Horns vs Antlers: what's the difference?

 

Horns and antlers. Both are headgear worn by hooved mammals, and can look similar, but they are actually very different structures. So what’s the difference?

Horns are found on ungulates like sheep and goats, as well as bovines like cows, bison, and antelope. They are also found on some non-mammals, like certain chameleons and, historically, on a number of different dinosaurs. But we’re here to talk about the ungulate version. 

 

A horn has a boney core, fused to the animal’s skull, and an exterior shell of keratin (like fingernails and hair). The keratin grows continuously throughout the animal’s life, so the older an animal is, the larger their horns tend to be. Most animals have a pair of horns, though some sheep breeds have been bred to possess more (shout out to the 4-horned Jacob sheep). In some species, horns are only found in males, while in others both sexes possess them. 

 These horns can be used for a variety of things. An obvious use is for defense against predators, though some species (usually males) also use them for fighting against other males of their own species. This is especially obvious in goats, with their love of headbutting things. 

 The keratin sheaths of the horn often slip off the bone after death when an animal becomes fully skeletonized. Horns can be used for a variety of things by humans hollowed out, like drinking horns or as instruments. (There’s a reason some brass instruments are also known as ‘horns’) 

 Horns can also be carved and shaped. Wetted with hot water, they become pliable for a time. They can also be sliced very thin and made flat, a technique used to make translucent windows in areas where glass production was unknown or rare.

Meanwhile, antlers are found exclusively in the Cervidae (or deer) family, and are worn only by males in all species that possess them except reindeer/caribou. 

 

Antlers are made purely of solid bone, and are used as a social and sexual signal. This means that hierarchy in a group of deer is determined by the size of a male’s antlers. During the rut season, males will grapple by interlocking their antlers and trying to force each other to the ground, with the winner gaining breeding access to the females. 

 

One of the things about antlers is, that being made of solid bone, they can only grow bigger if covered in skin (in this case, a fuzzy skin called Velvet). Velvet provides the blood vessels necessary for providing nutrients to the growing bone. 

 

However, deer can’t use them to fight if they are covered in velvet, so the velvet must be shed to allow the antlers to harden up for the breeding season. To do this, the bone actually dies (so at this point, it has no more sensation) This means they can no longer grow larger or heal if broken, however, so the only way for a male deer to develop larger antlers for the next breeding season is to shed the current pair and grow a new set. 

(Shedding velvet is messy and rather bloody, but harmless. It is, however, quite itchy, and deer will spend a couple days furiously trying to peel it all off, often eating it in the process)

So yes, this does mean that every year, antlers fall off and are regrown. This is one of the defining features of antlers. Antlers are the fastest growing bone in the animal kingdom, with some species such as Moose and Caribou exhibiting massive growth in less than a year. In fact, antler growth resembles a controlled form of bone cancer. 

(This shed antler from a bull reindeer reached this size in less than a year)

Growing so much bone in only months takes a lot of energy and minerals, so the size of a set of antlers is a good indication of the overall health of a deer. This is why males with larger antlers are more favored by females.

Antlers grow from a point on the skull called a “pedicle”, and their growth is largely controlled by hormone levels. After the completion of the rut, as hormone levels steeply drop, a mechanism in the pedicle actually eats away the bone at the pedicle until the antler harmlessly falls off. 

 

The hard bone of antlers has a variety of uses to humans, including carving it into various tools or decorative pieces. It is also often gnawed on by small forest animals as a source of calcium. Some people also consume antler velvet as a dietary supplement, and there are velvet farms in various parts of the world who raise deer to harvest their velvet every year. 

(vintage brooch made of carved antler)

The only species of deer in which both males and females grow antlers is caribou/reindeer. This is because they live in a very resource-scarce area. Because deer with antlers are socially higher in the herd, pregnant females retain their antlers through winter, after males have lost theirs, which allows them access to better feeding areas. This, of course, helps ensure the survival of mother and calf through winter. Their antlers shed shortly after giving birth. 

(This reindeer mother is already shedding her antlers after giving birth. The other one will fall off soon)
 

So, those are horns and antlers! There are a few other oddities in the Ungulate world (like the boney, skin covered ossicles of giraffes, or the strange horns of the Pronghorn which shed their keratin shell once a year), but overall, now you know what makes a horn and what makes an antler. Til next time!