indeed possibly a better flyer than Archaeopteryx. He noted that the Microraptor's fused sternum, asymmetrical feathers, and features of the shoulder girdle indicated that it could fly under its own power, rather than merely gliding. Today, most scientists agree that Microraptor had the anatomical features expected of a flying animal, though it would have been a less advanced form of flight compared to birds. For example, some studies suggest the shoulder joint was too primitive to allow a full flapping flight stroke. In the ancestral anatomy of theropod dinosaurs, the shoulder socket faced downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds. Studies of maniraptoran anatomy have suggested that the shoulder socket did not shift into the bird-like position of a high, upward orientation close to the vertebral column until relatively advanced avialans like the enantiornithes appeared. However, other scientists have argued that the shoulder girdle in some paravian theropods, including Microraptor, is curved in such a way that the shoulder joint could only have been positioned high on the back, allowing for a nearly vertical upstroke of the wing. This possibly advanced shoulder anatomy, combined with the presence of a propatagium linking the wrist to the shoulder (which fills the space in front of the flexed wing and may support the wing against drag in modern birds) and an alula, much like a "thumb-like" form of leading edge slot, may indicate that Microraptor was capable of true, powered flight. Other studies have demonstrated that the wings of Microraptor were large enough to generate the lift necessary for powered launching into flight even without a fully vertical flight stroke. A 2016 study of incipient flight ability in paravians demonstrated that Microraptor was capable of wing-assisted incline running, as well as wing-assisted leaping and even ground-based launching. Stephen Czerkas, Gregory S. Paul, and others have argued that the fact Microraptor could fly and yet is also very clearly a dromaeosaurid suggests that the Dromaeosauridae, including later and larger species such as Deinonychus, were secondarily flightless. The work of Xu and colleagues also suggested that the ancestors of dromaeosaurids were probably small, arboreal, and capable of gliding, although later discoveries of more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view. Work done on the question of flight ability in other paravians,