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

Abstract 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 track-bearing 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.