Abstract
Fossils of the avian clade Strisores (nightjars, swifts and allies) are well represented in some early Eocene localities. These birds were also taxonomically diverse in the British London Clay, but most of the previously described fossils belong to the Apodiformes (swifts and allies), or are represented by very fragmentary specimens. Here we report substantial new material of non-apodiform taxa of the Strisores from Walton-on-the-Naze (Essex, UK) that bears on the diversity and affinities of aerial insectivores from the London Clay. In addition to specimens of the recently described archaeotrogonid Archaeodromus , we report partial skeletons of the enigmatic taxon Palaeopsittacus , as well as two new species of the Fluvioviridavidae. The new Archaeodromus fossils reveal previously unknown osteological details, including features of the skull. The Palaeopsittacus specimens suggest that this poorly known taxon may be the earliest stem group representative of the Nyctibiiformes. The specimens of the Fluvioviridavidae elucidate some aspects of the osteology of these birds and the quadrate shows a morphology that is distinct from all extant Strisores. The non-apodiform Strisores from Walton-on-the-Naze exhibit disparate morphologies, which indicate that there was already significant ecological diversification of these birds by the early Eocene, and the diversity of these aerial insectivores in Walton-on-the-Naze contrasts with the absence of bats in this locality and other sites of the London Clay.