I have a tendency to refer to horns and antlers in a loosey-goosey manner that may not always reflect my profession as a biologist. The same thing occurs when fly fishing, as I generally identify an insect by their common rather than their scientific name. This is because it is more important to communicate in a manner that is understood rather than to bow to the dictionary or Linnaeus.
Despite my lexical shortcuts, in broader biological discussions it is important to understand that there are four types of boney structures that grow on the heads of ungulates. These are horns, antlers, ossicones, and pronghorns. Horns are permanently attached to the head while antlers are grown, shed and then regrown on an annual basis. Ossicones are the hardened bonelike material a top heads of giraffes and pronghorns adorn the heads of our native antelope.
It has always amazed me that antlers grow out of the frontal head bones of deer, elk and other Cervids (the family of mammals with antlers). The formation of antlers begins at a structure (pedicle) that forms on the lateral crest of the head during the first year of antler growth and remains after the antler has been shed. The biological process of forming bone in this location is so robust it can put 40 pounds of antlers on a moose in just over six months.
In contrast, the earliest formation of horns, ossicones and pronghorns occur in the womb. Horns have horncores that are covered with keratin. These horncores are attached to the skulls in fetal development. As horns grow, the oldest material is near the tip of the horn and the youngest material is at the base.
In contrast, the giraffe’s ossicones are bones that form and are unattached to the skull. The lack of attachment often persists but in older males these structures can bond to the skull for added stability. The bony structures on North American antelope are similar to horns in they consist of bone that is attached to the skull early in development and has a keratin covering. The primary differences are the boney structure has two areas of growth (one along the length of the horn and the second at the prong) and the keratinous material overlaying the bony structure is shed annually.
In many ungulates only the males have headgear. There are exceptions such as caribou, sheep, giraffe and pronghorn. In species where headgear is found on both sexes, the males is larger. All four types of these structures are found in pairs that are relatively symmetric. Asymmetry occurs more often in stressed situations. At the individual level asymmetric antlers are more likely when there is a high parasite load (e.g., ticks) or injuries. Differences in horn length are more often the result of uneven brooming (breaking of the ends of horns) that occurs during fights.
Males use these structures to indicate their social status and as weapons when appearance is not enough. There is a positive relationship between horn and antler growth, survival and the ability to have more offspring. These structures tend to increase in size with age, up to a point. For example, antler mass of elk around Jackson Hole tend to increase until they are 10 years of age and Oklahoma whitetails antlers grow until they exceed 5 years of age. After this amount of time, the animal loses vitality and horn growth is reduced. Across species, antler size is related to their shoulder height. This explains in part while moose in Canada have much greater antler mass than do the diminutive Coues deer of Arizona.
While there are many differences in the qualities and appearances of these bony structures, all three types of headgear found in North America can be found on huntable big game species present in Northern Utah and Southeastern Idaho. Many questions remain about why such a diversity of structures evolved for the same purpose. While the biological arguments for this diversity is interesting, the aesthetic difference between the huge palmated antlers of a moose and the 9-inch stiletto horns found on mountain goats are apparent to hunters and wildlife viewers alike. So, while I may still error and say I like to hunt for shed horns in the spring, it is for simplicity rather than being unaware of the variety of structures found on the heads of this region’s ruminants