The Aegialornithidae is a family of primitive caprimulgiform birds that mainly lived during the Eocene epoch (about 50 mya) of Europe. They resembled an intermediate between modern-day swifts and owlet-nightjars. They already had sickle-shaped wings, but they weren't adapted to a full aerial lifestyle like modern-day swifts have.
Distribution & Fossil evidence
Fossils of Aegialornithids have mostly been found in Western Europe, like Germany, France and the UK. Some are only known from isolated bones, but of others complete skeletons have been discovered.
Just a few genuses have been appointed to this family, but there's still much discussion about the validity of the family and its place in the phylogenetic tree.