PALMOXYLON ROMEROI SP. NOV., OF THE CHIQUIMIL FORMATION (UPPER MIOCENE) FROM VALLE DE SANTA MARÍA, CATAMARCA PROVINCE, ARGENTINA. Diverse palms types and other angiosperms represented by pollen records, fossil wood and leaf, stems and fruit impressions, have been found and studied in the Chiquimil Formation (upper Miocene) of the Santa María Group. In this contribution a new species of fossil Arecaceae is described, i.e., Palmoxylon romeroi sp. nov. It is represented by a silicified fossil palm trunk found in the Chiquimil Formation in Catamarca, northwestern Argentina. The fossil material has a Cocos-Type general stem structure; central cylinder well delimited from the cortical zone; fibrous-vascular bundles with vaginata shape; metaxylem usually with 3–5 vessels; one phloem strand; tabular, radiating and paravascular parenchyma present; ground parenchyma composed by spheroid to elongated cells, lobed with a rectangular shape and globular echinate stem stegmata. This taxon most closely compares to the Subfamily Coryphoideae, tribe Cryosophileae. Considering the distribution of most closely related extant taxon and the geological and paleobotanical records, Palmoxylon romeroi sp. nov. probably grew in savannah-like uplands characterized by a dry or seasonally dry tropical-subtropical climate.