郑少群博客

2013年7月2日星期二

Cattle flatulence doesn't stink with biotechnology: Farmers could improve air quality by using hormones

According to a new article in Animal Frontiers, biotechnologies increase food production and reduce harmful gas output from cattle.

"We are increasing the amount of product with same input," said Clayton Neumeier, PhD student at University of California, Davis, in an interview.

In the Animal Frontiers paper, Neumeier describes a recent experiment using biotechnologies. In the experiment, a test group of cattle were treated with biotechnologies. Different groups of cattle received implants, Ionophores and Beta-adrenergic agonists. These biotechnologies help cattle grow more efficiently. A control group of cattle were not treated with any of these biotechnologies.

Researchers measured gas output by placing finishing steers in a special corral that traps emissions. Each treatment group was tested four times to ensure accurate results.

The researchers also tested a dairy biotechnology called rBST. This biotechnology is a synthetic version of a cattle hormone that does not affect humans. Many producers inject cows with rBST to help them produce more milk.

In their experiment, the researchers gave rBST to a test group of cows and gave no rBST to a control group of cows. They discovered that the rBST group produced more milk per cow. When cows produce more milk, greenhouse gas emissions decrease because farms need fewer cows.

Dr. Kim Stackhouse, National Cattleman's Beef Association Director of Sustainability, said animal agriculture has reduced emissions through the use of technologies. Technologies that improve animal performance, crop yields, and manure management and the installation of biogas recovery systems have all contributed to reducing the environmental impact of beef.

Biogas recovery systems are used in processing facilities to produce energy from animal waste. Animal waste is collected in lagoons, where the gas is captured. The gas is transported through an internal combustion area that produces energy for heat and electricity.

"I expect there to be more improvement as we continue be more efficient, continue to do more with less and also strive to find new improvement opportunities," Stackhouse said.

Some consumers do not like the use of biotechnology in food production. Neumeier thinks these consumers are unaware of the benefits of biotechnology. His research shows that biotechnology can produce more food and lower gas emissions.

"We need to inform them that these are valuable tools for those two reasons and not be turned off by the use of biotechnology," Neumeier said.

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Identifying climate impact hotspots across sectors

It identifies the Amazon region, the Mediterranean and East Africa as regions that might experience severe change in multiple sectors. The article is part of the outcome of the Intersectoral Impact Model Intercomparison Project (ISI-MIP) that will be featured in a special issue of PNAS later this year.

"Overlapping impacts of climate change in different sectors have the potential to interact and thus multiply pressure on the livelihoods of people in the affected regions," says lead-author Franziska Piontek of the Potsdam Institute for Climate Impact Research. "This is why we focus on multisectoral impacts around the world, which turn out to be felt in developed as well as developing countries."

The study is the first to identify hotspots across these sectors while being based on a comprehensive set of computer simulations both for climate change and for the impacts it is causing. Modelling groups from all over the world collaborated under the roof of the ISI-MIP project to generate consistent data. This is an unprecedented community effort of climate impact researchers worldwide to elucidate the risks that humankind is running. It aims at laying a new foundation for future analyses of the consequences of global warming.

"Now we looked for instance into the water availability during the last thirty years," says co-author Qiuhong Tang of the Chinese Academy of Sciences. "We took as the threshold the water availability only undercut by the three driest years. When the average water availability in our projections under global warming sinks below this threshold, we call this severe. So what today is considered extreme could become the new normal." This is the case in the Mediterranean.

The combination of multiple different impact and climate models increases -- even though this at first glance seems to be a contradiction in terms -- both the robustness and the spread of results. "We get a broader range in projections of future crop yields, for example, when we recognize assumptions in both the climate and the impact model processes. However, locations with strong agreement among model approaches are more reliable hotspots than those identified by a projection based on just one model with all its underlying assumptions," says co-author Alex Ruane of the NASA Goddard Institute for Space Studies. "It allows for a risk management perspective -- in the hotspot parts of Africa, for instance, even small temperature rises can lead to additional losses that many small farmers simply cannot afford."

The study takes a conservative approach with regard to model agreement. To make allowance for the large spread of results, the scientists also computed a worst case-scenario, based on the most worrying 10 percent of computer runs. This assessment shows a large additional extent of multisectoral climate impacts overlap, with almost all the world's inhabitated areas affected.

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Cloud behavior expands habitable zone of alien planets

Researchers at the University of Chicago and Northwestern University based their study, which appears in Astrophysical Journal Letters, on rigorous computer simulations of cloud behavior on alien planets. This cloud behavior dramatically expanded the habitable zone of red dwarfs, which are much smaller and fainter than stars like the sun.

Current data from NASA's Kepler Mission, a space observatory searching for Earth-like planets orbiting other stars, suggest there is approximately one Earth-size planet in the habitable zone of each red dwarf. The UChicago-Northwestern study now doubles that number.

"Most of the planets in the Milky Way orbit red dwarfs," said Nicolas Cowan, a postdoctoral fellow at Northwestern's Center for Interdisciplinary Exploration and Research in Astrophysics. "A thermostat that makes such planets more clement means we don't have to look as far to find a habitable planet."

Cowan is one of three co-authors of the study, as are UChicago's Dorian Abbot and Jun Yang. The trio also provide astronomers with a means of verifying their conclusions with the James Webb Space Telescope, scheduled for launch in 2018.

The formula for calculating the habitable zone of alien planets -- where they can orbit their star while still maintaining liquid water at their surface -- has remained much the same for decades. But the formula largely neglects clouds, which exert a major climatic influence.

"Clouds cause warming, and they cause cooling on Earth," said Abbot, an assistant professor in geophysical sciences at UChicago. "They reflect sunlight to cool things off, and they absorb infrared radiation from the surface to make a greenhouse effect. That's part of what keeps the planet warm enough to sustain life."

A planet orbiting a star like the sun would have to complete an orbit approximately once a year to be far enough away to maintain water on its surface. "If you're orbiting around a low mass or dwarf star, you have to orbit about once a month, once every two months to receive the same amount of sunlight that we receive from the sun," Cowan said.

Tightly orbiting planets

Planets in such a tight orbit would eventually become tidally locked with their sun. They would always keep the same side facing the sun, like the moon does toward Earth. Calculations of the UChicago-Northwestern team indicate that the star-facing side of the planet would experience vigorous convection and highly reflective clouds at a point that astronomers call the sub-stellar region. At that location the sun always sits directly overhead, at high noon.

The team's three-dimensional global calculations determined for the first time the effect of water clouds on the inner edge of the habitable zone. The simulations are similar to the global climate simulations that scientists use to predict Earth climate. These required several months of processing, running mostly on a cluster of 216 networked computers at UChicago. Previous attempts to simulate the inner edge of exoplanet habitable zones were one-dimensional. They mostly neglected clouds, focusing instead on charting how temperature decreases with altitude.

"There's no way you can do clouds properly in one-dimension," Cowan said. "But in a three-dimensional model, you're actually simulating the way air moves and the way moisture moves through the entire atmosphere of the planet."

These new simulations show that if there is any surface water on the planet, water clouds result. The simulations further show that cloud behavior has a significant cooling effect on the inner portion of the habitable zone, enabling planets to sustain water on their surfaces much closer to their sun.

Astronomers observing with the James Webb Telescope will be able to test the validity of these findings by measuring the temperature of the planet at different points in its orbit. If a tidally locked exoplanet lacks significant cloud cover, astronomers will measure the highest temperatures when the dayside of the exoplanet is facing the telescope, which occurs when the planet is on the far side of its star. Once the planet comes back around to show its dark side to the telescope, temperatures would reach their lowest point.

But if highly reflective clouds dominate the dayside of the exoplanet, they will block a lot of infrared radiation from the surface, said Yang, a postdoctoral scientist in geophysical sciences at UChicago. In that situation "you would measure the coldest temperatures when the planet is on the opposite side, and you would measure the warmest temperatures when you are looking at the night side, because there you are actually looking at the surface rather than these high clouds," Yang said.

Earth-observing satellites have documented this effect. "If you look at Brazil or Indonesia with an infrared telescope from space, it can look cold, and that's because you're seeing the cloud deck," Cowan said. "The cloud deck is at high altitude, and it's extremely cold up there."

If the James Webb Telescope detects this signal from an exoplanet, Abbot noted, "it's almost definitely from clouds, and it's a confirmation that you do have surface liquid water."

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Curious mix of precision and brawn in a pouched super-predator

Australian and American marsupials are among the closest living relatives of the extinct Thylacosmilus atrox, which had tooth roots extending rearwards almost into its small braincase.

"Thylacosmilus looked and behaved like nothing alive today," says UNSW palaeontologist, Dr Stephen Wroe, leader of the research team.

"To achieve a kill the animal must have secured and immobilised large prey using its extremely powerful forearms, before inserting the sabre-teeth into the windpipe or major arteries of the neck -- a mix of brute force and delicate precision."

The iconic North American sabre-toothed 'tiger', Smilodon fatalis, is often regarded as the archetypal mammalian super-predator.

However, Smilodon -- a true cat -- was just the end point in one of at least five independent 'experiments' in sabre-tooth evolution through the Age of Mammals, which spanned some 65 million years.

Thylacosmilus atrox is the best preserved species of one of these evolutionary lines -- pouched sabre-tooths that terrorised South America until around 3.5 million years ago.

For its size, its huge canine teeth were larger than those of any other known sabre-tooth.

Smilodon's killing behaviour has long attracted controversy, but scientists now mostly agree that powerful neck muscles, as well as jaw muscles, played an important role in driving the sabre-teeth into the necks of large prey.

Little was known about the predatory behaviour in the pouched Thylacosmilus.

To shed light on this super-predator mystery, Dr Wroe's team of Australian and US scientists constructed and compared sophisticated computer models of Smilodon and Thylacosmilus, as well as a living conical-toothed cat, the leopard.

These models were digitally 'crash-tested' in simulations of biting and killing behaviour. The results are published in the journal PLoS ONE.

"We found that both sabre-tooth species were similar in possessing weak jaw-muscle-driven bites compared to the leopard, but the mechanical performance of the sabre-tooths skulls showed that they were both well-adapted to resist forces generated by very powerful neck muscles," says Dr Wroe.

"But compared to the placental Smilodon, Thylacosmilus was even more extreme."

"Frankly, the jaw muscles of Thylacosmilus were embarrassing. With its jaws wide open this 80-100 kg 'super-predator' had a bite less powerful than a domestic cat. On the other hand -- its skull easily outperformed that of the placental Smilodon in response to strong forces from hypothetical neck muscles."

"Bottom line is that the huge sabres of Thylacosmilus were driven home by the neck muscles alone and -- because the sabre-teeth were actually quite fragile -- this must have been achieved with surprising precision."

"For Thylacosmilus -- and other sabre-tooths -- it was all about a quick kill."

"Big prey are dangerous -- even to super-predators -- and the faster the kill the less likely it is that the predator will get hurt -- or for that matter attract unwanted attention from other predators."

"It may not have been the smartest of mammalian super-predators -- but in terms of specialisation -- Thylacosmilus took the already extreme sabre-tooth lifestyle to a whole new level," says Dr Wroe.

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2013年7月1日星期一

Climate change: Disequilibrium will become the norm in the plant communities of the future

This has been demonstrated by a new synthesis carried out by two researchers at Aarhus University -- Professor of Biology Jens-Christian Svenning and Assistant Professor Brody Sandel.

Professor Svenning explains: "In the climate debate, even researchers have had a tendency to overlook the fact that ecological dynamics can be slow. However, our forests take an extremely long time to adapt. For example, we still have a small amount of small-leaved lime in Denmark, which has held on since the warm period during the Bronze Age, i.e. about 3000 years. Perhaps it will now get another chance to spread when the summers once more get warmer. However, such expansion would take a long time, as lime is not a particularly fast-growing tree or particularly good at dispersing, even under optimum conditions. The climate will change considerably in the course of a single tree generation so we should not assume that the forest we're looking at in a given place is suitable for the climate. Future climate will constantly shift, which will increasingly result in these strange situations of disequilibrium."

Even fast spreaders such as some invasive exotic plants remain in disequilibrium for decades or centuries. Shown here is a Norway maple, a highly invasive tree species in North America that may nevertheless still take many decades to spread across even small landscapes.

The challenges we face

"Consequently, if you're trying to practise natural forest management with natural regeneration, you may see completely different plants regenerating compared with what you had before, because the climate has shifted to become suitable for another set of species. This also makes it challenging to adhere to a management plan granting preservation status to a particular type of nature at a certain site. At such a site, the existence of a large number of fully grown specimens of an endangered species is no guarantee that there will be a next generation.

This would be challenging for everyone -- for the managers, for the people who use the countryside in one way or another, and also for the researchers who are used to working with ecosystems that are much more balanced. Plant life and ecosystems will become much more dynamic and often out of sync with the climate.

We're causing so many changes to the climate, but at the same time nature is SO slow. Just think of a tree generation. Our entire culture is based on something that was, if not in complete equilibrium, then at least relatively predictable. We're used to a situation where flora, fauna and climate are reasonably well matched. In future, this equilibrium will shift on an ongoing basis, and there will be plenty of mismatches. That's what we'll have to work with."

Professor Svenning also calls for caution: "With nature in such a state of disequilibrium, human introduction of new species will play a key role. Take cherry laurel, for example, which we see in many gardens in Denmark. It's ready to spread throughout the Danish countryside. If it were to migrate unaided from its nearest native site in South-East Europe to Denmark, it would take thousands of years. Horticulturists now help it along. This will help the species survive, but can also cause northern species in Denmark to become extinct more rapidly. The cherry laurel is an evergreen, and if it disperses on the forest floor, it may create too much shade for the existing flora on the forest floor to survive. At the same time, the disequilibrium presents the advantage that such dispersal will take decades despite the contribution of horticulturists," Professor Svenning concludes.

Cherry laurel is another example of a species that has not yet returned to Northern Europe since the last Ice Age, but which we have helped along by planting in our gardens. Here it was found in the English countryside. Photo: Jens-Christian Svenning, Aarhus University.

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Can watching an avatar translate to real-life weight loss?

July 1, 2013 — An estimated two-thirds of all Americans are overweight or obese and many find it difficult to lose weight and keep it off. They've tried fad diets, exercise programs, diet pills and other methods but the battle continues. Now, a new study suggests that watching an avatar model weight-loss behavior in a virtual community might help some women shed pounds in the real world.

"This pilot study showed that you don't have to be a gamer to use virtual reality to learn some important skills for weight loss," said Melissa Napolitano, PhD, an associate professor of prevention and community health at the George Washington University School of Public Health and Health Services (SPHHS). "This small study suggests that virtual reality could be a promising new tool for building healthier habits."

If proven effective, such a program might offer an inexpensive way to help millions of Americans -- including overweight men--learn the skills and behavior they need to lose weight over the long run.

Previous research had suggested that using virtual reality to model skills or provide reinforcement was effective. For example, people who watched an avatar that resembled them run on a treadmill were more likely to exercise the next day than if they watched an unfamiliar avatar, according to a Stanford University study.

Napolitano, who did the study while at Temple University's Center for Obesity Research and Education, in collaboration with Temple's Sbarro Institute for Cancer Research and Molecular Medicine, and her colleagues, wondered if avatars could be used as a tool to model weight loss behavior for overweight women.

To find out, the team first conducted a survey among 128 overweight women. Most of them had tried to lose weight during the last year and the majority had never used a virtual reality game. Despite the fact that most of these women had no experience using virtual reality or even playing online games, the researchers found that 88 percent said they would be willing to use a program with an avatar modeling habits that might give them an edge in the battle to lose weight.

Many of the study participants thought that watching an avatar could help them visualize and then put in place healthy behavior, such as taking a walk every day or picking healthy options when food shopping. And in fact, theory and research tells us that modeling or seeing the steps one needs to take in order to achieve a desired goal makes behavioral change easier to accomplish, Napolitano said.

But to test the concept, the team first had to create videos that showed an avatar in a variety of different situations such as walking on a treadmill or navigating a cart through the aisles of a grocery store. The end result was a partnership from the treatment side drawing on Napolitano's expertise as well as the experts on the technical programming front to show the avatars in action. Using their extensive expertise in virtual reality, Director Antonio Giordano, MD, PhD, and Giuseppe Russo, PhD, of Temple's Sbarro Institute for Cancer Research and Molecular Medicine, developed a virtual reality simulation featuring such an avatar.

"With our vast experience in creating custom virtual reality environments for eHealth, we were able to assist Dr. Napolitano in this pilot study from the technical point of view," said Russo. "This study is a perfect example of how virtual reality can be used in promoting human health."

Given that not all the woman who participated were avid tech users, the team created a DVD that showed the avatar in four real-world environments. The women did not have to manipulate the avatar, they just watched the video; however they did pick out the skin color and shape of the avatar to more closely resemble their own appearance--a feature that might help the study participants visualize and learn a new behavior, Napolitano said.

In the next part of the trial, the team enrolled eight overweight women in a four-week pilot test to see if watching the videos could help these women learn new skills that could lead to weight loss. The women came to the clinic once a week and watched a 15-minute DVD featuring an avatar demonstrating healthy weight loss behaviors.

For example, in one lesson the women watched the avatar sitting down for dinner and learned about portion sizes. Participants watched as the avatar viewed a plate with a serving size that was too large and one that was just right. In another lesson, they watched an avatar walk with moderate intensity on a treadmill and learned the walking pace needed to help with weight loss goals, Napolitano said. The women in this pilot study also set weight-loss and exercise goals and kept a food and exercise log.

Based on theory and previous research, the team thought that watching the avatar in the virtual world might make it more likely women would practice those skills in real life. The virtual "model" was the key to helping participants break healthy behaviors into manageable steps, Napolitano noted.

And after four weeks of treatment, the women in this pilot study had lost an average of 3.5 pounds, a fairly typical amount for traditional diet plans, Napolitano said. However, the researchers hope that by watching the avatar the women using this program will be much more likely to put healthy habits in place over the long run -- keep the weight off for good.

Additional studies must be conducted in order to solidify these early findings and show that men and women who use the tool really do lose weight and maintain that loss. "This is just the first step to show that women, even those who are not gamers, are interested in an avatar-based technology to help them with a weight-loss plan," said Napolitano. "We are excited by the potential of this technology as a scalable tool to help people learn the skills to be successful at weight loss over the long run."

The study, "Using Avatars to Model Weight Loss Behaviors: Participant attitudes and technology development," appears in the July 1 Journal of Diabetes Science and Technology. Other authors of the study include Sharon Hayes and Gary Foster, both at Temple's Center for Obesity Research and Education, and Giuseppe Russo, Debora Muresu and Antonio Giordano of Temple's Sbarro Institute for Cancer Research and Molecular Medicine.

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Long-term cannabis use may blunt the brain's motivation system

Researchers found that dopamine levels in a part of the brain called the striatum were lower in people who smoke more cannabis and those who began taking the drug at a younger age.

They suggest this finding could explain why some cannabis users appear to lack motivation to work or pursue their normal interests.

The study, by scientists at Imperial College London, UCL and King's College London, was funded by the Medical Research Council and published in the journal Biological Psychiatry.

The researchers used PET brain imaging to look at dopamine production in the striatum of 19 regular cannabis users and 19 non-users of matching age and sex.

The cannabis users in the study had all experienced psychotic-like symptoms while smoking the drug, such as experiencing strange sensations or having bizarre thoughts like feeling as though they are being threatened by an unknown force.

The researchers expected that dopamine production might be higher in this group, since increased dopamine production has been linked with psychosis. Instead, they found the opposite effect.

The cannabis users in the study had their first experience with the drug between the ages of 12 and 18. There was a trend for lower dopamine levels in those who started earlier, and also in those who smoke more cannabis. The researchers say these findings suggest that cannabis use may be the cause of the difference in dopamine levels.

The lowest dopamine levels were seen in users who meet diagnostic criteria for cannabis abuse or dependence, raising the possibility that this measure could provide a marker of addiction severity.

Previous research has shown that cannabis users have a higher risk of mental illnesses that involve repeated episodes of psychosis, such as schizophrenia.

"It has been assumed that cannabis increases the risk of schizophrenia by inducing the same effects on the dopamine system that we see in schizophrenia, but this hasn't been studied in active cannabis users until now," said Dr Michael Bloomfield, from the Institute of Clinical Sciences at Imperial, who led the study.

"The results weren't what we expected, but they tie in with previous research on addiction, which has found that substance abusers -- people who are dependent on cocaine or amphetamine, for example -- have altered dopamine systems.

"Although we only looked at cannabis users who have had psychotic-like experiences while using the drug, we think the findings would apply to cannabis users in general, since we didn't see a stronger effect in the subjects who have more psychotic-like symptoms. This needs to be tested though.

"It could also explain the 'amotivational syndrome' which has been described in cannabis users, but whether such a syndrome exists is controversial."

Other studies have looked at dopamine release in former cannabis users and not seen differences with people who haven't taken cannabis, suggesting that the effects seen in this study are likely to be reversible.

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Rocket-launched camera reveals highways and sparkles in the solar atmosphere

With partners in the United States and Russia, the UCLan team used a sounding rocket to launch the NASA High Resolution Coronal Imager (Hi-C) from the White Sands Missile Range in New Mexico, USA. During its short flight, the Hi-C team obtained images of the solar atmosphere (the solar corona) five times sharper than anything seen before and acquired data at a rate of about one image every five seconds.

The new camera observed the Sun in extreme ultraviolet light and focused on a large, magnetically-active sunspot region. Images from Hi-C reveal a number of new features in the corona, including 'blobs' of gas ricocheting along 'highways' and bright dots that switch on and off rapidly which the group call 'sparkles'.

In the new images, small clumps of electrified gas (plasma) at a temperature of about one million degrees Celsius are seen racing along highways shaped by the Sun's magnetic field. These blobs travel at around 80 km per second (the equivalent of 235 times the speed of sound on Earth), fast enough to travel the distance from Glasgow to London in 7 seconds. The highways are 450 km across, roughly the length of Ireland from north to south.

The flows of material are inside a so-called solar filament, a region of dense plasma that can erupt outwards from the Sun. These eruptions, known as coronal mass ejections (CMEs), carry billions of tonnes of plasma into space. If a CME travels in the right direction it can interact with Earth, disturbing the terrestrial magnetic field in a 'space weather' event that can have a range of destructive consequences from damaging satellite electronics to overloading power grids on the ground. The discovery and nature of the solar highways allows scientists to better understand the driving force for these eruptions and help predict with greater accuracy when CMEs might take place.

Another new set of images could help explain an enduring mystery of the Sun. Astronomers have long struggled to understand why, with a temperature of two million degrees, the corona is around 400 times hotter than the solar surface. Hi-C images reveal dynamic bright dots which switch on and off at high speed.

These 'sparkles' typically last around 25 seconds, are about 680 km across (the size of the UK) and release at least 1024 (one million million million million) Joules of energy in each event, or around 10,000 times the annual energy consumption of the population of the UK (based on information from the UK Department of Energy and Climate Change). The sparkles are thus a clear signal that enormous amounts of energy are being added into the corona and may then be released violently to heat the plasma.

Solar physicist Professor Robert Walsh, UCLan's University Director of Research, added: "I'm incredibly proud of the work of my colleagues in developing Hi-C. The camera is effectively a microscope that lets us view small scale events on the Sun in unprecedented detail. For the first time we can unpick the detailed nature of the solar corona, helping us to predict when outbursts from this region might head towards the Earth."

NASA Marshall heliophysicist Dr Jonathan Cirtain, principal investigator for the Hi-C mission said: "Our team developed an exceptional instrument capable of revolutionary image resolution of the solar atmosphere. We took advantage of the high level of solar activity to focus in on an active sunspot and obtained these remarkable pictures."

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Different neuronal groups govern right-left alternation when walking

Most land animals can walk or run by alternating their left and right legs in different coordinated patterns. Some animals, such as rabbits, move both leg pairs simultaneously to obtain a hopping motion. In the present study, the researchers Adolfo Talpalar and Julien Bouvier together with professor Ole Kiehn and colleagues, have studied the spinal networks that control these movement patterns in mice. By using advanced genetic methods that allow the elimination of discrete groups of neurons from the spinal cord, they were able to remove a type of neurons characterized by the expression of the gene Dbx1.

"It was classically thought that only one group of nerve cells controls left right alternation," says Ole Kiehn who leads the laboratory behind the study at the Department of Neuroscience. "It was then very interesting to find that there are actually two specific neuronal populations involved, and on top of that that they each control different aspect of the limb coordination."

Indeed, the researchers found that the gene Dbx1 is expressed in two different groups of nerve cells, one of which is inhibitory and one that is excitatory. The new study shows that the two cellular populations control different forms of the behaviour. Just like when we change gear to accelerate in a car, one part of the neuronal circuit controls the mouse's alternating gait at low speeds, while the other population is engaged when the animal moves faster. Accordingly, the study also show that when the two populations are removed altogether in the same animal, the mice were unable to alternate at all, and hopped like rabbits instead.

There are some animals, such as desert mice and kangaroos, which only hop. The researchers behind the study speculate that the locomotive pattern of these animals could be attributable to the lack of the Dbx1 controlled alternating system.

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2013年6月28日星期五

How 'parrot dinosaur' switched from four feet to two as it grew

June 28, 2013 — Tracking the growth of dinosaurs and how they changed as they grew is difficult. Using a combination of biomechanical analysis and bone histology, palaeontologists from Beijing, Bristol, and Bonn have shown how one of the best-known dinosaurs switched from four feet to two as it grew.

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Psittacosaurus, the 'parrot dinosaur' is known from more than 1000 specimens from the Cretaceous, 100 million years ago, of China and other parts of east Asia. As part of his PhD thesis at the University of Bristol, Qi Zhao, now on the staff of the Institute for Vertebrate Paleontology in Beijing, carried out the intricate study on bones of babies, juveniles and adults.

Dr Zhao said: "Some of the bones from baby Psittacosaurus were only a few millimetres across, so I had to handle them extremely carefully to be able to make useful bone sections. I also had to be sure to cause as little damage to these valuable specimens as possible."

With special permission from the Beijing Institute, Zhao sectioned two arm and two leg bones from 16 individual dinosaurs, ranging in age from less than one year to 10 years old, or fully-grown. He did the intricate sectioning work in a special palaeohistology laboratory in Bonn, Germany,

The one-year-olds had long arms and short legs, and scuttled about on all fours soon after hatching. The bone sections showed that the arm bones were growing fastest when the animals were ages one to three years. Then, from four to six years, arm growth slowed down, and the leg bones showed a massive growth spurt, meaning they ended up twice as long as the arms, necessary for an animal that stood up on its hind legs as an adult.

Professor Xing Xu of the Beijing Institute, one of Dr Zhao's thesis supervisors, said: "This remarkable study, the first of its kind, shows how much information is locked in the bones of dinosaurs. We are delighted the study worked so well, and see many ways to use the new methods to understand even more about the astonishing lives of the dinosaurs."

Professor Mike Benton of the University of Bristol, Dr Zhao's other PhD supervisor, said: "These kinds of studies can also throw light on the evolution of a dinosaur like Psittacosaurus. Having four-legged babies and juveniles suggests that at some time in their ancestry, both juveniles and adults were also four-legged, and Psittacosaurus and dinosaurs in general became secondarily bipedal."

The paper is published in Nature Communications.

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