Friday, July 24, 2009

PRIMATE ARCHAEOLOGY SHEDS LIGHT ON HUMAN ORIGINS

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A University of Calgary archaeologist who is one of the few researchers in the world studying the material culture of human beings' closest living relatives – the great apes – is joining his colleagues in creating a new discipline devoted to the history of tool use in all primate species in order to better understand human evolution.

Julio Mercader, holder of the Canada Research Chair in Tropical Archaeology in the U of C's Department of Archaeology, is the only Canadian author of a new paper titled "Primate archaeology" published this week in the prestigious scientific journal Nature. Mercader is one of 18 co-authors from universities including Cambridge, Rutgers, Kyoto University and schools in Spain, Italy and France. They argue that recent discoveries of tool use by a wide variety of wild primates and archaeological evidence of chimpanzees using stone tools for thousands of years is forcing experts to re-think the traditional dividing lines between humans and other primate species as well as the belief that tool use is the exclusive domain of the genus Homo. The researchers advocate for a new inter-disciplinary field of primate archaeology to examine tool use by primates in a long-term, evolutionary context. The paper is the result of the international symposium "Palaeoanthropology meets Primatology" held on Oct. 18, 2008 at Cambridge.

"There is a need for systematic collaboration between diverse research programs to understand the broader questions in human evolution and primatology," Mercader says. "For example, few archaeologists have seen a wild primate use a tool, while few primatologists have taken part in archaeological excavations," he explains.

Mercader was the lead author of a team that laid the foundations of the emerging discipline of chimpanzee archaeology in two previously-published papers in Science and the Proceedings of the National Academy of Sciences (PNAS). He is the archaeologist who uncovered the first prehistoric evidence of chimpanzee technology in 2007 — a 4,300-year-old nut-cracking site in the rainforests of Côte D'Ivoire, West Africa that provides proof of a long-standing chimpanzee "stone age" that likely emerged independently of influence from humans.

"It's not clear whether we hominins invented this kind of stone technology, or whether both humans and the great apes inherited it from a common forebear," says Mercader. "We used to think that culture and, above anything else, technology was the exclusive domain of humans, but this is not the case. We need comparable methods of data collection among researchers dealing with 2 million year old hominin sites and modern primatological assemblages."

The official inauguration of the new field of primate archaeology marks the culmination of several years of work on the part of the handful of researchers including Mercader, who joined the U of C in 2002 with the support of the Canada Research Chairs program and the Canada Foundation for Innovation.

"This is truly at the vanguard of archaeology and I am so pleased these agencies and the University of Calgary had the vision seven years ago to be a part of creating a new discipline that is seeing its birth now," Mercader says.

(Photo: Tetsuro Matsuzawa, Kyoto University)

University of Calgary

PRIMITIVE ASTEROIDS IN THE MAIN ASTEROID BELT MAY HAVE FORMED FAR FROM THE SUN

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Many of the objects found today in the asteroid belt located between the orbits of Mars and Jupiter may have formed in the outermost reaches of the solar system, according to an international team of astronomers led by scientists from Southwest Research Institute (SwRI).

The team used numerical simulations to show that some comet-like objects residing in a disk outside the original orbit of the planets were scattered across the solar system and into the outer asteroid belt during a violent phase of planetary evolution.

Usually, the solar system is considered a place of relative permanence, with changes occurring gradually over hundreds of millions to billions of years. New models of planet formation indicate, however, that at specific times, the architecture of the solar system experienced dramatic upheaval.

In particular, it now seems probable that approximately 3.9 billion years ago, the giant planets of our solar system -- Jupiter, Saturn, Uranus and Neptune -- rearranged themselves in a tumultuous spasm. "This last major event of planet formation appears to have affected nearly every nook and cranny of the solar system," says lead author Dr. Hal Levison of SwRI.

Key evidence for this event was first identified in the samples returned from the Moon by the Apollo astronauts. They tell us about an ancient cataclysmic bombardment where large asteroids and comets rained down on the Moon.

Scientists now recognize that this event was not limited solely to the Moon; it also affected the Earth and many other solar system bodies. "The existence of life on Earth, as well as the conditions that made our world habitable for us, are strongly linked to what happened at this distant time," states Dr. David Nesvorny of SwRI.

The same dynamical conditions that devastated the planets also led to the capture of some would-be impactors in the asteroid belt. "In the classic movie 'Casablanca,' everybody comes to Rick's. Apparently throughout the solar system, the cool hangout for small objects is the asteroid belt," says Dr. William Bottke of SwRI.

Once in the asteroid belt, the embedded comet-like objects began to beat up both themselves and the asteroids. "Our model shows that comets are relatively easy to break up when hit by something, at least when compared to typical asteroids. It is unavoidable that some of the debris went on to land on asteroids, the Moon and the Earth. In fact, some of the leftovers may still be arriving today," says Dr. Alessandro Morbidelli of the Observatoire de la Cote d'Azur in Nice, France.

The team believes the surprising similarities between some micrometeorites landing on Earth and comet samples returned by NASA's Stardust mission are no accident. "There has been lots of debate about the nature of micrometeorites reaching the Earth," says Dr. Matthieu Gounelle of the Museum National d'Histoire Naturelle in Paris. "Some believe they are asteroidal, while others argue they are cometary. Our work suggests that in a sense, both camps may be right."

"Some of the meteorites that once resided in the asteroid belt show signs they were hit by 3.5 to 3.9 billion years ago. Our model allows us to make the case they were hit by captured comets or perhaps their fragments," adds Dr. Kleomenis Tsiganis of Aristotle University of Thessaloniki, Greece. "If so, they are telling us the same intriguing story as the lunar samples, namely that the solar system apparently went berserk and reconfigured itself about 4 billion years ago."

Overall, the main asteroid belt contains a surprising diversity of objects ranging from primitive ice/rock mixtures to igneous rocks. The standard model used to explain this assumes that most asteroids formed in place from a primordial disk that experienced radical chemical changes within this zone. This model shows, however, that the observed diversity of the asteroid belt is not a direct reflection of the intrinsic compositional variation of the proto-planetary disk. These results fundamentally change our view of the asteroid belt.

Additional tests of this model will come from studies of meteorites, the asteroid belt, planet formation and the Moon. "The Moon and the asteroid belt may be the best and most accessible places in the solar system to understand this critical part of solar system history," says Levison. "We believe key evidence from these cold airless bodies may help us unlock the biggest 'cold case' of all time."

(Photo: CSNSM-Orsay-CNRS / IPEV)

Southwest Research Institute

POSSIBLE DINOSAUR BURROWS CLUES TO SURVIVAL STRATEGIES

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Internationally renowned palaeontologist and Monash University Honorary Research Associate, Dr Anthony Martin has found evidence of a dinosaur burrow along the coast of Victoria, which helps to explain how dinosaurs protected themselves from climate extremes during the Cretaceous period – the final era for dinosaurs before their extinction.

Dr Martin made the discovery of the 2 metre-long burrow in 2006 while researching dinosaur tracks at Knowledge Creek, west of Melbourne, and has had the findings published this week.

Three years earlier Dr Martin and his colleagues found a similar pre-historic "shelter" in Montana, USA where he identified skeletal remains of a dinosaur and two juveniles in a fossilised burrow.

Dr Martin said the burrows, the oldest identified on record, help to explain how dinosaurs managed extremes in climate, shedding more light on dinosaur behaviour and suggest that dinosaurs of different species, on different continents, in different hemispheres may have engaged in similar living habits.

"We knew that some dinosaurs may have cared for their young in burrows but the latest discovery can also suggest that dinosaurs may have used the burrows to shelter from the cooling and warming effects of the Cretaceous Period – a time of great climate transformation which ended in complete extinction of all dinosaur species," Dr Martin said.

The location of possible dinosaur burrows on the south coast of Victoria are from a time when Australia which was attached to Antarctica, and lay near the South Pole.

Dr Martin estimates the fossilised burrow is about 106 million years old when Antarctica and Australia were about to part company and a time when earth underwent global warming where temperatures climbed over past times. Even though the average temperatures on the globe may have higher by several degrees, Victoria still lay near the South Pole – and during winter temperatures likely plunged to below freezing, forcing the resident dinosaurs to seek shelter.

"Heat and cold meant that at least some dinosaurs needed shelter. We had thought they sought cover under trees, but the burrows indicate that some dinosaurs were adept at creating secure accommodation for themselves during times of stress."

The burrow, measuring two metres in length and 30 centimetres across, spirals down to a large chamber and is located in an outcrop a few kilometers from Dinosaur Cove – the site of popular dinosaur digs led in the past by Monash and Museum Victoria palaeontologists Professor Pat Rich and Tom Rich, also an honorary researcher in the School of Geosciences at Monash.

Professor Rich said the discovery is providing new insights in an ever-growing body of knowledge of these polar dinosaurs living at the extremes. "We have wondered for some time what these structures were and when Tony found burrows with dinosaur bones in them in Montana, he became suspicious that these structures in southern Victoria were of a similar nature. Now all we have to do is find the bones in them.

(Photo: Monash U.)

Monash University

EARLY INITIATION OF ARCTIC SEA-ICE FORMATION

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Significant sea ice formation occurred in the Arctic earlier than previously thought is the conclusion of a study published in Nature. "The results are also especially exciting because they suggest that sea ice formed in the Arctic before it did in Antarctica, which goes against scientific expectation," says scientific team member Dr Richard Pearce of the University of Southampton's School of Ocean and Earth Science based at the National Oceanography Centre, Southampton (NOCS).

The international collaborative research team led by Dr Catherine Stickley and Professor Nalân Koç of the University of Tromsø and Norwegian Polar Insitute (Tromsø) analysed oceanic sediment cores collected from the Lomonosov ridge in the central Arctic by Integrated Ocean Drilling Program Expedition 302 ('ACEX'). Previous analyses of cores drilled in this region revealed ice-rafted debris dating back to the middle Eocene epoch, prompting suggestions that ice appeared in the Arctic about 46 million years ago. But records of ice-rafted debris do not differentiate sea ice from glacial (continental) ice, which is important because sea ice influences climate by directly affecting ocean–atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity.

Instead of focusing solely on ice-rafted debris, Stickley and her colleagues also garner information about ancient climate by analysing fossilised remains of tiny single-celled plants called diatoms in the sediment cores. Today, different living diatom species are adapted to particular environmental conditions. Assuming that this was also true in the past – for which there is ample evidence – the presence of particular diatom species in sediment cores is diagnostic of conditions prevailing at the time.

Coincident with ice-rafted debris in the cores, the researchers found high abundances of delicately silicified diatoms belong to the genus Synedropsis. "We were astonished by this", said team member Richard Pearce of NOCS, who imaged the samples using a scanning electron microscope at the NOCS: "Weakly silicified diatoms are preserved only under exceptional circumstances, so to find fossilised Synedropsis species so well preserved and in such abundance is truly remarkable." In fact, the ACEX Synedropsis species represent the earliest known fossil record of sea-ice diatoms.

The researchers attribute the presence of Synedropsis fossils in these sediments to the presence of sea ice, and silica-enriched waters that favour their preservation. They propose that, like Synedropsis species found in polar regions today, the ACEX species were also sea-ice specialists uniquely adapted for surviving the lengthy polar darkness and freezing temperatures. "These diatoms provide the most compelling evidence for ancient sea ice, as they rely on this medium for their survival," said Catherine Stickley. Moreover, their analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of ice-rafted debris at this time.

"It is likely that sea ice formed in autumn and winter and melted in spring and summer, as seasonal sea ice does today," they say. Synedropsis species probably over-wintered within the sea ice and then bloomed there in the spring when there was enough sunlight. They would have been released into stratified surface waters as the ice melted, rapidly sinking to the sea bottom as aggregates, leaving other diatom species to dominate summer production. And, indeed, these seasonal changes can be discerned in the sediment cores.

The researchers conclude from their analysis, which cover a two-million year period, that episodic sea ice formation in marginal shelf areas of the Arctic started around 47.5 million years ago, about a million years earlier than previous estimates based on ice-raft debris evidence only. This appears to have been followed half a million years later by the onset of seasonal sea-ice formation in offshore areas of the central Arctic, and about 24 million years before major ice-sheet expansion in the region.

The findings have potentially important implications for climate. Spring sea ice and summer cloud formation would have reduced oceanic heat loss to the atmosphere and increased the amount of solar radiation reflected back out into space. "A stable sea-ice regime also suggests the possibility of concomitant glacial ice," say the researchers, and indeed they find some evidence for the presence of small isolated glaciers at the time.

Furthermore, their data indicate that sea ice formed in the Arctic before it did in Antarctica. Atmospheric levels of the greenhouse gas carbon dioxide were declining in the middle Eocene, one of the reasons postulated in causing the Earth to cool. However, the new findings imply that the threshold for sea-ice formation was first crossed in the Arctic, which, say the authors, is "a hypothesis opposite to that modelled for glacial ice, whereby Antarctica is shown to glaciate much earlier (that is, at higher levels of carbon dioxide) than circum-Arctic continents."

National Oceanography Centre, Southampton

STUDY CATCHES 2 BIRD POPULATIONS AS THEY SPLIT INTO SEPARATE SPECIES

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A new study finds that a change in a single gene has sent two closely related bird populations on their way to becoming two distinct species. The study, published in the August issue of the American Naturalist, is one of only a few to investigate the specific genetic changes that drive two populations toward speciation.

Speciation, the process by which different populations of the same species split into separate species, is central to evolution. But it's notoriously hard to observe in action. This study, led by biologist J. Albert Uy of Syracuse University, captures two populations of monarch flycatcher birds just as they arrive at that evolutionary crossroads.

Monarch flycatchers are small, insect-eating birds common in the Solomon Islands, east of Papua New Guinea. Uy and his team looked at two flycatcher populations: one found mostly on the large island of Makira, the other on smaller surrounding islands. Besides where they live, the only discernable difference between the two populations is the color of their feathers. The birds on Makira have all black feathers. Birds on the smaller islands have the same black feathers, but with a chestnut-colored belly.

The question of whether these two populations are on the road to speciation comes down to sex. When two populations stop exchanging genes—that is, stop mating with each other—then they can be considered distinct species. Uy and his team wanted to see if these flycatchers were heading in that direction.

It would be all but impossible to try to catalog every occasion on which an all-black flycatcher mated with a chestnut-bellied. So Uy and his team used another test.

Flycatcher males defend their mating territories. If a potential rival male enters another's territory, fights often ensue. If all-black males react less violently to chestnut-bellied males and vice versa, that's an indication that the two don't recognize each other as reproductive rivals. If they don't see each other as rivals, then one can assume that mating between members of the two populations is rare.

So Uy and his team made all-black and chestnut-bellied taxidermy models. They used the models to invade mating territories in each population. As expected, when all-black birds were presented with all-black models, they attacked. But when all-black birds encountered chestnut-bellied models, they were much less likely to go on the offensive. The same scenario held for the chestnut-bellied birds.

That males from the two populations no longer view the other as a reproductive threat is a good indication that not much mating is taking place between the two groups. Their evolutionary paths are diverging, Uy and his team found—all because of a change in plumage.

The researchers then went a step further. They looked into the birds' genomes to see what genes may have played a role in the different plumage pattern. They found only one: the melanocortin-1 receptor gene (MC1R). The MC1R gene regulates the production of melanin, which gives skin and feathers their color. The all-black and chestnut-bellied birds had different versions of the MC1R gene, which gave rise to the plumage change.

That change appears to have been enough to create a reproductive barrier for flycatchers. Not every species is so picky, so a color change doesn't always drive speciation. Nonetheless, these results suggest that it can take as little as one gene, in the right spot in the genome, to cause a fork in the evolutionary road.

Chicago Journals

SWEDISH RESEARCHER FINDS MISSING PIECE OF FOSSIL PUZZLE

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In February this year, a paper published in Nature by a team of Australian and British researchers showed that placoderms, a group of ancient fishes that died out more than 350 million years ago, gave birth to live young. Beautifully preserved fossil embryos in the body cavity of the placoderm Incisoscutum showed that these fishes, close to the common origin of all jawed vertebrates, had a mode of reproduction similar to modern sharks. Live birth requires internal fertilisation; sharks achieve this by using a "clasper", an extension of the pelvic fin that functions like a penis. The authors looked for a clasper in their placoderm fossils but couldn't find one, so they were forced to argue that it had been made of soft cartilage and had not been preserved.

Shortly afterwards, Per Erik Ahlberg from Uppsala University visited one of the Australian researchers and spotted a perfectly preserved bony clasper in one of their Incisoscutum fossils.

"It was lying in plain view but had been misinterpreted as part of the pelvis and overlooked," he says.

Together with the original authors he is publishing a short paper in this week's Nature that presents this missing piece of the puzzle and completes the picture of placoderm reproduction from mating to birth.

"It provides a pedigree of nearly 400 million years for the "advanced" and seemingly specialised reproductive biology of modern sharks," says Per Ahlberg.

Uppsala University

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