Three new fossil landbirds from the early Paleogene of Denmark

Abstract

Well-preserved remains of fossil modern birds are rare, especially from the earliest stages of their evolution. In this paper we describe three new fossil specimens that can be referred to two of the major clades of extant ‘landbirds’, namely Apodiformes (‘swifts’) and Coliiformes (‘mousebirds’). Because the fossils presented here are from the earliest tertiary of Denmark, they represent some of the oldest certain records for both these major clades of modern birds (Neornithes). This new material, from the Paleocene – Lower Eocene Fur Formation (Isle-of-Mors, Jutland, Denmark) is referred to the fossil apodiform genus Eocypselus Harrison, 1984 and the coliiform genus Chascacocolius Houde & Olson, 1992. Eocypselus has been referred to within the clade Hemiprocnidae (‘tree and crested swifts’) and Chascacocolius to the Sandcoleidae, a clade of stem representatives of extant Coliiformes. The description of Chascacocolius from the Danish early tertiary increases the known diversity of stem-lineage coliiforms (Sandcoleidae) known from European deposits. New fossil material of Eocypselus shows that this taxon was a perching bird as are extant hemiprocnids – the hindlimb and foot of Eocypselus is elongate and anisodactyl, with digit III the longest of the pedal digits. Swifts and mousebirds are known to have been diverse in the earliest tertiary of Europe and North America; both these neornithine clades have a much lower extant diversity in terms of known species than that evidenced by their global fossil records, a temporal effect perhaps related to global cooling throughout the latest Tertiary.