Skeletons from the early Oligocene of Poland fill a significant temporal gap in the fossil record of upupiform birds (hoopoes and allies)

Upupiformes is the avian clade including extant hoopoes (Upupidae) and wood hoopoes(Phoeniculidae). Upupiform birds are abundantly represented in some Eocene fossil sites and arealso known from early Miocene localities, but the fossil record in between is surprisingly scant. Thisgap of over 25 million years is bridged by two skeletons from the early Oligocene of Poland. One ofthe fossils is described as a new species, ?Laurillardia smoleni, sp. nov., the other is tentativelyreferred toLaurillardia munieriFlot, 1891. We detail that these stem group Upupiformes are moreclosely related to the crown group than are the Eocene Messelirrisoridae. The specimens show thatvery small upupiform birds coexisted with passerines (Passeriformes) for at least ten million yearsand challenge previous hypotheses that the arrival of passerines in Europe led to the demise ofsmall non-passeriform arboreal birds. It remains elusive, why small upupiform birds became extinctin the Northern Hemisphere. Even though these insectivorous birds may not have found enoughfood after the emergence of cold Northern Hemispheric winters, it is an open question why verysmall-sized upupiform birds do not occur in the tropical regions of Asia but are today restricted to Africa south of the Sahara.