An Important Ornithischian Tracksite in the Early Jurassic of the Shenmu Region,Shaanxi,China

A large track site with multiple, well-preserved trackways of an Early Jurassic quadrupedal ornithischian dinosaur is the first report of Moyenisauripus-like trackways from Asia, herein named Shenmuichnus youngteilhardorum. The tracks occur in a clastic fluvial sequence in the Fuxian Formation in Shenmu County, Shaanxi Province, which is in the same general region as the discovery site of Sinoichnites, the first dinosaur track reported from China. Based on size and morphology, it is likely that Sinoichnites, which is now lost, also represents an ornithischian. The Shenmuichnus youngteilhardorum trackways show two modes of preservation： the first representing deeper tracks, with sediment rims, results in Deltapodus-like tracks, with indistinct pes digit traces and sub-circular manus traces, the second produces Moyenosauripus-like tracks, with clear tridactyl and pentadactyl digit traces in the pes and manus respectively. Thus the Shenmu trackways play a key role in resolving globally significant ichnotaxonomic problems surrounding the nomenclature of Sinoichnites, Moyenosauripus, Deltapodus and other named （Ravatichnus） and unnamed trackways from Asia, Africa and Europe. In addition they shed important light on the paleogeographical and paleoecological distribution of quadrupedal ornithischians in the Early Mesozoic. The track site has been the focus of a major excavation to transfer the trackways from their original remote location to the new Shenmu Museum, in Shenmu City. Other tracksites in the area which reveal Anomoepus, Grallator and the Deltapodus morphotype, together with Shenmuichnus and plant fossil evidence, suggest an Early Jurassic age for the tracksite.

Distribution of sand dunes and sand shifts along the southern fringe of the Mu Us Desert since the Ming Dynasty

This article takes the two segments of the Ming Great Walls,Dabian and Erbian,and their associated barracks and forts as geographical references. Based on a detailed scrutiny of historical records of the Ming and Qing dynasties,and on field surveys,the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in the Ming and Qing dynasties are carefully reconstructed. A comparison of the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in Ming and Qing with the modern boundary revealed in remote sensing imagery clearly shows that the southern boundary of dunes and shifts in the Mu us Desert has expanded only in a few areas and on a small scale. In the area to the south of Changle Fort,along the direction of annually prevailing winds,sand drifts have pene-trated through the Jialu River valley into the loess region and have formed a sand strip of 32 km long and 3 km wide. To the east of Qingping Fort,sand drifts penetrated toward the eastern loess region through the Luhe River valley and have formed another sand strip of 8 km long and 2 km wide. Gener-ally speaking,though the intensity of human activity has been increasing in this area since the Ming Dynasty,the Mu Us Desert has not significantly expanded toward the southeast or southwest. The sand-loess boundary in the southern fringe of the Mu Us Desert has been almost unchanged since the Ming Dynasty.