Scientists led by Dr Stephen Brusatte from the University of Edinburgh, UK, have produced the most comprehensive family tree of prehistoric birds and their closest dinosaur relatives to date.
Family tree of coelurosaurian theropods and birds. Image credit: Stephen L. Brusatte et al.
In their study, reported in the journal Current Biology, Dr Brusatte and his colleagues examined the evolutionary links between ancient birds and coelurosaurs – a subgroup of theropod dinosaurs closely related to birds.
The scientists analyzed the anatomical make-up of more than 853 body features in 150 species of coelurosaurs and then assembled a detailed family tree.
They found that the familiar anatomical features of birds – such as feathers, wings and wishbones – all first evolved in their dinosaur ancestors.
Once a fully functioning bird body shape was complete, an evolutionary explosion began, causing a rapid increase in the rate at which birds evolved. This led eventually to the thousands of bird species that we know today.
The findings support a controversial theory proposed by George Gaylord Simpson in the 1940s that the emergence of new body shapes in groups of species could result in a surge in their evolution.
“The evolution of birds from their dinosaur ancestors was a landmark in the history of life. This process was so gradual that if you traveled back in time to the Jurassic, you’d find that the earliest birds looked indistinguishable from many other dinosaurs,” said co-author Dr Steve Wang of Swarthmore College.
Dr Brusatte added: “there was no moment in time when a dinosaur became a bird, and there is no single missing link between them.”
“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.”
“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,” said co-author Dr Graeme Lloyd of the University of Oxford.
“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.”
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Stephen L. Brusatte et al. Gradual Assembly of Avian Body Plan Culminated in Rapid Rates of Evolution across the Dinosaur-Bird Transition. Current Biology, published online September 25, 2014; doi: 10.1016/j.cub.2014.08.034
