John Hutchinson
Tyrannosaurus was not a fast runner
Paper Summary
What the paper DOES say:
- Bottom Line: Tyrannosaurus could not run quickly, if at all.
- Underlying Principle: Large animals have more restricted locomotor performance, such as lower maximum forward velocity (speed).
These so-called "scaling principles" have been well established in the literature. For earlier related research, see papers by A.V. Hill, R. McNeil Alexander, and Andrew Biewener (examples provided in the Nature references).
- Word-For-Word Abstract:
The fastest gait and speed of the largest theropod (carnivorous) dinosaurs, such as Tyrannosaurus, is controversial. Some studies contend that Tyrannosaurus was limited to walking, or at best a "conservative" (11 m/s) top speed, whereas others argue for at least 20 m/s running speeds. We demonstrate a method to gauge running ability by estimating the minimum mass of extensor (supportive) muscle needed for fast running. The model's predictions are validated for a living alligator and chicken. Applying the method to small dinosaurs corroborates other studies by showing that they could have been competent runners. However, models show that in order to run quickly, an adult Tyrannosaurus would have needed an unreasonably large mass of extensor muscle, even with generous assumptions. Therefore, it is doubtful that Tyrannosaurus and other huge dinosaurs (~6000 kg) were capable runners or could reach high speeds.
- Simplified Abstract:
How fast could large dinosaurs run? Could they run at all? This issue has been controversial in dinosaur research, especially with regard to Tyrannosaurus rex. Some believe that Tyrannosaurus could not run, or at best was limited to a top speed of 11 m/s (40 km/hr, 25 miles/hr), while others argue for speeds of 20 m/s (72 km/hr, 45 miles/hr) or more. Using simple equations from physics and biology, we demonstrate a method to gauge running ability by estimating the minimum amount of leg muscle needed for fast two-legged running. The calculations are based on size, weight, posture, and other parameters. For living animals, we can compare the predicted minimum amount to the actual amount. If the animal does not have enough muscle, then it cannot run bipedally. If the animal has much more muscle than it needs, chances are it is a good runner. The method correctly predicts that an alligator cannot run on two legs, whereas a chicken is a good runner. For extinct animals, we compare the predicted minimum amount of leg muscle needed to what we know about the animal's body. Applying the method to smaller dinosaurs agrees with fossil findings which suggest that they could have been competent runners. For T. rex, our best guess is that in order to be a good runner, it required 80% of its weight to be in its leg muscles, which is next to impossible given what we know about its size and shape. So it is doubtful that T. rex or other large dinosaurs were good runners.
What the paper DOES NOT say:
- We DO NOT specify exactly how fast Tyrannosaurus could have moved, or that it definitely could not run.
Why? These are very difficult problems to solve for living animals, let alone extinct ones. We specify a very rough upper-end estimate of walking speed (about 5 meters per second; 11 mph or 18 kph), but faster or slower speeds are not impossible. We argue that faster speeds of 20 m/s (45 mph or 72 kph) would be biomechanically unfeasible, and even the more "conservative" speed estimates of 11 m/s (25 mph or 40 kph) are questionable. Thus the maximum speed of Tyrannosaurus might be in the range of 5-11 m/s, or perhaps slower. Honestly, it is too hard to say for sure; currently there are too many unknowns.
- Our research has NO bearing on the possible metabolic physiology of Tyrannosaurus or other extinct dinosaurs.
Why? Our model and equations do not require information on metabolic physiology or energetics. The parameters we use are relatively independent of whether the animal modeled is "warm/cold-blooded" (endo/ectothermic). If we are correct that Tyrannosaurus was not a fast runner, that does not mean that it was cold-blooded or sluggish, nor does it mean that it was warm-blooded or agile. We merely show that it is unreasonable to reconstruct Tyrannosaurus (and other larger dinosaurs) as very fast runners. Consequently, the metabolism of Tyrannosaurus had no need to fuel fast running.
- We DO NOT argue that Tyrannosaurus was only a scavenger, or only a predator.
Why? This dichotomy is false; living carnivores generally scavenge and hunt opportunistically. Our study only shows that large dinosaurs probably were too large to run quickly. This hypothesis should hold for all large dinosaurs, including potential prey items of Tyrannosaurus such as Edmontosaurus (large duckbill) and Triceratops (horned dinosaur). Conversely, smaller dinosaurs should have been relatively fleeter. The argument that if Tyrannosaurus could not run quickly, it could not have been a predator because it could not have caught potential prey, is nonsensical because the aforementioned potential prey were likely just as inept at running as Tyrannosaurus was. In fact, these potential prey might have been even slower than Tyrannosaurus.
- Our model IS NOT an extremely complex three-dimensional simulation or animation.
Why? All the information we needed could be obtained from a simple model; In fact, more complex models make more assumptions and can be misleading. We used a quasi-static (stationary at an instant in time, but accelerating) 2-D computer model (in Matlab) to estimate the internal and external moments (torques; or rotational forces) acting about the limb joints at the midpoint of stance phase (ground contact) during fast bipedal running. This quasi-static approach is valid for snapshots of the motion where the limb velocities are small. These estimates of the joint moments were used in an equation that incorporates anatomical data from muscles to calculate how much muscle mass would be needed to balance those moments. This muscle mass, expressed as a percentage of body mass, was either insufficient or sufficient for running.
- Our research DOES NOT explain why large dinosaurs such as Tyrannosaurus went extinct.
Why? There is simply no evidence for any connection.
This page was last modified on 23 Dec 2008
