The question of which animal has the biggest mouth depends on the metric used: absolute physical dimensions, volume capacity, or size relative to the body. Analyzing these different definitions reveals creatures whose mouths are engineered for their survival strategy, whether filtering water or swallowing large prey.
The Undisputed Champion: Absolute Volume and Length
The title for the largest mouth in terms of sheer length and physical size belongs to the Bowhead Whale (Balaena mysticetus). This Arctic giant’s arched mouth can measure up to 16 feet (5 meters) long, 13 feet (4 meters) high, and 8 feet (2.5 meters) wide. This structure represents nearly one-third of the whale’s entire body length, making it the winner for absolute dimensions.
This oral cavity is used for continuous ram filtration, or skim feeding, not swallowing large prey. The whale swims slowly with its mouth partially open, allowing water to flow over its long baleen plates, which can reach up to 13 feet (4 meters) in length. These plates act like a sieve, trapping tiny organisms like copepods and krill as the water exits. The Blue Whale (Balaenoptera musculus) uses lunge feeding, offering the largest capacity by volume. A single lunge allows a Blue Whale to engulf a volume of water and prey that can weigh up to 90 metric tons.
The Proportional Champions: Largest Relative to Body Size
Shifting the definition of “biggest” to proportionality reveals animals whose mouths are disproportionately large compared to their small bodies. Among all known animals, a deep-sea fish called Linophryne coronata, a species of anglerfish, holds the record for the largest mouth relative to its body size. Its mouth, measured from snout to the jaw’s corner, accounts for over 45% of the fish’s total length.
This adaptation is driven by the deep-sea environment, ensuring that rare encounters with prey are never missed, even if the food item is larger than the predator. The Pelican Eel (Eurypharynx pelecanoides) is another example, using its loosely hinged lower jaw and expansive, balloon-like throat pouch to swallow prey significantly larger than itself. On land, the Pelican’s pouch, a specialized extension of the lower bill, holds up to three gallons of water. This volume is nearly three times the capacity of the bird’s stomach, allowing it to scoop up fish and drain the water before swallowing its meal.
Terrestrial Giants: Gape, Girth, and Jaw Power
In the terrestrial world, a large mouth is often defined by the maximum gape, girth, and jaw power. The Common Hippopotamus (Hippopotamus amphibius) possesses the widest gape of any mammal, capable of opening its jaws up to 180 degrees. This creates a gape of up to 4 feet (1.2 meters) in a mature male.
This opening is primarily a form of intimidation and territorial defense, not a feeding mechanism. The hippo’s continuously growing canine teeth, which can reach up to 28 inches (71 centimeters), are displayed during this gape as a warning against rivals. For consuming large prey whole, the Burmese Python offers a unique form of mouth expansion, with its gape circumference reaching over 32 inches (81 centimeters) in large individuals. Lacking a fused lower jaw, this snake can stretch its mouth to swallow animals like deer and alligators that are far wider than its own head.