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Enantiornithes - dominujaca grupa ladowych ptakow kredowych

100%
Bochenski Z.
Przegląd Zoologiczny
|
1996
|
tom 40
|
nr 3-4
175-184
2
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Revisiting Sabath's "Larger Avian Eggs" from the Gobi Cretaceous

63%
Varricchio D. J., Barta D. E.
Acta Palaeontologica Polonica
|
2015
|
tom 60
|
nr 1
In 1991, Sabath described “larger avian eggs” from the Upper Cretaceous Barun Goyot and Djadokhta Formations of Mongolia. These were later included in the ootaxon Gobioolithus major. Here we recognize the larger avian eggs of Sabath as a distinct ootaxon, Styloolithus sabathi, oogen. et oosp. nov. These eggs differ from those of Gobioolithus in being larger (70 by 32 mm) and more elongate. Microscopically, the shell bears a third layer (possible external zone) thicker than the mammillary layer and nearly as thick as the second layer (possible squamatic zone); the continuous layer (including layers two and three) to mammillary layer thickness ratio is 3.1:1. Within the clutch, the tightly spaced eggs stand with their long axes steeply inclined. Adult remains are associated with two clutches, suggesting an incubation mode similar to that of troodontid maniraptorans, where adults sat atop largely buried eggs. S. sabathi provides evidence that relative egg size in Mesozoic non-ornithuromorph birds had increased markedly from the non-avian theropod condition in oviraptorids and troodontids, but had not yet reached the modern egg-adult proportions of Neornithes. Sediment-bound upright eggs appear common to Enantiornithes and more basal avians, suggesting that like non-avian theropods, these birds lacked chalazae, the chords of albumen allowing egg rotation in modern birds. Absence of this simple structure may have restricted these basal birds to ground nesting in areas with appropriate substrates and not permitted the type of nesting diversity found in Neornithes. Neornithes are the only Mesozoic clade of Dinosauria to nest completely free of sediment; this may have played a crucial role in their surviving the K-Pg mass extinction event.
3
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A partial skeleton of an enantiornithine bird from the Early Cretaceous of Northwestern China

51%
Lamanna M. C., You H.-L., Harris J. D., Chiappe L. M., Ji S.-A., Lu J.-C., Ji Q.
Acta Palaeontologica Polonica
|
2006
|
tom 51
|
nr 3
Although recent discoveries from Lower Cretaceous sediments in northeastern China have greatly improved our understanding of the initial stages of avian diversification in eastern Asia, the early evolution of Aves elsewhere on the continent remains poorly understood. In 2004, a collaborative field effort directed by personnel from the Chinese Academy of Geological Sciences and Carnegie Museum of Natural History recovered multiple partial to nearly complete avian skeletons from outcrops of the Lower Cretaceous Xiagou Formation exposed in the Changma Basin of northwestern Gansu Province, China. Here we describe a thrush−sized partial skeleton comprised of a fragmentary pelvic girdle and largely complete hind limbs. A phylogenetic analysis of 20 avian ingroup taxa and 169 anatomical characters places the specimen in Enantiornithes, and within that clade, in Euenantiornithes. When coupled with additional recent discoveries from the Changma Basin, the new skeleton improves our understanding of early avian evolution and diversification in central Asia.
4
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Anatomy of the Early Cretaceous enantiornithine bird Rapaxavis pani

51%
O'Connor J. K., Chiappe L. M., Gao C., Zhao B.
Acta Palaeontologica Polonica
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2011
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tom 56
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nr 3
The exquisitely preserved longipterygid enantiornithine Rapaxavis pani is redescribed here after more extensive preparation. A complete review of its morphology is presented based on information gathered before and after preparation. Among other features, Rapaxavis pani is characterized by having an elongate rostrum (close to 60% of the skull length), rostrally restricted dentition, and schizorhinal external nares. Yet, the most puzzling feature of this bird is the presence of a pair of pectoral bones (here termed paracoracoidal ossifications) that, with the exception of the enantiornithine Concornis lacustris, are unknown within Aves. Particularly notable is the presence of a distal tarsal cap, formed by the fusion of distal tarsal elements, a feature that is controversial in non−ornithuromorph birds. The holotype and only known specimen of Rapaxavis pani thus reveals important information for better understanding the anatomy and phylogenetic relationships of longipterygids, in particular, as well as basal birds as a whole.
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