ornithurans

Ornithurans represent a major clade of birds that encompasses almost all living bird species. This group is characterized by a number of skeletal and soft-tissue features, including a reduced number of tail vertebrae, a fused pelvis, and the presence of a keel on the sternum for flight muscle attachment. The name "Ornithurae" literally means "bird tail," referring to this characteristic reduction and fusion of tail bones, which differs significantly from the long, bony tails of their non-avian dinosaur ancestors.

The evolutionary origin of ornithurans is placed within the Mesozoic Era. While the exact timing and ancestral lineage are subjects of ongoing research, the group diversified significantly during the Cretaceous period. The vast majority of extant bird families are considered to be ornithurans, highlighting the ecological success and adaptive radiation of this lineage. This includes a wide array of groups such as waterfowl, gamebirds, shorebirds, and all passerines (perching birds).

Key anatomical developments within ornithurans facilitated increased flight efficiency and maneuverability, contributing to their widespread distribution and ecological dominance. While some species have secondarily lost the ability to fly, the underlying skeletal structure generally reflects their volant ancestry. The study of ornithurans is fundamental to understanding avian evolution, paleontology, and the diversity of life on Earth.