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New review of bird origins and evolution in Naturwissenschaften

From: Ben Creisler bh480@scn.org

The online version of Naturwissenschaften has posted a 
prepublication online article that reviews recent work on 
Mesozoic birds and related dinosaurs.  I could only access 
the text in html form, not pdf.

Zhonghe Zhou. The origin and early evolution of birds: 
discoveries, disputes, and perspectives from fossil 
Naturwissenschaften online publication Sept. 8, 2004.

Abstract The study of the origin and early evolution of 
birds has never produced as much excitement and public 
attention as in the past decade. Well preserved and 
abundant new fossils of birds and dinosaurs have provided 
unprecedented new evidence on the dinosaurian origin of 
birds, the arboreal origin of avian flight, and the origin 
of feathers prior to flapping flight. The Mesozoic avian 
assemblage mainly comprises two major lineages: the 
prevalent extinct group Enantiornithes, and the 
Ornithurae, which gave rise to all modern birds, as well 
as several more basal taxa. Cretaceous birds radiated into 
various paleoecological niches that included fish- and 
seed-eating. Significant size and morphological 
differences and variation in flight capabilities, ranging 
from gliding to powerful flight among early birds, 
highlight the diversification of birds in the Early 
Cretaceous. There is little evidence, however, to support 
a Mesozoic origin of modern avian groups. Controversy and 
debate, nevertheless, surround many of these findings, and 
more details are needed to give a better appreciation of 
the significance of these new discoveries. .........
The past decade has witnessed one of the most exciting 
periods in the study of the origin and early evolution of 
birds. Many extremely interesting birds have been 
described from the Cretaceous, and our understanding of 
the early evolution and diversification of birds has been 
improved in an unprecedented way, yet there is still no 
fossil evidence indicating the origin of modern groups in 
the Mesozoic. The evolution of birds from theropod 
dinosaurs has never been so much in the limelight and so 
popular as today, largely thanks to the discoveries of 
feathered dinosaurs from the Early Cretaceous of China. 
Traditional views on the origin and early evolution of 
flight and feathers have also been challenged, and the 
arboreal origin of avian flight is attracting a wider 
range of supporters, including some of those who also 
believe in the dinosaurian origin of birds. Many of the 
features, such as feathers, wishbones, uncinate processes, 
and pygostyle, which are traditionally associated with 
birds, are now found to have appeared first in much more 
remote avian ancestors, and the mosaic pattern of 
character evolution has been recognized as more complex in 
early avian evolution than thought previously.
It must be emphasized that the significance of this wealth 
of new evidence on Mesozoic birds and dinosaurs will come 
to be better appreciated in the years to come. The present 
conflicts between evidence from fossils, embryology, and 
molecular biology highlights problems that merit more 
attention. Scientific breakthroughs usually result from 
analysis of problems and debate rather than the 
celebration of achievements that have already been made. 
Hence, debate should be encouraged rather than discouraged.