Two unusual, well-preserved, tridactyl trackways associated with sinuous grooves from the Lower Cretaceous Yanguoxia tracksite (Yongjing County, Gansu Province, China) are described and the behavior they present is discussed. The sinuous grooves are protracted and simple, with high percent interruption metric values and a low sinuosity. They are located between left and right pes tracks that have three separated, rounded distal digit impressions but lack plantar impressions. The presence of fine details such as delicate, double-sided, branching mud wrinkles in the grooves, coupled with backward drag marks at the rear of the tracks, indicate that the tracks and grooves are true tracks. We interpret the sinuous grooves as tail traces, and suggest that the tracks were made by a tridactyl dinosaur, probably by an ornithopod. It is hypothesized that the trackmakers made these trackways while partially submerged, propelled by toe-only steps, and leaving a subaqueously emplaced trail.