LOWER MIOCENE BIRD AND MAMMAL FOOTPRINTS FROM LA RIOJA (EBRO BASIN, SPAIN). A new site carrying vertebrate footprints is described at Cenicero (Ebro Basin, Spain). The footprints are preserved in sandstone beds located within the “Transition Unit”, between the Agenian (early Miocene) Nájera and Haro formations. This level is placed between local biozones Y and Z. Fourteen blocks are studied; they contain 72 bird, 46 artiodactyl, and six perissodactyl footprints. Bird footprints include two ichnotaxa. The first one includes large to enormous tetradactyl footprints, with an incumbent hallux. It is identified as Gruipeda cf. maxima Panin and Avram. The second bird ichnotaxon is tridactyl with a prominent central pad, very large to enormous and with toes not joining at the proximal end. The latter feature suggests that it is probably a new bird ichnotaxon. Several ichnogeneric taxobases are proposed for bird footprints with the purpose of unifying the existing criteria between studies on extant and fossils bird ichnites. The artiodactyl footprints are small and identified as the ichnogenus Pecoripeda Vialov. The perissodactyl tracks are small and monodactyl, produced by equids, and classified as cf. Hippipeda Vialov.