Sea turtles, like all modern turtles, do not possess true teeth; they are classified as edentulous. Instead, their bony jaws are covered by a highly specialized, hard tissue known as a rhamphotheca, which forms a beak. This structure is made of keratin—the same material found in human fingernails—and is adapted to their specific diets, serving the functions of cutting, gripping, and crushing food.
The Keratinous Beak: A Substitute for Teeth
The rhamphotheca, or beak, is a tough, horny sheath that overlays the turtle’s upper and lower jawbones. This keratinous covering acts as a functional substitute for teeth, allowing the animals to capture and process marine prey. The shape and strength of the beak vary significantly among species, reflecting their specialized feeding habits.
For example, the Loggerhead sea turtle (Caretta caretta) has a massive head and an exceptionally strong beak with broad, bony plates inside. This powerful structure is designed for durophagy, enabling the turtle to crush the hard shells of prey like crabs, conchs, and whelks. Conversely, the Green sea turtle (Chelonia mydas), which is herbivorous as an adult, possesses a finely serrated, saw-like beak. These sharp edges allow it to scrape algae from hard substrates and efficiently shear tough sea grasses and seaweeds.
Internal Anatomy: The Role of Esophageal Papillae
Once food is captured by the beak, it moves into a throat structure lined with a unique internal feature called esophageal papillae. These are backward-pointing, spine-like protrusions composed of keratinized tissue, similar to the beak. The papillae line the entire length of the esophagus, growing progressively larger toward the stomach.
The conical, backward-pointing orientation of the papillae facilitates the transport of food toward the stomach. They prevent slippery prey, such as jellyfish or seaweed, from escaping back out of the mouth. The tough keratinized layer also protects the delicate esophageal lining from friction and helps the turtle expel excess seawater ingested during feeding.
How Different Sea Turtle Species Feed
The Leatherback sea turtle (Dermochelys coriacea), a specialist feeder, subsists almost entirely on gelatinous prey like jellyfish and tunicates. Its delicate, scissor-like beak has sharp cusps that pierce and hold the soft-bodied animals without damaging the jaw structure. The Leatherback’s papillae are especially effective at ensuring the slippery jellyfish cannot be regurgitated.
The Hawksbill sea turtle (Eretmochelys imbricata) is often called a spongivore because its diet consists primarily of sponges. It possesses a sharp, narrow beak, much like a bird’s, which allows it to reach into crevices on coral reefs to access its prey. The digestive system of the Hawksbill is uniquely adapted to neutralize the sharp, glass-like spicules and toxic chemicals found in many sponges.