The animal kingdom showcases diverse adaptations, with mouths varying dramatically in size and function across species. These structures play a central role in how animals acquire sustenance. Exploring the diversity of mouth sizes reveals insights into evolutionary pressures and how life thrives.
The Blue Whale’s Enormous Gape
The blue whale, the largest animal known to have ever lived, possesses a mouth of unparalleled scale. Its mouth can extend up to 20 feet (6 meters) in length, for an animal that can reach over 90 feet (27 meters) long and weigh more than 150 tons. This gape is not for biting or chewing, as blue whales lack teeth. Instead, their upper jaw is lined with hundreds of baleen plates, made of keratin, which form a filtration system.
Blue whales employ a unique feeding strategy known as lunge feeding. They accelerate to high speeds, then open their mouths wide to engulf massive volumes of water containing their primary food source: tiny, shrimp-like crustaceans called krill. The whale’s throat possesses expandable pleats that allow its mouth and an elastic pouch to inflate, accommodating a volume of water and krill that can exceed 80,000 liters.
After engulfing the water and prey, the blue whale expels the water through its baleen plates, trapping the krill inside its mouth. The whale then uses its enormous tongue, which can weigh around 2.7 tonnes, to scrape the trapped krill off the baleen plates and swallow them. This filter-feeding method allows the blue whale to consume up to 4 tons of krill per day, sustaining its immense size.
Other Animals with Impressive Mouths
Many other animals exhibit large mouths adapted to their specific ecological niches. The bowhead whale, another baleen whale residing in Arctic waters, has the longest baleen plates of any whale, reaching lengths of up to 13 feet (4 meters). Its mouth can be up to 16 feet (5 meters) long, 12 feet (4 meters) high, and 8 feet (2.5 meters) wide, enabling it to skim-feed on marine invertebrates by continuously swimming with its mouth open.
The whale shark, the largest fish in the world, relies on filter feeding with its expansive mouth, which can measure up to 5 feet (1.5 meters) wide. The whale shark has numerous rows of tiny teeth, but these are not used for biting or chewing. Similarly, the basking shark, the second largest shark, has a mouth that can open up to 3 feet (1 meter) wide, allowing it to filter vast quantities of plankton from the water.
Among terrestrial animals, the hippopotamus holds the record for the largest mouth. A hippo can open its jaws to 150 to 180 degrees, creating a gape of up to 4 feet (1.2 meters) tall. While their diet is primarily vegetarian, this mouth is used for territorial displays and defense, showcasing their canine teeth that can grow up to 28 inches (71 cm) long. Pelicans possess a large mouth structure, featuring a gular pouch beneath their long bill. This expandable pouch can hold up to 3 gallons (11.36 liters) of water and fish, allowing the bird to scoop up prey after a dive and then drain the water before swallowing the catch.
Why Big Mouths Matter Adaptations for Survival
The evolution of large mouths in animals is directly linked to their feeding strategies and survival. For filter feeders like baleen whales and large sharks, an expansive mouth maximizes the volume of water they can process to capture abundant, tiny prey such as krill or plankton. This efficiency helps sustain their large body sizes, as they must consume vast amounts of these small organisms. The ability to engulf large quantities of food in a single action reduces the energy expenditure per unit of food acquired.
In predatory animals, a large mouth can enable the engulfment of larger prey items whole or provide a wider strike zone, increasing hunting success. The size and structure of a mouth are tuned to the type and availability of food in an animal’s habitat. Animals that consume soft or liquid diets may develop different jaw structures compared to those that eat hard foods.
Beyond feeding, large mouths serve other functions, such as intimidation and display, as seen in the hippopotamus. The opening of its jaws serves as a warning to rivals, asserting dominance and protecting its territory. Pelicans utilize their large pouches for fishing, cooling their bodies through gular fluttering, and as a temporary “trough” from which their young can retrieve regurgitated fish. These diverse roles show how mouth size and design are adaptations that contribute to an animal’s ecological success.