18,000 Dinosaur Footprints Set a Record: And Some Are Swim Tracks

A vast sandstone surface in Torotoro National Park has revealed one of the most detailed records of dinosaur movement ever documented. At the Carreras Pampa tracksite, researchers have identified nearly 18,000 fossil traces, including more than 16,000 walking footprints and over 1,300 marks interpreted as swim tracks. The findings, published in PLOS ONE, transform a simple footprint into evidence of behaviour, environment, and adaptation during the Late Cretaceous period.

A Record-Breaking Concentration of Tracks

The Carreras Pampa surface contains the highest number of dinosaur footprints ever recorded at a single locality. The research team, led by palaeontologists including Raúl Esperante and Jeremy A. McLarty, mapped more than 1,300 distinct trackways across an expansive rock exposure. The sediments are dated to roughly 70 million years ago, placing them in the Late Cretaceous, when diverse dinosaur groups inhabited what is now South America.


Unlike isolated footprints discovered elsewhere, this site preserves a dense concentration of overlapping paths. Some trackways extend for dozens of meters, allowing scientists to analyse consistent stride patterns rather than isolated impressions. This density provides statistical strength because repeated patterns help distinguish individual animals and reduce interpretive uncertainty.

How Scientists Study Thousands of Footprints

Documenting a site of this scale requires systematic field methods. Researchers used drones to photograph the entire surface and generate high-resolution three-dimensional models. They then measured footprint length, width, depth, stride distance, and orientation. By comparing repeating sequences of left and right prints, palaeontologists identified individual trackways that likely represent single animals moving across the mudflat.

Sedimentology plays an equally important role. According to researchers at the Natural History Museum, footprints form under specific conditions in which sediment is sufficiently moist to record detail but sufficiently firm to retain shape. Shoreline environments are particularly favourable because thin layers of mud can quickly be buried by new sediment, preserving impressions before erosion destroys them. By applying formulas relating stride length to hip height, scientists can estimate body size and walking speed. These calculations, first developed in ichnology decades ago, allow researchers to infer whether animals were strolling, moving steadily, or accelerating.

Distinguishing Walking from Swimming

One of the most intriguing aspects of Carreras Pampa is the abundance of swim tracks. These are not full footprints but elongated claw scratches formed when a dinosaur’s body became buoyant in deeper water. Instead of pressing its entire foot into mud, the animal’s toes grazed the lake bottom as it paddled.

Scientists distinguish swim traces from walking tracks using several criteria. Swim marks often consist only of claw grooves without heel impressions. They appear as alternating left and right scratches that align in consistent patterns. The spacing between marks differs from normal stride lengths because buoyancy alters gait. In several cases, swim tracks cross earlier walking footprints, indicating that water levels rose after the initial tracks formed. Previous ichnological research, including work by palaeontologist Martin Lockley in North America, established that such claw marks represent swimming behaviour rather than unusual walking. The Bolivian site substantially expands the evidence by preserving long, continuous swim sequences that document transitions from walking into deeper water.

Reconstructing a Late Cretaceous Shoreline

Geologists dated the Carreras Pampa layers through regional stratigraphy, correlating the sedimentary rocks with known Upper Cretaceous formations. Ripple marks and shoreline structures indicate that the tracks formed along a shallow freshwater lake or coastal margin. Seasonal flooding or storm events likely altered water depth, explaining why dinosaurs left both walking and swimming traces in the same area.

The presence of repeated parallel trackways suggests that animals frequently crossed this shoreline, possibly following established routes toward water or feeding grounds. Tail drag marks preserved in some areas indicate moments when animals sank deeper into soft mud or changed posture.

Why Tracksites Matter

Footprints are trace fossils, which means they record activity rather than anatomy. As palaeontologist Susannah Maidment of the Natural History Museum has noted in discussions of trackway research, trace fossils preserve behaviour in real time, revealing movement and interaction that skeletons alone cannot show. A bone reveals what an animal looked like, but a trackway shows how it moved across its environment.

At Carreras Pampa, thousands of impressions depict dinosaurs walking in parallel lines, turning, pausing, and, in some cases, paddling through rising water. These traces provide a rare behavioural archive that complements skeletal fossils found elsewhere.

A Window into Living Dinosaurs

The discovery of nearly 18,000 tracks in Bolivia is significant not only for its scale but also for the behavioural insights it provides. By combining sediment analysis, three-dimensional mapping, and biomechanical modelling, scientists reconstructed scenes of dinosaurs navigating a dynamic lakeshore. Some animals walked steadily across firm mud, while others transitioned into swimming as the water deepened.

This tracksite reminds us that dinosaurs were not static museum skeletons but living animals interacting with changing landscapes. Their footprints, preserved for 70 million years, record movement, adaptation, and survival in ways that bones alone cannot capture.