In chapter 4, Shubin discusses the importance of teeth. He notes the importance of the structure of an animal's teeth in understanding the life of the animal. Using your knowledge of evolution, explain how teeth have evolved from the first oceanic life all the way to humans.
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ReplyDeleteAs Shubin describes it, "teeth are a powerful window into an animal's lifestyle" (Shubin 61). Therefore, teeth change according to a certain species' preferred diet. If the organism is a carnivore, it will have sharper teeth like canines or incisors to tear through flesh. If the organism is a herbivore, it will most likely have larger and flatter teeth like molars to grind up plants. Omnivores can contain both types of teeth to suit their eating habits of both meat and plants. (http://www.earthlife.net/mammals/teeth.html)
ReplyDeleteTeeth come in many sizes and shapes. Many mollusks have teeth like structure called radula. This structure is a belt of teeth that scrapes its food into its mouth (Campbell 678). This benefits molluscs because they don't have hands to put their food into their mouth, nor do they have jaws to clamp down on their food. Fish then began to develop jaws through evolution. As Shubin stated, smaller fish developed armor to avoid being eaten by bigger fish, causing bigger fish to develop larger and stronger jaws to crack the armor. As this cycle continued, teeth would grow larger as well. Animals such as sharks have large, sharp teeth. Their powerful jaws allow them to sink their teeth into prey to instantly kill them. Because sharks can easily lose their teeth when scavenging for food, or fighting off predators to survive, sharks contain many rows of teeth that will shift to replace lost teeth (http://www.kidzone.ws/sharks/facts2.htm). In this way, they will always have teeth available to optimize their survival.
As animals shifted to land, teeth structure became even more diverse. Many reptiles, such as poisonous snakes contain venom in their teeth that instantly kills their prey. Other reptiles like crocodiles have large jaws and pointed teeth, like sharks, to powerfully grasp their prey and keep it from escaping. Later in earth’s evolutionary history, mammals also had teeth specifically fit for their diet. The human mouth contains both molars and incisors because we are omnivores. The incisors are conveniently located at the front so that humans can bite through their food and make it into smaller pieces before entering the mouth. The molars are located in the back for chewing and grinding food. It would be extremely difficult to grind food with just the incisors at the front because those teeth aren’t flat enough. Similarly, having only molars would make it harder to take smaller bites of food to make it fit in the human mouth. This is why human jaws must contain both types of teeth to work together in mechanical digestion.
Claire Yao (claire.yao521@gmail.com)
As Claire said, the different kinds of teeth an animal has can tell a lot about the animal. It can help us to understand what an animal eats and whether it is a carnivore, an herbivore, or an omnivore. By looking at the teeth found in fossils, scientists have found many changes and developments from the teeth of primitive reptiles to those of more recent mammals. One thing that mammals have that reptiles like crocodiles, lizards, and snakes do not, is the “precise occlusion – the fit between upper and lower teeth” (61). Mammals’ teeth have developed so that when the mouth is closed, the teeth always fit together exactly. This is because as species began to evolve into mammals, the bones in the jaw became smaller and moved to the ear. This allowed the teeth in mammals to fit together in precise ways. This allows humans to be able to “break up food with maximal efficiency” (61). It also prevents the teeth from shattering. This may be why mammals only replace their teeth once in a lifetime, whereas reptiles have to continually replace damaged and worn-down teeth. So, mammalian teeth have evolved to be more efficient. However, the efficiency of the teeth depends on how the teeth are used and what kind of food the animal eats which Claire explained by showing the need for humans to have both molars and incisors because we are omnivores. So, it’s hard to say that mammalian teeth are more efficient than reptilian teeth because they are both efficient in their own ways.
ReplyDeleteThe species, the Pseudotribos robustus, was a species found that helped to see the development and the evolution of teeth in mammals. This creature “departed considerably from the ancestral pattern where it could only cut up things; now it [could] grind things up” (http://news.nationalgeographic.com/news/2007/10/071031-new-mammal.html). This cut-and-grind tooth found in this animal showed a step towards mammalian features because this is the kind of teeth that mammals have. Overall, evidence of the evolution of teeth from the first animals to those in mammals today is seen in many new species being found in fossils, just like the Pseudotribos robustus.
Sources:
Your Inner Fish
http://news.nationalgeographic.com/news/2007/10/071031-new-mammal.html
http://www.earthlife.net/mammals/teeth.html
Danielle Webb (dwebb456@gmail.com)
As Danielle and Claire both mentioned, "the little tooth contains so much of our connection to the rest of life that it is virtually impossible to understand our bodies without knowing teeth" (Shubin 60). In studying an animal's teeth, one can deduce what food the animal consumed; since the search for food in order to survive has always been an environmental pressure, the selective advantages that animals developed in evolutionary history many times had to do with better ways of obtaining food, which often had to do with the development and structure of teeth.
ReplyDeleteFirst, it is crucial to investigate why hard skeletons, those containing hydroxyapatite arose in the first place. In fact, the first hard hydroxypatite-containing body parts were teeth. The discovery of the conodont supports this claim; they were orignally found isolated, but as whole animals because known, they found that "many of them functioned together as a tooth row in the mouths of these soft-bodied jawless fish" (Shubin 77). Also, it is thought that "fish as early as the late Cambrian had dentine in their exoskeleton, which may have functioned in defense or for sensing their environment" (http://en.wikipedia.org/wiki/Teeth#Fossilization_and_taphonomy). With this development of teeth, the "fish-eat-fish" world really began; little fish developed armor, big fish obtained bigger jaws to crack the armor, and so on. Simply put, these teeth grew larger and larger. Sharks, like Claire pointed out, have large, sharp teeth that can kill prey instantly, a huge selective advantage for these huge predators.
As animals moved from water to land, the diet and the search for food was very different, which is reflected in the evolution of teeth, with even more diversity of different kinds of teeth, such as the similar blade-like shape of crocodile's teeth, good for killing prey for consumption. When mammals came about, their teeth had precise occlusion, "the fit between upper and lower teeth" (Shubin 61). This came about because the bones in the jaw of mammals became smaller and moved to the ear, allowing the teeth to have a perfect fit. This allows humans to break up food very efficiently. Also, humans have both molars and incisors, like Claire mentioned, which coordinates with our omnivore diet. Thus, from studying the evolution of teeth, we are able to trace the whereabouts, jaw structure, diet, and much more of different animals in evolutionary history.
Hannah Kay (hgkay@aol.com)