The Ankylosaurus was a massive, heavily armored herbivore that roamed Western North America during the Late Cretaceous period. It is recognizable by the thick plating of bone, known as osteoderms, that covered its body and the formidable club at the end of its tail. This creature was essentially a walking tank built for defense, raising the question: How fast could this giant armored animal actually move? Determining the speed of any extinct animal requires careful scientific inference, drawing on the fossil record and principles of biomechanics.
Physical Constraints on Locomotion
The sheer mass and unique body structure of Ankylosaurus imposed significant limits on its potential speed. Weighing between 4.8 and 8 metric tons, its body was burdened by an extensive coat of dense, bony armor. This massive weight required its limbs to be columnar and stocky, built for stability and load-bearing rather than for swift movement.
The structure of the body further inhibited high-speed movement. Its wide, low-slung stance supported its enormous girth and kept its vulnerable underbelly close to the ground, but this posture limited the length of its stride. The dinosaur’s name, meaning “fused lizard,” refers to the fact that bones throughout its skull and body were fused together, increasing strength and rigidity. This rigid structure, particularly in the vertebral column, meant the animal lacked the flexibility needed for the powerful movements required for a true run or gallop.
Paleontological Methods for Speed Calculation
Paleontologists cannot directly observe a dinosaur in motion, so they rely on physical evidence and mathematical models to estimate speed. The most direct evidence comes from trackway analysis, which involves measuring fossilized footprints left behind in ancient mud or sand. Measuring the distance between successive prints made by the same foot provides the stride length.
This stride length is then used in conjunction with a mathematical equation, most famously Alexander’s formula. This formula relates an animal’s speed to its stride length and its hip height, a measurement derived from the size of the footprint. The result is expressed as a Froude number, a dimensionless value used to compare the gaits of animals of different sizes. A Froude number below one indicates a walking gait, while a number above 2.5 suggests a true running gait, where the limbs are momentarily off the ground.
Beyond trackways, researchers use computer modeling and comparative biomechanics to refine their estimates. By comparing the limb proportions and muscle attachment scars on Ankylosaurus bones to those of modern large animals like rhinoceroses or elephants, scientists can model the dinosaur’s gait. These simulations help determine the maximum mechanical stress the bones and joints could withstand, providing a theoretical upper limit for the animal’s top speed. The exact muscle mass and soft tissue distribution remain unknown, introducing uncertainty into the final speed estimates.
The Estimated Top Speed and Movement Style
Based on biomechanical constraints and trackway analysis, the Ankylosaurus was a slow-moving animal. Consensus estimates suggest the maximum speed it could achieve ranged between 5 and 8 miles per hour (8 to 13 kilometers per hour). This top speed is comparable to a brisk human walk or a slow jog, highlighting the animal’s prioritization of defense over mobility.
It is unlikely that Ankylosaurus ever engaged in a true run, a gait characterized by a suspension phase where feet are simultaneously off the ground. Instead, its fastest movement was probably a rapid walk or a shuffling trot, where at least one foot maintained contact with the ground to support its enormous mass. Attempting a true run would have placed excessive stress on its leg bones and joints, given its low center of gravity and fused skeletal elements.
The low maximum speed was not a disadvantage for its survival strategy. Its primary defense was not to outrun predators like Tyrannosaurus rex, but to withstand them using its formidable armor and actively defend itself with its tail club. By crouching low to the ground, the Ankylosaurus presented a nearly impenetrable, armored shell. The tail club was a weapon capable of delivering a bone-breaking blow, a much more effective deterrent than a futile attempt at escape.