Wisdom Teeth

Now On Display in Exley Science Library

The jaws seen in this display demonstrate some of the amazing dental morphology that has evolved in the vertebrate lineage. In addition, these bones offer a chance to explore some of specimens held within Wesleyan University's George Brown Goode Biology Collections.

An Introduction to Dental Anatomy


Homodont Teeth

Rattlesnake Crotalus sp.

Rattlesnake

Venomous snakes such as this rattlesnake produce powerful neurotoxins in their saliva which are used to deliver a killing bite to prey. Venom is delivered through specialized hollow fangs which act as hypodermic needles to inject toxins directly into the bloodstream. In order to prevent their fangs from going dull, adult rattlesnakes shed their fangs every 6–10 weeks. You can see the replacements for yourself, right behind the primary fangs. 

Like many reptiles, rattlesnakes tend to consume large meals once every several weeks. In order to swallow their prey whole their mandibular symphyses is left un-fused.

Dolphin

Dolphin Delphinus sp.

Dolphins, spending their entire lives in water, have adapted a peculiar set of cranial features that set them apart from other mammals. Most noticeably, the large bowl-shaped depression in their forehead holds the specialized “melon” used for focusing echo-locating “clicks”. In addition, unlike most other mammals, the dolphin's teeth are homodont and undifferentiated. In other words, there are no specialized teeth for biting, cutting, and grinding. Instead the dolphin uses these simple conical teeth to grip slippery fish before they’re swallowed whole.

Codfish Gadus morhua, Linnaeus, 1758

Codfish

As you can see, the thin struts of bone that make up the Codfish skull are unfused which allow for greater cranial flexibility. This flexible skull allows the Cod to extend their jaws forward and rapidly snatch prey by protruding the pre-maxilla. In addition, like many other teleosts- or bony fish, Cods use suction feeding by rapidly expanding the space in their mouth to create a negative pressure which sucks prey items into their jaws. 


Toothless Species

Green Sea Turtle

Green Sea Turtle Chelonia mydas, (Linnaeus, 1758)

The Green sea turtle, being highly migratory, changes its diet as it grows older to adapt to the environment of its life stage. When first hatched, the turtle is almost entirely carnivorous, feeding on the crustaceans, jellyfish, and ctenophores of the open ocean with a sharp keratin beak for catching prey. As the turtle matures and it moves to shallow coastal waters, its diet shifts to a more herbivorous habit consuming algae and seagrasses. As a result, the turtle's skull morphology changes as well: adult turtles, without the need to catch moving prey, tend to have smaller insertions for jaw muscles and more serrated beaks for cutting seagrass.

Woodpecker

Pileated Woodpecker Dryocopus pileatus, (Linnaeus, 1758)

Woodpeckers forage for insect larvae within the trunks and branches of trees by using their beak to drill into the bark. The evidence of this plundering can be seen across northern forested areas in Connecticut. This “tree-tapping” serves not only to catch prey, but also to communicate territory and call out to potential mates. Woodpeckers can peck at rates of up to 20 times a second, enduring around 1,200 gravities - which is around 14 times more force than is necessary to give a human a concussion. In order to withstand this force, Woodpeckers have developed elaborate adaptations for keeping their brains undamaged. Woodpecker beaks have layers of spongy bone for absorbing shock. In addition, their hyoid bone wraps around their skull and connects to the tongue through one nostril. When pecking, these tongue bones are retracted to stabilize the skull, acting somewhat like a seatbelt.

 

Pelican

Pelicanus sp.

The strange morphology of a pelican’s skull does not reveal the amazing anatomy it has in life. The pelican's long hooked beak allows it to dart into the water's surface to grapple with slippery prey items. Once caught, the pelican can store a fish in its pouch - or gular - while it continues to hunt. After the Pelican has filled its gular it can drain the water and swallow its catch. This amazing adaptation not only serves to assist in hunting, but also for courtship displays. 

American Black Duck

Anas rubripes, Brewster, 1902

Ducks, like all living birds, have lost their teeth but have evolved specialized bill structures which help to process and manipulate their food. In particular, the iconic spatulate shape of the duckbill helps the birds crush soft food. The size and shape of the bill, much like mammal teeth, can help reveal the diet of the duck. Flatter bills - like that of the American Black Duck - tend to be adapted to consume more plant material like algae or seeds, while sharper bills tend to be specialized for hunting animals. In addition, lamellae - the thin comb-like structures on the side of the bill- help to filter food from sediment. Lastly, the nail on the tip of the upper side of their bill is used to dig through muck to find roots and worms.

Myrmecophaga tridactyla, Linnaeus, 1758

Giant Anteater

As their name suggests, anteaters eat exclusively ants and termites, which they dig out of nests with strong forelimbs and sharp claws. Once inside the mound, the anteater uses its 2 foot long tongue to snatch up insects. The tongue is covered thousands of tiny hooks and produces a thick sticky saliva which aid in the hunt. The anteater's stomach is lined with hardened folds which it uses to crush its prey. Without the need to chew, the anteater has lost its teeth and nearly fused its lower jaw to the cranium. A ligament at the tip of the jaw allows the jaw to open just enough to let the tongue flick out.


 

Human dentition

Cracking the Code - Dental Formulas

In order to make the description of numbers and types of teeth within heterodont mammal jaws more efficient, biologists have standardized dentition into a code known as the dental formula. This formula is written as an expression of the number of each type of tooth in one side of the upper jaw over the number of teeth in one side of the lower jaw. The letters correspond to the type of teeth (I = Incisor, C = Canine, P = Premolar, M = Molar. For instance, Humans have 2 incisors on both top and bottom, 1 canine, 2 premolars, and 3 molars so our dental formula is:

I 2/2 C 1/1 P 2/2 M 3/3. 

The Human dental formula is relatively easy to read, however some mammals have varying numbers of premolars on top and bottom. Take for example the sheep, which has no incisors and no canines in its upper maxilla, but has 3 incisors and 1 canine in its lower mandible. The dental formula for sheep is:

I 0/3 C 0/1 P 3/3 M 3/3

The dental formula of each mammal is included below next to its label.

Heterodont Teeth

Castor canadensis Kuhl, 1820 (I 1/1, C 0/0, P 1/1, M 3/3)

American Beaver

Like all rodents, beaver’s teeth continue to grow throughout their life to prevent too much wear from accumulating. Beaver incisors are particularly durable as they are covered in a thick layer of enamel, with an orange tint from the presence of iron compounds. This iron oxidizes over time leaving beavers with orange teeth. This all makes sense when you consider the incredibly tough material that beavers must chew through to construct their dams.

African Bush Elephant

Loxodonta africana, (Blumenbach, 1797) (I 1/0, C 0/0, P 3/3, M 3/3)

This goliath of a molar is almost as remarkable as the giant incisors (tusks) of elephants. Unlike most mammals, which grow a pair of milk teeth which are later replaced with a permanent set of adult teeth, Elephants are polyphyodonts meaning they have cycles of teeth throughout their lives. As and premolars molars are worn down from grazing, they are lost and replaced with another tooth. These replacement molars originate from the back of the mouth and move forward to push out the old ones. Elephants only have 6 replacements, so once the last is worn down the organism can longer chew its own food.

Grizzly Bear Ursus arctos horribilis Ord, 1815 (I 3/3, C 1/1, P 2-4/2-4, M2/3)

Grizzly Bear

Omnivores like this grizzly bear have more generalist teeth that can be used to process a wide variety of foods. The incisors at the front can be used to slice through meat but are also commonly used to graze grass. The menacing canines can be used to rip apart flesh or take down squirrels and other small animals, but are also used to rip into logs to find grubs and ants. The molars and premolars can be used to crunch bones or crack nuts.

Macropus rufus (Desmarest, 1822) -- Odocoileus virginianus (Zimmermann, 1780) (I 3/1, C 1/0, P 2/2, M 4/4) -- (I 0/3, C 0/1, P 3/3, M 3/3)

Red Kangaroo and White Tailed Deer

Mammals can be generally classified into three broad lineages: monotremes, marsupials, and placentals. Monotremes such as platypuses and echidnas lay eggs while marsupials and placentals give birth to live young. Monotremes have secondarily lost their teeth entirely, and placentals and marsupials have their own unique dentition. While marsupials have 3 premolars and 4 molars on each side in both the upper and lower jaw (P3/3; M4/4), placentals have 4 premolars and 3 molars on either side in both the upper and lower jaw (P4/4; M3/3).

While Placentals have a maximum of three incisor, marsupials can have up to 5 (as seen in the opossum) a condition known as poly-protodonty. However, this difference in tooth number hasn’t stopped marsupials and placentals from developing very similar skull forms. As you can see the Australian Kangaroo and the North American Deer have developed similar skull morphology. Both have a diastema, or gap, between their premolars and incisors which can be used to strip leaves from branches. In addition, both use their incisors to tear foliage. The deer accomplishes this by pinning leaves between their lower incisors and rigid upper maxillary bone. On the other hand, the kangaroo has evolved extended lower incisors which the upper incisors pin against.  

Baboon

Papio sp. Erxleben, 1777 (I 2/2; C 1/1; P 2/2; M 3/3)

Another way of achieving efficient chewing often seen in primates, is to produce a grinding surface made up of two transverse cusps, a condition called bilophodont or bicuspid seen in the baboon molars as well as the molars in your own mouth.

Baboons, similar to humans, are omnivorous social primates that spend their days eating fruit, scavenging for meat, and attempting to maintain and gain social status. However, while humans use complex vocal speech to convey their emotions and intentions, baboons use a set of prominent canines along with a language of yawns and lip curls to indicate sentiments of friendliness, aggression and even erotic passions.


Specimens from The George Brown Goode Biological Collections (GBGBC)

Developed with the assistance of Professor Ann C. Burke, Katherine Brunson, Ellen Thomas, Andy Tan '21, Yu Kai Tan MA '21, Joel LaBella, Bruce Strickland, Andrew White and Linda Hurteau.

Rattlesnake Crotalus sp.

Dolphin Delphinus sp.

Codfish Gadus morhua, Linnaeus, 1758

Green Sea Turtle Chelonia mydas, (Linnaeus, 1758)

Pileated Woodpecker Dryocopus pileatus, (Linnaeus, 1758)

Pelicanus sp.

Anas rubripes, Brewster, 1902

Myrmecophaga tridactyla, Linnaeus, 1758

Human dentition

Castor canadensis Kuhl, 1820 (I 1/1, C 0/0, P 1/1, M 3/3)

Loxodonta africana, (Blumenbach, 1797) (I 1/0, C 0/0, P 3/3, M 3/3)

Grizzly Bear Ursus arctos horribilis Ord, 1815 (I 3/3, C 1/1, P 2-4/2-4, M2/3)

Macropus rufus (Desmarest, 1822) -- Odocoileus virginianus (Zimmermann, 1780) (I 3/1, C 1/0, P 2/2, M 4/4) -- (I 0/3, C 0/1, P 3/3, M 3/3)

Papio sp. Erxleben, 1777 (I 2/2; C 1/1; P 2/2; M 3/3)