Mounted specimen on display at the America Museum of Natural History, NYC
Reconstruction by Charles Knight.
When: Miocene to Pliocene (~12 - 3.5 million years ago)
Where: North America, Europe, Asia, and Africa
What: Gomphotheirum is a four tusked extinct proboscidean. Unlike modern elephants which only have enlarged upper incisors as their tusks, Gomphotheirum and its kin had enlarged upper and lower incisors. Neither set of tusks grew as large as living elephants, but the lower jaw was heavily modified and elongated to support the lower tusks. If you look at the photograph of the mounted specimen above, you can see that the actual bone of the mandible extends to almost the tip of the upper tusk. Based on the structure of the skull of Gomphotheirum it is thought the animal had a trunk, though again not one as log as the living species of elephants. Gomphotheirum is on the small side compared to the mammoth and mastodon in the photo with it, and also is a bit smaller than the living african elephant, but about the same size as the asian elephant - standing about 10 ft (3.2 meters) tall at the shoulder. These fourtuskers were proportioned very differently from the asian elephant, however. Their legs were much shorter in proportion to their body. The genus Gomphotheirum originated in North America, but spread throughout most of the world before going extinct in the Pliocene.
Gomphotheirum in the group Gomphotheriidae (shocking I know). Gomphotheres ranged almost world-wide for over ten million years, and it is possible the last one died less than 10,000 years ago. I say only possible as relationships of gomphotheres, and really proboscideans as a whole, are really not well understood. Gomphotheriidae may be a paraphyletic series of taxa (not a ‘real’ group), with some taxa more closely related to the living species than others. Basically if you are interested in paleontology the study of proboscideans is an area that desperately needs more people in it. You also get to look at other cool extinct forms like Deinotherium!