Dinosaur fossils and super-strength X-rays could reveal why birds fly

The link between dinosaurs and birds has fascinated scientists for decades but the answer remains elusive. Now, modern imaging techniques are opening up a new world of virtual palaeontology and allowing scientists to take a fresh approach to the question of how dinosaurs evolved into birds.

Dr Peter Falkingham from the Royal Veterinary College, London, and Brown University, US, has been investigating dinosaur and bird locomotion by looking at fossilised dinosaur footprints and comparing them to footprints and X-rays of modern birds moving. 

‘Fossil footprints offer the only direct record of locomotion in the fossil record. So our idea was to look at the footprint and see if we can back calculate the way the limb was moving and compare that through time,’ he said.

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‘My hopes are that eventually palaeontology will lead to … a comprehensive computer-generated palaeoworld.’

To get data from modern birds, Dr Falkingham, who leads the TRACKEVOL project, has been getting guinea fowl to run along a specific track between two X-ray beams, a process known as XROMM.

Two fluoroscope X-ray machines are positioned so that their beams cross. Then the bird runs along a track until it hits the point where the beams overlap. Here X-ray video is recorded, which allows researchers to see three dimensional movements of the foot that would otherwise be hidden by the sediment.

By looking at those motions, and at the substrate along which the bird is running and the impression that is left, scientists can hypothesise how dinosaurs might have moved.

‘We’ve been using a combination of X-ray techniques and computer simulations so that we can record the bird’s foot as a bird is making a footprint,’ said Dr Falkingham. ‘And then we can use simulation to model what the soil is doing around the foot as the foot plunges into it. We can then try to link specific motions and features of the modern bird track with 200 million-year-old dinosaur tracks.’

The fossilised footprints that Dr Falkingham and his team study are not like the impressions that a person might leave in the sand as they walk along the beach.

‘The kinds of footprints that we are looking at are very, very different,’ he explained. ‘So if you can imagine quite deep mud, you sink through it and the mud closes up above your foot and then you extract your foot again. This records a lot more motion of the foot, but results in a really complex problem to untangle.’

Computer simulations

The team input the data from the X-rays and from the fossil footprints into a computer simulation, which gives us a real-life idea of how dinosaurs might have moved and the link to motion in birds. It's a crucial step towards working out why birds evolved flight. 

‘Birds have evolved from dinosaurs, and birds and dinosaurs differ in a number of ways,’ said Dr Falkingham. ‘Particularly we’re interested in the way that theropod dinosaurs (from which birds descend) differ from birds in their hind limbs.'

The simulation that the team have created is also adding to knowledge of how today's birds move. 'In trying to study dinosaurs we discovered that no one really knows how birds move over compliant terrain so we’re feeding back into the biology side,' said Dr Falkingham.

He says the next step for the research is to vary the motion. 'Essentially the simulation is a way of testing hypotheses of motion. We think dinosaurs moved this way, if we put that into a simulation, does that produce virtual tracks that look like the fossil tracks that we find?’

Scientists are also using information from prehistoric fossilised bird samples to create computer simulations and study how flight evolved in birds.

Dr Fabien Knoll from the University of Manchester, UK, leads the AVATAR project, which began in September 2014 and aims to study the evolution of avian flight using both fossils and imaging technology. He uses computer modelling and synchrotron-based imaging in order to get the most accurate picture possible of what the fossilised birds would have looked like when they were alive.

Synchrotron facilities produce a type of intense, high-energy electromagnetic radiation, billions of times more brilliant than a hospital X-ray source. The beam is so strong that researchers can even tell how pigmented a fossil might have been.

‘We particularly use X-ray from synchrotron radiation sources. This is not only for 3D reconstructions but also the recognition of original pigments in fossils,’ said Dr Knoll. ‘This is a field of research that is still in its infancy.’

Dr Knoll builds virtual models and computer simulations based on the information that he collects about the pigmentation, the skeleton and the muscle structure of the birds from the X-rays of the fossils.

3D models

‘In terms of the models we build, they are generic musculoskeletal models and we can simulate anything,’ he said. ‘It is now possible to achieve highly detailed musculoskeletal models that can be used to explore the locomotor abilities of both extant and extinct animals. The skeletal elements can be articulated in 3D and the musculature can be reconstructed in 3D.’

Dr Knoll, who plans to make videos of these models later in the project, says the new imaging and simulation techniques are changing palaeontology.

‘Computer-aided investigation of fossils has transfigured our understanding of extinct organisms,’ he said. ‘Key to unravelling the origins of bird flight is the possibility to bring fossil birds and their feathered ancestors to life via various state-of-the-art techniques.

‘My hopes are, therefore, that eventually palaeontology will lead to the virtual reconstruction of not only individual plants or animals but also their environment: a comprehensive computer-generated palaeoworld.’