ScienceDaily (Mar. 29, 2010) — A new study published in the scientific journal Zootaxa by Chinese, Canadian and British researchers describes a new dinosaur that was one of the smallest known and also one of the best adapted for running. The fossil skeleton of the tiny animal, named Xixianykus zhangi, is highly incomplete but would probably have measured around half a meter in length. The specimen comes from Xixia County in Henan province, China.
Artist's reconstruction of Xixianykus. (Credit: Matt van Rooijen)
Dr. Corwin Sullivan, a Canadian researcher and one of the authors of the study said: "The limb proportions of Xixianykus are among the most extreme ever recorded for a theropod dinosaur. This doesn't provide a basis for estimating its top speed, but it does show that Xixianykus was a highly efficient runner. Several other characteristics of the skeleton reinforce this impression."
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A basal parvicursorine (Theropoda: Alvarezsauridae) from the Upper
Cretaceous of China
XING XU1, DE-YOU WANG2, CORWIN SULLIVAN1, DAVID W. E. HONE1, FENG-LU HAN1,
RONG-HAO YAN3, & FU-MING DU3
1Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology & Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China
2Scientific Academy of Land and Resources of Henan, Zhengzhou 450000, China
3Xixia Museum of Dinosaur Fossil Eggs of China, Xixia, Henan 474550, China
Abstract
A new alvarezsaurid theropod, Xixianykus zhangi gen. et sp. nov., is described based on a partial postcranial skeleton collected from the Upper Cretaceous Majiacun Formation of Xixia County, Henan Province. The new taxon can be diagnosed by the following autapomorphies: sacral rib-transverse process complexes and zygapophyses fused to form separate anterior and posterior laminae; distinct fossa dorsal to antitrochanter on lateral surface of ilium; short ridge along posterior surface of pubic shaft near proximal end; distinct depression on lateral surface of ischium near proximal end; sharp groove along posterior surface of ischium; distal end of femur with transversely narrow ectocondylar tuber that extends considerable distance proximally as sharp ridge; transversely narrow tibial cnemial crest with sharp, ridgelike distal half; lateral margin of tibiotarsus forms step near distal end; fibula with substantial extension of proximal articular surface onto posterior face of posteriorly curving shaft; distal tarsals and metatarsals co-ossified to form tarsometatarsus; and sharp flange along anteromedial margin of metatarsal IV near proximal end. Cladistic analysis places this taxon as a basal parvicursorine within the Alvarezsauridae, a position consistent with the presence of several incipiently developed parvicursorine features in this taxon and also with its relatively early geological age. A brief analysis of vertebral functional morphology, together with data from the hindlimb, suggests that parvicursorines represent extreme cursors among non-avian dinosaurs.
Key words: Late Cretaceous, Majiacun Formation, Parvicursorinae, Theropoda, cursoriality
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