The pronghorn (Antilocapra americana) is a remarkable North American mammal known for its incredible speed across the continent’s open plains. Female pronghorn typically do have horns, although they are far less prominent than those seen on males. The presence of headgear in both sexes is relatively common in species that possess true horns, but the pronghorn’s cranial appendages exhibit a specialized structure that blends characteristics of both horns and antlers.
The Presence of Horns in Female Pronghorn
The vast majority of female pronghorn, often estimated to be between 70% and 90%, possess horns. These horns are not always easily visible from a distance, which contributes to the common misconception that only males have them. The female’s horn is a small, dark spike that is relatively straight and generally lacks the distinctive forward-pointing tine.
These appendages are composed of a permanent bony core that emerges from the skull, which is then covered by a keratinous outer sheath. In some females, the horns may be so small that they barely project beyond the surrounding hair, appearing as only slight bumps. The development of these small horns in does is a biological norm, differentiating them from species where horn growth is exclusive to the male sex.
Structural Differences Between Male and Female Horns
The difference in size between male and female pronghorn horns is substantial and serves as a reliable sex identifier. Male horns can reach lengths of up to 12 inches (30 centimeters), while female horns are significantly shorter, typically measuring less than 4 inches (10 centimeters). The male’s horns develop a pronounced, forward-pointing prong, which gives the species its name.
Female horns are generally unpronged, presenting as simple, slightly curved spikes. The pronghorn’s headgear is unique because it involves the annual shedding of the outer keratin sheath, a trait not seen in other horned mammals. However, the shedding pattern is less defined in females than in males.
Males shed their sheath annually after the rut, typically in late fall or early winter. Female shedding is often irregular or barely noticeable; some females retain their small sheaths throughout the year, while others shed them in mid to late summer. The smaller size and simpler structure of the female’s horn mean the annual growth and shedding process is less dramatic than the prominent display seen on males.
Why Pronghorns Are Not True Antelope
The common name “pronghorn antelope” is a misnomer, as this animal is not a member of the Bovidae family, which includes true antelopes, cattle, and goats. The pronghorn belongs to its own unique family, Antilocapridae, and is the sole surviving species of this ancient North American lineage. This classification distinction is based on the structure of its horns.
True antelopes, native to Africa and Asia, possess permanent horns that never shed the outer keratin sheath, growing continuously. The pronghorn is the only mammal in the world that grows horns with a permanent bony core but sheds and regrows the outer keratin sheath every year.
This characteristic places the pronghorn in a taxonomic category separate from both true antelopes and deer, which shed their entire bony antlers. The similar appearance to Old World antelopes is a result of convergent evolution, where unrelated species evolve similar traits to fill comparable ecological niches.