On the site of Carreras Pampalocated in Torotoro National Park, in Central Boliviahave been discovered approximately 16,600 fossil footprints of dinosaurs and birdsorganized in 1,321 routes And 289 isolated tracks of various nature. The great variety and quality of the footprints makes the site a unique example, capable of providing unprecedented information on the behavior of dinosaurs.
Dinosaur tracks, dated between 70 and 66 million years agoshow different levels of depth and styles of preservation on the sediment: shallow and deep impressions, many of which preserve details such as fingernails, big toe impressions or lateral reliefs of displaced sand. The analytical study on the traces was conducted by a joint US-Bolivian research teamled by Raul Esperante of theLoma Linda Institute of GeosciencesCalifornia. Tail tracks are particularly abundant and well preserved, suggesting that some dinosaurs rested their tails on the ground to stabilize themselves on a soft substrate.
The footprints indicate that most of the dinosaurs present were small to medium sized, with a hip height between 65 and 115 cm, and that they moved mainly in parallel or semi-parallel directions. At the end of Cretaceousthe period to which the footprints date back, this area was probably a coastal-lagoon or coastal environmentwhich would explain the direction of the movements. This pattern, along with overlapping and crossing paths, suggests that dinosaurs moved through this environment in groups or in multiple events close together in time, indicating forms of gregarious behavior.
Alongside the walking footprints, the site also features gods swim marksthat is, traces left by dinosaurs that they swam or they wadedwith the hind limbs barely touching the bottom and left alternating scratches on the submerged sediment. Some of these swims overlap with walking tracks, confirming that dinosaurs used the same area multiple times under different tidal conditions. The bird footprints they are also numerous and well preserved, often associated with those of dinosaurs, and the presence of small fossil gastropods is also attested.
The substrate on which the traces were left was variable: sand and silt transported by water they formed a coherent but deformable terrain, with softer areas and other more compact ones. Local variations in the consistency of the sediment explain the presence of very deep footprints alongside shallow footprints in the same path (some footprints were left on a wet shoreline, while others on drier sand). The motion of the waves and the flow of water they left visible traces on the sediment, indicating that the area was originally a lacustrine transition zone between fresh and marine waters, subject to slight oscillations in the water level. The rapid initial cementation of the sediments and the deposition of clay layers (as often happens in these natural contexts) ensured the exceptional preservation of the traces.
The dinosaur tracks of Carreras Pampa offer a unique insight into life at the end of the Cretaceous, showing several dinosaurs active in a lake-coastal environmentengaged in walking, swimming and group movements, with a substrate soft enough to preserve extraordinary details.
