Primate Dentition comparison

Lemurs (Prosimians/Strepsirhini)

Lemurs are primates and prosimians, indigenous to Madagascar and the Comoro Islands.  Madagascar is a large (226,597 sq. mi) island off the coast of Africa. Because the topography of Madagascar includes a mountainous ridge that bisects the island and because of its position and latitude in the Indian Ocean, it has quite a diversity of climatic zones and resulting ecoregions.

The eastern side of the island receives the tropical moisture of the Indian Ocean along a narrow strip creating a lowland. In the center of the island there is are mountain ranges and extinct volcanoes. This area contains rocky outcrops and even contains lakes formed in craters. The southern end of the island is mostly arid with fewer year round rivers. There is a great cliff Angavo that becomes a single wall of rock as it approaches the sea.

There are over 100 species of lemur and they range in size from the Indri, which can reach about 7 to 10 kilograms, to the Madame Berthe’s mouse lemur, weighing about 39 Grams.
 Madame Berthe’s mouse lemur is the smallest lemur and the smallest primate in the world. A lemur’s tail is often longer that it’s body. They have long toes which they use for climbing, with nails instead of claws (most species.) he  

 

 Lemurs, through the assistance of isolation from the other old world primates, have managed to fill just about every regional ecological niche. Many are arboreal and diurnal but there are notable exceptions. The Ringtail lemur is largely terrestrial and several species are nocturnal notably the smaller species.   

  

O.K now let's get a closer look at their dentition.  The lemur dentition is heterodont (having multiple tooth morphologies) and is generally a dental formula of 2.1.3.3, but there are also notable differences in dental morphology and tooth topography between lemurs.   

Most Lemurs possess a tooth comb, a four to six tooth set of incisors. Different lemurs, however, use them differently and they are not just for grooming as the name might have you suspect. Where lemurs live, and how they have specialized, tells the tale how an animal’s dentition bears the morphology of consequence. Common parts of a lemur diet in the wild include fruits, leaves, and other edible plant materials. Insects and their larvae may also be on the menu, especially for the smaller lemurs.

 

As stated earlier there are over 100 species of lemur which is far too many to cover entirely, so I have selected a few to demonstrate the variety of eco-niches they inhabit, their diet and corresponding dentition.  

 

Indri have teeth specifically adapted for shearing leaves and crushing seeds. In other leaf eating lemurs the upper incisors are greatly reduced or absent.

Red ruffed lemurs are frugivorous; they eat mainly fruit, as well as leaves, flowers, and nectar.

 

 Golden bamboo lemur is one of the rarest of the world's lemurs. They feed on young shoots, creepers and leaf bases of the endemic giant     bamboo, and has evolved to be resistant to the high concentrations of cyanide found within the tissues of this plant. Around 500 grams of bamboo are eaten every day; this represents roughly 12 times the usual mammalian lethal dose of cyanide.  

 

Alaotran lemurs are active during the day and night with peaks of activity at dawn and dusk. Members of this species walk on all fours along the reed stalks of their habitat, bending one stalk until it allows them to reach the next. These lemurs specialize on eating papyrus leaves.

                   Here are some lemur dental formulas and there variation.

Lemur dentitions
Family	Common Name	Dental formula
Cheirogaleidae,	Dwarf lemurs and Mouse lemurs	2.1.3.3 × 2 = 36
Lepilemuridae	Sportive Lemur	0.1.3.3 × 2 = 32
Indriidae	Indri	2.1.2.3 × 2 = 30
Daubentoniidae	Aye Aye	1.0.1.3 × 2 = 18

 
 


Lemur dentition varies from species to species the combination of incisors, tooth comb, canine, premolars and molars assist them in making a wide variety of Eco-regions habitable and exploit wide-ranging diverse foodstuffs.

 

The most notable exception to the classic dentition formula is the Aye Aye.  This nocturnal lemur is highly specialized for what has been called the “Role of a woodpecker.” There are no woodpeckers on Madagascar so this is one of the aforementioned eco-niches occupied by these prosimians. They have an especially adapted elongated middle finger and extremely large ears. They use percussive foraging for auditory clues to locate hollow pockets in tree branches a likely locale for insect larvae, one of their favorite foods.  This specialty has led to a different dentition as well.  The aye-aye lack a functional strepsirrhine toothcomb.  The aye-aye starts with deciduous incisors which are lost shortly after birth, which indicates that its ancestors had a toothcomb. These teeth are replaced by open-rooted, continually growing (hypselodont) incisors. Teeth that constantly grow and never form roots. It is these teeth that the Aye Aye uses to gnaw through the wood to access the larvae. This gnawing wears the teeth down, but they continually grow back.  This feature of hypselodont teeth is unique among primates. So it appears that when it comes to the most specialized dentition the Aye Aye’s have it.

 

Spider Monkey (New World Monkey/Platyrrhini)

Spider monkeys (of several species) live in the tropical rain forests of Central and South America. They can occur as far north as Mexico. 

   

 

   They have long, lanky arms and prehensile tails.  The spider monkey’s long and slender limbs especially the forelimbs are used in suspensory locomotion (brachiating.) The average body mass for males is about 10 kilograms and for females it is between 6-8 kilograms. This species lacks a thumb. They are arboreal and spend most of their time off of the ground. With this as a basic background let’s swing over into their dentition. 

Spider Monkey Dentition:

Spider monkeys differ from Prosimians, in regard to their jaw and teeth. Their dental formula is 2.1.3.3. which is to say they have two incisors, one canine, three pre-molars, and three molars. Spider monkeys remain in the treetops presumably as protection from predation. This dictates a diet of arboreal availability, namely seeds, fruits, insects, birds and their eggs.  Although plant based food appear to make up the bulk of the monkey’s diet, the availability of other food sources is supported by an “omnivore’s mouth” which is to say heterodonty. 

 

 Baboon (Old World Monkey/Cercopithecidae)

There are five different species of baboons indigenous to Africa or Arabia. Baboons are some of the world's largest monkeys.  They range in size and weight depending on species. The Guinea baboon is about 50 centimeters and weighs about 14 kilograms while the largest Chacma baboon can be 120 centimeters and weigh 40 kilos. In addition to this body length are substantial tails of varying lengths.  Baboons prefer savanna and other semi-arid habitats, although some live in tropical forests. Like other Old World monkeys, baboons do not have prehensile tails, but they can and do climb trees to sleep, eat, or look out for trouble. They spend significant time on the ground.  Baboons are opportunistic feeders, fond of crops, much to the chagrin of African farmers, fruits, grasses, seeds, bark, and roots. They will also eat meat. They will eat fish, shellfish, hares, birds, rodents, vervet monkeys and small antelopes. They have been known to raid human dwellings and prey on sheep and goats.

 The Baboon’s dental appointments:
The Baboon dental formula is 2.1.2.3. which again is to say two incisors, one canine, two pre-molars and three molars. In baboons, size of teeth is inherited but generally all baboons have very strong, and long canine teeth (especially upper canines). These are well developed in males. In addition to the obvious grasping functions, they also have social functions. Males use them in offense and defense, but more commonly they are used in threatening behaviors. Threats have a major role in maintaining order within a group, and in group defense. It could be speculated that the more terrestrial nature, or the semi-arid savanna of the Baboons habitat, or both, exposes them to a greater threat of predation. This threat could account not only for their larger physical size but also for the size of their canine teeth. Their less arboreal lifestyle, whether forced or chosen, could add a selection pressure for a larger more robust individual with more fearsome mouth. In this comparison it appears the most prominent use of dentition as display and armament.  Meat acquisition may have been the impetus or a byproduct of this more terrestrial existence. Also their sexual dimorphism and polygyny is likely tied to their more terrestrial nature. At any rate the dentition pattern alone belies the fearsome appearance their gaping maw.
  
 

Gibbon (Lesser ape/Hylobatidae)

There are 15 recognized species of gibbon, ranging from India to south China. The largest species are known as Siamangs, and can grow to about thirteen kilograms, and the smaller species attain only about four kilos. Gibbons flourish on the plentiful fruit trees of their tropical range, and are especially fond of figs. They will occasionally supplement their diet with leaves and insects.  Their primary form of locomotion is brachiating. Gibbons can move through the jungle by this method at up to 56 kilometers an hour, bridging gaps as wide as 15 meters in a single leap. Now we’ll bridge the much shorter gap into their dentition.

   Gibbon Dentition:

 In parallel to the spider monkey their diet appears to follow a pattern of arboreal availability. The dental formula in Gibbons is the same as in Baboons (i.e. 2.1.2.3) but its outward appearance is considerably less menacing.  The Hominoidea differ from the old world monkeys in several dentition characteristics. These include a Y-5 molar pattern in their lower dentition. The upper molars have four cusps with a diagonal crest (crista obliqua.) This appears to be a more primitive molar pattern without bilophodont shearing crests.  The lower molars are distinguished by an enlarged talonid section and by 5 main cusps. When observed from the below, the grooves between the cusps take a y-shaped form, hence the name Y5-pattern. The upper molars are of a more square shape. They are from a more primitive molar pattern compared to the Cercopithecoidea. Well that was more than a mouth full for me, but for the Gibbons it was just that, a mouthful. Their mouthful seems to support a more herbivorous and arboreal diet with fewer terrestrial transition foodstuffs as in baboons.  This would support the hypothesis that terrestrial forces may be involved in these variations. Again their arboreal lifestyle allows them to avoid many predators and their primarily frugivorous diet could be construed as a more primitive eco-niche that matches their more primitive dentition. It seems more similar to the spider monkey than to the baboons.  The arboreal existence may also help explain the lesser sexual dimorphism, more monogamist, and offspring supporting natures between the gibbons, spider monkeys as opposed to baboons.

  

 Chimpanzee (Great ape/Hominidae)

 Chimpanzees live in African rain forests, woodlands, and grasslands. They are about 1.2 to 1.7 meters and weigh about 32 to 60 kilos. They normally walk quadrapedally, “knuckle-walking” to be more exact, but can stand and walk upright. They can also move quite efficiently in the trees by brachiating.  Chimpanzees normally sleep in trees, employing leaf nests. Chimps are generally fruit and plant eaters, but will also consume insects, eggs, and meat, including carrion. They have a tremendously varied diet including hundreds of known foods.

 

The Chimpanzee dental plan:

 
A Chimpanzee dentition is similar to that of other simians with a dental formula is 2.1.2.3.  They have 2 incisors, 1 canine, 2 pre-molars, and 3 molars.  Despite being less primitive, a chimpanzees canines are not as pronounced as the baboon; although still formidable. While we still have the omnivore’s dentition, and a more terrestrial presence perhaps this reflects a selection pressure favoring socialization and greater facial expression. Chimpanzees are more intelligent and appear to communicate intraspecially to a greater extent than do other simians. One could speculate that this may be the product of a “bark over bite” logic that would favor the advantage of communication over confrontation.

Our final dental checkup:

 Heterodonty appears to be the common winning omnivore strategy in all of these simians. A mix of different types of teeth making more types of available food ingestible. They are truly the masticators of their domain.  We must also brace ourselves as we arrive at the inescapable conclusion that teeth are much more that simple masticators. They are food acquisition devices. They are food preparation devices. They are hunting and foraging tools. They are grooming tools. They are defensive and offensive weapons and they have evolved to suit all of these purposes. The less obvious deduction, that cannot be easily brushed away, is that evolution appears to have placed a greater emphasis on them as communication devices. They warn, they greet, and they convey intent.  I don’t mean to propose that communication is supplanting dentition’s primary role of nutritional acquisition.  Just that, in this comparison, their role as information conductors is increasing. In all of these creatures the dentition most certainly can display warning, intent and capability. Beyond this however, they appear to have evolved into a more generalized communicative role.  Specifically, along with the other facial features, they appear to be conveying emotion.