Aves is a class of tetrapods. On Home Earth only the Neornithes, or Modern Birds are the only surviving birds. But on Alternative KT the paleognaths (ratites, kiwis, and tinamous) were the only surviving neornith, and the hesperornithiformes (toothed seabirds with giant toes) and enantiornithes (3 fingeres toothed birds) survived instead. On South America and Australia in the absecense of dinosaurs and pterosaurs metatherians, gondwanatheres, paleognaths, and enantiornithes were allowed to grow huge with wierd fauna like HE has never seen before.
