Avisaurus

Abstract: The most complete known North American enantiornithine was collected in 1992 but never formally described. The so-called "Kaiparowits avisaurid" remains one of the most exceptional Late Cretaceous enantiornithine fossils. We recognize this specimen as a new taxon, Mirarce eatoni (gen. et sp. nov.), and provide a complete anatomical description. We maintain that the specimen is referable to the Avisauridae, a clade previously only known in North America from isolated tarsometatarsi. Information from this specimen helps to clarify evolutionary trends within the Enantiornithes. Its large body size supports previously observed trends toward larger body mass in the Late Cretaceous. However, trends toward increased fusion of compound elements across the clade as a whole are weak compared to the Ornithuromorpha. The new specimen reveals for the first time the presence of remige papillae in the enantiornithines, indicating this feature was evolved in parallel to dromaeosaurids and derived ornithuromorphs. Although morphology of the pygostyle and (to a lesser degree) the coracoid and manus appear to remain fairly static during the 65 million years plus of enantiornithine evolution, by the end of the Mesozoic at least some enantiornithine birds had evolved several features convergent with the Neornithes including a deeply keeled sternum, a narrow furcula with a short hypocleidium, and ulnar quill knobs-all features that indicate refinement of the flight apparatus and increased aerial abilities. We conduct the first cladistic analysis to include all purported avisuarid enantiornithines, recovering an Avisauridae consisting of a dichotomy between North and South American taxa. Based on morphological observations and supported by cladistic analysis, we demonstrate Avisaurus to be paraphyletic and erect a new genus for "A. gloriae," Gettyia gen. nov.

Abstract: In addition to the two described Avisaurus species ( A archibaldi Brett-Surman and Paul and A gloriae Varrichio and Chiappe), undescribed material from the Maastrichtian contributes important morphologic, biostratigraphic, and biogeographic data on North American avisaurids A juvenile Avisaurus specimen of an undescribed species from the Maastrichtian Hell Creek Formation of Montana reveals the presence of distal tarsals in enantiornithines and an ontogenetic stage shared with non-avian dinosaurs All known Avisaurus fossils were deposited in a variety of habitats along the Western Interior Seaway of North America and areas more interior The presence of other clades of birds in the Hell Creek Formation indicates that avisaurids formed only part of a diverse avifauna at the close of the Cretaceous in North America Phylogenetic analysis of the new Maastrichtian material places these new specimens as the sister to the other known Avisaurus species within Avisauridae This hypothesis of avisaurid relationships points to a South American origin of this clade with a dispersal or vicariant event to North America before or early in the Campanian This event was penecontemporaneous with the Laurasian movement of alvarezsaurids and sauropods These Montanan enantiornithine specimens represent the northern-most record of this bird clade in North America These Maastrichtian species and specimens are from very late in the Maastrichtian and are probably the youngest known enantiornithines The stratigraphic position of these birds with respect to the rest of the fauna indicate that their extinction was nearly synchronous with the extinction of other toothed bird clades and other vertebrates at the end of the Cretaceous KEY WORDS Aves Enantiornithes Avisaurus Biogeography

Abstract: We review the previously described Late Cretaceous (Santonian) bird remains from the Csehbanya Formation in the Bakony Mountains of Hungary, augmenting initial work by Ősi (2008), and add a number of newly collected fossils. All together, the eight fossil specimens so far collected from this site are important to our understanding of avian evolution because they document a large range of taxon body sizes from at least one major lineage (Enantiornithes) and come from a critically undersampled time period in the Cretaceous. Globally, very little fossil bird material has been collected from the middle stages of the Late Cretaceous, the Coniacian and Santonian; most known taxa are either Early Cretaceous (ca. 120 Ma) in age or are from the terminal Campanian and Maastrichtian (ca. 70–65 Ma). Indeed, one of the Csehbanya Formation fossil birds is recognized as a new taxon of large enantiornithine, an avisaurid apparently similar in its largely unfused foot morphology to the Argentine Soroavisaurus and to the North American Avisaurus. The Central European records reviewed in this paper highlight the wide distribution of some Late Cretaceous fossil birds, particularly avisaurid enantiornithines, and lead us to a brief discussion of avian biogeography at the end of the Mesozoic. Copyright © 2010 John Wiley & Sons, Ltd.