Super-Class Gnathostomata

Abstract

The Gnathostomata includes all vertebrates with upper and lower jaws. It comprises a wide range of animals, from fish to the various tetrapod classes, which have in turn been derived from a fish or fish-like ancestor. An entirely satisfactory classification of fishes is not easy to construct, because of the incompleteness of several parts of the fossil record, and the consequent lack of connecting links. Complete agreement as to their arrangement, therefore, has not been reached, and the student will meet with a considerable choice of classi- fications. It is at least certain that within the old group of Pisces (fishes in the widest sense of the expression) there are fundamental divisions which are of great antiquity. Animals of these divisions appear to have little to do with one another beyond the possession of a possible, but unknown common ancestor at a very remote period.