Deer-like animals with branched horns dotted across North American prairies may look like antelope, but the pronghorn is an unique species that fills a niche unlike any African or Asian antelope. If you’re short on time, here’s the key difference: pronghorns are the only surviving member of the Antilocapridae family native to North America, while true antelopes belong to the Bovidae family mostly found in Africa and Asia.
In this comprehensive guide, we’ll unpack the taxonomic classification, evolutionary history, physical characteristics, habitat, diet, and behaviors that set pronghorns apart from their old world cousins.
Taxonomy and Evolutionary History
The Pronghorn’s Distinct Family Tree
The pronghorn (Antilocapra americana) is the sole surviving member of the family Antilocapridae and is native to interior western North America. This interesting mammal is not a true antelope at all and is only distantly related to the bovids found in Africa and Eurasia commonly referred to as antelope.
In fact, DNA analysis has shown that pronghorns diverged from the antelope lineage nearly 20 million years ago in the early Miocene epoch. This makes the pronghorn as distinct from true antelopes as giraffes and okapis are from other ruminants.
So why is the name “antelope” used at all for the pronghorn? Early American explorers likely saw a resemblance in appearance and behavior between pronghorns and African antelope which led to the misnomer that has persisted to this day.
When Did Pronghorns and Antelope Diverge?
As mentioned above, the pronghorn lineage split off from other ruminants around 20 million years ago during the Miocene epoch when the landscape of interior North America consisted largely of woodlands and forest.
In contrast, true antelopes are thought to have emerged as a group more recently around 14 million years ago during the middle Miocene in more open landscapes. So while pronghorns were adapting to North American habitats, early antelope species on other continents were just beginning to evolve and radiate.
The differing ecosystems and selection pressures caused pronghorns and antelope to develop along their own distinct evolutionary pathways. Some key differences that emerged over millions of years include:
So in evolutionary terms, it’s clear the pronghorn is an example of convergent evolution with antelope and not closely related at all. Its speed and agility enables it to fill an ecological niche similar to its namesake.
Physical Characteristics
Horns and Head Shape
Pronghorns have distinctive horns that curve slightly upwards and forward. Their horns are not true antlers like deer, but are actually composed of a bony core that sheds its outer covering annually. Males have horns up to 12 inches long with a forward prong up to 5 inches long.
Females have smaller horns around 5 inches long. Pronghorns have a tan muzzle and white circles around their eyes. Their head is proportionally large compared to their body.
Body Size and Covering
Pronghorns are relatively small antelope, with males weighing around 120 pounds and females around 105 pounds. They stand about 32 inches tall at the shoulder. Their coat is mostly short, thick, reddish-brown fur, with white on their rumps, bellies, and jaws.
They have a short white mane on the back of their neck. Their white rump patch is very conspicuous when they run. Pronghorns have excellent camouflage that allows them to blend into their prairie surroundings.
Vision
Pronghorns have amazing vision adapted to their open habitat. They have the largest eyes relative to body size of any North American ungulate. Their elliptical pupils allow them to see long distances in daylight. At night, their pupils widen to maximize light reception.
They have a 300-degree field of vision without moving their head. This allows them to spot predators while keeping their head down grazing. Their eyes are positioned on the sides of their head for maximum panoramic vision.
Scent Glands
Pronghorns have specialized scent glands on their rump and between their hooves. They use their rump gland to mark territory by depositing scent as they run through their range. The scent communicates information to other pronghorns in the area.
Their interdigital glands between their hooves leave an odoriferous trail when they walk. This allows pronghorns to follow each other’s scent trails.
Habitat and Diet
Where Pronghorns and Antelope Live
Pronghorns (Antilocapra americana) are endemic to North America, primarily residing in the western prairie regions of Canada, Mexico and the United States. They inhabit wide open grasslands, plains, deserts and scrublands.
According to the National Wildlife Federation, around 700,000 pronghorns still exist today, with the largest populations found in Wyoming, Montana, South Dakota, Colorado and New Mexico.
In contrast, true antelopes comprise a diverse group of bovine species endemic to Africa and Eurasia. There are over 90 recognized species that occupy a wide range of habitats including savannas, floodplains, alpine terrain, forests, deserts and more.
For example, the sable antelope inhabits African woodlands and forests while the Tibetan antelope is adapted to high altitudes in Central Asia.
What They Eat
Pronghorns are herbivores, feeding primarily on a variety of grasses, herbaceous plants, cacti, shrubs and sometimes crops. Their diverse diet allows them to utilize poor quality forage. A study by the US Forest Service found that pronghorns spend about 40% of their time grazing during summer.
Like pronghorns, antelopes are also herbivores, consuming grasses, herbs, shrubs, leaves and buds. But the exact diet varies amongst species and depending on habitat. For instance, gerenuks in the African savannas eat Acacia leaves and buds almost exclusively.
Whereas the blackbuck antelope grazes primarily on grasses but supplements its diet with herbs, fruits and pods. Diet composition also shifts seasonally due to food availability and nutritional requirements.
| Category | Pronghorn | True Antelope |
|---|---|---|
| Geo. Range | North America | Africa, Eurasia |
| Key Habitats | Grasslands, plains, deserts, shrublands | Savannas, woodlands, forests, floodplains, alpine areas, deserts |
| Diet | Grasses, herbaceous plants, cacti, shrubs, crops | Grasses, herbs, leaves, buds, shrubs; varies by species |
Herd Behavior and Migration
Social Structures
Pronghorns live in herds for much of the year, with herd sizes varying from small family groups of around 20 members to large herds numbering 1,000 animals or more. The core social unit is the female band, consisting of an older doe and her female offspring.
While the adult females tend to remain together for life, the young males leave their mothers at around 16-17 months old to join bachelor herds.
These bachelor herds tend to be loose-knit and highly dynamic, often splitting and recombining over time. The older males in the herds establish a hierarchy through displays of dominance. While conflicts can occur, they rarely lead to serious injury.
Most disputes are settled through posturing behaviors demonstrating an individual’s size and strength.
During the mating season or rut in autumn, the males compete intensely for breeding rights with the females. They use scent glands on their faces to mark territories and try to round up and guard small harems. However, the competition means most harems last less than a day before a rival takes over.
Long Distance Migration in Pronghorn
One of the most fascinating aspects of pronghorn behavior is their long distance seasonal migrations between winter and summer grounds. According to the National Parks Service, these migrations can span over 150 miles in spring and autumn.
Pronghorn make these perilous journeys across rugged landscapes and highways in search of newly sprouted green vegetation in spring and winter relief from deep snow. Their migratory instincts and routes have developed over thousands of years as the herds follow the emergence of nutritious plant forage.
Some key facts about pronghorn migration include:
- The pronghorn’s migration from Grand Teton National Park south to the Upper Green River Basin in winter is thought to be the longest land migration in the lower 48 states, spanning around 160 miles.
- A migrating pronghorn was recorded traveling an astonishing 62 miles in just one day.
- Development, fencing, roads, and other human barriers block many historical migration routes. Conservation efforts focus on maintaining safe passage along migration corridors through measures like installing wildlife overpasses and underpasses.
The pronghorn’s persistence in adhering to these ancestral migration patterns in the face of modern-day challenges is a testament to the ingrained nature of the behavior and their adaptability as a species.
Conclusion
While pronghorn may resemble African antelope species, they are the sole surviving members of an ancient North American lineage. Their evolutionary history gave rise to unique adaptations like forked horns, speed, and vision to thrive in the open plains.
Understanding the taxonomy and ecology behind pronghorn tells a fascinating story of a one-of-a-kind ruminant still dotting the Western landscapes.
