Class Aves
With around 10,000 species of birds, Class Aves is a massive and diverse group. The birds are one of the few groups of animals that are capable of flight. The main features that allow and improve their flight are:
- Hollow bones (flightless birds are an exception) and fusion of parts of the skeleton .
- A beak instead of teeth
- Oviparity (egg-laying) instead of viviparity (giving birth to live young)
- A four-chambered heart and air sacs with unidirectional airflow
- Feathers with large surface areas and wings which are evolved forelimbs.