Jonah N. Choiniere, X. Xu, J.M. Clark, C.A. Forster, Y. Guo, F. Han. 2010. A
Basal Alvarezsauroid Theropod from the Early Late Jurassic of Xinjiang,
China. Science 327:571-574 DOI: 10.1126/science.1182143
The fossil record of Jurassic theropod dinosaurs closely related to birds remains poor. A new theropod from the earliest Late Jurassic of western China represents the earliest diverging member of the enigmatic theropod group Alvarezsauroidea and confirms that this group is a basal member of Maniraptora, the clade containing birds and their closest theropod relatives. It extends the fossil record of Alvarezsauroidea by 63 million years and provides evidence for maniraptorans earlier in the fossil record than Archaeopteryx. The new taxon confirms extreme morphological convergence between birds and derived alvarezsauroids and illuminates incipient stages of the highly modified alvarezsaurid forelimb.
A newly discovered dinosaur species is helping paleontologists figure out how bird-like characteristics evolved in dinosaurs that aren't directly related to birds.The dinosaur, Haplocheirus sollers, was three-metres long with short, powerful arms and three claws on each hand. It is an early member of the alvarezsaur family, a strange group of dinosaurs characterized by stubby forelimbs and hands reduced to a single claw.Haplocheirus is 63 million years older than any other members of its family, helping to clear up the evolution of the meat-eating dinosaurs, the theropods, which includes velociraptors and T. rex."Haplocheirus is a transitional fossil, because it shows an early evolutionary step in how the bizarre hands of later alvarezsaurs evolved from earlier predatory dinosaurs," said Jonah Choiniere of George Washington University, in a statement.