Lemur - Anatomy and Physiology - Dentition

Dentition

The lemur dentition is heterodont (having multiple tooth morphologies) and derives from an ancestral primate permanent dentition of . Indriids, sportive lemurs, the aye-aye, and the extinct sloth lemurs, monkey lemurs, and koala lemurs have reduced dentitions, having lost incisors, canines, or premolars. The ancestral deciduous dentition is, but young indriids, aye-ayes, koala lemurs, sloth lemurs, and probably monkey lemurs have fewer deciduous teeth.

There are also noticeable differences in dental morphology and tooth topography between lemurs. Indri, for instance, have teeth that are perfectly adapted for shearing leaves and crushing seeds. In the toothcomb of most lemurs, the bottom incisors and canine teeth are procumbent (face forward rather than up) and finely spaced, thus providing a tool for either grooming or feeding. For instance, indri use their toothcomb not only for grooming, but also to pry out the large seeds from the tough exocarp of Beilschmiedia fruits, while fork-marked lemurs use their relatively long toothcomb to cut through tree bark to induce the flow of tree sap. The toothcomb is kept clean by the sublingua or "under-tongue", a specialized structure that acts like a toothbrush to remove hair and other debris. The sublingua extends below the tip of the tongue and is tipped with keratinized, serrated points that rake between the front teeth.

Only the aye-aye, the extinct giant aye-aye, and the largest of the extinct giant sloth lemurs lack a functional strepsirrhine toothcomb. In the case of the aye-aye, the morphology of the deciduous incisors, which are lost shortly after birth, indicate that its ancestors had a toothcomb. These milk teeth are lost shortly after birth and are replaced by open-rooted, continually growing (hypselodont) incisors.

The toothcomb in lemurs normally consists of six teeth (four incisors and two canines), although indriids, monkey lemurs, and some sloth lemurs only have a four-tooth toothcomb due to the loss of either a canine or an incisor. Because the lower canine is either included in the toothcomb or lost, the lower dentition can be difficult to read, especially since the first premolar (P2) is often shaped like a canine (caniniform) to fill the canine's role. In folivorous (leaf-eating) lemurs, except for indriids, the upper incisors are greatly reduced or absent. Used together with the toothcomb on the mandible (lower jaw), this complex is reminiscent of an ungulate browsing pad.

Lemurs are unusual among primates for their rapid dental development, particularly among the largest species. For example, indriids have relatively slow body growth but extremely fast tooth formation and eruption. By contrast, anthropoid primates exhibit slower dental development with increased size and slower morphological development. Lemurs are also dentally precocious at birth, and have their full permanent dentition at weaning.

Lemurs generally have thin tooth enamel compared to anthropoid primates. This may result in extra wear and breakage to the anterior (front) teeth due to heavy use in grooming, feeding, and fighting. Little other dental health information is available for lemurs, except that wild ring-tailed lemurs at Berenty Private Reserve occasionally exhibit abscessed maxillary canines (seen as open wounds on the muzzle) and tooth decay, possibly due to the consumption of non-native foods.