16,600 fossilized dinosaur footprints in Bolivia reveal herds of large theropods migrating near a prehistoric lake, with rare behavioral evidence.

Fossilized dinosaur footprints in Bolivia’s Toro Toro region, dating to around 66 million years ago, reveal unprecedented insights into theropod behavior, with 16,600 tracks—the highest number ever recorded—preserved in ancient lakebed sediment. The prints, left by large, two-legged dinosaurs including relatives of Tyrannosaurus rex, show evidence of walking, running, and attempted swimming, suggesting herds of varying sizes used the area as a migratory corridor near a freshwater shoreline. Despite the abundance of tracks, fossil bones, teeth, and eggs are nearly absent, possibly due to the site’s role as a temporary pathway rather than a permanent habitat. Human activity, including farming and road construction, has threatened preservation, but ongoing research continues to uncover new tracks, offering a rare behavioral record unmatched by skeletal remains.