New Mexico Geological Society Annual Spring Meeting — Abstracts

A nearly complete skull of the primitive proboscidean Gomphotherium, New Mexico Museum of Natural History (NMMNH) P-28972, was collected just east of Espanola, Rio Arriba County, in the area Galusha and Blick (1971, American Museum of Natural History Bulletin 144) referred to as "First Wash." This skull is from the Miocene (late Barstovian-early Clarendonian) Pojoaque Member of the Tesuque Formation. This is also the type horizon of Mastodon productus Cope, 1875, now referred to as Gomphotherium productum and supposedly the only Miocene proboscidean taxon from New Mexico.

NMMNH P-28972 has complete tusks and M2-3. The right tusk is worn, but the left tusk is unworn, indicating "right handedness" in this Miocene proboscidean. The M2's are worn, but the M3's are little worn and not completely erupted. Assignment of NMMNH P-28972 to Gomphotherium is justified by its relatively bunodont upper cheek teeth which have single trefoils, and its M3 with four lophs. Size of the M3 (length = 135 mm, width = 65 mm) is relatively small for Gomphotherium, but within the size range of a very polymorphic species, G. productum, as conceived by Tobien. We, however, are skeptical of the validity of so variable a species and note that the newly collected Gomphotherium skull falls into the size range of a small species of Santa Fe Group gomphotheres that should be called G. productum. A large size group of Santa Fe Group Gomphotherium, however, may better be termed a separate species for which the name G. pojoaquensis (Frick) is available.