wyoming, did not find any microspherule evidence at five of seven sites they tested, including two previously studied locations where Firestone reported large numbers of microspherules.

"In investigating the two common sites and a third tested only by Surovell's team, we found spherules in equal or greater abundance than did the Firestone team, and the reported enhancement was in strata dated to about 13,000 years before the present," LeCompte said. "What we've done is provide evidence that is consistent with an impact, but we don't think it proves the impact. We think there's a mystery contained in the Younger Dryas strata, and that we've provided some validation to the original research by Firestone's group."

The particles in question, the team concluded, are terrestrial as was claimed by the Firestone group, and not of meteoric origin as claimed by other challengers including Surovell's group, and are similar to metamorphic material in Earth's crust. That determination was made using electron microscopy and spectroscopy.

"These spherules have evidence of very high-temperature melting and very rapid cooling, which is characteristic of debris ejected from an impact," LeCompte said. Speherules would have melted at temperatures approaching 2,000 degrees Celsius (more than 3,000 degrees Fahrenheit), he added. Cosmic materials, including the some microspherules, regularly fall to earth from space due to meteorite ablation, but the spherules found in soils dating to 13,000 years ago are much different, he added. Other researchers had suggested that these spherules were deposited by a cosmic rain or resulted through slow, terrestrial processes occurring under ambient conditions.

LeCompte and some key collaborators wondered why Surovell didn't find any spherules, and that led them to Vogel. Many of the spherules investigated were tiny, ranging in size from 20 to 50 micrometers (microns); about the diameter of a human hair.

"The inherent difficulty in finding these small, relatively rare magnetic microspherules suggested there may be inherent limitations in human faculties that needed to be addressed, and that's how and why we sought out UO Professor Ed Vogel. His research into human cognitive capabilities proved so important in understanding both why the search was so difficult and why size-sorting was effective and important in making it easier," LeCompte said.

Vogel specializes in the ability of people to find specific items amid multiple distractions.

"A visual search is a very error-prone process," Vogel said. "This was a case of looking at millions of particles from which you are hoping to find something that might be present much less than 0.1 percent of the time." Size-sorting, he said, is vital because it is easier to find a target item with a characteristic shape and color when all of the many more-distracting objects are very similar. "It is a slow, tedious process to examine such quantities of materials with the human eyes when object sizes are extremely dissimilar."

"Science is only as good as the humans who conduct it, and this study shows how the minds of researchers can operate in some surprising ways," said Kimberly Andrews Espy, UO vice president for research and innovation, and dean of the graduate school. "Dr. Vogel's excellent work, which illustrates the importance of understanding how the human mind processes information and the consequences it can have beyond making everyday computations, reflects the University of Oregon's strengths in interdisciplinary research."

LeCompte described Surovell's study "as possibly the most damning of the reports that had challenged the original theory."

"Todd had worked very hard and couldn't find the spherules, but I think he made some fatal errors that need to be pointed out," LeCompte said. "It is instructive in that we initially made the same mistake and came to the same erroneous conclusion, but then we corrected our mistake. I would say this is a case of a missed opportunity due to their deviations from the protocol."

Two other critical protocol deviations not followed by the challengers involved the amounts of material examined and the use of microscopy techniques specified in Firestone's original research. Another two minor aspects of the protocol also were not repeated, reported LeCompte's team, which, in addition to Vogel, included an archaeologist, two materials scientists, a botanist, a periglacial geographer and an aerospace engineer.

LeCompte's team -- using the protocols of Firestone's group and electron microscopy -- additionally studied a quarry site in Topper, S.C., where Clovis-age people had made stone tools. After removing chert debris associated with tool making in soil at the depth of the Clovis occupation, LeCompte said, researchers observed virtually no spherules below it, while in soil just above the chert fragments they found a spike in the number of telltale spherules.

Further above that level, he noted, the soil layers were essentially "a dead zone" somewhat analogous to the K-T boundary, or "tombstone layer," from an extinction event that occurred 65 million years ago. At Topper, the dead zone showed almost no trace of human habitation for perhaps as long as 1,000 years duration.

"This suggests that something very dramatic happened," LeCompte said.

"The effects of such an impact would have been catastrophic on a global scale," said co-author Barrett Rock, a botanist at the University of New Hampshire. "On the order of 36 ice-age species became extinct, and the Clovis human culture eventually lost. All of this in response to dramatic changes in the vegetation at the base of the faunal food chain."
_________________________
References:

EurekAlert. 2012. “Challengers to Clovis-age impact theory missed key protocols, new study finds”. EurekAlert. Posted: September 17, 2012. Available online: http://www.eurekalert.org/pub_releases/2012-09/uoo-ctc091712.php

California islands give up evidence of early seafaring

Oregon, Smithsonian-led team uncovers numerous artifacts at late Pleistocene sites on the Channel Islands

Evidence for a diversified sea-based economy among North American inhabitants dating from 12,200 to 11,400 years ago is emerging from three sites on California's Channel Islands.

Reporting in the March 4 issue of Science, a 15-member team led by University of Oregon and Smithsonian Institution scholars describes the discovery of scores of stemmed projectile points and crescents dating to that time period. The artifacts are associated with the remains of shellfish, seals, geese, cormorants and fish.

Funded primarily by grants from the National Science Foundation, the team also found thousands of artifacts made from chert, a flint-like rock used to make projectile points and other stone tools.

Some of the intact projectiles are so delicate that their only practical use would have been for hunting on the water, said Jon Erlandson, professor of anthropology and director of the Museum of Natural and Cultural History at the University of Oregon. He has been conducting research on the islands for more than 30 years.

"This is among the earliest evidence of seafaring and maritime adaptations in the Americas, and another extension of the diversity of Paleoindian economies," Erlandson said. "The points we are finding are extraordinary, the workmanship amazing. They are ultra thin, serrated and have incredible barbs on them. It's a very sophisticated chipped-stone technology." He also noted that the stemmed points are much different than the iconic fluted points left throughout North America by Clovis and Folsom peoples who hunted big game on land.

The artifacts were recovered from three sites that date to the end of the Pleistocene epoch on Santa Rosa and San Miguel islands, which in those days were connected as one island off the California coast. Sea levels then were 50 to 60 meters (about 160-200 feet) below modern levels. Rising seas have since flooded the shorelines and coastal lowlands where early populations would have spent most of their time.

Erlandson and his colleagues have focused their search on upland features such as springs, caves, and chert outcrops that would have drawn early maritime peoples into the interior. Rising seas also may have submerged evidence of even older human habitation of the islands.

The newly released study focuses on the artifacts and animal remains recovered, but the implications for understanding the peopling of the Americas may run deeper.

The technologies involved suggest that these early islanders were not members of the land-based Clovis culture, Erlandson said. No fluted points have been found on the islands. Instead, the points and crescents are similar to artifacts found in the Great Basin and Columbia Plateau areas, including pre-Clovis levels at Paisley Caves in eastern Oregon that are being studied by another UO archaeologist, Dennis Jenkins.

Last year, Charlotte Beck and Tom Jones, archaeologists at New York's Hamilton College who study sites in the Great Basin, argued that stemmed and Clovis point technologies were separate, with the stemmed points originating from Pacific Coast populations and not, as conventional wisdom holds, from the Clovis people who moved westward from the Great Plains. Erlandson and colleagues noted that the Channel Island points are also broadly similar to stemmed points found early sites around the Pacific Rim, from Japan to South America.

Six years ago, Erlandson proposed that Late Pleistocene sea-going people may have followed a "kelp highway" stretching from Japan to Kamchatka, along the south coast of Beringia and Alaska, then southward down the Northwest Coast to California. Kelp forests are rich in seals, sea otters, fish, seabirds, and shellfish such as abalones and sea urchins.

"The technology and seafaring implications of what we've found on the Channel Islands are magnificent," said study co-author Torben C. Rick, curator of North American Archaeology at the Smithsonian Institution. "Some of the paleo-ecological and subsistence implications are also very important. These sites indicate very early and distinct coastal and island subsistence strategies, including harvest of red abalones and other shellfish and fish dependent on kelp forests, but also the exploitation of larger pinnipeds and waterfowl, including an extinct flightless duck.

"This combination of unique hunting technologies found with marine mammal and migratory waterfowl bones provides a very different picture of the Channel Islands than what we know today, and indicates very early and diverse maritime life ways and foraging practices," Rick said. "What is so interesting is that not only do the data we have document some of the earliest marine mammal and bird exploitation in North America, but they show that very early on New World coastal peoples were hunting such animals and birds with sophisticated technologies that appear to have been refined for life in coastal and aquatic habitats."

The stemmed points found on the Channel Islands range from tiny to large, probably indicating that they were used for hunting a variety of animals.

"We think the crescents were used as transverse projectile points, probably for hunting birds. Their broad stone tips, when attached to a dart shaft provided a stone age shotgun-approach to hunting birds in flight," Erlandson said. "These are very distinctive artifacts, hundreds of which have been found on the Channel Islands over the years, but rarely in a stratified context, he added. Often considered to be between 8,000 and 10,000 years old in California, "we now have crescents between 11,000 and 12,000 years old, some of them associated with thousands of bird bones."

The next challenge, Erlandson and Rick noted, is to find even older archaeological sites on the Channel Islands, which might prove that a coastal migration contributed to the initial peopling of the Americas, now thought to have occurred two to three millennia earlier.
_____________
References:

EurekAlert. 2011. "California islands give up evidence of early seafaring". EurekAlert. Posted: March 3, 2011. Available online: http://www.eurekalert.org/pub_releases/2011-03/uoo-cig022411.php

No evidence for Clovis comet catastrophe, archaeologists say

New research challenges the controversial theory that an ancient comet impact devastated the Clovis people, one of the earliest known cultures to inhabit North America.

Writing in the October issue of Current Anthropology, archaeologists Vance Holliday (University of Arizona) and David Meltzer (Southern Methodist University) argue that there is nothing in the archaeological record to suggest an abrupt collapse of Clovis populations. "Whether or not the proposed extraterrestrial impact occurred is a matter for empirical testing in the geological record," the researchers write. "Insofar as concerns the archaeological record, an extraterrestrial impact is an unnecessary solution for an archaeological problem that does not exist."

The comet theory first emerged in 2007 when a team of scientists announced evidence of a large extraterrestrial impact that occurred about 12,900 years ago. The impact was said to have caused a sudden cooling of the North American climate, killing off mammoths and other megafauna. It could also explain the apparent disappearance of the Clovis people, whose characteristic spear points vanish from the archaeological record shortly after the supposed impact.

As evidence for the rapid Clovis depopulation, comet theorists point out that very few Clovis archaeological sites show evidence of human occupation after the Clovis. At the few sites that do, Clovis and post-Clovis artifacts are separated by archaeologically sterile layers of sediments, indicating a time gap between the civilizations. In fact, comet theorists argue, there seems to be a dead zone in the human archaeological record in North America beginning with the comet impact and lasting about 500 years.

But Holliday and Meltzer dispute those claims. They argue that a lack of later human occupation at Clovis sites is no reason to assume a population collapse. "Single-occupation Paleoindian sites—Clovis or post-Clovis—are the norm," Holliday said. That's because many Paleoindian sites are hunting kill sites, and it would be highly unlikely for kills to be made repeatedly in the exact same spot.

"So there is nothing surprising about a Clovis occupation with no other Paleoindian zone above it, and it is no reason to infer a disaster," Holliday said.

In addition, Holliday and Meltzer compiled radiocarbon dates of 44 archaeological sites from across the U.S. and found no evidence of a post-comet gap. "Chronological gaps appear in the sequence only if one ignores standard deviations (a statistically inappropriate procedure), and doing so creates gaps not just around [12,900 years ago] but also at many later points in time," they write.

Sterile layers separating occupation zones at some sites are easily explained by shifting settlement patterns and local geological processes, the researchers say. The separation should not be taken as evidence of an actual time gap between Clovis and post-Clovis cultures.

Holliday and Meltzer believe that the disappearance of Clovis spear points is more likely the result of a cultural choice rather than a population collapse. "There is no compelling data to indicate that North American Paleoindians had to cope with or were affected by a catastrophe, extraterrestrial or otherwise, in the terminal Pleistocene," they conclude.
_______________
References:

EurekAlert. 2010. "No evidence for Clovis comet catastrophe, archaeologists say". EurekAlert. Posted: September 29, 2010. Available online: http://www.eurekalert.org/pub_releases/2010-09/uocp-nef092910.php

Vance T. Holliday and David J. Meltzer, "The 12.9-ka ET Impact Hypothesis and North American Paleoindians." Current Anthropology 51:5 (October 2010).

Oldest American artefact unearthed

Archaeologists claim to have found the oldest known artefact in the Americas, a scraper-like tool in an Oregon cave that dates back 14,230 years.

The tool shows that people were living in North America well before the widespread Clovis culture of 12,900 to 12,400 years ago, says archaeologist Dennis Jenkins of the University of Oregon in Eugene.

Studies of sediment and radiocarbon dating showed the bone's age. Jenkins presented the finding late last month in a lecture at the University of Oregon.

His team found the tool in a rock shelter overlooking a lake in south-central Oregon, one of a series of caves near the town of Paisley.

Kevin Smith, the team member who uncovered the artefact, remembers the discovery. "We had bumped into a lot of extinct horse, bison and camel bone – then I heard and felt the familiar ring and feel when trowel hits bone," says Smith, now a master's student at California State University, Los Angeles. "I switched to a brush. Soon this huge bone emerged, then I saw the serrated edge. I stepped back and said: 'Hey everybody — we got something here.'"
Coprolite controversy

Whether the cave dwellers were Clovis people or belonged to an earlier culture is uncertain. None of the Clovis people's distinct fluted spear and arrow points have been found in the cave.

"They can't yet rule out the Paisley Cave people weren't Clovis," says Jon Erlandson, an archaeologist at the University of Oregon who wasn't involved in the research.

The only other American archaeological site older than Clovis is at Monte Verde in Chile, which is about 13,900 years old.

Last year, Jenkins and colleagues reported that Paisley Cave coprolites, or fossilized human excrement, dated to 14,000 to 14,270 years ago1. That report established the Paisley Caves as a key site for American archaeology.

Analysis of ancient DNA marked the coprolites as human. But in July, another group argued that the coprolites might be younger than the sediments that contained them2.

This team, led by Hendrik Poinar of McMaster University in Hamilton, Ontario, also questioned the 2008 report because no artefacts had been found in the crucial sediments. The Oregon team strongly disputed the criticisms3.
Laid to rest?

The dating of the bone tool, and the finding that the sediments encasing it range from 11,930 to 14,480 years old, might put these questions to rest. "You couldn't ask for better dated stratigraphy," Jenkins told the Oregon meeting.

"They have definitely made their argument even stronger," says Todd Surovell, an archaeologist at the University of Wyoming in Laramie who was not involved in the research.

ADVERTISEMENT
Submit your paper to Nature Chemistry

Other researchers questioned whether the cave's inhabitants would have been mainly vegetarian, as the coprolites suggested4. In his recent lecture Jenkins noted other evidence reflecting a diet short on meat but including edible plants such as the fernleaf biscuitroot Lomatium dissectum.

In late September, a group of archaeologists who study the peopling of the Americas met with federal officials and a representative of the local Klamath tribe to review the evidence at Paisley Caves. The specialists spent two days examining sediments, checking the tool, and assessing other plant and animal evidence.

"It was an impressive presentation," says David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas, who attended the meeting. "This is clearly an important site, but there are some tests that need to be done to seal the deal." One key, he says, is to better understand how the specimens got to the cave.
__________________
References:

Dalton, Rex. 2009. "Oldest American artefact unearthed". Nature. Posted: November 5, 2009. Available online: http://www.nature.com/news/2009/091105/full/news.2009.1058.html

1. Gilbert, W.T.P. et al. Science 320, 786-789 (2008).
2. Poinar, H. et al. Science 325, 148 (2009).
3. Rasmussen, M. et al. Science 325, 148 (2009).
4. Goldberg, P., Berna, F. & Macphail, R.I. Science 325, 5937, 148 (2009).