Premaxillae as a Unifying Characteristic
In his research on premaxillae, Johann Wolfgang von Goethe sought to establish an archetype for all animals (Goethe 111-112). The premaxilla, his chosen bone to focus on, is an interesting choice as it has many morphologies depending on the feeding habits and other needs of the mammal. For example, a reasonably basic version of the skull is shown in beavers, whose primaxillae are similar to many other groups in the class Mammalia.
Here one can see the basic structure of the beaver, whose premaxilla is located next to the nasal. The premaxilla is relatively small in comparison to surrounding structures like the prominent zygomatic arch.
In other mammals, evolution has driven unusual premaxilla morphologies. For example, grazing animals like horses have a significantly longer premaxilla. This is probably due their diet, which consists of grasses. In order to graze safely, long premaxilla, maxilla and nasal bones are required to push the eye back. Having a backset eye ensures that the horse will be able to see over the grass and watch for predators effectively while grazing. This supports Goethe’s assessment that an animals diet affects what type of premaxilla it has (Goethe 112). While Goethe was correct in this instance, there are also non-dietary reasons for changes in premaxilla shape.
A more extreme version of premaxilla elongation is seen in water mammals like porpoises and dolphins. In the specimen viewed in class, the premaxilla was clearly visible stretching from the front of the skull back to the top of the head. This extreme stretching of the premaxilla helps to allow the dolphins and porpoises to push back their nose holes. This morphology is necessary in underwater mammals because it allows a minimized surface area to be above the water when breathing. Breathing through the top of the head, as opposed to the front of the face, lets underwater mammals barely come above the surface, reducing risk of predation and exposure to air.
While Goethe’s work on the premaxilla wasn’t fully accepted by scientists of his time, we now know that premaxillae are one of the unifying charachteristics of animals. While they may vary in size and shape, the general structure remains an archetype as Goethe hoped.
Goethe, Johann W. Scientific Studies. Trans. Douglas Miller. New York: Suhrkamp Publishers, 1988.