Theropod tracks from the Jurassic–Cretaceous boundary, Tuchengzi Formation, Chengde, China: Review and new observations

Previously known theropod dinosaur footprints preserved as natural casts in the Tuchengzi Formation, on a rock wall beside the railway in Nanshuangmiao Village, Shangbancheng Town, Chengde City, were originally assigned to ichnogenus Anchisauripus and tentatively attributed to oviraptosaurs. The assemblage was restudied in more detail by examining the entire assemblage of 55 tracks associated with two horizons. The size range of the 27 measured tracks suggests a more diverse grallatorid–eubrontid assemblage and potentially greater diversity of theropod trackmakers. The label Anchisauripus, which has fallen into disuse in some recent literature, implies trackmakers of medium shape and size in the grallatorid–eubrontid morphological spectrum. However, given the presence of other theropod ichnotaxa in the Jurassic to Early Cretaceous strata of the Tuchengzi Formation and time equivalent units we suggest that explicit reference to the Grallator-Anchisauripus-Eubrontes (GAE) plexus, or simply the term Grallator-Eubrontes plexus be confined to Lower Jurassic assemblages as originally defined and intended. Further study centered on the 16 known Tuchengzi assemblages and older theropod ichnfaunas is necessary to confirm or refute the degree to which grallatorid–eubrontid assemblages from these different epochs are similar or convergent. Even if the tracks are morphologically very similar inferences regarding trackmaker identity are problematic because the same theropodan trackmaker species, genera or even families were not present in both epochs.

Monster polar shift, shifts back: paleoclimate and CA-ID-TIMS evidence from northern China

<p>The two great lacustrine fossil Konservat-Lagerstätten of northeastern China producing feathered dinosaurs, the Jurassic Yanliao Biota and the Jehol Biota, were deposited during relatively humid times and are separated by a major redbed interval, typified by the Tuchengzi Formation deposited under a much more arid climate (1). We present new zircon CA-TIMS U-Pb ages for the peaks of the Yanliao [~160 Ma] and the Jehol biotas [Yixian Fm ~125 Ma] constraining a shift in that region from a higher-latitude temperate zone to a lower-latitude semiarid zone consistent with a ~30° arc distance shift true polar wander shift (1, 2, 3). The Yanliao Biota and the Jehol Biota are preserved in remarkably similar facies almost lacking signs of desiccation, while the Tuchengzi Formation has abundant evidence for desiccation and even eolian dune sands. This suggests, under a simple zonal climate model, a rapid shift to the south from Jurassic times and a shift back into Early Cretaceous times. A very similar and even more dramatic shift is seen in northwest China in the Junggar Basin where Triassic-Middle Jurassic coal bearing sequences with evidence of seasonal freezing (4) is replaced by a Late Jurassic [~150 Ma (5)] redbed sequence [including the famous dinosaur- and crocodiliomorph-bearing Shishugou Formation], and again replaced by coal-bearing strata in the Early Cretaceous, suggesting a similar magnitude shift south and back north of the region. The hypothesis that the monster polar shift is transient, swinging south and then north in ~35 million years necessitates rigorous testing by inclination-error-corrected paleomagnetic data to cleanly separate rapid latitudinal effect from rapid global climate change or regional orographic effects.</p><ol><li>Olsen P E et al. (2015) Geological Society of America, Abstracts with Programs <strong>47</strong>, 378.</li> <li>Muttoni G, Kent D V (2019)Journal of Geophysical Research. Solid Earth <strong>124</strong>, 3288-3306.</li> <li>Yi Z, Liu J, Meert, G (2019) Geology <strong>47</strong>, 1112-1116.</li> <li>Olsen P E et al. (2018) Geological Society of America Abstracts with Programs <strong>50</strong>, doi: 10.1130/abs/2018AM-325061 (2018).</li> <li>Fang Y et al. (2019) Topographic evolution of the Tianshan Mountains and their relation to the Junggar and Turpan Basins, Central Asia, from the Permian to the Neogene. Gondwana Research <strong>75</strong>, 47-67 (2019).</li> </ol>