Pronghorn are the fastest North American land mammals. They first won this accolade more than 10,000 years ago when their ancestors successfully eluded cheetahs, long-legged hyenas, and huge bears, thought to be far swifter than modern varieties. All those ancient predators died off, perhaps because they could no longer have pronghorn for dinner. Today pronghorn remain a marvel of adaptations that equip them for speed across the Great Plains and western mountains from southern Canada to northern Mexico.
John J. Audubon described their locomotion this way:
The walk is a slow and somewhat pompous gait, their trot elegant and graceful, and their gallop or “run” light and inconceivably swift; they pass along, up and down hills, or along the level plain with the same apparent ease, while so rapidly do their legs perform their graceful movements in propelling their bodies over the ground, that like the spokes of a fast turning wheel we can hardly see them, but instead, observe a gauzy or film-like appearance where they should be visible.
Yes, modern cheetahs are the fastest land mammals on earth, topping out at about 70 miles per hour, but only for a few seconds and several hundred yards. Greyhounds also are fleet of foot, but they tire quickly as well. Pronghorn can sprint almost as fast, but they can also maintain a 45-mph pace for miles. At the end they appear not to be particularly winded as they look back with their keen eyesight and likely laugh at whatever perceived danger startled them. Compared to other hoofed creatures, their windpipes, hearts, and lungs are oversized—all which endow pronghorn with “horsepower.” Some enterprising investigators proved this by persuading two pronghorn, which had been raised in captivity, to wear face masks and measured their oxygen consumption while they ran on a treadmill. (I would have loved to see that spectacle.) The researchers showed that the pronghorns’ oxygen-delivery capacity was three times that of other animals of similar weight.
The combination of a large “carburetor” and “engine” and equally important adaptations in its “suspension system” and “wheels” results in an unparalleled speed machine. Of course, the “suspension system” and “wheels” are really this speedster’s arrangement of bones, muscles, and ligaments.
At about 110 pounds, a pronghorn’s is mostly torso. Imagine a thin head and neck sticking out of a steamer trunk that is supported on broomsticks. Its muscular shoulders, elbows, hips, and knees (stifle joints to veterinarians) appear to be part of its torso with only long, spindly legs visible beneath. These energy-efficient limbs can move quickly, just as the speed and ease of repeatedly swinging a broomstick greatly exceed the facility of swinging a bulgy baseball bat.
Three features make these long levers even more effective. Pronghorn lack collar bones, which adds to their forelimbs’ mobility in the direction of running. This increases both the tempo and length of their stride.
As with horses, a pronghorn’s metacarpals and metatarsals are reduced to two, which are fused together. They are called cannon bones (described in a previous post), and in pronghorn they are nine inches long and remarkably thin.
Thirdly, a strong ligament, the appropriately named springing ligament, attaches each cannon bone to its corresponding toe bone. The ligament stretches when the speedster puts weight on its hoof (toes), and it then snaps back like a rubber band to add stored energy to the power of the stride. And stride it does. A pronghorn can travel as far as 29 feet each time its hooves touch the ground; and at a pace of three strides per second, it runs a hundred yards in just over three seconds, about three times faster than Usain Bolt, the world’s fastest human.
The pronhorn’s anatomical features that favor speed do not, however, make them good jumpers. Whereas a deer can soar over a seven-foot-tall fence with ease and soften their landing on their forelegs, pronghorn look for a way under even a four-foot-tall barrier. When they do jump, even over a small gulley, they tend to land on their hind legs, which one observer described as “goofy-looking” maneuver. It would, however, spare their spindly front cannon bones from breaking.
Here is one final conversation point when you find yourself among bone, muscle, and ligament lovers. Antlers, found on deer, moose, and caribou, for instance, are made of bone and are shed every year. Horns, possessed by mountain sheep and rhinos, for example, are bony extensions of their skulls; they are sheathed in keratin (the same protein that constitutes hair and fingernails) and are permanent. Pronghorn are unique in that the keratin sheaths on their horns are shed annually.
MUSCLE will be perfect, the publisher has delayed its launch to July 25 to make it so.
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In this lively, lucid book, orthopedic surgeon Roy A. Meals takes us on a wide-ranging journey through anatomy, biology, history, and health to unlock the mysteries of our muscles. He breaks down the three different types of muscle—smooth, skeletal, and cardiac—and explores major advancements in medicine and fitness, including cutting-edge gene-editing research and the science behind popular muscle conditioning strategies. Along the way, he offers insight into the changing aesthetic and cultural conception of muscle, from Michelangelo’s David to present-day bodybuilders, and shares fascinating examples of strange muscular maladies and their treatment. Brimming with fun facts and infectious enthusiasm, Muscle sheds light on the astonishing, essential tissue that moves us through life.