Passerines are considered the most highly evolved avian group, having undergone a massive evolutionary radiation during the Paleogene period. Researchers from Nature note that they originated in the Southern Hemisphere (Gondwana) before spreading to every continent except Antarctica. Classification: Oscines vs. Suboscines

A tendon in the leg automatically tightens when the bird perches, locking the toes around the branch.

Many passerines are "songbirds" (Oscines), possessing a complex vocal organ called a syrinx that allows for intricate melodies.

The order is primarily divided into two main groups based on the anatomy of their syrinx muscles:

The eye of a passeriform bird, the European Starling (Sturnus vulgaris)