A new paper supports the traditional relationship of dromaeosaurid ('raptors') and troodontid theropods as the closest relatives of birds, but also supports the status of the controversial anchiornithine theropods as the earliest birds.

The authors say theirs is the most comprehensive study of feathered dinosaurs and early birds into the evolutionary relationships of dinosaurs at the origin of birds. They used an analytical pipeline to search for evolutionary trees, and estimated how each species may have crossed the stringent thresholds for powered flight.

Using their evolutionary tree, the team reconstructed the potential of bird-like theropods for powered flight, using proxies borrowed from the study flight in living birds.

Graphic: Julius Csotonyi

They were able to map biomechanical limits to all these species and propose a picture of experimentation within a spectrum of near-flight to fully-flighted capabilities. This goes against linear stepping forward through evolution model of bird origins and is instead an explosive radiation of feathered dinosaurs with many kinds of wing-assisted locomotion. 

They found that the potential for powered flight evolved at least three times in theropods: once in birds and twice in dromaeosaurids. Gliding flight in some dromaeosaurids is well established but finding at least two origins of powered flight potential among dromaeosaurids is really exciting, if evidence bears out their model.