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Aviraptor longicrus n. gen. et sp.Â
Gerald Mayr & JÃrn H. Hurum (2020)
A tiny, long-legged raptor from the early Oligocene of Poland may be the earliest bird-eating diurnal bird of prey.
The Science of Nature 107, Article number: 48
DOI:
https://doi.org/10.1007/s00114-020-01703-zhttps://link.springer.com/article/10.1007/s00114-020-01703-zWe report a small hawk-like diurnal bird from the early Oligocene (30â31 million years ago) of Poland. Aviraptor longicrus, n. gen. et sp. is of a size comparable with the smallest extant Accipitridae. The new species is characterized by very long legs, which, together with the small size, suggest an avivorous (bird-eating) feeding behavior. Overall, the new species resembles extant sparrowhawks (Accipiter spp.) in the length proportions of the major limb bones, even though some features indicate that it convergently acquired an Accipiter-like morphology. Most specialized avivores amongst extant accipitrids belong to the taxon Accipiter and predominantly predate small forest passerines; the smallest Accipiter species also hunts hummingbirds. Occurrence of a possibly avivorous raptor in the early Oligocene of Europe is particularly notable because A. longicrus coexisted with the earliest Northern Hemispheric passerines and modern-type hummingbirds. We therefore hypothesize that the diversification of these birds towards the early Oligocene may have triggered the evolution of small-sized avivorous raptors, and the new fossil may exemplify one of the earliest examples of avian predator/prey coevolution.
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Cousteauvia kustovia gen. et sp. nov.Â
A specialized diving lifestyle has repeatedly evolved in several lineages of modern and fossil waterfowl (Anseriformes), with the oldest previously known representative being the late Oligocene Australian oxyurine ducks Pinpanetta. However, diving specializations have never been previously documented for any of the primitive Paleogene anseriforms ( "stem-anatids"), and thus may be associated with the origin of modern anatid-like body plan. Here I describe a tarsometatarsus of a new duck-sized diving anseriform bird from the latest Eocene (late Priabonian) Kusto Svita in Eastern Kazakhstan, which predates the previously reported occurrence of diving specialization in Anseriformes by at least 6 MA. The new taxon Cousteauvia kustovia gen. et sp. nov. has an unusual and previously undocumented morphology, but partly resembles the stem-anatids Paranyrocidae and Romainvilliidae, thus representing the first known occurrence of diving adaptations in primitive non-anatid anseriforms. The evolutionary appearance of specialized waterfowl taxa in the late Eocene of Central Asia supports a view that this region might have played an important role in the evolution of morphologically derived Anseriformes. The structure of the intertarsal joint in basal and modern anseriforms is here further discussed in relation with adaptations for aquatic locomotion. The presence of elongate and evenly narrow condyles of the tibiotarsus in Anatidae and other swimming/diving birds allows a firm contact with the hyperprotracted tarsometatarsus at the initial phase of the propulsion. This morphology contrasts with the restricted condyles of Presbyornithidae, which indicate a different, strictly wading locomotory specialization. Cousteauvia obviously evolved diving specializations on the basis of a more primitive structure of the intertarsal joint.
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Stenornis kanmonensis gen. et sp. nov.Â
Four coracoids belonging to the family Plotopteridae have been found from the Oligocene Ashiya Group, northern Kyushu, Japan. One coracoid is assigned to Copepteryx hexeris, and the other coracoids are assigned to new genera and species: Stenornis kanmonensis gen. et sp. nov., and Empeirodytes okazakii gen. et sp. nov., of the Plotopteridae. Stenornis and Empeirodytes share a synapomorphy: an elongate sulcus on the ventral surface of the facies articularis humeralis portion of the shaft, which is not observed in coracoids of other plotopterids. These new plotopterids reveal that the diversity of this group in the Oligocene Ashiya Group is higher than previously realized.