LACM 149371 (Natural History Museum of Los Angeles County specimen 149371) is an enigmatic fossil mammalian tooth from the Paleogene (66 to 23 million years ago, mya) of Peru. It is from the Santa Rosa fossil site, which is of uncertain age but possibly late Eocene (55 to 34 mya) or Oligocene (34 to 23 mya). The tooth is poorly preserved and may have been degraded by acidic water or because it passed through a predator's digestive tract. Its largest dimension is 2.65 mm. It is triangular in shape and bears six cusps that surround the middle of the tooth, where there are three basins (fossae). Crests connects the cusps and separate the fossae. The microscopic structure of the enamel is poorly preserved. LACM 149371 was described in 2004 by Francisco Goin and colleagues, who tentatively interpreted the tooth as a left last upper molar. Although they saw similarities with South American ungulates, some early rodents, and multituberculates, they believed the tooth was most likely of a gondwanathere. Among gondwanatheres—a small and poorly known group otherwise known from the Cretaceous through Eocene of some of the southern continents (Gondwana)—they thought the Cretaceous Argentinian Ferugliotherium to be the most similar. Discovery and context LACM 149371 was discovered in 1998 at the Santa Rosa fossil site in the Ucayali Region of Peru. The Santa Rosa fauna also contains fossils of various unique species of marsupials and hystricognath rodents, a possible bat, and some notoungulates. The fauna was published in a volume of the Science Series of the Natural History Museum of Los Angeles County in 2004, which included a paper by Francisco Goin and colleagues that described and discussed LACM 149371. The age of the Santa Rosa fauna remains highly uncertain, as the outcrop where the fossils were found cannot easily be placed in a known stratigraphical unit, and the fossils are so distinct from other known fossil faunas that biostratigraphy cannot provide a precise estimate. In a summary of the 2004 volume, Kenneth Campbell tentatively referred Santa Rosa to the Mustersan South American Land Mammal Age (SALMA), which he placed near the Eocene–Oligocene boundary, around 35 million years ago. However, Mario Vucetich and colleagues suggested in 2010 that the Santa Rosa fauna may be substantially later—perhaps as young as the Deseadan SALMA (late Oligocene, around 25 million years ago). According to Campbell, the Santa Rosa mammals likely lived in a savanna