All animals are awesome, but some are more awesome than others. This includes the pronghorn antelope – no, wait, an antelope it isn’t, even though it sure looks like one, and that’s one of the things that make it amazing.
How come it ain’t no antelope?
Pronghorn belong to the family Antilocapridae, and if the second part of that name flashes “Goat!” in your mountain hunter’s brain, you’ve got it right. Pronghorns are sort of half antelopes, half goats (Capra), and their scientific name reflects it. Scientific terms are supposed to be suggestive, that is, anyone who knows the logic of the nomination can have an idea of what the animal looks like, even though they never saw it. Here it can be slightly misleading as there’s nothing from a goat in pronghorn’s appearance, so it’s absolutely logical that Lewis and Clark, who were the first Europeans to document the animal’s existence on the continent, defined it as antelope.
The goat part of the design is in the interior. Like many other members of the same order, including cattle and goats, pronghorns have complicated digestive tracts with numerous stomachs. They chew cud, and that allows them to extract a lot of energy from low-calorie vegetation of arid semi-deserts. I’m not a certified biologist, but it sure looks like many million years ago the Antilocapridae started out as goats. Then adaptation to hard and fast life on open plains, swarming with predators of all description, made the family develop the same traits that ensure survival of an ungulate in similar environments; form followed function and made them look like African and Asian antelopes.
Built to outran a cheetah
Antelocapridae are all-American creatures. Many, many years ago they had family in the Old World, but those went into early extinction, while for millions of years many species of Antelocapridae existed in America. It may sound unbelievable, but until the end of the last Ice Age wildlife in North America was even more diverse and abundant than today. There were giant sloths, wooly mammoths, horses, and tons of predators to feed on them. The saber-toothed cats were probably not much of a threat to the ancestors of pronghorn, as they specialized on the megafauna. But there were a few varieties of canines that appeared to be tireless endurance runners, and the now extinct American cheetah, a relative of the puma family, that was bigger and probably even faster than its existing African cousin. This was the predator that probably influenced the pronghorn evolution (some experts believe, however, that the American cheetah fed mostly on bighorn sheep and were sort of the American snow leopard).
Pronghorn bodies are incredibly designed for maintaining high velocity over long intervals of time. Powerful muscles and flexible spine are only a part of the story. Pronghorn have light bones, to save weight, and a short digestive tract, which serves the same purpose – the food inside is a ballast, and the less of it the better the run.
To say that pronghorns are fast is an underestimation. They are the second fastest land animal on Earth, second only to cheetah. With top speed reaching 60 mph in bursts, and 40 mph for sustained running, pronghorns will outrun any African antelope – and literally hardly break a sweat! Indeed, unlike humans, pronghorns don’t use sweat for thermal regulations. To prevent overheating, they rely on a system of blood vessels located close to the skin, dissipating heat into atmosphere. A special network of such vessels is located in the nasal cavity, to cool the blood that enters the brain and thus keep that valuable organ from boiling over.
One of the first things you learn when you study proper English animal lingo, is that horns are permanent, they remain with the animal across its life span, while antlers are typically shed and grown each year. Pronghorns may be confusing in this respect. The things they wear on their heads and use to fight each other with during the rut have a bony inner core that remains with the animal all across its life span. There’s also the outer shell that is shed and regrown every year. So they have horns, but shed them.
Admittedly, they are not the only creatures that apply the same strategy of shedding the outer shell of the horns every year. What makes them unique is the fact that most such animals have simple, straightforward spike horn shapes. The male pronghorns horns, however, branch into two prongs, that are just so shaped that in spite of the forks the shells can still come off. This gives pronghorn horns their unique shape.
Speed is not the only defensive weapon of a pronghorn. They have an astonishing eyesight, too. Their enormous eyes give pronghorn a 320 degree field of vision, part of which is binocular. Some researchers compared pronghorn vision to human with 8x binoculars. There’s a limit to their visual ability, however. Studies show that pronghorn can well see a silhouette against the conspicuous background of the sky. When a human was below sky level, however, they couldn’t see it all that well. Motionless, a human can be ignored at distances as close as 10 or 15 yards. But the slightest motion caused immediate flight. The pronghorns have blind zones both in front and behind them, so a direct approach often works better than tangential.
What that means for a hunter is, no matter how long-range your rifle, and how confident you are at long-range shooting, you’d better get ready for a long and painful stalk, often involving crawling. Once you’ve mastered it, however, you can harvest pronghorns even with short-ranged weapons such as shotguns and muzzleloaders.
The most amazing thing about the pronghorns is how overqualified they are for the levels of threat presented by modern environment. Pronghorns evolved in a much harsher world than today, and their fight for survival starts literally from the womb. A female starts out with half a dozen of embryos that compete for survival in the womb, trying to penetrate their siblings’ fetal membranes with outshoots growing from their own membranes, until only two embryos remain.
However, there’s no predator, humans inclusive, that require such speed and endurance to escape from. The American cheetah hasn’t been around since the Pleistocene (i.e., for the last 12,000 years). Why didn’t the pronghorn relax and became a slightly slower species? Why, when you see them on the wide open plains of the West, you’re seeing the same animal that roamed these spaces 3-4 million years ago?
Many traits can appear and disappear at random, due to the process known as genetic drift, but drift takes a lot of time. Much longer than 10,000 years, which, in terms of change in mammal genome, is a blink of an eye. For any meaningful change to appear in such a short interval there must be a strong selective factor at work. If you’re wired to be fast, you don’t lose your speed just because there’s no need to be fast any longer. You’ll become slow only if being slow gives you an advantage over being fast. This, obviously, isn’t the case with pronghorns. One possible explanation may be all too human – the need for keeping up with the Joneses. Pronghorns are herd animals, and those that fall behind the herd apparently have lower chances of survival and reproduction.
Whatever the explanation, pronghorns remain pretty much as they were in the Holocene, and keep the qualities that helped them survive when many, including the predators that fed on them, failed. Hmm… A species that no longer needs to do something it evolved to do, but still does it, because it’s wired to do it, and because you don’t give up an evolutionary advantage for nothing? Sounds familiar!