Extinct family of mastodons, characterized by the development of multiple accessory tooth cusps and believed to be ancestral to the later mastodons, though not to modern elephants. These long-jawed mastodons or gomphotheres were one of three distinct proboscidean lines established by the Miocene. They in turn diverged into a variety of descendant lines, several of which had highly specialized lower jaws. The family persisted into the Pleistocene in both Old and New Worlds. Long snouts appeared in the earliest forms and in the Miocene Gomphotherium the lower jaw and premaxilla (front bone of the upper jaw) were very long, both bearing tusks, which may have been used for digging, and probably permitting only a short trunk. In later forms the face became shorter and the trunk presumably longer. There were many genera and species. The evolutionary importance of the gomphotheres lies in the probable parallel between their development and that of the line which led to the true elephants.