Chapter+04

Place your questions and answers for Chapter 4 here.

A: On the boys' (Bill, Chuck, and Shubin) trip to the Bay of Fundy, their discovery was very lucky. In their first trip, while Bill was uncovering a speck of a fossil in one of the rocks that they brought back, he found a very small jaw of an early mammal/ reptile. The name of the reptile is the tritheledont. The special thing about the tritheledont is this organisms teeth. The reason I said early mammal/reptile earlier in my answer is because of the teeth. The tritheledont showed early signs of occlusion which is the fitment of teeth between each other in the lower and upper mandibles when you bite down. Bill and Shubin noticed the wear on the sides of the teeth that showed this evolutionary trend for mammals. (J. Speelman)
 * Q: What kind of fossils did Shubin and company find in the Bay of Fundy in Nova Scotia and why are they so important to the evolutionary history of teeth (especially occlusion)? (I. Perler)**

A: Humans, along with most mammals, are diphyodonts, which means they only possess two sets of teeth throughout their lifetime. In contrast, most other vertebrates or polyphyodonts, which mean they possess multiple sets of teeth throughout their lifetimes. One likely reason for the development of diphyodontism is the presence of occluded teeth for chewing. Unless the teeth are correctly fit together, the constant contact will cause rubbing and loose of enamel, weakening the tooth and potentially exposing the pulp. With the multiple roots and well developed teeth sockets, the teeth of mammals will remain in their growths of location, helping cut downs of the amount of friction that would be due to poorly grown-in teeth. This would allow for chewing without the constant need to replace teeth over time, meaning the materials and energy otherwise used to replace teeth could be invested elsewhere (M. Purdon).
 * Q: Teeth have changed greatly over millions of years. Before organisms started developing features of mammals, their teeth were replaced by new teeth in a reptilian way. Why do you think that, in mammals, teeth don't get replaced if damaged or broken (apart from growth after one loses baby teeth or has wisdom teeth removed) like they used to in reptiles long ago? (N. Sarkar)**

A: I think that human teeth will change very very slightly -- if at all. I say this because in the world that we humans live in today, there is so much advanced medical care that a person will be able to reproduce and pass on our teeth genes no matter what kind of diet he/she eats. This will significantly lag teeth evolution. However, it is possible that over a very large collection of years human teeth may gradually evolve to more efficiently grind up certain diets that we have discovered as better for our health, for example, teeth may evolve to better grind up vegetation for a vegetarian diet. (L. Bercz)
 * Q: Based on what our teeth reveal about humans, how do you think they will change over the next large collection of years? (M. Blanchard)**

A. Teeth are the hardest part of our bodies and are therefore oftentimes the best preserved part of a fossil. This is because tooth enamel has a high proportion of mineral hydroxyapatite. They are so hard that if the upper and lower jaw are not lined up, they can shatter each other. Teeth are also stand outs in the rock because unlike bone, teeth remain hard over time without becoming fragile and brittle. (E.Olson)
 * Q: Why are teeth said to be "hard as rocks" (A. Schmidt)**


 * Q: How did the development of teeth in prehistoric organisms lead to future skin adaptions in present-day animals? (C. Nikolai)**
 * A:** In teeth, there is an interaction between two layers of tissue that help develop the teeth. There is an inner layer and an outer layer that eventually fold, make proteins, and change shape to build the teeth. The development of teeth was the key for animals to evolve and be able to develop structures within their skin. Hair and feathers for example also develop from the interaction of two layers coming together and folding and secreting proteins. Teeth revealed the origin of making of organs (T Gebhart).

A: In addition to the fossils of the tritheledont being extremely rare, this creature is described in the book as part mammal and part reptile. This indicates this creature's (the organism from which the fossil found is derived from) role as an evolutionary stepping stone between reptile and mammal, helping the scientific community determine the evolutionary lineage of organisms and coming closer to the answer of "How did mammals evolve from reptiles/other classifications of animals?". (N. Braun)
 * Q: Shubin, Bill, Chuck, and Paul found a fossil called a** tritheledont **when exploring in Nova Scotia. What is the importance of this fossil, and how does this find support both the evolutionary theory and the theme of this book? (J. terHorst)**

A: Shubin's great breakthrough discovery in this chapter was the finding of the tritheledont fossil in Nova Scotia. This particular reptile fossil had a tiny jaw, and within this jaw were teeth that evidently contained patches of wear and tear where a tooth-to-tooth impact would have occurred. This fossil lended itself to being part mammal and part reptile. This finding is significant because of the fact that it bridges the gap between different types of teeth and jaws organisms would have needed in order to process food. In other words, this fossil is representative of the start of an organism that could eat varying types of food much like humans rather than being confined to a meat eater or a plant eater. This variation is important because it would have enhanced the availability of nutrients/food and thus the organisms and future organisms' survival. (O. Heltman)
 * Q: What was Shubin's great breakthrough discovery in this chapter and why in your opinion was it so significant? (H. Schwarz)**


 * Q: Recall Shubin's experience of being marooned by high tides by the cliffs of Nova Scotia before the tooth jackpot. What is it about teeth that make them more likely to find than organs, for instance? What does that particular story say about the nature of science and discovery? (P Oakes).**


 * Q: Describe Shubin’s first experience at a paleontological dig. Explain the transformation he went through regarding his method to finding fossils. In your opinion, why was it so hard for Shubin to locate fossils using his original way of thinking? (R. Heis) **

**Q: Shubin describes how the development of teeth breast and hair are all very similar. How are they developmental process similar and how is it advantageous for an organism to use these processes to develop certain organs? (C. Hurst)** A: The development of teeth, mammary glands, and hair are all very similar in the idea that two layers of tissue come together, fold, and secrete proteins. Because the process is similar for many different types of organ development, it proved to be advantageous for organisms as they now have the ability to develop many different organisms through a very similar process and allow for a more complex organism with more variety. The development of teeth led to the development of numerous other organs and characteristics such as feathers, hair, sweat and mammary glands. (M. McKinney)

**Q: What are some of the ways reptilian teeth differ from mammalian teeth? What could have caused these specific differences? (L. Bentley)** A: Reptilian teeth lack differentiation between teeth based on shape, and are only different based on size within an animal's mouth. Also, reptilian teeth lack precise occlusion, or a precise fit between upper and lower teeth, that mammals have. Finally, reptiles get their teeth replaced throughout their entire lives as they continue to break down. Mammalian teeth, however, do have differently shaped teeth within their mouths, they have a precise fit between their upper and lower teeth, and their teeth are only replaced once per lifetime. Differently shaped teeth could have been caused by a mutation that proved to be beneficial for animals to eat different kinds of things, such as plants. Having flatter teeth would help to grind up plants, whereas sharp teeth help to tear things apart, such as meat. If this mutation was beneficial, it would help the animal survive and be passed on through generations. The precise fit would also help to grind food in the most efficient way possible, and therefore this mutation would also be beneficial and therefore passed on. Finally, having teeth that were only replaced once could have happened because the teeth grew stronger, so they weren't worn down as much, or, because they became specialized, the each tooth only did the job that it was best at when it needed to be doing it, so there was less wear on the teeth in general. (A. Nolan)

**Q: Imagine you have found a fossil of a jaw that has a set of teeth. These teeth appear to be organized neatly in a row. What are some examples of animals that may have previously owned this set of teeth? (T. Russell)**

**Q: What would you assume is Bill, Chuck, and Neil’s favorite season and why? (A. Gatje)** Bill, Chuck, and Neil had to wait until summer to return to Nova Scotia for a second time, even though Neil "spent the whole winter tense with anticipation" (Shubin 70). The problem with searching in the winter is the ice. It would be a pure guessing game to chip through random spots of ice to possibly find fossils. (C. Sanders)

**Q: In what way does having teeth effectively "level out the playing field" among little fish and big fish? (T. McDaniel)** A: Having good teeth effectively levels out the playing field among little fish and big fish because smaller fish can munch on bigger fish if they have good teeth. Smaller fish can use their teeth to scrape scales, feed on particles, or take out entire chunks of flesh from the bigger fish. (A. Gatje).