Yawning appears in many mammals and even in some birds and reptiles.

The longer version

The wide gape, deep inhale and slow close appear across nearly every vertebrate group examined, from cats and horses to parrots, penguins and turtles. Foetuses show similar mouth openings before birth, long before any social meaning could apply. Fish and amphibians show related gaping movements, widening the picture still further.

Such broad distribution means the behaviour is ancient, inherited from a common ancestor rather than invented separately. Documenting it across such distant groups is one way researchers argue that it predates the split between them. The details vary: some species combine the gape with throat puffing or display, hinting that a basic motor pattern was folded into signalling later.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.