Messelornithids and messelornithid-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)

Abstract

We describe gruiform and gruiform-like birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). One species belongs to the Messelornithidae and is classified as Nasiornis messelornithoides nov. gen., nov. sp.; the coracoid of this species resembles that of Bumbaniralla from the early Eocene of Mongolia. Another possible messelornithid species is tentatively assigned to the poorly known taxon Parvirallus Harrison and Walker, 1979, as ?P. incertus nov. sp. A further species is referred to the taxon Walbeckornis Mayr, 2007, as W. waltonensis nov. sp., and extends the geographical and temporal range of this taxon, which so far was only known from the Paleocene of Germany. Even though similarities between Walbeckornis and messelornithids were previously noted, a plesiomorphic morphology of the quadrate suggests a position of Walbeckornis outside crown group Gruiformes. Furthermore, all fossil taxa described in the present study lack a deeply concave facies articularis alularis (carpometacarpus), which we identify as a previously overlooked apomorphy of crown group Ralloidea. Therefore, resemblances between Walbeckornis and the Messelornithidae, which are the sister taxon of crown group Ralloidea, are likely to be plesiomorphic for a more inclusive clade.