A new avian footprint taxon (Gragliavipes gavenskii, Ignotornidae) from the Cenozoic of South America and a reappraisal of avian ichnofamilies from the Cretaceous and Cenozoic

We describe a new avian ichnotaxon Gragliavipes gavenskii ichnogen. nov. ichnosp. nov. from the Miocene Vinchina Formation (La Rioja Province, Argentina) attributed to the Ignotornidae ichnofamily, thus constituting the first Cenozoic record from South America. These are semipalmate tetradactyl footprints with a very short interdigital web more developed between digits III and IV. Digits II, III and IV point forward, while digit I is posteromedially oriented and connected by a tarsal-metatarsal joint. It differs from other ichnotaxa within Ignotornidae due to the presence of an interdigital web, digit I being 50% of the total footprint length, an average divarication angle of 123°, and average stride and pace lengths that are 30% to 50% smaller than those of other ichnospecies within the ichnogenus. The estimated body mass of the trackmaker is approximately 521 gr. The backward position of digit I, its relative length compared to the footprint length and size of the animal, suggests that the trackmaker was most likely a small ibis (Threskiornithidae). We include an ichnotaxonomic review of the Cretaceous and Cenozoic avian ichnofamilies to achieve a more simplified supra-generic systematics for avian footprints. The new ichnotaxon extends the stratigraphic and spatial range of Ignotornidae within the Cenozoic and to South America.