Of the North American gomphotheres, the status of Tetralophodon, primarily known from the Old World, is among the most controversial. This controversy stems from the incompleteness of the North American specimens. Along with elongation of the M/m3s and a tendency towards double trefoiling on the cheek teeth, Tetralophodon is diagnosed by complete tetralophodonty (i.e., four lophs on D/d 4-M/m2). However, of those progressive North American gomphothere specimens that have plausibly been referred to Tetralophodon only the M/m2s are known to be tetralophodont, with the condition of the M/mls and P/p4s unknown. Thus, it has proven impossible to determine whether these purported Tetralophodon species represent true Tetralophodon immigrants, or one or more parallel radiations from North American Gomphotherium stock. The discovery of an unusual gomphothere in the Clarendonian Kepler Quarry fauna of Nebraska has possible bearing on North American Tetralophodon. This gomphothere resembles North American Tetralophodon in having M/m3 that are both highly elongated and double trefoiled only on the anterior two lophs, and a tetralophodont M/m2. However, more significantly its M/ml and D/d4 are preserved, neither of which is tetralophodont. Thus, the Kepler Quarry gomphothere cannot be referred to Tetralophodon and along with the other North American Tetralophodon species is referred to a new genus, Pediolophodon. The existence of Pediolophodon suggests that during the Clarendonian North American Gomphotherium stock was evolving in parallel with progressive Old World gomphotheres such as Tetralophodon.
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