There are nearly 10,000 species of neognaths. Since the Cretaceous they have undergone an adaptive radiation. This has produced the variety of form, function, and behavior which we see today. The Passeriformes (perching birds) are the largest order of land vertebrates. They are some 60% of living birds.
The neognaths have fused hand bones, an elongate third finger, and 13 or fewer vertebrae. They differ from the Palaeognathae in features like the structure of their jawbones. "Neognathae" means "new jaws" but, ironically, paleognath jaws are one of the few derived) features of that group.