The world’s smallest owl, the earliest unambiguous charadriiform bird, and other avian remains from the early Eocene Nanjemoy Formation of Virginia (USA)

Abstract

New avian remains from the early Eocene Nanjemoy Formation in Virginia (USA) are described. The material stems from the Fisher/Sullivan site and consists of isolated bones. These belong to at least 13 species, most of which have not yet been reported from the Nanjemoy Formation. The fossil material includes the oldest unambiguous record of a charadriiform bird and a new species of protostrigid owl, which represents the smallest known owl species. Other specimens are tentatively assigned to the Procellariiformes, the suliform Fregatidae, the gruiform Messelornithidae, and the apodiform Eocypselidae. A complete and well-preserved tarsometatarsus of the psittacopasserine Halcyornithidae provides new data on the osteology of these enigmatic birds, and a distal tibiotarsus is tentatively assigned to the Trogoniformes. The identification of a number of fossils is uncertain, with the bones showing similarities to Threskiornithidae and extinct taxa from the early Eocene of Europe (Microena, Morsoravis). All bird fossils from the Nanjemoy Formation are three-dimensionally preserved and, therefore, allow a detailed assessment of osteological features, which complements studies of compression fossils from lagerstatten-type fossil sites.