Built for Speed
Contents Updated: Thursday, August 05, 1999
Speed
Adrian Desmond, author of The Hot-Blooded Dinosaurs, says the monstrous carnivorous dinosaur, tyrannosaurus rex, could have reached no more than three or four mph if it were cold-blooded. You or I would have little need to fear such a creature—if we jogged away from it, it could not catch us moving even at its fastest. Yet it gives every appearance of being built for speed as well as strength. Indeed for almost a hundred years dinosaurs have been illustrated as active creatures. Just after the turn of the century, Charles Beecher of Yale University constructed a mock-up of a hadrosaur, claosaurus, in a running posture.
From analyzing dinosaur tracks we know a dinosaur’ normal walking pace was faster than would be expected for the maximum speed of an equal sized lizard. McNeil Alexander of Britains’s Leeds University has a formula for working out travelling velocities from imprints of an animal’s tracks. Carnivorous dinosaurs seemed to travel commonly at speeds of between five and ten miles per hour. Herbivores sauntered around apparently at about four miles per hour. A fast walking pace for a human being is about three miles an hour so these speeds are respectable for large animals no more likely to be making haste than a grazing cow. And, like the cow, when the occasion demanded it they could move a lot faster.
Even a cursory glance at dinosaurian limbs and joints, says Adrian Desmond, should be evidence enough that many dinosaurs were built on the same lines as modern hoofed mammals.
A useful yet simple guideline in this respect is the length of the shinbone to the thigh bone. Relatively slow moving animals have longer thighs than shins whereas swift animals have evolved longer bones in their lower leg giving them a longer stride to increase their speed.
Take a look at some modern animals: the elephant rarely has need for speed and its shins are shorter than its thighs, the ratio being about 0.6. A gazelle needs speed as its means of avoiding predators—its shins are 1.25 times longer than its thighs, the highest such ratio of all animals.
Bone Ratios
What do we know from the fossil record of the shin to thigh ratios of dinosaurs? The brontosaurus had short shins compared with its thighs similar to an elephant’s—both are heavy, slow moving, browsing animals. What of the hadrosaurs? Their shins were between 0.8 and 0.9 times the length of their thighs, much longer than the brontosaurus’s (and the elephant’s) but much smaller than the gazelle. It seems that, relatively, they were faster than an elephant but not as fast as a gazelle. So, what modern animal is comparable? The racehorse! A racehorse’s shinbone is about 0.9 of the length of its thighbone showing that the hadrosaurs occupied a similar ecological niche. Finding similar leg measurements on modern animals and dinosaur fossils suggests similar lifestyles.
Another sensitive measure is the length of the middle metatarsal (middle toe) to the thighbone, because fast running animals tend to lift themselves on to their toes to increase their stride still further.
The brontosaurus had a middle toe to thigh ratio the same as that of an elephant (0.13). Dinosaurs evidently built for speed were the coelurosaurs which had a middle toe 0.77 of the length of its thigh comparing favorably with a horse (0.78).
Struthiomimus and the Ostrich
Sometimes the similarities went further. Indeed dinosaurs could be so astonishingly similar to modern beasts that it is difficult to accept they did not have the same ecological role. The coelurosaurs occupied the biological niche now held by the ostriches and similar flightless birds. Characteristic of them was the struthiomimus, so called because it was felt to mimic the ostrich (Struthio camelus).
- It is aptly named because its similarity to the ostrich is quite remarkable.
- It was seven feet tall, slightly taller than an ostrich.
- Its back was short and its hind legs were long.
- It had a shin to thigh ratio of 1.0 with its leg length effectively increased by an additional extended metatarsal bone.
- Its mouth was toothless and beak-like.
- It might even have had a flap of skin from its arms to its body to perform the same role as the ostrich’s wings when it was running.
- There is only one essential difference between the two creatures—the dinosaur had a tail which was more than six feet long.
The functional anatomist can only read into such a remarkable resemblance the closest similarity of lifestyle. Convergent evolution has led these animals to look alike. In Desmond’s words, they have come to look like one another because they have come to live like one another. The conclusion is that struthiomimus behaved similarly to Struthio camelus.
The ostrich is capable of sustaining speeds of over 45 mph. From its physiology, the dinosaur equivalent looks capable of the same, yet Bakker calculates that if struthiomimus had the constitution of a lizard it would be capable of sustaining hardly two mph!
The kneebones of animals provide another measure of their speed. Fast running creatures have strong muscles attached to the knee to snap the leg straight to provide much of the thrust while running. A protrusion at the knee, the knee crest, is the point of attachment of these muscles. Fast runners have larger muscles and need a stronger knee crest to withstand the stresses.
Elephants are large animals with big muscles but they do not run at more than 22 mph. Their knee crests are relatively small. Similar arguments can be used for the ceratopsian dinosaurs like triceratops, the plated three horned dinosaur looking much like a rhinoceros. These animals were herbivorous and with their powerful armor one might be forgiven for thinking they had no need to run fast. Today the rhino which occupies the same ecological niche is able to run at 30 mph even though it has no natural predators. But the ceratopsians had genuine reason to be able to run fast—they were sought as a nourishing feast by the voracious tyrannosaurus rex. Sure enough, both the prehistoric creature and the modern one have pronounced knee crests and triceratops can be assumed to have moved as fast as the rhinoceros.
Predators
What of predators? The arch enemy of the horned dinosaurs, the tyrannosaurs, had exceptionally large knee crests suggestive of a speed of 40 mph. McNeil Alexander’s formula supports this view indicating that some types, especially of smaller bipedal dinosaurs, did reach speeds of 40 mph.
Quite fascinating is the deinonychus, the eight feet long carnivorous dinosaur, living in the early part of the Cretaceous period, discovered in 1964 by John Ostrom. Ostrom describes his find as being a fleet-footed, highly predacious, extremely agile and very active animal, sensitive to many stimuli and quick in its responses. These indicate an unusual level of activity for a reptile and suggest an unusually high metabolic rate.
The interesting features of this dinosaur were:
- its legs were long marking it as a fast predator;
- marks on the backbones, reminiscent of those in ostriches, were channels for ligaments which held the spine horizontally as it ran;
- parts of its vertebrae had grown to lengths of about 18 inches and functioned as struts to brace the tail rigid when deinonychus gave chase;
- its feet had three toes but only two of them were used for running, the third having become adapted as a villainous hook for gouging its prey;
- its arms were long and its hands ideally suited to grabbing hold of its victims.
Plainly, deinonychus hunted by giving chase to its intended victim, caught hold of it using its highly developed hands then struck at it with its vicious claw. In so doing it had to balance on its other foot with its tail as a counterpoise to keep its balance.
It must have borne some resemblance to the cassowary, a most dangerous modern ground bird weighing 200 pounds. The cassowary also has a large hind claw with which it strikes its enemies using the full power of its strong thigh muscles. Considering that there is reason to believe deinonychus might have been feathered, the resemblance could have been closer than one might initially imagine. We shall have more to say about this remarkable creature later.
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