Alligators and birds share lung structure and ancestor

Alligators and birds share a breathing mechanism which may have helped their ancestors dominate Earth more than 200 million years ago, scientists say.

Research published in the journal Science found that like birds, in alligators air flows in one direction.

Birds' lung structure allows them to breathe when flying in low oxygen, or hypoxic, conditions.

This breathing may have helped a common ancestor of birds and alligators thrive in the hypoxic period of the Triassic.

Mammals 'hiding'

"It might explain a mystery that has been around for quite some time", Dr Colleen Farmer from the University of Utah told BBC News.

The mystery in question is why the archosaurs came to dominate Earth after the planet's worst mass extinction 251 million years ago.

Archosaurs evolved into two different branches which developed into crocodilians, dinosaurs, flying pterosaurs and eventually birds.

Synapsids, which evolved to include mammals, had been dominant in the Permian period before the mass extinction.

Some survived but were toppled from their perch by the archosaurs.

Any mammal-like synapsid survivors "were teeny liittle things hiding in cracks" said Dr Farmer. "I think it's because they couldn't compete.

"It wasn't until the die-off of the large dinosaurs 65 million years ago that mammals made a comeback and started occupying body sizes larger than an opossum."

To demonstrate alligator lung mechanisms, the scientists measured airflow in anesthetised animals, showing it flows in one direction rather than in and out of chambers.

They also pumped water containing tiny fluorescent beads into the lungs of dead alligators to observe the flow.

Puzzle solved

The researchers believe the similarity in lung structure may explain why some animals were better able to adapt after the extinction, when oxygen levels dropped.

"We know that birds are really good at breathing in hypoxic conditions. They can fly at altitudes that would kill a mammal," said Dr Farmer.

"Many archosaurs, such as pterosaurs, apparently were capable of sustaining vigorous exercise. Lung design may have played a key role in this capacity.

"That's been a puzzle, why do birds have these very different lungs? But now we can date it back to the common ancestor of birds and crocodilians.

"It implies that all dinosaurs, herbivores like Triceratops and carnivores like Tyrannosaurus, had bird-like lungs," Dr Farmer added.

Europe cold snap kills dozens across continent

Dozens of people have died across Europe as days of snow storms and sub-zero temperatures swept the continent, causing traffic chaos for millions.

At least 29 people froze to death in Poland as temperatures fell far below freezing, while in southern Germany a figure of -33C (-27F) was recorded.

Moscow said it was deploying 9,000 snow ploughs to clear the city's streets.

Air, rail and road transport links were disrupted across northern Europe where more snow was expected in coming days.

Eurostar services between the UK and the continent were suspended on Monday for a third day, as the company launched an immediate review into train breakdowns which have stranded and delayed tens of thousands of passengers since Friday.

'Saturation point'

The crisis prompted French President Nicolas Sarkozy to call the head of national rail carrier SNCF - the majority stakeholder in Eurostar - to order a normal resumption of service by Tuesday.

Meanwhile Eurotunnel - which carries vehicles under the Channel between England and France - said its terminal at Folkestone was at "saturation point" and closed its shuttle car service to new arrivals.

In Poland, police appealed for people to help if they came across homeless or drunk people lying outside, as temperatures dropped towards -20C in some areas.

Most of the 42 people who froze to death in the country over the weekend were homeless, police said.

Meanwhile, one restaurant owner offered tens of thousands of homeless people a hot meal in Krakow's main square.

"The food is not the only important thing," restaurateur Janusz Kosciuszko was quoted as telling Euronews.

"What is also important is that these people know that someone is thinking about them."

Treacherous travel conditions on roads and railway lines caused a spike in accidents across the continent, with several people reportedly killed in accidents in Austria and Germany.

Fifty people were injured when a train hit a buffer in the Croatian city of Zagreb, while 36 were injured when a passenger train derailed in Paris.

Parts of the continent saw 20in (50cm) of snow over the weekend.

In France, Germany, Belgium and the Netherlands, airport operators struggled to clear runways amid thick snowfall, with major disruption to flight patterns.

In France, a second wave of snowstorms hit the country's north on Sunday with Paris' Charles de Gaulle airport warning as many as one in five flights was likely to be cancelled on Monday.

Germany's third largest airport - in Dusseldorf - was also closed because of Sunday's heavy snow.

In Belgium, the three biggest airports - Brussels, Charleroi and Liege - were completely shut. Severe delays and cancellations were reported at Amsterdam's Schiphol airport.

Temperatures were forecast to rise later in the week.