Friday, February 18, 2011

Bone Lab

Goethe observed that, in fetus skulls, there appeared a bone which scientists at the time didn’t accept was present in humans. Yet Goethe’s findings of the premaxillary bone are accepted today, though it is much harder to make out the premaxillary in adult skulls than those which Goethe observed. Because bones fuze as an animal grows and matures, sometimes the premaxillary bone fuzes to itself and to the maxillary bone. An example of this fusion can be observed in figure 5. In the adolescent lion skull, the suture between the premaxillary bone and the maxillary bone is clearly defined. However, when looking at the adult lion, this distinction is not so clear. This fusion may occur for many reasons, scientists are not quite sure. One reason is that the skeletal system is dynamic, that is, it is always changing. So when more pressure is placed on the suture as time goes on, this suture may just close up. Scientists have also suspected that bones may fuze together for greater stability.

Despite the fact that bones do indeed fuze together, the premaxillary bones are much more visible in other mammals than in humans. This is due to their primary function as a structure; that is, to hold the incisor teeth. However, in some mammals like the manatee, they have a leathery pad on top of their mouths which is also connected to the premaxillary bone. While it isn’t exactly known why some mammals have a more defined premaxillary than others, there seems to be some correlation between diets and the size of the premaxilla in mammals. In animals that rely heavily on gnawing with their incisors, such as the beaver, the premaxillary bone is much more pronounced (figure 7 and figure 8). Whereas in animals that use their incisors similarly to how man does, like a chimp, the premaxillary bone is much less defined (figure 6). In animals like the anteater which don’t even have teeth or which don’t use them to gnaw or tear, there is no premaxillary bone present at all. A sloth, which is similar to the anteater, similarly does not use its incisors for gnawing or ripping, thus, a sloth has no need for a large premaxillary bone as evident in figure 1.

There are also different branches of the premaxillary bone. These branches are either well defined or not. In the lion, for example, these different branches are well defined. Figure 3 demonstrates one such branch and figure 4 demonstrates the other. These two branches are the palatal branch and the nasal branch, respectively. These branches can also be seen in a beaver (figure 8). However, because the premaxillary bone is much more defined in the beaver, it is larger. Thus, these two branches are not as distinct.

The shape and scale of the premaxillary bones differs between animals. A whale skull (figure 9), for example has premaxillary bones very different to that of a lion. Figure 10 is of premaxillary bones in a whale and figure 2 shows a premaxillary bone of a lion. These two animals eat in very different ways, so it is understandable that their premaxillary bones would be shaped differently. While this bone may be used to demonstrate differences between animals, it may also be used to describe how animals may be similar. Families of bats, for example, are distinguishable in many ways, one of which is by the size and shape of the premaxillary bones.

Goethe’s method is thus still widely used today; pure and simple observations are necessary in order to note similarities and differences between families and species. While genetic evidence is more widely accepted, genetic evidence is not always available to use for identification. A solid classification is based on both observation and genetic evidence. Either way, it shouldn’t make that much of an impact because, as Professor Phil said, “there is one and only one history”.

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