Aaron Berger
2-9-99
Seminar
The evolution of teeth.
Fossilized teeth have played a very important role in understanding the evolution of man. Teeth can tell you a lot about an animal. You can learn what an animal ate, what their face would have looked like, and you can usually tell a little bit more about the way they lived. For instance, when a skull is found that has very large and ferocious canine teeth, one possible assumption is that the animal was a male that reined over a group of females. He may have needed those large canines to ward off other males, or to protect himself. He quite possibly just needed for whatever type of diet he assumed.
That’s not all you can get out of fossilized teeth though. You can make predictions about an animal’s diet by the amount of wear and tear on the enamel of the tooth. Scientists are able to look at tooth enamel under a scanning electron microscope to see what are called microwear patterns on the surfaces of tooth enamel. These microwear patterns consist of tiny pits and scratches on teeth. We have figured out that the linear scratches on the tooth, are caused by grasses. Eating leaves produces a polished looking effect, and the bone crunching consistently found in carnivore diets gouges out tiny pits in the enamel.
By finding and analyzing fossil teeth, professionals have been able to distinguish pongids from australopithecines from hominids from homos. Some of the characteristic features of Pongids include an increase in the size of their incisors, and the widening of the mandible to form the simian shelf. Canines of pongids are sexually dimorphic because of their strong conical shape. This means that their canines probably had a role in the social status of the pongid. To aid in the cutting function of the first lower premolar, a strong anterior root has developed. Also, teeth behind the canines, which would be the premolars and molars, are arranged in rows and are fairly parallel. The first deciduous molars remain predominantly unicuspid in pongid dentition.
Robust australopithicines have distinct dental specialization in the size of their teeth. Their anterior, front teeth, and their posterior, or back teeth, are somewhat disproportionate in size. Their front teeth, or incisors, along with their canines, are much smaller than the premolars and molars. Archaeologists have interpreted their large molars as an adaptation for crushing. Early australopithicines had the type of microwear patterns on their teeth which would indicate that their diet did not consist of tough plant material like what pongids ate. Their diet instead had more in common with modern chimpanzees that eat fruits. With the hominid line there come new characteristics. For instance, hominid dentitions show a reduction in the size of the incisors and the canines. The premolars are now bicuspid instead of unicuspid. There is no pronounced sexual dimorphism of the canines, actually, canines have now diminished to appear like spatulas instead of sharp pointy teeth. Diastemata, places between teeth, have now mostly disappeared. This helps the dental arcade to be fairly even and round.
The next group to talk about is Homo habilis. You can see by comparison that as we begin to get more into modern man, the features tend to reflect our own. For instance, the incisors and canines of habilis become more spatulate. They are smaller and flatter like ours instead of like a gorilla’s. Their premolars and molars also become smaller in size and proportion which could accentuate a dietary shift of some sort.
The enamel patterns of Homo erectus show heavy wear that include polish, pits, and scratches. This information indicates an unspecialized, omnivorous diet. Homo sapien dentistry revolves around the reduced jaw bone size. Possibly due to the smaller jawbones, as a whole, tooth crowding occurs even in spite of the smaller sized individual teeth and marked reduction in the size of the third molar. The wisdom teeth, or third molars, are somewhat unstable. By unstable, I mean inconsistent. Sometimes the wisdom teeth are fine and sometimes they are in bad positions, or not there at all.
Yet another way to gain insight into the life and diet of an early human is to use isotopes. Scientific studies have shown that the ratio of Carbon 13 to Carbon 12 in tooth enamel can be used to deduce dietary information about the specimen in question. This process is rooted in the knowledge of photosynthesis in green plants. During photosynthesis, or at the beginning rather, 1 Carbon dioxide molecule is added to a 5 carbon compound that immediately splits into two – 3 Carbon molecules. I think this is just before the Calvin cycle takes place. Plants such as these are known as C3 plants and are things like trees, bushes, and shrubs. Grasses are a little different in that they have a Carbon dioxide molecule added to a 3 carbon compound to give a total of 4 Carbons. Thus, grasses are known as C4 plants and trees are C3 plants.
Finally, by analyzing tooth enamel with stable isotope mass spectrometry, the relative proportions of C3 and C4 vegetation can be determined and we can learn what a species at more of.
Works Cited
Human Evolution. (Online) Available. http://www.eb.com: 180/cgi-bin/g?DocF=macro/5002/23/75.html, January 29,99.
World book Encyclopedia of Science. Volume 6, The Animal World. Hominid Ancestors. Chicago 1989
Looking at microwear patterns on fossilized teeth is an excellent way to see what types of food pongids, australopithecines, and hominids consumed. By looking at these teeth we not only can discover what types of foods they were eating but also a little about their society. By using a scanning electron microscope, scientists are able to see tiny pits and scratches on the surfaces of tooth enamel. These pits and scratches provide the information desired by the scientists in regard to the diet of the animal in question. It is important to study the teeth of these animals because fossilized food remains are usually animal bones; they are preserved more frequently than vegetable matter. It has been observed that grasses leave linear scratches on teeth, leaves produce a polished effect, and the bone crunching of carnivores gouges out tiny pits in the enamel.
By examining the dentition of a pongid we see that there is a progressive increase in the size of the incisors and widening of the mandible. This widening eventually formed the simian shelf. The cutting function of the first lower premolar is accentuated by the development of a strong anterior root. The postcanine teeth preserve parallel or slightly divergent alignment in relatively straight rows as opposed to the rounded dental arcade of the hominid. The first deciduous molars remain predominantly unicuspid. By using a scanning electron microscope it is discovered that the "pongid dentition belongs to an animal that feeds on large stalks of vegetation and fruit, tearing with its incisors, crushing with its large molar teeth, and chiseling with its enormous canines"(Britannica Online). By looking at the size and strength of the canines it can be concluded that the pongids lived in a sexually dimorphic society. This is very similar to the societies you see in apes, such as Silverbacks, today.
By looking at microwear patterns on the teeth of some australopithecines we see that their diet did not consist of tough plants like that of pongids. Their diet was more like that of modern, fruit-eating chimpanzees. The robust australopithecines show dental specializations of a high order in that there is massive disproportion between anterior and posterior dentition. By this I mean that the incisors and canines were small, but the premolars and molars were extremely large. The specialization of these teeth is for crushing.
The difference in the dentitions of hominids and pongids is quite notable. There is a large reduction in incisors and canines. Because of this decrease in canine size there is no pronounced sexual dimorphism. There was a change in the appearance of the bicuspid premolars and a change in the occlusal relationship of the jaws. This change in the occlusal relationship tended to promote even wear of the surface of all of the teeth. The canines diminished to a spatulate form and, unlike the pongids, slightly, if at all, interlocked. The spaces around the canine teeth in the pongids and australopithecines have disappeared in the hominids. The hominid dental arcade is even and rounded, and there is a reduction in molar size.
The incisors of Homo habilis became more spatulate and the molars became smaller in both size and proportion. The changes possibly indicate a shift in diet.
Homo erectus dentitions show heavy wear patterns that include pits, scratches, and polish. All of these marks indicate an unspecialized, omnivorous dietary preference.
Dental characteristics of Homo sapiens revolve around the reduced jaw bone size. Because of this reduction the dentition as a whole shows tooth crowding. Overall reduction in the size of the individual teeth and marked reduction in the third molar or wisdom tooth accompany this decrease.
Aside from microwear patterns, isotopes are also used for evidence of hominid diets. Studies have shown that the ratio of 13C to 12C in tooth enamel can be used to provide dietary information about extinct fauna. The approach his based on the knowledge of photosynthesis in plants. C3 plants consist of trees, bushes, shrubs, and forbs. C4 plants consist of tropical grasses and sedges. The proportions of C3 and C4 vegetation in an animal’s diet can be determined by analyzing its tooth enamel with stable isotope mass spectrometry.
By using all of these techniques, we can discover what types of animals we have evolved from. The things we find can answer our questions about the locations our ancestors inhabited and what types of social classes they held.
Works Cited
Sponheimer, Matt; Lee-Thorp, Julia A., Isotopic Evidence for the Diet of an Early Hominid, Australopithecus africanus. [Online] Available
http://cas.bellarmine.edu/tietjen/images/isotopic_evidence_for_the diet_o.htm, Jan. 15 1999.
Human Evolution. [Online] Available
http:www.eb.com:180/cgi-bin/g?DocF=macro/5002/23/27.html, Jan. 29, 1999.