Let that sink in: track depth as a driving factor in the formation of dinosaur tail traces

To date, most reports of dinosaur tail traces have been limited to a small number per tracksite and have not included a detailed analysis of the associated trackways. Carreras Pampa comprises an Upper Maastrichtian theropod-dominated tracksite in Torotoro National Park, Bolivia. This tracksite preserves the largest number of theropod trackways associated with tail traces worldwide, allowing us to compare trackways to better understand how dinosaurs moved when producing tail traces. We applied multiple statistical analyses to 10 trackways with associated tail traces at the Carreras Pampa tracksite. Trackway measurements indicated that dinosaurs leaving tail traces were all of a similar size, with an estimated height at hip of 1.1–1.5 m. All trackways suggested that the dinosaurs were moving at a walking gait, with speed estimates of 4.1–8.8 km/h. Many of the trackways preserved deep tracks with a metatarsal mark. Statistical analyses using runs tests and generalised estimating equations (GEEs) suggested that the walking kinematics of a dinosaur’s foot sinking into the substrate was a driving factor in the formation of tail traces. The Carreras Pampa tracksite presented a unique opportunity to understand the effect of substrate consistency on theropod body posture and the formation of tail traces.