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Early evolution of biological bird

Ben Creisler

A new paper:

Jingmai O’Connor & Zhonghe Zhou (2015)
Early evolution of the biological bird: perspectives from new fossil
discoveries in China.
Journal of Ornithology (advance online publication)
DOI: 10.1007/s10336-015-1222-5

New discoveries of fossil birds belonging to the Jehol Biota uncovered
from Lower Cretaceous lacustrine deposits in northeastern China
continue to greatly enrich our understanding of the first major avian
radiation. The exceptional preservation of some fossils provides a
rare chance to discuss many biological issues that are usually
impossible to address in paleontological studies, such as: the
ossification pattern of the sternum in the extinct group
Enantiornithes, which is unlike that of modern birds and all other
archosaurs; the discovery of preserved crop, gizzard, and intestinal
contents in several clades which suggest that a near-modern digestive
tract including specialized crop morphologies evolved early during
avian evolution; and the rare preservation of ovarian follicles which
support hypotheses that the right ovary was lost in Aves due to the
limitations of powered flight. Together, these data allow a partial
reconstruction of the biology of Aves very close to its origin. While
no skeletal or integumentary features are recognized to define Aves,
we identify two possible soft tissue features that may biologically
define Aves relative to other amniotes: the presence of a crop and the
loss of the right ovary.