Birds Evolved From Dinosaurs Gradually, Capped With Diversity Burst

Researchers assembling the most comprehensive family tree of two-legged, meat-eating dinosaurs to date reveal that familiar bird features – like feathers, wings, wishbones, hollow bones, and bills -- evolved over millions and millions of years, slowly accumulating small shifts in shape and function. But once these pieces were in place, an evolutionary explosion began. The gradual assembly of the bird body plan as we now know it, culminated in rapid rates of evolution. The work was published in Current Biology this week.

To examine the evolutionary links, tempo, and pace of the dinosaur-bird transition, Brusatte and colleagues analyzed the anatomical make-up of 853 features (ranging from air sacs to wrist bones, or lack thereof) in 152 extinct birds and their closest non-avian dinosaur relatives. Then they used statistical methods to assemble a family tree called a phylogeny (pictured below).  

The famous early bird, 150-million-year-old Archaeopteryx, was thought to represent a great evolutionary leap from dinosaurs, National Geographic explains, but these findings show that its avian traits evolved in dinosaur forebears long before. This 80-million-year transition was capped by unusually elevated bursts of evolution.