Gular skin

Gular skin can be very prominent, for example in members of the order Phalacrocoraciformes as well as in pelicans (which likely share a common ancestor).

In cormorants, the gular skin is often colored, contrasting with the otherwise plain black or black-and-white appearance of the bird.

During courtship display, the male forces air into the sac, causing it to inflate over a period of 20 minutes into a startling huge red balloon.

The gular sac in this instance amplifies their voice to be heard louder and seemingly closer.

The theropod dinosaur Pelecanimimus, which lived in the early Cretaceous Period 130 million years ago, also had a gular pouch, similar to the pelican after which it is named.