A new discovery of a skeleton of the horse Protohippus?, and a summary of the Miocene (Barstovian) fossil localities near Dixon, Rio Arriba County, New Mexico
— Gary S. Morgan, Aby, Scott, B., and Makaela Vogel

A partial skeleton of the horse Protohippus? was found and collected from the middle Miocene Chama-El Rito Member of the Tesuque Formation near Dixon in Rio Arriba County, New Mexico, in early 2009. This specimen consists of a nearly complete skull and articulated front and hind limbs. Neogene strata near Dixon are sparsely fossiliferous, with only five other specimens known from over 100 years of sporadic collecting, including fossils representing the borophagine canid Aelu­rodon taxoides, a second unidentified equid, the oreodont Merychyus medius, the camel Protolabis sp., and a second smaller camel. Most of this fossil assemblage is derived from the Chama-El Rito Member and is indicative of the late Barstovian land-mammal “age” (~13.5-14.5 Ma); however, the occurrence of Aelurodon taxoides in the overlying Dixon Member(?) suggests a somewhat younger latest Barstovian age (~12.5-13.5 Ma) for that unit.