A Late Cretaceous (maastrichtian) Avifauna from the Maevarano Formation, Madagascar

Recent field efforts in the Mahajanga Basin of northwestern Madagascar have recovered a diverse Late Cretaceous terrestrial and freshwater vertebrate fauna, including a growing diversity of avialans. Previous work on associated bird skeletons resulted in the description of two named avialans (Rahonavis, Vorona). Other materials, including two synsacra and numerous appendicular elements, represent at least five additional taxa of basal (non-neornithine) birds. Among the materials described herein are two humeri tentatively referred to Rahonavis and numerous elements (e.g., humeri, ulnae, tibiotarsi, tarsometatarsi) assigned to Vorona. A near-complete carpometacarpus exhibits a minor metacarpal that exceeds the major metacarpal in length, documenting an enantiornithine in the fauna. Moreover, two additional, small humeri, an ulna, a femur, and a tarsometatarsus also compare favorably with enantiornithines. Finally, two other isolated humeri and a synsacrum are referable to Ornithurae. The latter specimen is notable in the presence of distinct, transversely oriented lumbosacral canals along the inner surface of the bony neural canal. This reveals for the first time a hard-tissue correlate of an anatomical specialization related to increased sensorimotor integration, one likely related to the unique form of avialan bipedal locomotion. Bird fossils recovered from the Maevarano Formation document one of the most sizeand phylogenetically diverse Cretaceous-age Gondwanan avifaunas, including representative (1) basal pygostylian, (2) enantiornithine, (3) nonenantiornithine, ornithothoracine, and (4) ornithurine taxa. This Maastrichtian avifauna is notable in that it demonstrates the co-existence of multiple clades of basal (non-neornithine) birds until at least the end of the Mesozoic. MALAGASY ABSTRACT (FAMINTINANA)—Ireo fikarohana natao tao amin’ny Debok’ i Mahajanga tany amin’ny faritra avaratra andrefan’i Madagasikara dia nahita karazam-biby an-tanety sy trondron-dranomamy misy taolan-damosina tamin’ny vanim-potoanan’ny Crétacées Aoriana ka anisan’ireny ny fisian’ny ireo vorona (avialans) mbola eo an-dalampisandrahana. Ny asa fikarohana teo aloha natao tamin’ireo taolam-borona natambatra dia nafahana nanadihady ireo vorona roa (Rahonavis, Vorona). Ireo taolana hafa ka anisan’ireny synsacra roa sy fivontosana maro isan-karazany, izay milaza ny fisihan’ireo karazam-borona dimy tena hafa tanteraka ka tsy ao amin’ny fianakavian’ny Neornithinae. Anisan’ireo vokampikarohana hita ka nanaovana fanadihadiana dia nahita taolana lavan’ny tànana misy ahitana fitovizana amin’i Rahonavis sy hafa maro koa (ohatra : taolan-tanana toy ny hita amin’ny sandry (humerus), lanton-tsandry (ulnae), sy tongotra toy ny talondranjo sy vodi-tongota (tibiotarse, tarsometatarse) izay iraisany amin’ny Vorona. Nahitana koa taolam-pela-tanana efa saika feno tanteraka dia ny carpometacarpe mampiseho tsy fitoviana eo amin’ny halavan’ny taolana kely (minor) amin’io kanefa lehibe noho an’ny major, mampahantatra ny fisian’ny enantiornithine eo amin’ny biby. Ankoatr’izay dia misy taolana roa fanampiny toy ny taolan-tanana dia ny sandry sy lanton-tsandry sy taolan-tongotra iray dia ny taolam-pe (femur) ary taolampelan-tongotra tarsometatarsi koa ahahana nampitaha tsara amin’ny enantiornithines . Farany dia nahitana taolantsandry mitokana roa sy synsacrum maneho fitoviana amin’ny Ornithurae. Ny vokatra hita taorina dia nahitana mazava ny fisian’ny fivelaran’ny fantsona “lumbosacral” manaraka ny lalan’ny fantson’ny taolana mitondra ny ritsika. Io tranga io dia mampatsiahy ny fahitana voalohany ny fisian’ny rary matevina maneho ny firafitry ny vatana manana asa voatokana eo amin’ny fampitomboana fiasan’ny ritsika, izay endrika mampiavaka ny vondron’ireo vorona mamindra amin’ny tongotra roa rehefa mihetsika. Ireo vorona fahagola hita tao amin’ny Forona Maevarano dia nahitana ny iray amin’ny goavana indrindra sy maro fisandrahana ara-pivoarana (phylogenetique) ny biby vorona avy tamin’ny Gondwana tamin’ny vanim-potoanan’ny Crétacées, ka anisan’izany (1) pygostylian fototra, (2) enantiornithines, (3) tsy enantiornithine, ornithothoracine, ary (4) vondrona ornithurine. Io biby vorona Maastichtian io dia mampiseho mazava ny fisian’ny ireo karazam-borona isan-karazany (tsy neornithine) hatramin’ny faran’ny Mesozoique farafaharatsiny.