What Fossil Trackways Teach Us About How Dinosaurs Moved
A skeleton can tell you a great deal about an extinct animal's size and rough proportions, but it can't tell you how that animal actually moved — whether it habitually walked, whether it could break into a run, how its legs swung underneath its body. For that, paleontologists turn to a different kind of fossil entirely: not bone, but the trace an animal's foot left in soft ground that later hardened into stone. The study of these trace fossils is called ichnology, and it's essentially tracking applied to deep time.
How a footprint becomes a fossil
A trackway fossilizes the same way a modern print in mud can survive if conditions cooperate: an animal steps into soft sediment — mud, sand, volcanic ash — leaving a clear impression, and that impression is then covered by another layer of sediment before rain, wind, or another animal's feet can erase it. Over enormous spans of time, the layers compress into rock, preserving the print's shape as a permanent record. It's a much rarer event than a bone fossilizing, which is exactly why a well-preserved dinosaur trackway is treated as such a valuable find — sites like Dinosaur State Park in Connecticut, the Paluxy River tracks in Texas, Cal Orcko in Bolivia, and Lark Quarry in Australia are each famous for exactly this kind of preservation.
Preservation quality varies a great deal depending on exactly how the print formed. A track pressed into firm, fine-grained mud under calm conditions can preserve remarkably crisp toe and pad detail, not unlike a good modern print in the same substrate. A track in coarser or looser sediment loses that fine detail even before fossilization, the same way a print in loose dust or dry sand degrades quickly today. Ichnologists also distinguish a true surface track from an "undertrack" — a fainter impression transmitted down into a lower layer of sediment by the animal's weight, without the animal's foot ever directly touching that lower layer. Undertracks can look deceptively different in size and sharpness from the surface track that produced them, which is one of many reasons a single isolated fossil print gets interpreted cautiously. Depth and shape can also be distorted by exactly how wet or firm the original sediment was, the same way a modern print in soft mud spreads wider than the same foot would leave on firmer ground — a distortion problem ichnologists and modern trackers both have to account for, just separated by an enormous span of time rather than a difference in the underlying physics.
What a single track reveals
Even one isolated fossil footprint carries real information: foot shape and toe arrangement can indicate whether the trackmaker walked on two legs or four, general foot structure can hint at broad locomotor style, and the track's size gives a rough sense of how large the animal's foot was. Ichnologists even give some distinctive fossil track shapes their own names, separate from the species that made them, since the same foot shape sometimes can't be tied definitively to one known skeleton — Grallator and Eubrontes are two well-known examples of track types named this way. This naming-the-track-not-the-animal approach is a direct parallel to how a modern tracker sometimes has to describe a print's evidence honestly ("a mid-sized canid track") rather than force it into a single confident species label the evidence doesn't fully support.
Where it gets powerful: the trackway
A single print is useful, but a full trackway — a sequence of footprints from the same moving animal — is where the science becomes genuinely revealing. The distance between successive prints of the same foot (the stride length) and an estimate of the animal's hip height, usually inferred from the track's size and known body proportions of similar animals, feed directly into a speed-estimation formula developed by biomechanist R. McNeill Alexander in 1976. The same equation is the basis of the Stride Length Gait & Speed Calculator on this site — the same physics that estimates whether a modern coyote was walking or running from its trackway also estimates whether a theropod dinosaur was strolling or sprinting from its fossilized one. Our Animal Track & Sign Reference shows the same formula applied at a few illustrative sizes side by side, which is a fast way to get a feel for how much a bigger hip height changes the resulting speed estimate for the same relative stride.
Like any model built on an estimate, the speed the equation returns is only as good as the hip-height figure that goes into it, and that figure is itself inferred rather than directly measured on a living animal — which is why published dinosaur speed estimates are usually presented as a plausible range rather than one single precise number, the same honest hedging a careful tracker uses when estimating a modern animal's speed from an imperfect, partially degraded trail.
Herds, not just individuals
Some of the most striking trackway sites preserve dozens of parallel trails moving in the same direction at once — suggestive evidence of herding or group behavior that bones alone could never demonstrate on their own, since a bone bed just shows that animals died in the same place, not that they were moving together in life. Lark Quarry in Australia is a famous example that has been interpreted by researchers as evidence of a mass movement of smaller dinosaurs, though like much of paleontology, the exact interpretation of any single site is regularly revisited as new analysis methods and evidence emerge, and reasonable, ongoing disagreement between researchers about a site's exact meaning is a normal, healthy part of how the science progresses over time rather than a sign the underlying trackway evidence itself is unreliable.
How trackways get found today
Most fossil trackways aren't dug up so much as they're revealed — a riverbank cutting deeper over years, a construction excavation exposing a layer that had been buried for ages, or ordinary weathering stripping away the rock that sat above a track-bearing layer. This means new trackway sites turn up unpredictably, sometimes on private or actively used land, and it's a large part of why paleontologists and land managers generally ask members of the public not to disturb a suspected trackway site if one happens to be found — walking on or removing pieces of an exposed trackway can destroy scientifically valuable context (the exact layer sequence, the full extent of the trackway, associated body fossils) even when a single track looks unremarkable on its own. If you ever come across what looks like a genuine fossil trackway, the tracker's habit of observing and documenting rather than disturbing applies here too: note the exact location, photograph what you see from a few angles, and report it to a local museum, university geology department, or land management agency rather than collecting a piece or altering it yourself — the same observe-and-report instinct that serves you well with any other kind of sensitive wildlife sign in the field.
What trackways can't tell you
It's worth being honest about the limits, the same way this site is honest about the limits of reading a fresh print. A trackway generally can't tell you the trackmaker's exact species with certainty, only its rough size and general body plan, unless the track can be tied to a body fossil found in direct association. It can't tell you the animal's age, sex, or health with any confidence. And a speed estimate from the stride-length equation describes that specific animal's pace at that specific moment on that specific trackway — not a species-wide top speed, and not necessarily a typical pace for the animal on other terrain or in other circumstances. Treating a single trackway's speed estimate as "how fast this species could run" overstates what the evidence actually supports, in exactly the same way one modern print overstates a confident species identification without a trail, a habitat, and a second or third piece of corroborating evidence behind it.
The same skill, a much longer timescale
What makes fossil trackways genuinely remarkable is how directly the reading skill transfers. The habit of examining stride length, straddle, and gait pattern that lets a tracker read a fresh coyote trail in the mud this morning is the same habit, applied with the same underlying math, that lets a paleontologist read a dinosaur trackway many millions of years old, preserved in stone. Tracking, in that sense, is one of the few outdoor skills that connects directly to the deep history of life on Earth — the ground has been recording how animals move for a very, very long time, and the questions a tracker asks of a fresh print (how big was it, which direction was it going, how fast, was it alone) are close to the exact same questions an ichnologist asks of one turned to stone. Next time you measure a stride in the mud with the calculator on this site, it's worth remembering that you're using the same reasoning a paleontologist uses on a trackway that outdates the mud itself by a margin of geologic time that's genuinely hard to picture.