Description, classification, and geologic context of a Lower Pleistocene primitive mammoth jaw from Matanza Arroyo near Socorro, New Mexico

A mammoth jaw found as a large clast in the channel of Matanza Arroyo near Socorro, New Mexico, is here termed the Matanza mammoth. Cemented pebbly sandstone attached to the jaw shows that it was reworked from partially cemented ancestral Rio Grande sediments exposed in the channel 50–90 m upstream. This jaw is from one of the geologically oldest and most primitive North American mammoths. The mammoth fossil is a left dentary fragment with incomplete m2-3. The small size of the molars, widely spaced plates, very thick enamel and shape of the dentary identify it as a very early mammoth, Mammuthus meridionalis. The Matanza mammoth is comparable in morphology and geologic age to other primitive Irvingtonian mammoths from New Mexico that document the pres-ence of Mammuthus in the state between 1.6 and 1.25 Ma. Ancestral Rio Grande (ARG) sediments associated with the jaw ar