About 255 million years ago, during the late Permian, our mammalian ancestory, the synapsids ruled the land.
Neoaves is the enormous living bird branch that includes all birds that are not part of the ostrich-tinamou branch and not part of the duck-chicken branch.
Ornithodirans were the early branch that later gave rise to both pterosaurs and dinosaurs, including birds.
Weird carryovers and side experiments: clawed wings, elaborate ribbon-like tail feathers, and a mix of advanced beak features with a still primitive dinosaurian body.
Hesperornithiformes were early, highly specialized diving birds that evolved before modern birds.