A Well-Preserved Partial Skeleton of the Poorly Known Early Miocene Seriema Noriegavis santacrucensis

Seriemas (Cariamidae) include two extant species, Cariama cristata and Chunga burmeisteri, which live in semi-open plains of South America and have a poorly documented evolutionary history. One of the earliest fossil representatives of Cariamidae is the recently described Noriegavis santacrucensis from the early Miocene Santa Cruz Formation (Argentina). So far, however, this species was only known from a cranium and tentatively referred distal tibiotarsi, and its phylogenetic assignment has been questioned. Here we describe a well-preserved partial skeleton from the Santa Cruz Formation, which substantiates the classification of Noriegavis in Cariamidae. Plesiomorphic features show N. santacrucensis to be outside crown group Cariamidae, but the species is nevertheless very similar to its modern relatives and documents that the osteology of seriemas underwent only few changes during the past 16 million years.