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The most comprehensive family tree ever made of meat-eating dinosaurs has revealed how they evolved into birds.

And as a result of the research, experts believe there was no 'missing link' between modern-day birds and their ancestors - as was previously thought.

Instead, an 'evolutionary explosion' 150 million years ago ultimately led to the thousands of avian species that are in existence today.

Research led by the University of Edinburgh proposes new evidence for how birds evolved from dinosaurs (illustration shown). Previously it had been thought there was a 'missing link' between the two.  But now it's thought an 'evolutionary explosion' may have led to the thousands of avian species alive today

The study, published in the journal Current Biology, was led by the University of Edinburgh.

The team of researchers examined the evolutionary links between ancient birds and their closest dinosaur relatives.

Based on fossil records, researchers said the emergence of individual bird-like features in dinosaurs was a gradual process, spanning tens of millions of years, during which time dinosaurs became ever-more bird-like.

However, once a fully functioning bird body shape was complete, an evolutionary explosion began, causing a rapid increase in the rate at which birds evolved. 

The researchers established this by analysing the anatomical make-up of more than 850 body features in 150 extinct species. 

They then used statistical techniques to analyse their findings and assemble a detailed family tree. 

This theory makes it very difficult to draw a dividing line on the family tree between dinosaurs and birds.

This is because there isn't one animal in particular - a 'missing link' - that heralded a switch from dinosaurs to birds.

Rather there was the gradual shift, and as mentioned and, once birds began to take shape, they quickly evolved and eventually became widespread. 

Findings from the study support a controversial theory proposed in the 1940s that the emergence of new body shapes in groups of species could result in a surge in their evolution.

'There was no moment in time when a dinosaur became a bird, and there is no single missing link between them,' said Dr Steve Brusatte, of the University of Edinburgh's School of GeoSciences, who led the study.

'What we think of as the classic bird skeleton was pieced together gradually over tens of millions of years.

'Once it came together fully, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate.'

Dr Graeme Lloyd of the University of Oxford, who was also involved in the research, added: 'Our study adds to a growing number of works that approach this problem from different angles, but all seem to confirm that the origin of birds was a truly special event in Earth history.

'It is particularly cool that it is evidence from the fossil record that shows how an oddball offshoot of the dinosaurs paved the way for the spectacular variety of bird species we see today.'

The research is based on the most comprehensive family tree ever made of meat-eating dinosaurs (shown). The study showed that the familiar anatomical features of birds - such as feathers and wings - all first evolved slowly in their dinosaur ancestors. Once a bird shape was complete, it led to an 'evolutionary explosion'