That's Archaeopteryx, the theropod dinosaur Deinonychus, and a modern bird (Hoatzin) that as a juvenile has a "throwback" clawed forelimb similar to fossil early birds but grows out of it to become a flying adult.
Fig. 1: Archaeopteryx Fig. 2: Deinonychus Fig. 3: Hoatzin chick Fig. 4: Hoatzin adult
From the article:
"Whatever the ancestor of birds was, it must have had five fingers, not the three-fingered hand of theropod dinosaurs," Feduccia said.The standard reptilian forelimb has five fingers, of course. Theropods evolved to lose two. Most scientists think birds simply inherited this same manus. In fact, this similarity was one of the lines of evidence that suggested a dinosaur ancestry for birds in the first place.
"Scientists agree that dinosaurs developed 'hands' with digits one, two and three -- which are the same as the thumb, index and middle fingers of humans -- because digits four and five remain as vestiges or tiny bumps on early dinosaur skeletons. Apparently many dinosaurs developed very specialized, almost unique 'hands' for grasping and raking.I can't tell where the problem is. Maybe the observation of which fingers are lost on the dinosaur is wrong.
"Our studies of ostrich embryos, however, showed conclusively that in birds, only digits two, three and four, which correspond to the human index, middle and ring fingers, develop, and we have pictures to prove it," said Feduccia, professor and former chair of biology at UNC. "This creates a new problem for those who insist that dinosaurs were ancestors of modern birds. How can a bird hand, for example, with digits two, three and four evolve from a dinosaur hand that has only digits one, two and three? That would be almost impossible."Or maybe Feduccia is seeing what he wants, not what is there. I can't tell where the problem is, but it's unlikely that the figure above is just a misleading coincidence.