On pages 61 and 62, Shubin described the difference between mammal and reptile teeth. One of the differences is that throughout a reptile's life, their teeth are replaced continuously while for mammals, their teeth are only replaced once their whole life. Would having the same teeth one's whole life be an advantage or disadvantage? How does this relate to the fact that all of mammals teeth fit perfectly together?
Jackie James
(jackie.james@comcast.net)
Although teeth are not essential to living as humans, NCIB reports that an estimated 85% of adults undergo dental treatment. Humans now have highly specialized teeth, including incisors, canines, and multicuspids. This is an example of the theme of structure versus function. As mammals have evolved, they have expanded their diet to not only include plants, but also other animals, thus creating the need for different kinds of teeth. Since we are omnivores and eat both plants and animals, it created the need for teeth to fit this function. We also see this in the size of teeth as baby teeth are replaced with adult teeth; young children have smaller mouths and thus when their jaws grow, they need larger teeth to fit their larger mouth and vice versa. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2100358/)
ReplyDeleteSharks are one animal that replace their teeth periodically throughout their lifetime. This is also due to their changes in diet. Younger sharks mainly grab fish to eat, but as they grow older they must have teeth suitable for eating other larger sea mammals. (World of Sharks)
The advantage of replacing teeth lies in the ability to replace worn out teeth. This is common in animals that frequently use their teeth. While there is no species that only has one set of teeth their whole life, keeping the same set would be a disadvantage as the organism is growing and also when the teeth get worn out, as they would have no way to repair the teeth. The number of times an animal replaces their teeth can be attributed to how they use their teeth. Sharks, for example, use their teeth to rip apart prey, often having to chew through bone. Humans on the other hand, chew their food, thus not being as damaging to the teeth.
Anna Leng (annaissbananas@gmail.com)
All mammals have unique sets of teeth that provide an immense amount of information about the animal’s lifestyle. In comparison to reptiles, each mammalian species has a distinct set of teeth, while many reptiles have similar teeth. A journey into the inside of a crocodile’s mouth will show that all of its teeth have the same blade-like shape, only differing in size. Human teeth have a selective advantage in terms of shape because we are “all-purpose eaters”, according to Shubin. By this he means that we have several kinds of teeth(incisors, premolars, molars), and each type is used to break down different types of food. The different tooth shapes of different animals reflect on their eating habits, giving each animal a selective advantage in survival by helping them break down their own food.
ReplyDeleteNot only are reptiles lacking the highly specialized teeth of mammals, but they must also constantly replace them. A single crocodile can use up to 3,000 teeth in its lifetime. This is a large disadvantage because replacement is only necessary when teeth wear down, showing that reptile teeth are much weaker than mammal teeth. Our teeth don’t wear down over time when used properly. Also, replacement takes time, and new teeth won’t be fully available for use until they have grown out sufficiently.
However, having a permanent set of teeth for an entire lifetime can have its disadvantages. For example, as Anna Leng stated previously, many adults go through dental procedures to fix their teeth. This is only necessary because we cannot replace our teeth like reptiles do so often. Mammals have precise occlusion, allowing the upper teeth and the lower teeth to fit together perfectly. However, a very large percentage of humans acquire some sort of malocclusion, which is any irregular growth or alignment of the teeth. Malocclusion in humans is as permanent as the teeth themselves are, unless dental measures, such as braces or surgery, are taken. However, these solutions can take a long time and bear a heavy price tag.
Sources:
Shubin
http://www.nlm.nih.gov/medlineplus/ency/article/001058.htm
http://en.wikipedia.org/wiki/Tooth#Reptiles
Austin Lee (austinklee7@gmail.com)
As Anna pointed out, the biggest advantage to replacing teeth is that the teeth may get worn out and thus replacement keeps them sharp and efficient for chewing. What she didn’t point out, however, was that tooth wear itself has a strong link to how teeth fit in the mouth. As Austin noted, there is a clear link between bad fit of teeth and overall wear; it was even found in a study that horizontal overjet and vertical overbite are predictors of wear of maxillary and mandibular central incisors in humans (http://www.ncbi.nlm.nih.gov/pubmed/8451919). When teeth fit perfectly, humans can chew with “maximal efficiency” (61), so any shifts in fit can cause decrease in food break-up efficiency and thus create wear, or even shatter our teeth (61). Fit is very influential in how often an animal needs to replace its teeth, as even the slightest decrease in chewing efficiency will eventually lead to breakdown of enamel and require replacement.
ReplyDeleteAs Austin described, the teeth we have differ depending on what they are used for. Most mammals have shearing teeth - incisors and canines - and grinding teeth - premolars and molars (Campbell 721). The shearing teeth are used for our carnivorous tendencies, as we need to rip apart meat, while the grinding teeth are needed to mash plants up. Different teeth mean different necessity for replacement; animals that have sharp teeth, like crocodiles and other reptiles, have imprecise occlusion and thus wear and tear much more readily (61), becoming dull and useless and requiring replacement. Animals that have varied teeth, like humans, don’t need as many replacements because our diet is more varied and our teeth fit better, so our chewing is more efficient. More unusually, there are some animals whose teeth never stop growing; lagomorphs (like rabbits) and rodents have perpetually growing incisors, as the aridacular process continually produces enamel in rodents while elodent dentition in rabbits creates constantly erupting incisors. Because their teeth never stop growing, but are never replaced either, lagomorphs and rodents have to constantly wear down their teeth by gnawing on food or eating a high-fiber diet (http://www.suite101.com/content/the-difference-between-rodents-and-lagomorphs-a94546). This is an example of having the same teeth throughout an animal’s life, but having to deal with the prospect of constantly wearing them down to deal with not being able to replace them; therefore, of the animals that developed teeth throughout their whole lives, those that developed a trait that would allow them to prevent excessive wear had a selective advantage over those that did not, and thus survived with the ability to deal with those issues.
Eugene Bulkin (doubleaw002@gmail.com)
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