Lungfish Teeth—Their Enduring Structure and Feeding Role

Lungfish are fascinating creatures known for their ability to survive in both aquatic and oxygen-poor environments. One of their most distinctive features is their teeth, which play a crucial role in their survival and feeding habits. Unlike the sharp, replaceable teeth of many fish, lungfish possess durable dental structures that have remained remarkably consistent over millions of years.

Understanding their structure and function provides insight into how these ancient fish process food and adapt to different habitats.

Shape And Arrangement

Lungfish teeth differ from those of most modern fish. Instead of individual, replaceable teeth lining the jaws, they have robust dental plates fused to the bones of the mouth. These plates feature tightly packed ridges and cusps, forming a surface well-suited for crushing and grinding. While the arrangement varies slightly among species, all lungfish share a general pattern in which the upper and lower dental plates interlock to create a powerful grinding mechanism. This configuration enables them to process a wide range of food, from hard-shelled invertebrates to plant material.

The upper dental plates are broader and more expansive than the lower ones, providing a stable surface against which food is pressed and broken down. Positioned within the palatal region of the skull, they form a continuous surface extending across the roof of the mouth. The lower plates, though slightly narrower, align precisely with the upper ones, ensuring even force distribution during feeding and reducing the risk of structural damage.

The ridges and cusps on the dental plates vary in height and spacing, corresponding to different dietary habits. Some species have pronounced ridges for crushing hard-shelled prey like mollusks and crustaceans, while others have smoother surfaces better suited for grinding softer food items like plant matter. These variations suggest a degree of dietary specialization even among closely related species.

Hard Tissue Composition

Lungfish dental plates are composed of dense, mineralized tissue that withstands repeated mechanical stress. Unlike the enamel-covered teeth of many vertebrates, their plates consist primarily of dentine, reinforced by layers of petrodentine, a highly mineralized form of dentine that enhances resistance to wear. This composition allows them to process tough food items while maintaining structural integrity over time.

Petrodentine contains tightly packed hydroxyapatite crystallites, contributing to its exceptional hardness. Studies on fossilized lungfish dental plates suggest this material has remained largely unchanged for hundreds of millions of years, indicating its mechanical properties have been optimized through evolution. The presence of petrodentine ensures the grinding surfaces resist erosion, allowing lungfish to process food efficiently without frequent degradation.

Beneath the petrodentine, conventional dentine provides a slightly softer, shock-absorbent foundation that distributes feeding forces and reduces fracture risk. The transition between petrodentine and regular dentine is gradual, creating a composite structure that balances hardness and flexibility. Microscopic analyses reveal an organized network of tubules within the dentine, likely aiding in stress dissipation across the structure.

Replacement Patterns

Unlike many fish that continuously replace individual teeth, lungfish exhibit a different approach to dental renewal. Their plates do not shed and regrow; instead, new layers of tissue are gradually deposited, reinforcing the existing structure. This accretionary growth maintains functionality despite prolonged wear.

Dental reinforcement occurs in response to mechanical stress, with heavily used areas accumulating new layers more rapidly. This adaptive mechanism prevents the plates from becoming too thin or fragile. Histological examinations reveal growth lines similar to tree rings, marking periods of deposition and wear. These lines provide insight into the lifespan and feeding history of individual lungfish, as deposition rates vary based on diet and environmental conditions.

Role In Feeding

Lungfish rely on their dental plates to process a diverse array of food sources, making their feeding strategy highly adaptable. Rather than slicing or tearing prey, they use powerful jaws to crush, grind, and macerate food before swallowing. This approach is particularly effective for consuming hard-shelled organisms like mollusks and crustaceans, as it ensures exoskeletons are broken down into digestible fragments.

Their feeding efficiency is enhanced by how they manipulate food within their mouths. By generating controlled pressure against their dental plates, they systematically reduce food particles to a digestible consistency. Rhythmic jaw movements reposition tougher food items multiple times before swallowing, maximizing mechanical breakdown and optimizing nutrient extraction.

Variation Among Known Species

While all lungfish share the fundamental structure of fused dental plates, differences in size, shape, and surface texture reflect distinct ecological niches and feeding behaviors. Fossil records indicate even greater diversity in dental morphology among past species, suggesting environmental shifts have influenced their feeding strategies over time.

The African lungfish (Protopterus spp.) has relatively slender dental plates with fine ridges, suited for crushing small invertebrates and consuming soft vegetation. The South American lungfish (Lepidosiren paradoxa) possesses broader, more robust plates with pronounced grooves, enabling it to process a wider variety of plant material and harder prey. The Australian lungfish (Neoceratodus forsteri) features smoother plates with less pronounced ridges, reflecting its diet of mollusks, crustaceans, and softer aquatic vegetation. These differences highlight how lungfish species have adapted their feeding structures to optimize resource use in their respective environments.