Small vertebrates have remained relatively poorly known from the Nemegt Formation, although it has produced abundant and well-preserved large dinosaur remains. Here we report three new avialan specimens from the late Cretaceous (Maastrichtian) of Omnogov Aimag, Mongolia. These fossils were collected from the Nemegt Formation exposed at the locality of Tsaagan Khushu in the southern Gobi Desert. All of the new finds are partial isolated bones with a limited number of preserved morphologies; however, they further understanding of dinosaur diversity in the late Cretaceous of Mongolia and, specifically, from the Nemegt Formation. The new specimens are described and evaluated in phylogenetic analyses. These analyses indicate that all three fossils are placed as part of the clade Ornithurae.
Avialan diversity of the Nemegt Formation is reviewed and briefly compared with that of the underlying Djadokhta and Barun Goyot Formations. These formations have been considered to represent at least two distinct late Cretaceous environments, with the Nemegt typically interpreted as representing more humid conditions. Ornithurine and enantiornithine birds are known from the Nemegt as well as the Djadokhta and Barun Goyot Formations, although ornithurine remains are more common in the Nemegt. No avialan species known from the Djadokhta, or Barun Goyot, are also known from the Nemegt Formation and, overall, the avialan taxa from these formations do not appear more closely related to each other than to other avialans. Whether these faunal differences are best interpreted as environmental, temporal, or sampling/preservational should be further investigated
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