Albert Chen, Daniel J. Field

Fossils represent the only direct evidence for the ancestral morphologies, antiquity, and historical geographic distributions of life on Earth. The fossil record of the avian clade Strisores (which includes nightjars, oilbirds, potoos, frogmouths, owlet-nightjars, treeswifts, swifts, and hummingbirds) has been richly documented by avian standards, with well-corroborated stem-group representatives of the oilbird, potoo, frogmouth, swift, and hummingbird lineages all having been identified based on fossils dating to the Paleogene Period (66–23.03 million years ago). However, current understanding of the nightjar fossil record remains limited. Nonetheless, new fossil descriptions and restudy of previously known specimens, together with findings from recent phylogenomic studies, have started to provide insight into nightjar evolutionary history. In particular, the recent reinterpretation of the Archaeotrogonidae, a group of fossil birds represented by numerous specimens from the Paleogene of Europe, as stem-group nightjars may offer valuable information on the origins of nightjar morphology (including soft tissue anatomy), ecology, and behavior. Although available fossil material of total-group nightjars tends to be relatively incomplete, the integration of fossil data into future studies holds great potential for elucidating the evolution, timing of origin, and biogeography of this distinctive and mysterious group of birds.