Photo in the News: First View of Mercury's "Other Face"

January 16, 2008—The first of many planned images from NASA's MESSENGER spacecraft is showing astronomers a side of Mercury no one's ever seen before.

Mercury is tough to view from Earth, since it's so close to the sun. And when the Mariner 10 probe flew past the innermost planet in 1974 and 1975, only one side of the body was facing sunlight.

That's because Mercury rotates three times during every two orbits, so the same side of the planet is lit up every other time it is nearest to the sun—including during all of Mariner's flybys.

Added up, these factors have meant that although Mercury sits only about 57 million miles (92 million kilometers) away from Earth, for more than 30 years scientists have had almost no details about its other face.

But on Monday MESSENGER, the first mission to Mercury since the 1970s, snapped the first image of the "missing" half of the rocky world.

Among many new sights, the picture features the full Caloris Basin, a huge impact basin more than 620 miles (1,000 kilometers) across that sits on the border between the known and previously unknown regions of the planet.

More unprecedented images of the tiny planet are expected as the MESSENGER craft completes three flybys of Mercury before settling into orbit in March 2011.

From that point on, writes astronomer Phil Plait on the Bad Astronomy blog, "we'll get as many images of this tiny, hot, battered, dense and neglected planet as we can handle."

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Ancient "Lost City" Discovered in Peru, Official Claims

Ruins recently discovered in southern Peru could be the ancient "lost city" of Paititi, according to claims that are drawing serious but cautious response from experts.

The presumptive lost city, described in written records as a stone settlement adorned with gold statues, has long been a grail for explorers—as well as a lure for local tourism businesses.

A commonly cited legend claims that Paititi was built by the Inca hero Inkarri, who founded the city of Cusco before retreating into the jungle after Spanish conquerors arrived.

On January 10 Peru's state news agency reported that "an archaeological fortress" had been discovered in the district of Kimbiri and that the district's mayor suggested it was the lost city.

Mayor Guillermo Torres described the ruins as a 430,000-square-foot (40,000-square-meter) fortification near an area known as Lobo Tahuantinsuyo.

Few other details about the site were offered, but initial reports described elaborately carved stone structures forming the base of a set of walls.

The state media report quotes Torres as saying the area will be "immediately declared" a cultural tourism site.

Officials from the Peruvian government's Cusco-based National Institute of Culture (INC) met with Torres on Tuesday, according to Francisco Solís, an INC official.

"It is far too early to make any definitive judgments," Solís told National Geographic News. "We are going to dispatch a team to investigate."

Officials expect more details to emerge in the coming days, he said.

Legend of Paititi

Paititi is believed to have been located somewhere east of the Andes Mountains in the rain forest of southeastern Peru, southwestern Brazil, or northern Bolivia.

In 1600 a missionary reported seeing a large "city of gold" in the region where Paititi is believed to have been built, according to archival records discovered by an Italian archaeologist in 2001.

However, the location of the newfound site falls counter to where historical records indicate Paititi should be, Solís said.

Officials were nonetheless intrigued by the possibilities, he added.

The first task will be to determine if the newfound ruins are the work of the Inca or pre-Inca ethnic groups, Solís said.

Gregory Deyermenjian, a U.S.-based psychologist and explorer who has led many expeditions to investigate the Paititi legend, said many people in the tourism-rich region of Cusco have embraced the legend as a business promotion.

But he said the claims could have merit, as there are still many important sites to be found.

"It is a bit off the beaten path but still within the Inca's reach," Deyermenjian said. "I'm very interested to know more."

Daniel Gade, professor emeritus in geography at the University of Vermont, cautioned about jumping to conclusions.

"Paititi is frequently the first thing people mention when something like this is found," Gade said, adding that there are many ruins in the jungle regions of the area.

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Did Columbus Bring Syphilis to Europe?

Famed explorer Christopher Columbus and his crew unleashed the scourge of syphilis on Europe, a new genetic study suggests, though some experts say the data is not conclusive.

The research adds more fuel to a controversial debate on the origins of the devastating sexually transmitted disease that can cause blindness, mental illness, and death.

Europe's first-known venereal syphilis epidemic occurred during the years immediately following Columbus's return, fueling a long-held theory that the explorer carried the disease to the continent.

Study lead author Kristin Harper and colleagues compared genetic data from 26 strains of the treponema bacteria family—those responsible for venereal syphilis as well as nonvenereal forms of the disease—and closely related ailments such as yaws, a tropical bacterial infection.

The results showed that modern-day syphilis strains resembled those found in South America.

This New World origin for syphilis strongly supports the Columbus theory, said Harper, an evolutionary biologist at Atlanta's Emory University.

"We hope to find genetic differences we can use to build a family tree of these bacteria," she added. "In doing that we hope to get an idea of where and when syphilis evolved."

Incomplete Tale

Bones on each side of the Atlantic have yielded some tantalizing but inconclusive clues suggesting where and when the disease existed before Columbus's voyages.

Numerous pre-Columbian Old World remains appear to show signs of syphilis, including pitted skulls and unnaturally fat lower leg bones, some researchers say.

But few examples survive, and those that appear to show syphilis may in fact be evidence of other related viruses.

"Diagnosis of specific [syphilis-causing] diseases can be problematic in skeletal remains from archaeological sites, because they are often fragmentary and poorly preserved," said Charlotte Roberts, a bioarchaeologist at Durham University in the United Kingdom.

"Without the complete skeleton—or in the case of treponemal disease diagnosis, the skull and long bones—a specific diagnosis cannot be made with ease."

While some argue that Old World bones "proving" the existence of pre-Columbian syphilis are suspect, Roberts claims the same can be said of New World remains suggesting an American origin.

Connie Mulligan, a molecular anthropologist at the University of Florida, disagrees with Harper's conclusions—saying that the existing genetic data does not begin to answer that question.

"Opportunistic timing and the fact that [the voyage and European syphilis outbreak] are so closely tied has provided this interesting historical question: Did he bring it back to the Old World, or was it already present in the Old World?" Mulligan asked.

"We just don't know."

She also notes that at least one theory suggests there is no genetic difference at all between syphilis and its relative ailments.

"Is it just the same disease that has different manifestations in different climates?" she asked.

"That's what I think Harper's data might be showing. ... To me that is very interesting, almost more interesting than the single geographic origin of venereal syphilis.

"In that case, asking where venereal syphilis evolved is the wrong question."

Harper's study was published recently in the journal PLoS Neglected Tropical Diseases.

Tandem Evolution

Geneticist Spencer Wells is a National Geographic Society Explorer-in-Residence and director of the society's Genographic Project. (The National Geographic Society owns National Geographic News.)

He said Harper's study "basically says we need to do a lot more work and look at a lot more of the genome, more DNA, and more strains of syphilis from around the world."

The syphilis mystery also spotlights how infectious diseases and humans have genetically evolved in tandem over time, he added.

Yaws, which many scientists believe descended from syphilis, has likely been with humans since their origins in Africa.

"We probably carried it around the world with us," Wells said. "Over hundreds of thousands or even millions of years, you slowly start to adjust to each other so that the organism still causes a disease, but it doesn't cause a very bad disease."

"But something happened at some [recent] point that likely allowed it to develop into syphilis, and it took off as a new kind of disease that caused all kinds of problems."

Wells notes that the genetic study of such diseases can teach us a great deal about the way our own genes have evolved.

"We see clear evidence in our own genome of adaptations to disease," he said. "Recently people have started looking at the genomes of infectious diseases, and we tend to see overlap in those processes [of adaptation]."

The use of genetics to track the origins and movements of disease is a rapidly growing field.

But even Harper suggests that we may never be able to definitively identify the mysterious origins of syphilis and Columbus's possible role in its spread.

"The truth is I think we're never going to nail this thing—we just don't have the strains to do that," she said.

"We have to work with what we have, and we have an [incomplete] picture that we have to make the most of."

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Parasite Makes Ants Resemble Berries

Scientists have discovered a parasite in the tropical forests of Central and South America that makes its ant hosts look like juicy, red berries ripe for the picking.Presumably the change in appearance tricks foraging birds into eating the otherwise unappetizing ants—parasites and all. The parasites travel through the birds' guts intact and are pooped out, which allows them to spread.

"These ants, in nature, go out and collect bird feces," explained Steve Yanoviak, an insect ecologist at the University of Arkansas in Little Rock.

The finding is the first known example of fruit mimicry caused by a parasite, he and his colleagues conclude in their study, which has been accepted for publication in the journal The American Naturalist.
Red Rears

Yanoviak's colleague Robert Dudley, a professor of integrative biology at the University of California, Berkeley, happened upon the infected tree-dwelling ants in Panama while studying their ability to glide.

Cephalotes atratus ants can make midair maneuvers, so that if knocked off a branch, they can steer toward the tree trunk, grab hold, and climb back up, the team showed in earlier work.

Dudley also noticed that some ants' gasters—the rear segments of their abdomens—were bright red. Yanoviak sliced open such a gaster in the lab and found it was full of the eggs of a parasitic nematode, or roundworm.

The researchers suspect the nematodes grow up inside the ants, then cause the hard outer layer of the gasters to thin. When combined with the yellowish coloring of worm eggs, this makes the body segments appear amber. "When you combine those two effects in the sunlight, you get a nice, bright red ant rear end.

Infected ants tend to hold their infested gasters in an elevated position over the rest of their bodies, making them "really conspicuous," he added.

The ants also become sluggish, and the gaster itself weakens, making it easily plucked off by birds, the researchers noted.

"[The ants] often feed out on leaf surfaces collecting pollen, collecting bird droppings, so they are pretty highly exposed," Yanoviak said.

Tricked Birds?

Yanoviak and his colleagues hypothesize that birds are tricked into thinking infected ants are ripe berries and eating them. Birds don't normally feast on Cephalotes atratus ants, which are thickly armored and full of bad-tasting chemicals.

The eggs pass unharmed through the birds' digestive systems. Ants then eat the bird feces, giving rise to a new generation of parasites in a new population of ants.

However, the researchers have not yet observed a bird actually eat one of the ants.

To test the hypothesis in the lab, Yanoviak fed an infected ant to a chicken. The parasite eggs came out in the chicken feces unscathed, he noted.

He also examined pieces of bird droppings collected from ants marching back to their colonies and found a parasite similar to the one that turns the ant gasters red.

"No matter how we look at it, somehow that parasite has to infect new colonies, or else it would die with its host colony. So there has to be a mechanism for transport to a new colony," Yanoviak said.

"And the association of this ant species in particular with bird droppings makes the message even stronger for implicating the bird as the vector."

Janice Moore is a biologist at Colorado State University in Fort Collins and an expert on the ecology and evolution of parasitic worms.

She said the researchers have done just about everything they could to show the infected ants might be fruit mimics and how the parasite could spread among ant colonies.

"That's pretty cool," she said.

Humans notice the fruit mimic ants readily because they are readily visible, she added, but other examples of parasite-induced change probably abound.

"As humans, we are highly visual and we notice visual modifications," she wrote in a follow-up email. "We are less conscious of, say, olfactory or auditory alterations.

"We know of a few such cases," she said, "but they are thin on the ground—probably because we don't notice them."

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Ancient Pandas Competed With Giant Apes for Bamboo

New fossils suggest ancient pandas competed with the largest known apes for habitat and food nearly half a million years ago on the tropical coast of southern China, scientists say.

The 400,000-year-old fossils of a giant panda were uncovered alongside the remains of a titan-sized, ancient ape called Gigantopithecus blacki, said Huang Wanbo, a paleontologist at Beijing's Institute of Vertebrate Paleontology and Paleoanthropology.

Excavated from a limestone cave on the island province of Hainan, the fossils suggest that both the giant pandas and the Giganto apes survived on a mostly bamboo diet, said Huang.

Hainan island was a bamboo-covered, hilly peninsula 400,000 years ago, Huang said. Today it is an island separated from the Chinese mainland by a 15-mile-wide (25-kilometer-wide) strait.

Three-Way Competition

Russell Ciochon, a professor at the University of Iowa who has joined several fossil digs in China but was not involved in the Hainan excavation, said the findings expand the known geographic range of nine- to ten-foot (three-meter) Giganto, which he called "the largest ape that ever existed."

The Giganto ape became extinct about 300,000 years ago, after about a half-million years of overlap with early humans, according to Ciochon.

Huang said he believes the ape lost out in a three-way struggle with giant pandas and early humans over food and habitat.

Ancient panda fossils have been found before near Giganto ape remnants, and early human fossils in China have been found in the vicinity of ancient pandas.

If early humans—armed with primitive weapons like stone axes and fire—migrated like the panda through what is now southern China, they likely had contact with the giant apes, Huang said.

Fossils of this early human species—a hunter-gatherer known as Peking Man or Homo erectus—have been uncovered around Beijing in northern China, about 1,200 miles (2,000 kilometers) north of Hainan.

Ciochon said he once agreed that the Giganto ape was the first loser in a survival competition with pandas and primitive humans, but today he is not so sure.

"The panda and the Giganto were living side by side in these subtropical forests, and probably competing for food resources," he said, "but Homo erectus was likely to be living in other habitats."

No Homo erectus fossils have been found in what is now southern China, but the area has not been thoroughly studied by paleontologists.

Panda Struggles

Huang said that the Hainan panda fossil provided a new piece in the puzzle of the panda's eight-million-year-long evolution from a meat-eater into a reclusive bamboo-eater.

The earliest pandas were fierce carnivores, scientists say. While technically classified as omnivores, today's pandas primarily depend on bamboo, which they spend an average of 12 hours a day eating.

The new fossils suggest the panda of 400,000 years ago, which was slightly larger than the modern giant panda, had by that time already become completely dependent on bamboo for survival, Huang said.

Huang said pandas were traditionally hunted for their pelts, and this may have been the case as far back as several hundred thousand years ago.

According to Huang, "400,000 years ago, there were many more pandas than humans here."

The human population in China has since grown to more than 1.3 billion, while the number of pandas has dwindled to about 1,600, according to Chinese conservationists.

Alarmed by a government inspection that turned up only 1,100 giant pandas in the late 1980s, China began at that time working with a global coalition of conservationists to save the species.

Fan Zhiyong, species program director for the conservation nonprofit WWF China, said the giant panda population has been decimated by large-scale human activities including "road and dam construction, mining, tourism, logging, and poaching."

Making panda poaching a capital crime, setting up a patchwork of panda nature reserves in the Himalayan foothills of western China, and creating a captive breeding program have all helped forestall the panda's extinction, conservationists say.

Paleontologist Huang, meanwhile, has proposed creating a panda DNA database that could help map the evolutionary history of the giant panda. He said that unlocking the secrets of the panda's genetic past might one day provide the key to protecting its future.

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Climate Change Put Big Chill on Neandertals, Study Says

Neandertals in western Europe were ravaged by an increasingly hostile climate rather than an invasion of modern humans, according to new research.

Beset by freezing conditions and food shortages, populations of Neandertals (often spelled "Neanderthals") dwindled between 40,000 and 35,000 years ago, the research suggests.

Modern humans, meanwhile, didn't settle western Europe until much later than had been thought, the study says.

The findings challenge the commonly held view that modern humans migrated to Europe from Africa about 40,000 years ago and quickly outcompeted or slaughtered their hairy, thickset cousins.

Instead, the new research supports the theory that Neandertals gave rise to the first modern humans in Europe.

Neandertals were the prehistoric ancestors of western Europeans, said Eugène Morin of Canada's Trent University in Ontario, lead author of the new study.

Morin argues that Neandertal populations thinned out gradually as Europe's environment became harsher, with some groups going extinct.

But climate stresses may have wrought evolutionary adaptations in surviving Neandertals, leading them to develop characteristics like those of modern humans, Morin added.

"Neandertals adapted to this harsher climate by expanding their social networks, a process that allowed the diffusion of 'modern traits' into the Neandertal gene pool," he said.

Some modern humans may have migrated to Europe during this period, Morin added, "but I don't think it happened to the large scale implied by many scholars."

Such an influx probably didn't occur until about 10,000 years ago, with the spread of agriculture from the Middle East, he said.

The new study, published in the current issue of the Proceedings of the National Academy of Sciences, is based on mammal remains from Saint-Césaire, a Stone Age site in southwestern France.

Analysis of bones found there suggests a decrease in the variety of large mammals that prehistoric hunters would have targeted, the study found.

Prey species found at the site include bison, horses, red deer, and reindeer.

Unlike the other species, however, reindeer became increasingly abundant about 40,000 years ago, the evidence suggests.

The ratio of reindeer bones at the French site rose from 35 to 87 percent during this period, Morin said, indicating a rapidly cooling climate.

Remains of a tundra-dwelling rodent species, the narrow-skulled vole, likewise suggest suddenly colder conditions.

"About 40,000 years ago, the diversity of animals that could be hunted shrank severely, and that would have impacted human populations," Morin said.

This shift coincides with a period called the Middle/Upper Paleolithic transition, a period marked by significant changes in early-human culture, including the use of more sophisticated stone tools, he added.

But "there were fewer people around after the transition than before," he said.

Neandertals' reliance on reindeer would have been especially risky, since the mammals experienced extreme fluctuations in population, Morin said.

"This was also likely to have impacted human populations that depended on them," the anthropologist said.

Furthermore, if large mammals such as bison and horses were frozen out of the region, there wouldn't have been enough prey to support incoming modern-human migrants from Africa, he added.

Were Modern Humans More Prepared?

Paul Mellars, professor of human evolution at the University of Cambridge, U.K., said the new study provides a good analysis of the mammal fauna and climate during the transition period.

The new findings are supported by evidence from deep seabed sediments that indicate a dramatic drop in temperature of at least 14.4 degrees Fahrenheit (8 degrees Celsius), Mellars said.

"This occurs pretty well at precisely the time that you get the transition," he added.

But the Saint-Césaire site also shows an abrupt transition in artifacts that only an invasion by modern humans can explain, Mellars said.

Entirely different stone-tool technologies suddenly appear in the region, he said.

"Just on the basis of the technology alone, it looks like a sudden population replacement of Neandertals by modern humans [took place]," Mellars commented.

Evidence from similarly dated human bones also indicates the presence of anatomically modern humans that spread from the east across Europe, he noted.

Mellars said other researchers argue that the dramatic climatic cooling highlighted by the study would have given incoming modern humans, with their more advanced tools, a competitive advantage over the Neandertals.

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"Hobbits" May Have Been Genetic Mutants

A rare disease characterized by small brain and body size but near normal intelligence is caused by mutations in a gene coding for the protein pericentrin, researchers have found.

The scientists speculate that the condition may explain the tiny, hobbitlike people that occupied a remote, Indonesian island about 18,000 years ago—adding fuel to the debate over whether the unusual creatures were a new species or just diseased modern humans.

Pericentrin helps separate chromosomes during cell division, which is needed for growth.

"The whole body loses its capacity to grow, because cell division is so difficult for people with this defect," said study co-author Anita Rauch of the Institute for Human Genetics at the University of Erlangen in Germany.

On average, disease sufferers grow about three feet (a meter) tall and have a brain the size of a three-month-old baby. However, their intelligence is near normal.

People with the defect also exhibit subtle bony anomalies in their hands and wrists, skull asymmetry, small chins, abnormal teeth, and abnormal shoulders, Rauch said.

Mysterious Hobbit

Descriptions of the hobbitlike people match those of modern humans with this genetic defect, Rauch added.

When the hobbit was discovered in 2004 on the Indonesian island of Flores, scientists hailed it as a new species: Homo floresiensis.

Since then, scientists have debated whether the hobbit is indeed a new species or a modern human with a genetic disease that causes small brains called microcephaly.

The new study links the genetic mutations to a type of microcephaly that limits all growth—that of the brain and the body.

She added that, on islands like Flores, inherited diseases become commonplace because of the higher levels of mating among closely related people.

The finding is reported online today in the journal Science.

Down to the Details

Richard Potts, director of the human origins program at the Smithsonian Institution in Washington, D.C., closely monitors the scientific debate over Homo floresiensis.

He said the new study's link between genetics and human growth is "neat" but disagreed with the suggestion that Homo floresiensis represents a modern human with a genetic disorder.

Proof that the hobbit is indeed a unique species, he said, is found in recent detailed studies of its wrist and upper arm bone.

A wrist bone study published in Science last September found that the hobbit's wrist bones were primitive, like those in gorillas or chimpanzees.

No known genetic diseases, including any type of microcephaly, results in an apelike wrist similar to the hobbit's, the authors of the wrist bone study concluded.

"For many of us in the field, we have taken those studies, especially the one [on the wrist bone] as really being the death blow to the idea that we're dealing with a modern human," Potts said.

And even if the researchers find a gene in the hobbits connected with dwarfism in modern humans, they would "still have to go down to the details of the morphology and try to explain [them]," he added.

Dean Falk is an anthropologist at Florida State University in Tallahassee who has led several studies demonstrating Homo floresiensis is a unique species, not a diseased modern human.

She commented via email that the new study is unconvincing—for one, the pictures shown of people with this defect look nothing like the hobbit.

"Their heads are too large relative to their bodies, the limb proportions are all wrong, the profiles of the face do not come close, and these individuals are from 8 to 12 years old," she wrote.

The hobbit fossil, known as LB1, is from an individual about 30 years old.

Modern Variation

Study co-author Rauch and her colleagues, meanwhile, hope that improved technology may soon allow them to extract DNA from the Flores fossils and test it for mutations to the pericentrin gene.

The new research, Rauch noted, demonstrates that a single genetic defect can lead to miniaturization and distinct bone shape in humans.

Rauch also plans to investigate connections between pericentrin mutations and natural variation in the modern human population.

She said that there are a lot of small changes in the gene between normal people—not enough to cause dwarfism but sufficient to make one person smaller than another, for example.

"If you don't have the full mutation which leads to absence [of the protein]," she said, "but only a little change, this might cause little differences in the normal population."

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Aztec Pyramid, Elite Graves Unearthed in Mexico City

A structure believed to be an 800-year-old Aztec pyramid has been discovered in central Mexico City and could drastically revise the early history of the ancient empire, officials announced.

The structure was found inside a larger pyramid known as the Grand Temple at the site of the Aztec city of Tlatelolco.

If the age of the edifice is confirmed, the discovery could push back the age of Tlatelolco—as well as that of its nearby "twin city" Tenochtitlán—by a century or more, said Salvador Guilliem of Mexico's National Institute of Anthropology and History.

Guilliem, who is leading an archaeological effort to study Tlatelolco, said the structure's construction suggests it could have been built as early as A.D. 1100 or 1200, at least a century earlier than historical accounts suggest the city was founded.

While Guilliem's team continues to work on determining the new pyramid's age, the researchers have already uncovered new insights into the Grand Temple.

"Until now we thought Tlatelolco's Grand Temple had seven phases of construction," Guilliem told National Geographic News.

"Now we know that there are eight."

The team also used ground-penetrating radar to locate a series of other structures near the Grand Temple containing human remains and grave offerings.

"We dug 2 meters [6.5 feet] and found an offering of green stones and five skulls," Guilliem said.

The remains—belonging to four adults and a child—appear to have been positioned with heads turned toward the north and bodies to the south, he added.

"We will explore more next season, but we think this building corresponds to the military elite," he said.

Ancient Legends

Modern interpretations of Aztec legends say Tlatelolco was built around A.D. 1358, the same year as Tenochtitlán, although archaeological evidence has cast doubt on that date in recent years, experts say.

"If true, the date of this pyramid fits with many other archaeological finds that reveal evidence of Aztec occupation earlier than the traditional dates," said Susan Gillespie, a University of Florida anthropologist.

The find could also shed light on the poorly understood early relationship between Tlatelolco—a massive market province—and Tenochtitlán, the Aztec capital and one of Mesoamerica's largest cities.

"The nature of Tlatelolco and Tenochtitlán's entwined origins and histories remains one of the underexplored mysteries of the Aztec era," Gillespie said.

The new discovery could challenge the notion that Tenochtitlán was the dominant twin during the early, entangled development of the two Aztec provinces, said Michael Smith, an Aztec expert at Arizona State University.

"There are vague traces in the historical sources that Tlatelolco may have been more powerful than Tenochtitlán in its early decades," he said.

"If there was indeed a large pyramid in Tlatelolco in the Early Aztec period, given that no such find exists in Tenochtitlán, it may suggest that Tlatelolco was indeed the dominant city in their early years. That would be significant."

What's Inside the Pyramid?

Guilliem and his colleagues believe that an offering to Tezcatlipoca Black, the Aztec god of commerce, will be found inside the newly discovered pyramid.

Guilliem theorizes that workers intentionally broke into the smaller pyramid in 1368 while building a subsequent phase.

"When they broke it, it is very probable that they deposited a deity that's likely to be Tezcatlipoca," he said.

"They most likely deposited an offering to the deity [Tezcatlipoca Black], conducted a ceremony, [and] then closed it again."

The team also wants to determine if the Grand Temple at Tenochtitlán has a similar stage of construction—a key to untangling the early power balance between the two city-states, Guilliem said.

Gillespie, the University of Florida anthropologist, said such a comparison could yield crucial clues to the dynamics of the ancient Aztec cities.

"The great temple at Tenochtitlán similarly had many cached offerings as part of the different building phases," Gillespie said.

"It will be interesting to see how the Tlatelolcan corpus of offerings compares to that of Tenochtitlán."

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Bone Ice Skates Invented by Ancient Finns, Study Says

Ice-skating—the oldest human-powered means of transportation—was invented in Finland not for fun but for survival, according to a new study.

Skates made from animal bones have been found throughout Scandinavia and Russia, including some that date back to around 3000 B.C.

The wide dispersal of the ancient artifacts has made it difficult for archaeologists to pin down exactly when and where ice-skating first developed.

Now scientists from Italy and the United Kingdom have calculated that people living in what is now southern Finland would have benefited the most from skating on the crude blades.

The researchers showed that people traveling across the region's frozen lakes reduced their physical energy cost by 10 percent.

By contrast, skaters in other northern European countries would have had only a one percent energy reduction (see a map of Europe).

"People developed this ingenious locomotion tool in order to travel more quickly and by using not as much energy as if they had walked around all the lakes," said study co-author Federico Formenti of the University of Oxford in England.

The study appears in this month's issue of the Biological Journal of the Linnean Society of London.

Leather Straps

Southern Finland has more lakes within 40 square miles (about 100 square kilometers) than any other region in the world.

"I think ice-skating happened in [this] area because of the several long and thin lakes that people had to cross in order to get around, hunting for food or for any daily activity," Formenti said.

"Those lakes froze during the long winters, when sunlight was there only for a few hours per day."

The earliest skates were made mostly of horse bones, but other bones were also used depending on the animals available, Formenti said.

Holes carved in the ends of the bones were likely strung with leather straps tied around the skaters' feet.

Woodcuts from the 1500s show bone skates being used together with a stick, which was pushed between the legs to help the user pick up speed.

To study the energy efficiency of this early ice-skating, Formenti's team tested replicas of bone skates at an ice rink in the Italian Alps.

The researchers measured five skaters' heart rates, oxygen intake, and speed while maneuvering on the blades.

The skates took some time to get used to, Formenti said, but "once you get the movement pattern, they glide really well."

"The oily external surface of the animal bones makes a natural wax which limits resistance to motion."

The team then constructed mathematical models and computer simulations of energy use for 240 6-mile (10-kilometer) skating trips across different parts of northern Europe.

"This research suggests that ancient Finland would have been the most practical birthplace of the now popular winter sport," the authors write in their paper.

Other studies by the same scientists have shown how fast and how far people could skate at various times in history, as bone blades gave way to iron and then to steel.

The earliest skaters were probably not fast. The people testing the bone skates for the latest study reached an average speed of about 5 miles (8 kilometers) an hour.

Modern speed skaters, on the other hand, can reach speeds of up to 37 miles (60 kilometers) an hour.

Skates and Skis

Steven Vogel is a biology professor at Duke University in Durham, North Carolina, who was not involved in the study.

The skating research is "especially important, because just about no one else does this kind of thing—showing how biomechanical work can reveal things about history, prehistory, and anthropology," Vogel said.

Like with ice skates, other modes of transportation probably developed as people searched for more efficient ways of getting around, Formenti added.

"Cross-country skis … seem to have developed in Scandinavia at about the same time as bone skates," he said.

(Related news: "Skiing: From the Stone Age to Torino" [January 31, 2006].)

"In Scandinavia there were heavy snowfalls, and skis allowed people to move around the woods without sinking in the snow with bare feet."

Long, flat skis redistribute the wearer's weight, lessening the depth of each step, while heat from friction melts a thin layer of snow underneath, allowing the wearer to glide over the terrain.

"The origins of skis and skates as passive tools enhancing human-powered locomotion share common roots, probably small wooden plates," Formenti said.

"These became longer and wider skis on snow or shorter and thinner plates—and, for sure, animal bones—used to glide on ice."

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Ancient Tomb Art Found in Path of Irish Highway

Tomb engravings dating back 6,000 years are among the latest discoveries unearthed on the route of a controversial highway under construction in Ireland.

The historic site, at Lismullin in County Meath, was handed over to road builders last month, just weeks after the Stone Age art was found inside a medieval bunker.

The engravings have been removed to allow construction of the highway to proceed.

The new find follows the discovery last spring of a prehistoric open-air temple nearby, causing construction of the 37-mile-long (60-kilometer-long) M3 highway northwest of Dublin to be temporarily suspended (see map).

The timber temple enclosure was found just 1.25 miles (2 kilometers) from the Hill of Tara, once the seat of power of ancient Celtic kings.

The latest excavations at Lismullin revealed part of a huge stone monument, or megalith, decorated with engravings dating to the Late Stone Age, according to archaeologists from Ireland's National Roads Authority (NRA).

Discovered some 165 feet (50 meters) from the temple's enclosure, the stone features a series of zigzags, concentric circles, and arcs.

"It's classic megalithic art," said Mary Deevy, NRA's chief archaeologist.

The engravings are similar to those that decorate other burial chambers in the region known as passage tombs, Deevy noted.

"We've only got half a boulder, but we think originally it was probably a curbstone from a passage tomb," she said.

The stone would have formed a wall that kept the burial mound together, with the artwork displayed on the outer surface, Deevy said.

What the motifs symbolized remains a mystery, the archaeologist added.

Viking Attacks

The stone was discovered within an early medieval souterrain, an underground structure that may have been used by local inhabitants to defend themselves against Viking raiders, the excavation team reported.

Dating to around the 10th century A.D., the souterrain was probably constructed using the broken megalith as building material.

"The souterrain builders robbed or quarried the stone from a Neolithic [Late Stone Age] monument," Deevy said.

"Souterrains are common in Ireland, and it's not unusual to have stones from earlier monuments reused on them," she added.

The rock art will eventually go on public display, according to Deevy, who describes the Lismullin site as "100 percent excavated."

The site was handed over to road builders on December 18, with construction work expected to start soon.

Campaigners who want the highway re-routed away from the Hill of Tara area have attacked the decision.

"Significant damage has already been done," said Vincent Salafia of Dublin-based protest group TaraWatch.

"But until the road is built on top of the site, I suppose there is still hope."

One of the "Top Discoveries"

Irish citizens opposed to the road project are currently fielding legal advice with a view to obtaining a court injunction to halt construction, the campaigner said.

The European Commission has criticized the Irish government for failing to properly reassess the impact of the road project after the ruins of the open-air temple were uncovered last year.

Under European law, the discovery should have triggered a so-called environmental impact assessment, Salafia said.

While the Lismullin site was declared a national monument, "this has made no difference whatsoever," he added.

Upward of 40 archaeological sites have been uncovered along the route of the highway, Salafia said.

"The bigger argument that's at stake is that Lismullin is connected to all these other 40 sites, and that they are all part and parcel of one single large national monument, which is the Hill of Tara complex," he said.

"If a new environment impact assessment were done, that's what would be shown, and that the motorway should go outside that complex rather than straight through it."

Lismullin's timber enclosure site was recently named one of the top ten discoveries of 2007 by the magazine Archaeology, published by the Archaeological Institute of America.

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Big Dinosaurs Had "Teen Sex"

Big dinosaurs, like humans, reached sexual maturity during the messy growth spurts of adolescence, according to a new study.

The reproductive strategy of dinosaurs was unlike that of their reptilian ancestors or their bird descendants, the study concludes.

"They are growing really fast and yet maturing early," said Sarah Werning, a graduate student in paleontology and integrative biology at the University of California, Berkeley.

"Among living animals, the only things that do that are medium- to large-size mammals, including us."

Though reptiles like crocodiles reach sexual maturity before they are fully grown, they grow slowly. Birds grow to their full adult size within a year but delay sex for a year or longer, Werning noted.

She and colleague Andrew Lee, now at Ohio University in Athens, report the finding in tomorrow's issue of the journal Proceedings of the National Academy of Sciences.

Growth Rings

Like tree trunks, dinosaur bones have annual growth rings, Werning said.

The researchers were studying these rings in the bones of the meat-eater Allosaurus and the plant eater Tenontosaurus to determine how fast they grew at different points in their lives.

In a specimen of each type of dinosaur, the team happened upon a type of calcium-rich tissue called medullary bone. Modern-day birds also produce this type of bone prior to laying eggs.

The finding indicates that both the Allosaurus and the Tenontosaurus died shortly before laying eggs—and therefore that they were able to reproduce at the times of their deaths.

"They wouldn't be ovulating if they weren't of reproductive age," Werning noted.

The researchers added this onset of sexual maturity to their growth graphs and found that the dinosaurs were reaching sexual maturity in the midst of a teenage growth spurt.

"They are definitely not juveniles, but they are not fully grown yet, and they are also going through a time of really rapid growth … it's very similar to what we call adolescence," Werning said.

The team also confirmed that a Tyrannosaurus rex bone that North Carolina State University paleontologist Mary Schweitzer found in 2005 contained medullary tissue when it died at 18.

(Related: He Rex or She Rex? Experts Find Way to Tell Dino Gender [June 2, 2005].)

All three types of dinosaurs had life spans of about 25 to 30 years. But they didn't reach full adult size until age 20 to 25. Waiting until they were fully grown to reproduce would have been risky, according to Werning.

"It makes a lot of sense that [dinosaurs] wouldn't have the same strategy as birds," she said.

Birds Are Unique

The finding complements research published last year that showed that birdlike dinosaurs—discovered sitting on their eggs just like birds do—also had sex as teenagers.

"What Sarah and Andrew have done in their paper is find exactly the same thing but in a different group of dinosaurs and by using a different marker of reproductive maturity," said Kristi Curry Rogers, a paleontologist at Macalester College in St. Paul, Minnesota.

Curry Rogers is a co-author of the 2007 birdlike-dino study with Gregory Erickson, a paleontologist at Florida State University.

She said both studies highlight the uniqueness of sexual maturity in birds.

"[Bird] evolution is a very fascinating mosaic of characteristics that deserves a lot more study," she said. "We're still at the beginning of teasing apart all the fine details."

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Mysterious Clouds More Common Due to Climate Change?

Mysterious "night-shining clouds" that light up the polar skies have become more luminous and frequent in recent years—and climate change may be the culprit, scientists announced Monday.

So-called noctilucent clouds, which streak across the sky in vibrant colors during polar summers, are ten times brighter than previously believed, according to recent data from NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite.

The data, collected during two polar cloud seasons, also suggest the formations appear daily, are more widespread, and have started to form at lower latitudes than before.

Climate Change Canary

Night-shining clouds are made mostly of ice particles that form when water vapor condenses onto atmospheric dust.

The AIM mission is the first detailed exploration of the clouds, which form about 50 miles (80 kilometers) above Earth's surface—"literally on the edge of space," AIM principal investigator James Russell III said yesterday at a press briefing at the American Geophysical Union fall meeting in San Francisco, California.

The air there is a thousand times drier than the Sahara, and the temperature can drop to minus 235 degrees Fahrenheit (minus 148 degrees Celsius)—ideal conditions for creating clouds.

A likely explanation for the clouds' surge is that temperatures in the upper atmosphere have gotten even colder due to the build-up of carbon dioxide in the atmosphere, Russell said.

Yearly emissions of carbon dioxide levels have grown about 20 percent since 1990. Most scientists agree the buildup is causing climate change and heating up Earth's surface.

In the upper atmosphere, however, carbon dioxide does not act like a thick, heat-trapping blanket.

Instead it forms a thin layer, allowing heat to escape, temperatures to drop, and ice particles to form.

"[These] clouds are the mine's canary of global warming," Russell told National Geographic News.

No Other Plausible Reason

The evidence linking carbon dioxide to changes in night-shining clouds is still tentative, Russell said.

But "in all honesty, we don't know of any other plausible reasons why it wouldn't be global climate change," he said.

"If that's true, that says not only are we changing the atmosphere where we're living, we're changing a very remote, rarified part of our atmosphere."

Such far-reaching change means that "we need to be concerned," Russell said.

"If [the cloud changes] are indeed tied to carbon dioxide buildup, here's another confirming reason we should strive to do something about it."

"Exquisite Thermometer"

AIM also discovered "dramatic changes" in cloud behavior, said Scott Bailey, AIM's deputy principal investigator.

The data suggest the clouds are highly variable, rotating every five days according to minute shifts in temperature—even as little as 5 degrees Fahrenheit (2.7 degrees Celsius).

"These clouds are exquisite thermometers," he said.

"Now we're able to see the whole life cycle [of a cloud] for the first time," Bailey told National Geographic News.

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