The naked mole-rat, Heterocephalus glaber, is an unusual mammal native to the Horn of Africa, in Ethiopia, Kenya, and Somalia. These burrowing rodents possess remarkable physical characteristics that allow them to thrive in their subterranean world, from their wrinkled, nearly hairless skin to their unique social structure. Among their most striking adaptations, their teeth are particularly noteworthy, serving as specialized tools for their underground existence. These dental features are central to their survival and colony life, enabling them to navigate their harsh environment.
External and Independent Incisors
The incisors of the naked mole-rat are a defining anatomical feature, protruding significantly outside their lips. This external positioning allows the animals to dig and gnaw through soil and other materials without ingesting dirt, as their lips seal behind the teeth, preventing debris from entering the mouth. This adaptation is particularly beneficial for a species that spends its entire life excavating extensive tunnel systems. Their large, powerful incisors are supported by strong, muscular jaws, with approximately a quarter of their muscle mass dedicated to jaw closure.
The naked mole-rat’s lower incisors can move independently of each other, operating much like a pair of chopsticks. This unique mobility is facilitated by a flexible mandibular symphysis, the connection between the two halves of their lower jaw. This independent movement provides a greater range of dexterity, which is important for efficient gnawing and manipulating objects within their tunnels. This specialized dental arrangement offers an advantage for life in their underground habitat, where precise and powerful excavation is required.
Continuous Growth and Self-Sharpening
Naked mole-rat incisors, like those of other rodents, exhibit continuous growth throughout the animal’s life. This ongoing eruption compensates for the constant wear and tear experienced from their primary activity of digging through abrasive soil and gnawing on tough roots and tubers. The maintenance of proper tooth morphology relies on this continuous growth.
The self-sharpening mechanism of their incisors is another notable adaptation. The front surface of each incisor is covered by a layer of hard enamel, while the bulk of the tooth is composed of softer dentin. As the naked mole-rat uses its teeth for gnawing, the softer dentin wears away more quickly than the harder enamel on the outer surface. This differential wear creates a consistently sharp, chisel-like edge, ensuring their digging tools remain effective without manual sharpening. This design allows their teeth to withstand constant use in their abrasive environment, maintaining functionality over their long lifespans.
Purpose and Use in Their Environment
The specialized incisors of the naked mole-rat are primarily employed for extensive burrowing and the excavation of complex tunnel systems. Their powerful teeth allow them to loosen compacted soil and gnaw through obstacles such as tough underground roots and tubers, which are their main food source. These tunnels can reach depths of up to 2 meters (6.5 feet) and extend for kilometers, sometimes up to 4 kilometers (2.5 miles) in total length for a single colony.
When excavating, the naked mole-rats work cooperatively in an assembly-line fashion. An individual at the front uses its incisors to break up the dirt, while a chain of other workers sweeps the loosened soil backward through the tunnel system. This material is then kicked to the surface, forming the characteristic molehills. Beyond excavation, their incisors are also used to manipulate and transport excavated material, and to access and consume underground plant parts, such as tubers, often leaving enough of the plant intact for regeneration to provide a sustainable food source.