Hoofed animals are among some of the most diverse mammals on Earth. They can be found all across the globe in a variety of different habitats. One characteristic that is widespread amongst ungulates is the development of some form of cranial ornamentation, such as horns or antlers. These structures are typically paired and serve a variety of functions, such as display, species recognition, fighting other animals, thermoregulation, and territorial marking. Despite these similarities, horns and antlers are not the same thing and this article is meant to help clarify some of the confusion.
The most common form of cranial ornamentation are horns, which are found in members of the Bovidae family, including cattle, sheep, goats, antelope, and their relatives. Horns consist of a core of living bone covered in a keratin sheath. They are permanently attached to the animal’s head and grow throughout its lifetime. The keratin sheath can be up to twice the length of the horn core in some species. Some of the largest horns belong to the giant long-horned bison, Bison latifrons, and the ancient cape buffalo, Pelorovis antiquus. These two monstrous bovines had horns whose cores were over a yard long each; in life, with there keratin sheathes present, the horns would have been double that length, a span of around 8 feet tip-to-tip! In many species, females either have smaller horns than the males or no horns at all. Horns come in a wide range of shapes and sizes but typically tend to be curved or spiraled. Many species’ horns bear ridges and fluting, which causes them to interlock during male-on-male combat and prevent opponents landing overly lethal blows. Horns are often spaced too close together to permit a rival’s horn to fit through and because the tips point back or to the side, it is not possible to attack an opponent simply by lowering the head and charging straight forward; the neck must be manipulated so the horns can be effectively wielded, thus minimizing the risk of inflicting serious injury on each other. Some species use their horns like daggers to stab or gore at rivals, while others prefer to ram each other. Some breed of domestic livestock are specifically bred lacking horns, a condition known as being polled. Polled livestock often have growths of horny skin called scurs around where the horns would normally grow. On the opposite side of the spectrum, there are a few varieties of sheep than have more than two horns, sometimes as many as eight. The condition of having extra horns is known as being polycerate.
Deer are the only animals that develop antlers and only in the males, with the exception of the reindeer. Antlers are a sexually selected organ the males grow both to display their fitness to potential mates and fight other males. Reindeer also use their antlers to clear snow while foraging and the shape of moose antlers acts like an ear trust to increase their already acute hearing. Unlike horns, which remain forever attached to the head, antlers are shed after the rut and regrown every year. Antlers contain no keratin and are made solely of bone tissue. In fact, antler is some of the fastest developing bone in the animal kingdom and as such require a tremendous amount of energy and resources to maintain. A small bump known as the pedicle serves as the base from which the antler grows. When they first develop, antlers are covered in a blood-rich skin known as velvet. Once the antler has reached full size, the velvet is sloughed off and the bone begins to die. Antlers are just as varied in size and shape as horns, but rather then ending in a single point they have multiple points, known as tines. This branched nature sometimes causes antlers to become interlocked during combat, a situation that can prove fatal for both males. The biggest antlers of all time belong to the extinct Megaloceros, also known as the Irish elk. From tip-to-tip, they spanned 12 feet and weighed almost 100 pounds.
Bovids are not the only ungulates with horns. Although often referred to as antelope, pronghorn belong to their own family, called the Antilocapridae, and are more closely related to giraffes than to bovids or deer. Today only a single species remains, but several dozen species have come and gone over the past 20 million years. The horns or pronghorn are different from those of bovids and several key aspects and as a result are not considered “true” horns. Like those of bovids, pronghorn horns are made of a bony core covered in keratin but the sheathe is shed annually. Pronghorns have horns that laterally flattened and forked, hence the origin of the “prong” in their name. Many extinct species had more elaborate headgear than the modern pronghorn. Some had multiple forks in their horns, and others even had more than two horns. Hexameryx had a grand total of six horns, each with a highly-pronounced fork!
Rhinos are among the most famous horned animals in the world. Indeed, the word rhinoceros is derived from Greek meaning “nose-horn.” All five extant species possess horns with the black, white, and Sumatran having two and the Indian and Javan sporting only one. Rhino horns are not true horns’ they lack a bony core and are made entirely out of keratin. In essence, it is a pointed, razored fingernail growing out of the animal’s snout. As a result a rhino skeleton does not display any horns, only a rugose boss from which the keratin grows. Both male and female rhinos grow horns and they are used primarily for defense. Depending on species, rhino horns grow from 4 inches to over several feet in length. The extinct rhino Elasmotherium had an immense horn believed to measure over 7 feet long! Humans have long hunted rhinos for their horns, which are used to make decorative knife handles and (falsely) believed to have healing and aphrodisiac properties.
Giraffes, and their relative the okapi, also have cranial ornamentation, although they have neither horns nor antlers. The protuberances on their heads are called ossicones and are derived primarily from ossified cartilage rather than bone. They are covered in skin very similar to deer velvet, but unlike velvet is not shed. While both male and female giraffes possess ossicones, they are larger in males and, most likely due to use in combat, often lack the tufts of fur seen on those of females, and only male okapis have them. Ossicones function as weapons, with male giraffes using them to club each other in dominance fights during the mating season. Giraffes and okapis have small nubs on their heads, but some of their extinct relatives sported much more elaborate headgear. Prolibytherium shows marked sexual dimorphism, males having leaf-shaped ossicones over a foot across while females have narrow, pointed ossicones that resemble horns. Sivatherium’s ossicones were expanded and flattened to resemble moose antlers, and Bramatherium had a total of five on its head.
Other Horned Animals
While bovids, deer, rhinos, and giraffes are the best known horned animals, there are other groups that have evolved cranial ornamentation. The rhinolike titanotheres had enormous, knobby horns on their snouts made up of the front bones of the skull. Unlike rhinos, whose horns are arranged front-to-back, titanothere horns were arranged side-to-side. Protoceratids were strange, deerlike animals paired, blunt, skin-covered horns on noses. Some species, like Synthetoceras, had forked horns. Ceratogaulus is the only rodent to have evolved horns. Also called the horned gopher, this burrowing mammal had a pair of sturdy horns in front of its eyes. Both male and female Ceratogaulus were horned, so this strongly suggests the horns were for defense. Among reptiles, chameleons and horned lizards both develop horns consists of keratin-covered bone cores. An entire family of dinosaurs specialized in evolving horns, the ceratopsians. This group includes animals like the famous Triceratops. Paleontologists still debate as to whether these horns were also covered in keratin.
For info on human uses of horn and antler, check out our Endangered Species Center!
For info on non-horned ungulates, check out our Mammal Center!
For info on the evolution of Triceratops, check out our Dino Center!