A new family tree of meat-eating dinosaurs published in the scientific journal, Current Biology, shows how birds evolved from these dinosaurs.

The new model shows the anatomical features of birds that evolved piecemeal from their dinosaur ancestors over tens of millions of years.

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It also showed the evolutionary explosion that led to thousands of avian species after the bird body shape was complete.

To come up with their findings, researchers examined the link between ancient birds and their closest dinosaur relatives.

They analyzed the anatomical make up of 850 body features of 150 extinct species and used data from this to build the family tree.

They found out that bird gradually emerged 150 million years ago as dinosaurs evolved into bird-like creatures.

Steve Wang, one of the researchers, said their study supports the 1940s theory that new body shapes in groups of species came from evolution.

He said the evolution of birds was a gradual process that travels back to the Jurassic era where you'd find the earliest birds that looked like other dinosaurs.

Wang also said the birds people know today had small shifts in shape and functions of their skeletons.

Steve Brusatte, one of the researchers, said there's no single missing link between the evolution of birds to dinosaurs. He said researchers believe the classic bird skeleton was developed over tens of millions of years.