Sloths are known for their slow movements, but this perception belies a highly specialized internal anatomy. Their dental characteristics are different from those of most other mammals. These dental features are a direct result of their evolutionary path and are linked to their specialized, low-energy lifestyle.
The Unique Structure of Sloth Teeth
Unlike humans and many other mammals, sloths possess a simplified but effective dental structure. They lack the distinct incisors and canines found in other animals; instead, their mouths are equipped with a single type of peg-like cheek teeth, technically known as molariforms. A sloth has 18 of these teeth, which are not set in sockets in the gums but are embedded directly into the jawbone.
Sloth teeth completely lack enamel, the hard, protective outer layer that covers the teeth of most mammals. Their teeth are composed primarily of two types of dentin and an outer layer of cementum. Without enamel, the teeth readily absorb tannins from the foliage sloths consume, often staining them dark brown or black. This discoloration is not a sign of decay but a natural consequence of their diet. Algae can also grow on their teeth, contributing to a greenish hue.
The two-fingered sloth presents a slight variation in this dental plan. They possess two pairs of prominent, sharp premolars that are often called caniniforms or “pseudo-canines.” These sharp teeth are located at the front of the mouth and are separated from the molars by a gap. The upper caniniforms are positioned slightly in front of the lower ones, creating an overbite that causes the teeth to constantly grind against each other. This action keeps them perpetually sharp.
Continuous Growth and Development
Sloth teeth grow continuously throughout the animal’s life. This condition, known as hypsodonty, is a characteristic they share with other animals like rabbits and horses. The teeth have open roots, which allows for this constant growth, compensating for the significant wear and tear they endure from chewing tough, fibrous plant material.
This pattern of dental development begins at birth. Sloths are born with their single set of teeth and do not develop a preliminary set of “baby” or deciduous teeth that are later replaced by permanent ones. This is a significant departure from the dental lifecycle of humans and many other mammals. The teeth they are born with are the same ones that will grow and wear down over their lifespan.
Diet and Dental Function
The unique structure and growth pattern of sloth teeth are perfectly adapted for their folivorous, or leaf-eating, diet. The peg-like molariforms provide an ideal surface for grinding down tough cellulose fibers in leaves into a digestible pulp. Since they lack front incisors for biting, sloths use their strong, muscular lips to pull leaves and twigs into their mouths.
The composition of the teeth provides a functional advantage. Because the inner dentin is softer than the outer layers, it wears down more quickly as the sloth chews. This uneven wear creates and maintains a sharp edge on the teeth, a self-sharpening mechanism that enhances their grinding efficiency.
This specialized diet and dental structure also contribute to their overall dental health. Cavities are uncommon in sloths, primarily due to their low-sugar diet. The absence of enamel, the substance that typically decays in other animals, means there is less opportunity for cavities to form. The constant growth and wear help to prevent the types of dental problems that can arise in animals with static teeth.