Early Jurassic basal sauropodomorpha dominated tracks from Guizhou, China: Morphology, ethology, and paleoenvironment

The newly discovered large(350 m^2) Yantan dinosaur tracksite, in the Lower Jurassic Ziliujing Formation of Guizhou Province, China, reveals at least 250 footprints of which ~97 can be resolved into trackways of sauropodomorphs. All the trackways are sub parallel likely indicating gregarious behavior. One theropod track(cf. Grallator) was recorded. The sauropodomorph tracks predominantly represent quadrupedal progression(Morphotype A), and footprint morphology is similar to the ichnospecies Liujianpusshunan, characterized by outward pes rotation. Three trackways indicate bipedal progression, and two of these(Morphotype B) indicate inward pes rotation, accompanied by elongate pes digit scratch marks. For the latter phenomenon three possible scenarios are discussed:(1) significant rotation changes accompanying changes in gait,(2) swimming behavior,(3) formation of undertracks.Sedimentological evidence indicates the tracks were made on a linguloid rippled, muddy, immature sandstone substrate characterized by significant differences in substrate consistency across the trackbearing surface. Microbially induced sedimentary structures(MISS) characterized by distinctive wrinkle marks indicate a stressed, probably semi-arid, paleoenvironment that was not conducive to habitation by invertebrate organisms. This is consistent with other evidence that Lower Jurassic sauropodomorph tracks are often associated with semi-arid paleoenvironments.

Late Triassic sauropodomorph and Middle Jurassic theropod tracks from the Xichang Basin,Sichuan Province,southwestern China:First report of the ichnogenus Carmelopodus

Upper Triassic and Middle Jurassic strata of the Xichang Basin in Sichuan Province, southwestern China, yielded important dinosaur ichnofossils. From the Xujiahe Formation of the Yiguojiao tracksite, we report a Late Triassic footprint assemblage in China and the first discovery of diagnostic Triassic sauropodomorph tracks in this region. The tracks share a number of features in common with the ichnogenera Eosauropus(Late Triassic) and Liujianpus(Early Jurassic). The neighboring Bingtu tracksite is stratigraphically younger(Shaximiao Formation, Middle Jurassic) and preserves small tridactyl theropod tracks that represent the first occurrence of the ichnotaxon Carmelopodus in China and Asia. While these tracks are morphologically comparable to those from the Middle Jurassic type locality in North America, the specimens from China show the proximal margin of the digit IV impression in a more cranial position, which may indicate a trackmaker with a relatively short metatarsal IV. In addition to the skeletal record, the Carmelopodus footprints document the presence of small theropods in the dinosaur fauna of the Middle Jurassic Shaximiao Formation.

Origin of postcranial skeletal pneumaticity in dinosaurs

The sauropodomorph Thecodontosaurus caducus and theropod Coelophysis bauri are the earliest known dinosaurs with postcranial skeletal pneumaticity.In both taxa,postcranial pneumatic features are confined to the cervical vertebrae.This distribution of pneumaticity in the skeleton is most consistent with pneumatization by diverticula of cervical air sacs similar to those of birds.Other hypotheses,including pneumatization by diverticula of the lungs,larynx and trachea,or cranial air spaces,are less well-supported.