Tetrapod track assemblages from Lower Cretaceous desert facies in the Ordos Basin, Shaanxi Province, China, and their implications for Mesozoic paleoecology

Tetrapod ichnofaunas are reported from desert, playa lake facies in the Lower Cretaceous Luohe Formation at Baodaoshili, Shaanxi Province, China, which represent the first Asian example of an ichnnofauna typical of the Chelichnus Ichnofacies (Brasilichnium sub-ichnofacies) characteristic of desert habitats. The mammaliomorph tracks, assigned to Brasilichnium, represent the first report of this ichnogenus from Asia. The assemblages also contain three different theropod trackway morphotypes: one very wide Magnoavipes-like morphotype, one relatively wide, broad-toed, small Eubrontes-like form with short steps and strides, and wide straddle, and an elongate morphotype (Sarmientichnus) with longer steps and narrower straddle representing a didactyl trackmaker, the latter being the first example of the enigmatic ichnogenus found outside its type area in Argentina. The Sarmientichnus occurrence, the first in Asia, has important implications, demonstrating that the trackmaker was not monodactyl, but didactyl with probable affinities to deinonychosaurians which are ichnologically well-represented in the Lower Cretaceous of Asia. Although morphologically distinctive, Sarmientichnus should be recognized as a “form” ichnotaxon compromised by suboptimal preservation. The combination of Brasilichnium isp., Sarmientichnus isp., and tridactyl theropod tracks, indicates mammaliomoprhs and small theropods, and is comparable to ichnofaunas from similar desert facies on other continents. Thus, Cretaceous desert ichnofaunas from China are consistent with global ichnofacies predictions.