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It was little more than a decade ago at a meeting of the Society of Vertebrate Paleontology in New York City that rumors of feathered dinosaurs from China were swirling in the halls between sessions. The presence of feathers on dinosaurs not only implied a direct relationship between dinosaurs and birds, but it also raised questions about Archaeopteryx, the earliest known bird, and what it means to be a bird.
Today, at another meeting of the Society of Vertebrate Paleontology in Bristol, UK, Dr. Xu Xing of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing announced the discovery of new geological formations in China, the Daohugou and Tiaojishan formations, that date to between 151 to 161 million years ago and contain more feathered dinosaur specimens. This announcement may bring what has been more than a decade of debate about dinosaur feathers and bird origins to a close. The reason is that one of the last remaining arguments used by opponents of the hypothesis that birds descended from dinosaurs was that the earliest bird, Archaeopteryx, actually predated the earliest feathered dinosaurs. That hurdle has now apparently been cleared. If the new dates for these beds are correct, they significantly predate Archaeopteryx, which lived around 150 to 145 million years ago. And there is no question that fossils found within these formations are feathered and very birdlike, particularly Anchiornis, a primitive troodontid.
Among the more interesting features preserved in the fossil specimens of Anchiornis is its four-winged body plan. In this way it is very similar to Microraptor. Anchiornis is more primitive than the dromaeosaur Microraptor, however, and Dr. Xu suggests that the four-winged body plan may have been the primitive condition of a whole group of dinosaurs, including troodontids, dromaeosaurs, and birds. These groups, collectively called Paraves, would then have experienced a rapid diversification in the Late Jurassic, leading eventually to the appearance of Archaeopteryx.
This diversification includes other feathery fossils known from the Daohuguo and Tiaojishan formations, including Pedopenna and Epidexipteryx. The continuing flow of amazing fossils from China makes one wonder how long Archaeopteryx can remain as the earliest-known bird. Archaeopteryx may continue to reign for some time as the world's earliest-known bird because that is what we want to call it, but I predict that it will be a diffcult perch to stay on.
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Sep 25, 2009 6AM #
The first thing one wants to do with this is to compare it with Archaeopteryx. This one's legs are longer, aren't they? and it apparently has symmetrical feathers- suggesting if it got lift, it was from the shape of the wing alone. The wing feathers, particularly the primaries are shorter. This looks like reduced flight ability compared to Archaeopteryx. Very interesting. Are we seeing an important stage in the evolution of flight between Arch. and Anch.? Wing shape providing lift for gliding but not thrust for powered flight? Anch's big leg feathers are also something Arch. seems not to have had, and this also looks to square with Anch still being a glider. Anch does seem to have a quite predatorial 2nd toe though, hinting at dromaeosaurs.
Seems to be a good candidate for a position near to the base of birds, troodonts and dromaeosaurs... as Arch. is too, so the likely joint ancestor was either just post or just pre powered flight. I still prefer Arch (post) but the plumed leg link between vodroms (volant dromaeosaurs) and Anch cutting Arch out doesn't help, but reversals are an occupational hazard in this part of the tree. I wonder what GSP thinks about that. Anyhow, the ancestor of the three groups clearly had wings :-> .
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