Question

2. Jaw comparisons xamine the following sets of laws and teeth and explain how the structure of the jaws and the dentition match the feeding habits of each vertebrate. Identify special adaptations to the ecological role of each organism. For example, why do sharks keep growing new teeth? Write out the dentition for each specimen. a. shark (grows new teeth continuously, cartilaginous jaws) b. beaver (incisors grow continuously) c. canine (dogs, wolves - why are their molars so sharp?) d. cow (has incisors on lower jaws only) e. cat (what is the difference between a pouncing predator's dentition and the canine dentition?)

Answer 1

a) SHARK

Jaw: The jaws of sharks are cartilagenous and not attached to their skull, instead moving separately with independent upper and lower jaws. This allows them to lift their head and thrust their mouth forward to bite its prey. While this varies among different species, most sharks have this ability to some degree..

Teeth: Sharks may have homodont type of dentition and can be up to 3,000 teeth at one time and are fully embedded into the gums, as opposed to being directly affixed to the jaw. The shape and size of the teeth vary depending on their purpose, and there are four main types of shark teeth:

i. Needle-like teeth are typically found in sharks whose diet consist of small to medium sized fish, or even other small sharks. They are particular effective at gripping onto agile and slippery fish.

ii. Serrated, wedge like teeth are found in larger species that feed on larger prey, and are effective at cutting off chunks of flesh for easy swallowing. The great white shark is a prime example of a specie with this feeding habit.

iii.Teeth which serve no purpose at all are found in plankton feeders such as the basking and whale shark, who use their gills to filter feed.

iv.Dense, plate like teeth are used to crush the shells of prey like bivalves and crustaceans, and are found in smaller sharks such as the nurse or angel.

Sharks continuously grow multiple rows of replacement teeth in a groove inside of the jaw, and are usually replaced one at a time as opposed to entire rows. It is estimated that some sharks may lose 30,000 or more teeth in their lifetime, with replacement rates varying from several days to several months.

b) BEAVER

Root- Back teeth Incisors

The dental formula of the American Beaver is: 1/1 0/0 1/1 3/3 = 20 teeth. This formula shows the number of top/bottom teeth on one side of the jaw, so the total number comes from adding the top and bottom numbers and multiplying by 2. The beaver's dental formula shows that they have a total of 2 incisors on top, 2 incisors on bottom, 0 canines on top, 0 canines on bottom, 2 premolars on top, 2 premolars on bottom (that look like molars), 6 molars on top and 6 molars on bottom, for a total of 20 teeth.

The roots of the incisors are open, that is, continue to grow throughout life if subjected to wear and tear.

A beaver's teeth grow continuously so they will not be worn down by chewing on wood. Their four incisors are composed of hard orange enamel on the front and a softer dentin on the back. The chisel-like ends of incisors are maintained by their self-sharpening wear pattern. The enamel in a beaver's incisors contains iron and is more resistant to acid than enamel in the teeth of other mammals.

c) CANINE

The canines dentition mainly consist of incisors, canines, premolars and molars with dental formula

2 x (3142 / 3143) = 42 teeth.

In carnivores (dog), canines are large, strong and pointed spear-like for tearing flesh.

in carnivores (dog), last premolar in the upper jaw and first molar in the lower jaw may have very sharp cusps for cracing bones and shearing tendons. These are called carnassial teeth.

d) COW

Dental formula- 2 x (0.0.3.3/3.1.3.3) = 32

Cattle have thirty-two teeth, including six incisors or biting teeth and two canines in the front on the bottom jaw. The canine teeth are not pointed but look like incisors. The incisor teeth meet with the thick hard dental pad of the upper jaw. Cattle have six premolars and six molars on both top and bottom jaws for a total of twenty-four molars. The teeth of cattle are designed primarily for grinding, and they use their rough tongues to grasp grass and then nip it off between their incisors and the dental pad.

Upoer Molers Maxilla) Louny SORODAJA Mand Lower Prestolars Lower Molars

ET

e) CAT

Cats are toothless at birth. Deciduous teeth are complete and functional within 2 months of birth. Permanent teeth are complete and functional by the end of the 6th month.

Formula for deciduous teeth: 2 (i3/3 c1/1 p3/2)

Formula for permanent teeth: 2 (I3/3 C1/1 P3/2 M1/1)

Incisors- Cats have six incisors in the maxilla and six in the mandible.

Canines- There is one canine tooth in each quadrant of the mouth. These teeth have a single root.

Premolars- Cats have three premolars in the maxilla and two in the mandible on each side.

The maxillary 1st premolar is normally missing and the 2nd premolar is very small and often not visible. The 3rd maxillary premolar is present. The 4th premolar is termed the carnassial tooth.

The mandibular 1st and 2nd premolars are normally missing. The 3rd and 4th premolars are present.

Molars- Cats have one molar in each quadrant of the mouth. The maxillary molars form a grinding surface. The mandibular molars are called the carnassial teeth.

A decrease in the number of molars leaves the cat with a shearing bite, rather than wider cusps for grinding.

DIFFERENCE-

Adult Dog Dentition:- Adult dogs have 42 teeth in total: 2 canines, 6 incisors, 8 premolars, and 4 molars on top; 2 canines, 6 incisors, 8 premolars, and 6 molars on the bottom. In general, the permanent (adult) teeth appear between the age of 16 and 24 weeks.

Adult incisors are very small, with a clover-like shape. It is possible to estimate a dog’s age based on wear patterns on these teeth. Also known as fangs or eye-teeth, the canines are most impressive when a dog bites into something. Molars may vary in number and size depending on the size of the dog. The main function of these teeth is to chew the food effectively.

Adult Cat Dentition:- Once they have reached maturity, cats will have 30 teeth, the last of which appear around the age of 20 to 24 weeks: 2 canines, 6 incisors, 6 premolars, and 2 molars on top; 2 canines, 6 incisors, 4 premolars, and 2 molars on the bottom.

Used mainly to tear into food, the canine teeth of cats are very sharp and protrude more than those of dogs. Incisors are very small and they help the cat remove debris from its haircoat during its grooming sessions. The premolars and molars are also called ”carnasial” teeth (meaning they include large three-rooted teeth) and are not flattened as they are in dogs. Contrary to dogs as well, it is not possible to determine a cat’s exact age based on dentition alone.