Trackway

A trackway consists of three or more consecutive footprints made by a single animal during locomotion. An individual footprint impression is termed a 'track,' and while two consecutive tracks can indicate direction of travel, they are generally not considered a trackway in the strict ichnological sense. Continuous marks left by non-limbed locomotion (e.g., belly or tail dragging) are classified as 'trails,' a distinct category within trace fossil taxonomy. The University of Kansas Ichnology glossary formally defines a trackway as 'an assemblage of tracks produced by one or more organisms.'

Trackways are preserved as true tracks (impressions made directly on the sediment surface where the animal walked, capable of retaining fine anatomical detail such as skin texture and claw marks), undertracks or underprints (deformations transmitted to subsurface layers by the pressure of the foot, which lose anatomical detail but may persist after the surface track has eroded), and natural casts (formed when overlying sediment fills the original impression).

The scientific study of fossil trackways traces its origins to the Connecticut River Valley of Massachusetts. In 1800, a farmer named Pliny Moody discovered three-toed footprint fossils on his property in South Hadley. These came to the attention of Edward Hitchcock, who published the first scientific paper on the Connecticut Valley tracks in 1836. Hitchcock interpreted the tracks as having been made by giant birds—a conclusion reached before the concept of Dinosauria was formally established by Richard Owen in 1842. Between 1836 and his death in 1864, Hitchcock amassed an extensive collection of trace fossils now known as the Hitchcock Ichnological Cabinet, housed at Amherst College. Hitchcock is widely regarded as the founder of vertebrate ichnology.

A transformative moment in trackway research came in 1938, when Roland T. Bird of the American Museum of Natural History identified unambiguous sauropod tracks along the Paluxy River near Glen Rose, Texas. This was the first clear evidence that sauropods walked on land, settling a long-standing debate about whether these massive animals were obligately aquatic. In 1940, Bird returned to excavate the famous 'chase sequence'—a set of parallel theropod and sauropod trackways widely interpreted as a predator pursuing its prey. The excavated section, over 9 meters long and 3.65 meters wide, was divided between the AMNH and the Texas Memorial Museum. Tragically, a portion was lost or destroyed during this process. In 2014, Falkingham et al. applied photogrammetric techniques to Bird's original 1940 photographs, digitally reconstructing the complete chase sequence (over 45 meters) for the first time in more than 70 years. The sauropod trackway from this site was later designated as the holotype of the ichnospecies Brontopodus birdi by Farlow et al. (1989).

Key measurements extracted from trackways include stride length (distance between two successive tracks of the same foot), pace length (distance between successive left and right tracks), pace angulation (the angle formed by three consecutive tracks), trackway gauge (width of the trackway relative to the midline), and individual track dimensions (length, width, digit lengths and angles). Narrow-gauge trackways indicate the limbs were held close beneath the body (erect posture), while wide-gauge trackways suggest a more sprawling stance.

In 1976, R. McNeill Alexander published a seminal paper in Nature proposing a formula to estimate locomotion speed from trackway data. Alexander's equation is: v = 0.25 × g^0.5 × λ^1.67 × h^−1.17, where v is speed (m/s), g is gravitational acceleration (9.81 m/s²), λ is stride length (m), and h is hip height (m), estimated as approximately four times the track length. This equation has been widely applied in dinosaur ichnology for nearly five decades.

However, in a 2025 study published in Biology Letters, Prescott et al. tested the equation using live helmeted guineafowl (Numida meleagris) walking on mud substrates. The researchers found that speeds calculated from trackways were consistently higher than measured speeds, by a factor of 1.2 to 4.7 times. The discrepancy was greatest at lower speeds. The authors attributed this to the non-steady-state nature of locomotion on compliant substrates—the very substrates required for track formation and preservation. Previous treadmill data had shown good correspondence between measured and calculated speeds, but treadmill conditions represent ideal, hard-surface, steady-state locomotion that does not reflect the conditions under which fossil tracks form. The study concluded that speed estimates from trackways should be presented as broad ranges rather than precise values. Earlier modifications to the formula by Thulborn (1982) and Ruiz & Torices (2021) similarly produced overestimates, as did an alternative equation by Demathieu based on compound pendulum theory.

One of the most consequential insights derived from trackway evidence concerns the posture of dinosaurs. Throughout the early and mid-20th century, dinosaurs—especially sauropods and large theropods—were routinely depicted with their tails dragging along the ground. However, the near-total absence of tail drag marks in virtually all known dinosaur trackways provided powerful evidence that dinosaurs held their tails horizontally, elevated above the ground during locomotion. This evidence was instrumental in the postural revolution of the 1970s onward, which replaced the sluggish, tail-dragging image with a dynamic, horizontally balanced body plan. Rare exceptions do exist: the Gigandipus trackways from the Lower Jurassic of the Connecticut Valley preserve intermittent tail drag marks, and recent work at Carreras Pampa in Bolivia has documented grooves associated with quadrupedal dinosaur trackways. These are interpreted as atypical situations rather than normal locomotion.

Carreras Pampa, Torotoro National Park, Bolivia: A 2025 study documented 16,600 three-toed theropod footprints and 1,378 swim tracks at this Upper Cretaceous site (approximately 101–66 million years old), making it the world's largest dinosaur tracksite by track count.

Cal Orck'o, Sucre, Bolivia: This limestone cliff face, approximately 1.5 km long and over 100 meters high, preserves 462 distinct trails made by at least eight dinosaur species approximately 68 million years ago. The originally horizontal lakeshore was tilted to near-vertical by tectonic activity.

Plagne, Jura Mountains, France: Discovered in 2009, this trackway extends 155 meters and comprises 110 individual footprints of a large sauropod from the early Tithonian (Late Jurassic, approximately 150 million years ago). It is the longest known sauropod trackway (Mazin et al., 2017).

West Gold Hill, Ouray, Colorado, USA: A Late Jurassic sauropod trackway of 134 consecutive prints extending 106 yards (approximately 97 meters), notable for recording a 270-degree directional change—one of only six such turning trackways known globally. The site was purchased by the U.S. Forest Service in 2024 for public protection.

Paluxy River, Glen Rose, Texas, USA: Trackways in the Glen Rose Formation (approximately 113 million years old) include the famous theropod-sauropod chase sequence excavated by Roland T. Bird. The site is now protected within Dinosaur Valley State Park.

Animal locomotion traces extend far beyond the Age of Dinosaurs. Among the oldest evidence of animal movement are Ediacaran-age fossils of Yilingia spiciformis, a segmented, millipede-like bilaterian from approximately 550 million years ago, found in southern China with both body fossils and associated locomotion trails (Chen et al., 2019, Nature). This represents some of the earliest evidence for directional locomotion by a bilaterian animal. Trilobite locomotion traces classified as Cruziana date to approximately 550 million years ago. The oldest known tracks of limbed vertebrates (tetrapods) date to approximately 391 million years ago (Middle Devonian), recorded on Valentia Island, Ireland, where trackways of early tetrapods document the transition from aquatic to terrestrial locomotion.

Parallel trackways of the same species have been interpreted as evidence of gregarious behavior. Ornithopod trackways in the Dakota Group of New Mexico were reported as evidence of herd movement (Matsukawa et al., 2001), and Late Cretaceous trackways in Denali National Park, Alaska, similarly suggest group locomotion (Fiorillo et al., 2014). In 2025, the Natural History Museum (London) announced the discovery of approximately 76-million-year-old trackways in Canada that provide the first evidence of mixed-species herding among dinosaurs.

However, caution is warranted in interpreting co-occurring trackways. Tracks at the same site may have been made hours, days, or even weeks apart. The famous Paluxy River 'chase sequence,' while dramatic, is subject to this interpretive uncertainty—the theropod and sauropod may not have been present simultaneously. Establishing temporal contemporaneity of multiple trackways at a single site remains one of the central challenges in vertebrate ichnology.

Fossil trackways are classified under ichnotaxonomy, a binomial system paralleling Linnaean biological nomenclature but independent of it. Ichnotaxa are assigned an ichnogenus and ichnospecies name based on track morphology rather than the evolutionary identity of the trackmaker. For example, Grallator is a common three-toed theropod track ichnogenus found from the Triassic through the Cretaceous, almost certainly produced by multiple unrelated theropod species. The sauropod track ichnogenus Brontopodus birdi was established from the Paluxy River trackways (Farlow et al., 1989). Ichnotaxonomic nomenclature follows the International Code of Zoological Nomenclature (ICZN). The difficulty of precisely identifying the biological trackmaker means that the same animal can produce different-looking tracks depending on substrate, speed, and gait, while different animals may produce similar-looking tracks. Exceptionally rare 'mortichnia'—trackways that terminate at a body fossil—provide the only certain association between trackmaker and track.

Traditionally, trackways were documented through field photography, measured sketches, and the production of latex molds and plaster casts. Modern research increasingly relies on 3D photogrammetry and LiDAR scanning, which generate millimeter-resolution digital models of trackway surfaces. These technologies have transformed the field by enabling remote analysis, comparative studies across distant sites, and the digital archiving of specimens vulnerable to weathering or erosion. As demonstrated by Falkingham et al. (2014), photogrammetric techniques can even be applied retrospectively to historical photographs to reconstruct sites that no longer exist in their original form. The development of portable photogrammetry has made trackway documentation accessible with consumer-grade cameras and free software, representing a democratization of ichnological research.