The young of a rhinoceros, known as a calf, is one of the world’s largest newborns, but it is not born with a developed, protruding horn. Instead, at birth, the calf possesses only a slight thickening or a small stub of tissue located on the nasal bone where the horn will eventually emerge. This initial absence helps prevent injury to the mother during the birthing process.
Horn Appearance and Early Development
The first sign of the horn’s growth is a small, hardened knob that becomes visible within the first few weeks or months of the calf’s life. The initial stages of growth are often the most rapid in proportion to the animal’s size. For example, studies on white rhino calves have documented the front horn measuring approximately one inch (2.54 cm) long by two months of age. The growth rate is variable, but the horn continues to lengthen steadily throughout the first year. The posterior, or second, horn on two-horned species usually begins to appear slightly later, often around six months of age.
The Unique Composition of the Rhino Horn
The composition of the rhino’s horn makes its structure unique among horned mammals. The horn is not made of bone and is not attached to the skull by a bony core, unlike the horns of cattle or sheep. Instead, the structure is composed primarily of keratin, the same fibrous structural protein that forms human hair and fingernails. This protein grows from the skin, specifically from a dense collection of dermal papillae over the nasal bone. The keratin fibers are densely packed and mineralized, creating a solid, tough structure.
Core Reinforcement
The center of the horn is often harder than the exterior because of higher concentrations of non-keratinous materials. Specifically, the core is reinforced with deposits of calcium and the pigment melanin. Calcium adds strength and hardness, while melanin helps protect the structure from ultraviolet radiation.
Purpose and Continued Growth
The horn serves multiple roles for the rhinoceros, extending beyond simple defense. Rhinos use their horns as tools for foraging, particularly to dig for water and minerals during dry seasons or to break branches and strip bark from trees to access food. The horn also functions in social interactions, playing a role in dominance displays and territorial marking.
Continuous Growth and Regrowth
The horn grows continuously throughout the rhino’s entire lifespan, much like a fingernail. This constant growth is necessary because the horn is continually worn down and reshaped by the rhino’s daily activities. The characteristic curve seen in many rhino horns results from the front part growing slightly faster than the back, combined with the way the animal wears it down. If a horn is damaged or broken during a fight or foraging, it can regrow, although the rate of regrowth can vary significantly. In adult males, the horn may regrow faster than in females, likely due to the increased need for the horn in territorial battles.