A full-grown T. rex foot, measured from the back of the ankle to the tip of the longest toe, stretched roughly three feet long as a living structure of bone, muscle, and skin. The skeletal elements alone are impressive: metatarsal bones in the upper foot reached over two feet, and fossilized footprints attributed to large tyrannosaurs measure around 47 centimeters (about 18.5 inches) in length from front to back. But these prints capture only the part of the foot that contacted the ground, not the full anatomy from heel to claw tip. Understanding the true size of a T. rex foot requires combining what we know from bones, footprints, and the soft tissue that once covered them.
What the Foot Bones Look Like
T. rex walked on three main toes, labeled digits II, III, and IV by paleontologists. A tiny vestigial first toe (digit I) hung off the inner side of the foot but did not bear weight. The animal was digitigrade, meaning it walked on its toes with its “heel” raised high off the ground, similar to a bird. What most people think of as the lower leg of a T. rex is actually the metatarsus, the elongated upper foot. The true knee sat much higher on the body, close to the belly.
The three main metatarsal bones in an adult T. rex were massive. In large specimens, the central metatarsal (metatarsal III) could exceed 65 centimeters in length. Stacked side by side, the three metatarsals formed a compact, tightly bundled structure. Viewed from the front, the central bone had a distinctly triangular cross-section, tapering to a narrow profile at the ankle joint. This unusual pinched shape, which paleontologist Thomas Holtz named “arctometatarsus” in the 1990s, is a hallmark of tyrannosaurs and appears in no other group of large carnivorous dinosaurs at comparable size. Tyrannosaurs as a family had proportionally longer feet than any other big predatory dinosaur lineage, a detail that hints at specialized locomotion.
Below the metatarsals, each toe consisted of several phalanges (toe bones), ending in large, curved claws. The middle toe (digit III) was the longest, while digits II and IV flanked it on either side. In a well-preserved skeleton, you can lay out the entire foot from ankle to claw tip and measure something approaching a meter in total skeletal length, though the exact number varies between individuals. The claws themselves were not slender hooks like those of raptors but rather blunt, robust structures suited to bearing enormous weight.
Fossilized Footprints and Their Dimensions
Footprints give a different kind of size measurement than bones do. A footprint records only the ground-contact portion of the foot, the underside of the toes and the fleshy pads, not the full skeletal length from ankle to tip. Still, tyrannosaur tracks are among the most dramatic trace fossils known, and they offer direct evidence of foot size in life rather than after fossilization stripped away everything but bone.
At Glenrock, Wyoming, a trackway preserved in the Lance Formation (dating to the very end of the Cretaceous, around 66 million years ago) contains three successive footprints attributed to a large tyrannosaur, almost certainly T. rex given the time and place. The best-preserved print measures 470 millimeters from front to back along its midline, about 18.5 inches. The spread between the outer tips of digits II and IV is 370 millimeters, roughly 14.5 inches. The track sank 190 millimeters (7.5 inches) into the substrate, which tells you something about the weight being delivered with each step. The second and third prints in the sequence are progressively shallower, at 170 and 130 millimeters deep, likely because the animal was moving forward and the ground conditions varied slightly along the path.1Cretaceous Research. A tyrannosaur trackway at Glenrock, Lance Formation (Maastrichtian), Wyoming
In British Columbia, Canada, a set of tracks named Bellatoripes fredlundi represents another important tyrannosaur footprint find. These prints preserve enough detail to show the outline of individual toes, which appear thickened at their base and taper strongly toward the tips. That tapering pattern is distinctive enough that researchers assigned these tracks to their own ichnofamily (a classification system for trace fossils based on shape rather than the animal’s skeleton). The shape reflects the soft tissue anatomy of the living foot, including skin, muscle, and tendons wrapped around the skeletal framework.2PLOS ONE. A ‘Terror of Tyrannosaurs’: The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae
The Soft Tissue Gap
One of the persistent challenges in reconstructing dinosaur foot size is that bones are almost all we have from body fossils. Skin, muscle, fat pads, tendons, and keratinous claw sheaths have almost universally rotted away before fossilization. This means that any foot skeleton you see in a museum is visibly smaller than the foot was in life. The soft tissue added meaningful bulk, especially on the underside where thick pads cushioned each step.
Footprints help bridge this gap. Because a track records the shape of the fleshed-out foot rather than the bare skeleton, it captures the combined effect of bone plus soft tissue. Researchers studying the Bellatoripes tracks noted that the overall morphology of tyrannosaur tracks, with their characteristically thickened toe bases and tapering tips, is a product of soft tissue anatomy that is essentially invisible in the skeletal fossil record.2PLOS ONE. A ‘Terror of Tyrannosaurs’: The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae The digit impressions in these tracks are broader and more robust-looking than a bare toe bone would suggest, which means reconstructions based solely on skeletons underestimate how wide and padded the living foot was.
Modern birds, the closest living relatives of tyrannosaurs, offer some analogy. Large ground birds like ostriches and emus have thick, fibrous foot pads that add substantially to the width and depth of their footprint compared to the underlying bone. Scaling that relationship up to a multi-ton predator suggests that a T. rex foot in life was noticeably bulkier than the skeleton alone would indicate, perhaps adding several centimeters of tissue on all sides of the toes and metatarsals.
Why Footprint Size Is Not Straightforward
It would be convenient if you could measure a tyrannosaur footprint, read off a length and width, and call that the foot size. But footprints are shaped by the interaction between the foot and the ground, and that interaction is complicated. The same foot stepping into soft mud produces a very different track than the same foot stepping onto firm, damp sand.
Research using computer simulations of how feet sink into sediment has shown that the print visible on the surface and the deformation happening below the surface can look quite different. When a heavy animal steps into soft ground, sediment collapses around the foot as it enters and again as it pulls out. The surface track can be messy and distorted, a poor representation of the actual foot shape. But deeper in the sediment, the deformation is more organized because the grains support each other. If the rock later splits along a layer below the original surface, it can expose a print that looks sharper and more foot-shaped than the one that was at ground level. These deeper impressions, sometimes called “undertracks,” can be mistaken for shallow prints, even though they formed well below the surface.3PubMed Central. The birth of a dinosaur footprint: subsurface 3D motion reconstruction and discrete element simulation reveal track ontogeny
This matters for size estimates because an undertrack is often smaller than the true surface track. The deeper the layer, the more the deformation has spread out and lost detail. A paleontologist who unknowingly measures an undertrack instead of the actual surface print could underestimate the foot’s size. Conversely, in very soft substrates, the foot sinks deep and the surrounding mud slumps inward, making the surface print larger and less defined than the foot itself. Knowing the sediment type, the depth of the print, and whether you are looking at the true surface or a deeper layer is essential for getting an accurate measurement.
How Modern Technology Is Improving Foot Measurements
For most of the history of paleontology, dinosaur tracks were documented with photographs, sketches, and plaster casts. All of these methods lose some information. Photographs flatten a three-dimensional object into two dimensions. Sketches depend on the judgment of the person drawing. Plaster casts are heavy, fragile, and can damage the original track during the molding process.
LiDAR scanning has changed the game considerably. By bouncing laser pulses off the track surface and measuring the return time, LiDAR builds a precise three-dimensional model of a footprint down to sub-millimeter accuracy. This level of detail captures subtle features like claw drag marks, skin texture impressions, and the exact depth profile across the track, features that are easy to miss or impossible to record with older methods.4Palaeontology. THREE‐DIMENSIONAL MODELLING AND ANALYSIS OF DINOSAUR TRACKWAYS Researchers can rotate the digital model, slice it along any plane, and run quantitative analyses that were previously impossible in the field.
Close-range photogrammetry, which stitches together many overlapping photographs to build a 3D model, offers a cheaper and more portable alternative. Combined with laser range sensors, photogrammetry has become a standard tool for documenting track sites. The 3D models it produces carry enough morphological detail to support serious analysis of foot shape, gait, and even the dynamics of how the animal was moving when it left the print.5The Photogrammetric Record. 3D Ichnology—recovering digital 3D models of dinosaur footprints For a fossil that cannot be removed from the ground, or that is eroding away on an exposed rock surface, having a permanent, high-resolution digital copy is invaluable.
Why T. Rex Feet Were Unusual Among Giant Predators
T. rex was not just big. Its feet were built differently from those of other large theropods. Earlier giant predators like Allosaurus and Giganotosaurus had relatively broad, robust metatarsals without the pinched, triangular arrangement seen in tyrannosaurs. The arctometatarsus condition, where the central metatarsal is squeezed into a wedge shape by its neighbors, is thought to have improved the mechanical efficiency of the foot during locomotion. It may have allowed the foot to function as a more rigid lever during push-off, transmitting force more effectively.
What makes the evolutionary story interesting is that this foot design did not originate in a giant animal. The skeletal features characteristic of tyrannosaurs, including the arctometatarsus, first appeared in much smaller species. Early tyrannosauroids were modest-sized predators, some no larger than a human. The specialized foot architecture was later scaled up dramatically when the lineage evolved to body masses approaching a hundred times greater during the Late Cretaceous, a transition that fueled the most dominant radiation of large predators during the Mesozoic.6PubMed. Tyrannosaurid skeletal design first evolved at small body size In other words, the foot that carried a nine-ton T. rex was a scaled-up version of a foot originally designed for an animal that weighed a few dozen kilograms.
Whether the arctometatarsus continued to provide the same functional advantages at T. rex scale is a question researchers have debated. At smaller body sizes, the design seems clearly linked to cursorial (running) ability. Some paleontologists have argued that even a full-grown T. rex could move at a brisk pace, while others think that at extreme body mass, the foot’s design was more about efficient walking than speed. The foot anatomy alone does not settle the debate, but it does confirm that T. rex inherited a foot that was originally optimized for agile, fast-moving predators.
Comparing Feet Across Growth Stages
Not every T. rex skeleton belongs to a fully grown adult, and foot size changed dramatically over the animal’s lifetime. Juvenile and sub-adult tyrannosaurs had proportionally longer, more slender legs and feet relative to their body size compared to the stocky, heavy-set adults. A young T. rex may have been a genuinely fast runner, with a foot-to-body ratio that would look more at home on an ostrich than on the hulking adult form most people picture.
As the animal grew, its body mass increased far faster than its limbs lengthened. Computational analyses of T. rex limb and body dimensions across different growth stages have shown that the proportional relationship between leg length and body mass shifted substantially during ontogeny.7Europe PMC / PLOS ONE. A computational analysis of limb and body dimensions in Tyrannosaurus rex with implications for locomotion, ontogeny, and growth A teenager T. rex, already several meters long but weighing a fraction of its eventual adult mass, would have left a footprint meaningfully smaller and narrower than an adult’s. Identifying the approximate age and size class of the animal that left a track is therefore important for interpreting what any given footprint tells us about “T. rex foot size” in general.
This growth pattern also means that the functional role of the foot changed as the animal matured. A juvenile’s foot was a speed-oriented structure on a relatively light body. An adult’s foot was a weight-bearing platform supporting many tons of muscle and bone. The same basic architectural plan, the arctometatarsus with three forward-facing toes, served both roles, but the mechanical demands were profoundly different. It is a bit like how a sports car and a freight truck can share the same basic wheel layout while doing very different jobs.
Footprints as Behavioral Evidence
Foot size is interesting on its own, but trackways, sequences of multiple footprints from the same animal or group, tell a richer story. A single print gives you foot dimensions. A series of prints gives you stride length, walking speed, gait pattern, and potentially whether the animal was traveling alone or with others.
The Glenrock trackway, with its three successive prints, preserves a stride pattern consistent with a large tyrannosaur walking at a steady pace rather than running. The depth of the impressions, nearly 20 centimeters for the deepest print, indicates the enormous force being transmitted through the foot with each step.1Cretaceous Research. A tyrannosaur trackway at Glenrock, Lance Formation (Maastrichtian), Wyoming At the British Columbia site, the presence of multiple tyrannosaur trackways in close association has been interpreted as possible evidence that these animals sometimes moved in groups, though that interpretation remains debated.2PLOS ONE. A ‘Terror of Tyrannosaurs’: The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae
Some tyrannosaur tracks also show signs of pathology, including abnormal toe spacing or unusual depth patterns that may reflect injuries or deformities in the living animal’s foot. A broken or arthritic toe would change how the animal distributed its weight, and that altered weight distribution would show up in the shape and depth of its footprints. Tracks, in other words, are not just rulers for measuring foot size. They are snapshots of how the foot was actually being used, including when something was going wrong with it. For a creature that has been extinct for 66 million years, that kind of detail is remarkably intimate.