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 just one of the things that make it amazing. Let’s talk about them: what is the pronghorn, what features of its body help it to be fast, and why does it have to be so overqualified for the job?
Because whatever creature it’s built to run from has been dead for about 12,000 years…
An antelope it ain’t, a goat neither
Scientific names are supposed to be suggestive — if you know the logic of the naming, you should be able to picture the animal without ever having seen it. In the case of the pronghorn, the logic fails twice over.
The pronghorn belongs to the family Antilocapridae. The first part doesn’t just resemble “antelope”, it’s a part of it, and if the second part flashes “Goat!” in your mountain hunter‘s brain, you’re correct: the scientific designation of the pronghorn, Antilocapra americana, translates roughly as “American antelope-goat”. Except that it’s neither.
What the pronghorn actually is, is a cousin of the giraffe. Antilocapridae sits in the superfamily Giraffoidea, alongside the giraffe and the okapi. The antilocaprid line split from the giraffids back in the Early Miocene. But a lot of family resemblance remains. Like giraffes, and unlike deer, pronghorn have no dewclaws. The pronghorn’s bony horn cores develop much the way a giraffe’s ossicones do.
The giraffe and the okapi are the pronghorn’s closest living relatives on Earth. There used to be some Eurasian family, too, but they went into early extinction. From an evolutionary perspective, the antilocaprids are as American as it gets.
So why was it called an “antelope-goat”? The confusion seems to stem from Lewis and Clark’s expedition records. Clark’s journal, when he shot the first specimen on 14 September 1804, calls it a “Buck Goat of this Countrey,” and the expedition used “goat,” “antelope,” and “speed goat” more or less interchangeably. And their journals is what George Ord worked with when he gave the pronghorn its formal scientific description in 1815.
The Spanish seemed to be equally confused at first. Pedro de Castañeda, chronicling Coronado’s expedition in 1540, wrote of flocks of “goats” that ran so fast they vanished almost at once. By 1776 the Spanish were calling them berrendos — “two-colored” — which is still their name in Mexico. And if that seems like a lot of names, wait till you talk to the peoples who’ve been there before Europeans: there are 330 recorded different names for the pronghorn across 219 Native American languages.
Built to outrun a cheetah
The pronghorns do look like antelopes, but the resemblance has nothing to do with heritage. It is the result of an amazing thing known as parallel evolution. Form follows function; if different species adapt to similar environments, with almost identical threats and opportunities, they often develop similar species.
Take an ungulate, drop it on a hot, dry, open plain swarming with fast predators, and you get the same animal over and over, be it the American pronghorn, the African springbok, or the Asian saiga. Protective coloring, long legs, big eyes, and a couple biological gimmicks that help run faster and longer without overheating.
In the case of the pronghorn, it happened during the Pleistocene. The fossil record for the family runs back over 25 million years; the genus Antilocapra itself is much younger, on the order of one to two million years. Back then, it included about twelve species, some sporting elaborately twisted horns. They all existed in a vanished world that was richer than today’s, sharing the continent with giant ground sloths, mammoths, native horses – and enough predators to keep them on their toes.
The saber-toothed cats were probably not the pronghorn’s problem; they were megafauna specialists. The likelier culprits were several tireless canid endurance hunters and, above all, the American cheetah, Miracinonyx — not a true cheetah but a close relative of the cougar, comparable in size to its African namesake and built along similar lines. (To be fair, some biologists believe the American cheetah may have been less of a sprinter than the African cheetah, and might have specialized on bighorn sheep in broken country, like the snow leopard).
Power and cooling
Whatever it was that the pronghorn ancestors ran away from, the adaptations they developed in response are spectacular. Powerful muscles and flexible spine are only a part of the story. Old textbooks will tell you that the pronghorns 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. The current research disclosed something even more amazing.
In a landmark 1991 study, Lindstedt and colleagues measured a pronghorn’s maximum rate of oxygen consumption at roughly 300 ml per kg per minute: around three times what an animal that size has any business achieving, and the highest figure recorded for any vertebrate except possibly hovering hummingbirds and bats. This helps the pronghorn move more oxygen across the lung, deliver more of it to working muscle, and pack a greater total volume of mitochondria into that muscle.
The output is a top speed somewhere around 55–60 mph in short bursts and, more impressively, about 40 mph sustained. That makes the pronghorn the second fastest land animal in the world, outperforming all African antelopes. The downside of this power is that it generates a lot of heat.
To dissipate it, the pronghorn developed an amazing cooling system. They sweat, and they pant, and they have a carotid rete: a network where arterial blood bound for the brain is cooled by venous blood returning from the nasal passages. When a pronghorn overheats, blood flow is shunted toward the head, channels open between the nasal arteries and veins to expand the evaporative surface, breathing rate climbs, and panting follows. The body may run hot; the brain is protected.
Double horny
One of the first lessons in English that beginning hunters and other wildlife lovers have to learn is the difference between horns and antlers. Horns are permanent, they remain with the animal across its life span, antlers are shed and grown each year. Well, the pronghorns couldn’t care less about the English language.
What sits on its head is a permanent bony core wearing a keratin sheath — matching the definition of “horns”. But the sheath drops off every fall and regrows over the following summer – like “antlers”.
No other animal on Earth does this.
And no other animal has branching horns. True horns are always simple spikes or curves, because a branched sheath can’t slide off a branched core. The pronghorn’s sheath is shaped precisely so that, forks and all, it still comes free.
All pronghorn bucks carry horns, which can grow to about 15 inches long, and have the forward-pointing prong that gives the species its name. But up to 40% of the does have horns, too. However, does only grow short spikes that rarely exceed ear length and never fork.
Eyes on everything
Speed is the pronghorn’s second line of defense. The first is seeing you. Those oversized eyes, set wide on the skull, give a field of view usually reported at around 320 degrees, with a binocular overlap to the front. Old hunting writers liked to say a pronghorn sees the way a man does through 8x binoculars — a comparison that has been repeated for a century without, as far as I can find, ever being tested. What is being tested and proven every hunting season across the West, is that the pronghorn’s long-range detection of movement across open ground is exceptional.
It isn’t perfect. A silhouette breaking the skyline is death; the same shape below the horizon line, against broken ground, is a much harder problem for them. There’s a genuine blind zone directly behind. What there isn’t is a blind zone in front — that’s where their binocular vision lives, and the persistent hunting-lore claim that you can walk straight in undetected doesn’t hold up.
What all this means for a hunter is unglamorous. It doesn’t matter how flat your rifle shoots or how confident you are past 400 yards; the pronghorn’s defense is arranged so that the hard part is the approach. Use the terrain, stay off the skyline, and expect to crawl. Master that and you can take pronghorn with a muzzleloader or even a bow.
Overqualified
The most amazing thing about the pronghorns is how overqualified they are for the levels of threat presented by the modern environment. This species evolved in a world that was much harsher than today, and their fight for survival starts literally from the womb. A female starts out with half a dozen embryos. And as soon as they are conceived, they begin to compete for survival in the womb. They grow outshoots from their fetal membranes, and try to penetrate other embryos’ membranes, until only two embryos remain.
That’s the level of competition this animal was tuned for. And there is nothing on the modern plains that requires it. No living predator — humans included — makes a pronghorn use the top of its range. Miracinonyx has been gone since the end of the Pleistocene. So why didn’t the pronghorn quietly relax into a slower, cheaper animal?
Part of the answer is simply that 12,000 years is nothing. Traits don’t evaporate the moment they stop being useful; they decay only under selection, and slowly. You don’t lose your speed because there’s no longer a reason to have it. You lose it when being slower is actively better — cheaper to build, cheaper to feed — and even then it takes far longer than the Holocene has lasted so far.
But relaxed selection probably isn’t the whole story, because selection on pronghorn speed hasn’t actually stopped. Coyotes, bobcats, and wolves still take fawns, and a fawn that can’t run doesn’t become an adult. Bucks still fight and chase and hold territory through the rut, so running ability is still being tested by other pronghorn even when nothing is hunting them. And the herd itself enforces a standard — a stray that falls behind is the one that gets eaten. Not only humans need to keep up with the Joneses.
There’s also the migration. The Path of the Pronghorn runs more than 150 miles between the Upper Green River Basin and Grand Teton — one of the longest land migrations in the Western Hemisphere. The pronghorn may not need all that speed to complete it, but the endurance is essential, and it’s being used and trained every year.
The irony is that the thing actually stopping pronghorn today isn’t a predator at all. They are magnificent runners and hopeless jumpers: faced with a barbed-wire fence, a pronghorn looks for a way under. An animal engineered to outrun an extinct cheetah can be stopped dead by a strand of wire at knee height. They were nearly finished off in the early twentieth century, dropping to a few tens of thousands, before recovering into the hundreds of thousands, not in the least with the help of regulated hunting.
Whatever the explanation, pronghorns remain pretty much as they were, 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!
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