Early miocene shorebird-like footprints from the ebro basin, La Rioja, Spain: Paleoecological and paleoenvironmental significance

Abstract

Small shorebird-like footprints have been discovered in Cenicero (La Rioja, Spain). They are preserved in a sandstone block of the transition unit between the Nájera and Haro Formations from the Ebro Basin. This level is positioned in the Y2 local zone (MN2), of Agenian age (early Miocene). The footprints are small, tridactyl or tetradactyl, with slender and proximally unconnected digit impressions. They have phalangeal pads and claw marks, and there is no evidence of a web or metatarsal pad. The footprints are compared with other shorebird-like ichnotaxa and assigned to the Cretaceous ichnotaxon Koreanaornis isp., which is herein identified for the first time in the Cenozoic. Other shorebird-like footprints from the late Eocene to early Miocene in the Ebro Basin and the early Miocene ichnotaxa Aviadactyla media and Aviadactyla vialovi are also related to this ichnotaxon. In addition to the shorebird-like footprints, the Cenicero tracksite has invertebrate traces and sedimentary and organic structures typical of the Scoyenia ichnofacies, suggesting a mud-dominated floodplain in a centraldistal alluvial fringe as the paleoenvironment. The morphology, habitat, and behavior inferred from the shorebird-like footprints in the Cenicero tracksite are similar to other fossil footprints found in the Mesozoic and Cenozoic as well as to modern shorebird tracks. This is likely due to morphological, ecological, and behavioral convergences among different avian clades from the Early Cretaceous to the present.