Nearly 18,000 Dinosaur Tracks Found on Ancient Bolivian Coastline, Revealing Walking, Running and Swimming Behaviors

Massive Assemblage of Dinosaur Tracks Discovered at Carreras Pampa

Paleontologists surveying a fossilized shoreline in Torotoro National Park, central Bolivia, have documented nearly 18,000 dinosaur trace fossils at the Carreras Pampa track site. Reported in PLOS One, the assemblage includes roughly 16,600 footprints, 1,378 swim tracks and several tail drag marks, preserved across about 80,570 square feet of rock.

Ripple Marks and Movement Direction

The site preserves ripple marks oriented northwest–southeast that likely record the direction animals moved along the paleocoastline. These aligned features, combined with the track orientations, help reconstruct travel routes along this ancient shore.

Dominant Track Types and Age

Most imprints are attributed to theropods — bipedal dinosaurs of the Cretaceous that include familiar predators such as Tyrannosaurus rex. Some footprints show avian characteristics consistent with early birds. The traces are dated to the Cretaceous period, roughly between 145 million and 66 million years ago.

Walking, Running, Swimming and Tail Traces

The extraordinary density of tracks captures a range of behaviors: walking and running gaits, alternating swim imprints, and occasional tail drags or sharp turns. The swim tracks likely formed when theropods touched or scratched the waterbed with their middle toe, leaving linear or comma‑shaped grooves. Unlike many other localities that preserve isolated swim marks, Carreras Pampa shows continuous, alternating left‑and‑right swim impressions, allowing more precise reconstructions of gait in shallow water.

Size Range and Likely Trackmakers

Track sizes vary widely. Some footprints measure under 4 inches — a rare find in the fossil record — which the authors suggest could belong to small theropods such as Coelophysis or to juveniles of larger species. Mid‑sized theropods (e.g., Dilophosaurus or Allosaurus) are plausible candidates for prints exceeding 12 inches, while very large theropods such as T. rex or Giganotosaurus typically leave prints over 16 inches.

Field Methods and Analysis

Researchers collected and analyzed data from more than 1,275 distinct trackways. Field teams exposed additional prints by clearing sediment and sweeping debris off rock surfaces, enabling measurements of track depth and stride. Variations in track depth and spacing allowed the team to estimate trackmakers’ speeds, gaits and approximate body sizes.

Scientific Significance and Regional Context

Carreras Pampa stands out for having one of the world’s largest concentrations of preserved dinosaur footprints and the highest-recorded number of continuous swim trackways. Bolivia also hosts the Cal Orck'o site, about 250 miles southeast, and together these localities contribute to one of the most extensive and diverse records of dinosaur track sites in the world, spanning Triassic, Jurassic and Cretaceous deposits.

These findings provide an unusually detailed snapshot of how multiple dinosaur species of different sizes used an ancient coastal landscape — walking, running and even swimming along a prehistoric shoreline.