Gomphotheres

Taxonomy

"Gomphotheres" are assigned to their own family, Gomphotheriidae, but are widely agreed to be a paraphyletic group. The families Choerolophodontidae and Amebelodontidae (the latter of which includes "shovel tuskers" with flattened lower tusks like Platybelodon) are often considered gomphotheres sensu lato, and sometimes considered subfamilies of Gomphotheriidae. Gomphotheres are divided into two informal groups, "trilophodont gomphotheres", and "tetralophodont gomphotheres". "Tetralophodont gomphotheres" are distinguished from "trilophodont gomphotheres" by the presence of four ridges on the fourth premolar and on the first and second molars, rather than the three present in trilophodont gomphotheres. Some authors choose to exclude "tetralophodont gomphotheres" from Gomphotheriidae, and instead assign them to the group Elephantoidea. "Tetralophodont gomphotheres" like Tetralophodon are thought to have evolved from "trilophodont gomphotheres", in particular having a close relationship with the Gomphotherium species G. steinhemense. "Tetralophodont gomphotheres" are suggested to be ancestral to Elephantidae, the group which contains modern elephants. It has been suggested that the Stegodontidae emerged from the species "Gomphotherium" annectens, which may fall outside of Gomphotheriidae proper.