When a pelican opens its mouth, you really see a mouth! I suppose a hippo can compete with it and a few other forms of wildlife. But the term 'bigmouth' came to my mind when I saw this.

How big is a pelican's mouth? "It can reach 18 inches in length. Underneath the bill, pelicans have throat pouch that can hold 3 gallons of water. Pouch is mainly used for feeding, but it can be also used as a cooling "device". During the warm days, pelican will swing its pouch to cool itself." http://www.softschools.com/facts/animals/pelican_facts/300/
(quote from www.softschools.com. check out their website for more facts about pelicans.)