Museum of Comparative Zoology (MCZ) VPM-4225, a carnivoran dentary, is described here for the first time, 82 years after it was collected in the Duchesnean (late middle Eocene) portion of the Galisteo Formation in New Mexico. It evidently corresponds to the specimen—never identified by its catalog number, never described, and considered missing for the last 41 years—that formed the basis for the purported occurrence of the early carnivoraform Uintacyon in the formation reported in 1943. The specimen is here reidentified as one of the earliest amphicyonids, Angelarctocyon, which was previously known from only two specimens from the Chambers Tuff of Texas. With this reidentification, there is no longer a valid occurrence of Uintacyon postdating the Uintan North American Land Mammal Age, adding to the evidence for rapid replacement of ancient carnivoramorphan lineages by early crown-clade carnivorans in the late middle Eocene, across a period of severe climatic fluctuations 42–40 million years ago.