The Lithornithiformes (Aves) from the early Eocene London Clay of Walton‐on‐the‐Naze (Essex, UK)

Abstract We describe multiple partial skeletons and isolated bones of the palaeognathous Lithornithiformes from the early Eocene London Clay of Walton‐on‐the‐Naze (Essex, UK). The well‐preserved specimens are assigned to at least four species of the taxa Lithornis and Pseudocrypturus. Two species of Lithornis are identified as L. nasi and L. cf. grandei . The latter species, which was established for fossils from the North American Green River Formation, was initially assigned to the monotypic taxon Calciavis , which is here considered synonymous with Lithornis . Two further new species are tentatively referred to the taxon Pseudocrypturus and are described as ? P. danielsi and ? P. gracilipes . In previous analyses, lithornithiforms most often resulted as the sister taxon of either the Tinamiformes or all crown group Palaeognathae. We detail that current morphological evidence conforms best to a position of these birds outside crown group Palaeognathae and discuss previously unrecognized plesiomorphic features of the foot and pelvis, which support this phylogenetic placement.