Ornithurae

Ornithurae is a clade of birds that lived from the Cretaceous period to the present day. This group is characterized by a number of skeletal features, most notably the fusion of the last caudal vertebrae into a pygostyle, which supports the tail feathers. Unlike earlier bird groups such as Enantiornithes, Ornithurae birds possessed a fused sternum with a keel for the attachment of flight muscles. They also had a fully ossified, fused tarsometatarsus and tibiotarsus, contributing to their increased agility and stability in flight.

The fossil record shows that Ornithurae emerged during the Early Cretaceous, with early representatives like Confuciusornis already displaying many of these modern avian traits. This clade includes all living birds, commonly referred to as Neornithes, as well as some extinct groups. The evolutionary success of Ornithurae is evident in their widespread distribution and diversification across virtually all terrestrial and aquatic environments on Earth today. Their skeletal adaptations for efficient flight and a generally gracile build have allowed them to exploit a vast array of ecological niches. The continued study of fossil Ornithurae provides crucial insights into the evolutionary transition from non-avian dinosaurs to modern birds.