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A fossil of a bird-like dinosaur with four wings has been discovered in northeastern China. The specimen bridges a critical gap in the transition from dinosaurs to birds, and reveals new insights into the origin evolution of feathers.
The transition from dinosaurs to birds is poorly understood because of the lack of well-preserved fossils, and many scientists argue that bird-like dinosaurs appear too late in the fossil record to be the true ancestors of birds.
In the journal Nature this week, Xing Xu and colleagues describe an exceptionally well-preserved fossil of Anchiornis huxleyi from the province of Liaoning, China. Long feathers cover the arms and tail, but also the feet, suggesting that a four-winged stage may have existed in the transition to birds.
Anchiornis huxleyi was previously thought to be a primitive bird, but closer inspection reveals that it should be assigned to the Troodontidae — a group of dinosaurs closely related to birds.
The authors date the fossil to the earliest Late Jurassic, meaning that it is the oldest bird-like dinosaur reported so far, and older than Archaeopteryx, the earliest known bird.
They conclude that the presence of such a species at this time in the fossil record effectively disputes the argument that bird-like dinosaurs appeared too late to be the ancestors of birds.
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A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus
Dongyu Hu1, Lianhai Hou1,2, Lijun Zhang1,3 & Xing Xu1,2
1. Paleontological Institute, Shenyang Normal University, 253 North Huanghe Street, Shenyang 110034, China
2. Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China
3. Shenyang Institute of Geology and Mineral Resources, 25 Beiling Street, Shenyang 110032, China
Correspondence to: Dongyu Hu1Xing Xu1,2 Correspondence and requests for materials should be addressed to X.X. (Email: email@example.com) or D.-Y.H. (Email: firstname.lastname@example.org).
The early evolution of the major groups of derived non-avialan theropods is still not well understood, mainly because of their poor fossil record in the Jurassic. A well-known result of this problem is the 'temporal paradox' argument that is sometimes made against the theropod hypothesis of avian origins1. Here we report on an exceptionally well-preserved small theropod specimen collected from the earliest Late Jurassic Tiaojishan Formation of western Liaoning, China2. The specimen is referable to the Troodontidae, which are among the theropods most closely related to birds. This new find refutes the 'temporal paradox'1 and provides significant information on the temporal framework of theropod divergence. Furthermore, the extensive feathering of this specimen, particularly the attachment of long pennaceous feathers to the pes, sheds new light on the early evolution of feathers and demonstrates the complex distribution of skeletal and integumentary features close to the DINOSAUR-BIRD TRANSITION.
Click to view image: '5cd389e5b260-250pxanchiornis_bw.jpg'
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