What dinosaurs and reptiles did for mammals

A study shows that a burst of global warming 300 million years ago was important for the development of vertebrate life

Evolution

What dinosaurs and reptiles did for mammals

New fossil analysis has highlighted two key developments in the evolution of Earth’s largest land animals. First, a burst of global warming 300 million years ago devastated tropical forests, triggering rapid evolutionary development of reptiles – and paving the way for the eventual rise of dinosaurs. Then, 235 million years later, the extinction of the dinosaurs enabled mammals to emerge from their shadow and grow spectacularly in size and diversity.

The earlier event – the intense warming near the end of the Carboniferous period – is less well known, though a study by scientists at Bristol University and Royal Holloway, University of London shows how important it was for the development of vertebrate life.

For mysterious reasons, the climate suddenly became hotter and dryer 300 million years ago, wiping out almost all the tropical forests on Earth. While amphibian populations suffered severe losses along with the forests, fossil analysis shows that reptiles – better able to adapt to dry habitats – underwent an evolutionary explosion.

The increasing reptilian diversity was a response to habitat fragmentation, the researchers say, as new species arose in the isolated fragments of surviving forest and the new arid habitats. The study appears in the journal Geology.

“It is fascinating that even in the face of devastating ecosystem collapse, animals may continue to diversify through the creation of endemic populations,” says Sarda Sahney of Bristol. “Life may not be so lucky again in the future, should the Amazon rainforest collapse.”

The extinction of the dinosaurs (successors to one reptilian line that arose after the Carboniferous forest collapse) 65 million years ago is one of the best-known episodes in geological history. Everyone has assumed that the dinos’ disappearance opened the evolutionary door to the mammals that survived the asteroid impact but only now, in an international study published in the journal Science, have researchers proved the point.

“The dinosaurs disappear and all of a sudden there is nobody else eating the vegetation,” says Jessica Theodor of the University of Calgary. As well as confirming the rapid growth in mammalian size after the dinosaurs, the study shows that the ecosystem can reset itself quickly. “You lose dinosaurs 65 million years ago, and within 25 million years the system is reset to a new maximum for the animals that are there in terms of body size. That’s a pretty short time-frame, geologically speaking,” she says.

The biggest mammal ever to walk the Earth was Indricotherium transouralicum, a herbivore that weighed about 17 tonnes. It lived in Eurasia 34 million years ago.

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Neuroscience

Could a video game advance anxiety therapy?

How does a neuroscientist create fear or anxiety in human subjects? Ethical and legal considerations prevent exposure to real danger but the volunteers must face the threat of something genuinely unpleasant.

Adam Perkins of King’s College London, who is researching the brain systems that control anxious or fearful feelings, has come up with a clever solution: the Joystick Operated Runway Task.

Volunteers play a video game while lying inside an fMRI (functional magnetic resonance imaging) brain scanner. They wear binocular goggles through which a runway is projected. Using a pressure-sensing joystick, they control the speed of a green dot moving along the runway. The game requires them to keep their dot moving at the right speed to avoid red dots in front of and behind it; if green touches red the player receives an electric shock – painful enough for the threat to generate anxiety, but not harmful.

Perkins and his colleagues measure the subjects’ emotions by the way they move the joystick and the pressure they exert on it. For example, oscillating the stick rapidly denotes anxiety. The scanner provides images to show which areas of the brain are most active during the task.

The study – funded partly by AXA, the insurance group – is investigating the suggestions from previous animal experiments that the hippocampus, a brain structure thought to be associated mainly with long-term memory and spatial awareness, is involved in controlling anxiety. Preliminary results from the first 12 subjects show signs of hippocampal activation.

“These are very exciting results and could lead to the development of new therapies in the treatment of generalised anxiety disorders focusing on the hippocampus,” says Stephen Williams, professor of neuroimaging at King’s.

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Light pollution

Let there be dark, say star gazers

The Campaign for Dark Skies, run by the British Astronomical Association and the Campaign to Protect Rural England (CPRE), will enlist “star gazers” early in the new year to build up its database of light pollution across the UK.

Volunteers will be asked to count the number of stars they can see with a naked eye in Orion, one of the best-known constellations in the winter sky, on any clear night between January 31 and February 6.

“The Star Count survey will help us measure the extent of light pollution,” says Emma Marrington, CPRE rural policy campaigner. “We want to use this evidence to convince ministers and local councils of the need to take action to tackle it, for example by ensuring that the correct lighting is used only where, and when, it is needed. This would cut light pollution, reduce carbon emissions and save money at the same time.”

The results of the 2011 survey will be compared with the last Star Count Week four years ago. Then, only two per cent of viewers could see more than 30 stars in Orion, compared with 54 per cent who saw fewer than 10 – a level indicating severe light pollution.

Instructions for the Star Count and a sky map will be available at www.cpre.org.uk/starcount from January 10 2011.

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Passive smoking

Second-hand smoke: the silent killer

Tobacco’s terrible toll on non-smokers is revealed in a World Health Organisation study, which estimates that passive smoking kills about 600,000 people a year – or 1 per cent of all deaths worldwide. By comparison, active smoking kills 5.1 million people a year.

The authors used the year 2004 for their analysis, published in the Lancet, because more recent comprehensive worldwide data is not available. Although many western countries have banned smoking in indoor public spaces and workplaces since then, stronger tobacco control measures are required, the WHO says.

This is partly because only 7.4 per cent of the world’s population lives in “jurisdictions with comprehensive smoke-free laws”, but mainly because most exposure to second-hand smoke comes at home from family members, not in public places.

Of the 603,000 deaths worldwide caused by passive smoking, the WHO research found that most – 379,000 – were due to heart disease. In addition there were 165,000 deaths from lower respiratory tract infection, 37,000 from asthma and 21,000 from lung cancer.

The death toll includes 165,000 children, almost entirely in the developing world. In western Europe, for example, passive smoking killed 35,000 adults and just 70 children, while in Africa there were 43,000 deaths of children and 9,500 of adults.

The statistical basis of the estimates can be challenged, as a Lancet editorial written by health experts at the University of Southern California notes. “However there can be no question that the 1.2bn smokers in the world are exposing billions of non-smokers to second-hand smoke, a disease-causing air pollutant,” they say.

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Prostate cancer

Size matters

Long index fingers reduce the risk of prostate cancer. A UK study of 4,500 men has found that those whose index finger is longer than their ring finger were one-third less likely to develop the disease than men with the opposite finger length pattern.

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