Avemetatarsalia
Bird-line archosaurs appear in the fossil record early in the Middle Triassic about 245 million years ago (mya), with the dinosaur-like Asilisaurus. However, Lower Triassic fossil footprints reported in 2010 from Poland may belong to a still more primitive type. If so, the origin of avemetatarsalians would be pushed back to around 249 mya. The oldest Polish footprints were made by an unknown small quadrupedal animal, but slightly later footprints show that moderately large bipedal dinosauromorphs had appeared by 246 mya.