Evolution of Birds

Birds originated from feathered theropod dinosaurs. Early avian evolution is marked by transitional species that retained both reptilian and avian traits, including teeth, clawed wings, and long bony tails.

Mesozoic Bird Lineages

Jurassic Period

• Archaeornithes were early birds that lived during the Jurassic.
• They retained many primitive features such as teeth and long tails.
• These forms represent the earliest divergence from non‑avian theropods.

Cretaceous Period

• Enantiornithes were the most diverse and widespread birds of the Cretaceous.
• Odontornithes included toothed birds such as Hesperornis and Ichthyornis.
• These groups dominated avian ecosystems until the end‑Cretaceous extinction.

Post‑Cretaceous Radiation

After the Cretaceous–Paleogene extinction event, modern birds (Neornithes) rapidly diversified. This radiation produced the major clades seen today, including:

• Palaeognathae (ratites and tinamous)
• Neognathae (all other modern birds)