Flap-run reveals flight evolution

27 June 2011 Last updated at 02:04 By Victoria Gill Science reporter, BBC Nature Slow motion video of pigeon running up ramp. Courtesy University of Montana Flight Lab.

The ungainly sight of a bird furiously flapping its wings as its spindly legs propel it forward could be a peek at evolutionary history.

"Flap-running", researchers say, may have been a key step in the evolution of flight.

Experiments with pigeons have shown that it helps birds ascend slopes and suggests the earliest flightless birds might have used the same technique.

The study was published in the Journal of Experimental Biology.

Brandon Jackson, from the University of Montana, US, who led the study, explained that he and his colleagues wanted to know why birds would flap-run when they were capable of flight.

His co-researcher, Ken Dial, noticed this behaviour when filming a type of partridge known as a chuckar.

As the rotund birds negotiated obstacles, they would run up the objects flapping their wings. When Dr Dial discussed this behaviour with local ranchers and hunters, some reported that adult chukars would flap to run up cliffs, rather than fly.

The birds used far less energy when flap-running than when flying

Dr Jackson and his team decided to find out if the birds might be using the technique to save energy by measuring the amount of power generated by the flight muscles when birds flew and when they were flap-running.

They surgically implanted electrodes into the flight muscles of pigeons - closely related birds that often flap and run even though they are very good fliers.

The electrodes measured muscle activity in the birds as they flapped and ran up ramps of varying inclines, and as they flew parallel to those same ramps.

The team was most surprised by what they saw when they compared the birds' muscle activity on a ramp with a 65 degree incline.

Running up that ramp, explained Dr Jackson, "required about 10% as much power from the flight muscles" as flying.

"The signal was imperceptible at first, and we actually thought we had a problem with the recording equipment. But when we zoomed in, there it was, about a tenth the magnitude that it was during flight," he said.

"The birds seemed to be using hardly any power to flap their wings as they ran up the slopes."

The method, the researchers say, is also an essential learning step for fledging chicks.

"Flap running... lets young birds that cannot yet fly - because of small muscles, small wings, weak feathers, etc - get off the ground and away from some predators," Dr Jackson told BBC Nature.

"And if baby birds can perform these behaviours, benefit from them, and transition gradually to flight in their life-time, we think it's probable that dinosaurs with (similarly small wings) could have performed these behaviours, benefited from them, and transitioned towards flight over evolutionary time."

So watching birds learn to fly could allow us a glimpse of the stages of flight's evolution.

Dr Jackson concluded: "Very small wings powered by small muscles had aerodynamic function and survival benefits when they were flapped.

"No more major steps were required after that, just gradual but beneficial steps. And we can actually observe [those steps] in developing birds today."

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Smell key to big brain evolution

20 May 2011 Last updated at 09:08 By Victoria Gill Science reporter, BBC Nature The researchers scanned the fossilised skulls of tiny, very early mammals A highly developed sense of smell kick-started the development of mammals' big brains.

Scientists used very high-resolution scanning to study the skulls of two of the earliest known mammal species.

Comparing the shape of their brain cases to those of slightly earlier animals, or "pre-mammals", revealed that the first brain areas to over-develop were those associated with the sense of smell.

The findings are published in Science.

An improved sense of smell may have allowed our tiny, furry ancestors to hunt at night.

The researchers were able to create 3D images of prehistoric animals' brains using the latest computed tomography, or CT, scanning methods.

"Before CT, one had to break open a fossil to get to the internal anatomy," explained Professor Timothy Rowe from the University of Texas at Austin, one of the researchers involved in the study.

"[This technique] is non-destructive, so we can measure internal anatomy in ways that were never before possible."

Evolution timeline

Mammals, and humans in particular, have the largest brains in the animal kingdom, relative to the size of their bodies. So the scientists wanted to work out why mammal brains evolved to become so very large and complex.

Scan of Hadrocodium brain shown in pink

To do this, they studied the earliest known mammals - the tiny fossilised skulls of 190-million-year-old Morganucodon oehleri and Hadrocodium wui, both of which were discovered in China.

By comparing these skulls to those of more primitive animals, and to living mammals, they were able to build a sequence of events in the evolution of mammal brains.

The team found that, in early mammals, the brain regions associated with smell were much larger than in more primitive or "pre-mammal" ancestors.

"Based on what we know from living species, interpreting the [brain scans] of these 200 million year old fossils was pretty straight forward," said Professor Rowe.

He and his colleagues concluded that smell "drove most of the early expansion of the brain in these first 'proto-mammals' and in the last common ancestor of living mammal species".

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Smell was not really on the radar screens of most palaeontologists”

End Quote Professor Timothy Rowe University of Texas at Austin Dr R Glenn Northcutt from the University of California, San Diego, who was not involved in the research, wrote an accompanying article in the same issue of Science describing its significance.

He said that the study provided "the first solid evidence of the stages in mammalian brain evolution".

The researchers think that, 200 million years ago, mammals probably used their keen sense of smell to hunt at night, which meant that they could avoid competing for food resources with dinosaurs that shared their habitats.

"This would allow them to take advantage of nocturnal food sources like some of the insects and other arthropods that are active at night," Professor Rowe suggested.

He told BBC Nature that he was surprised to learn that smell was so important in mammal evolution.

"Most of the fossil record consists of just teeth and broken jaws, so most of the speculation was about innovations in feeding and hearing, which is tied to the jaw," he said.

"Until now, [smell] was not really on the radar screens of most palaeontologists."

Dr Zhexi Luo from the Carnegie Museum of Natural History in Pittsburgh, who was also involved in the study said: "Our mammal ancestors didn't develop that larger brain for contemplation, but for the sense of smell and touch.

"But thanks to these evolutionary advancements, which gave mammals a head start toward developing a large brain, humans some 190 million years later can ponder these very questions of natural history and evolution."

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