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It’s a matter of horns

Some beetles, lizards... have horn-like structures, but mammals have the most diverse horns without doubt. Are all horns the same? What are they used for? Do they have economic value? Find out more in the following post.

WHAT ARE HORNS?

Bulls, deer, rhinos… all of them have structures on their heads that we call horns, but they are not all the same. Strictly horns are two bony structures that emerge from the frontal bones of the skull, they are permanent (never fall off) and unbranched. In some species they grow throughout life.

El watusi, el bóvido con los cuernos más grandes del mundo. Foto: Marina Calvo
Watusi (Bos taurus watusii), the bovid with the biggest horns in the world. Photo: Marina Calvo

They are made up of a bony nucleus and an outer coating of keratin (the same protein from our hair and nails).

Horns have different shapes and sizes depending on the species: straight, curved or spiral; flipped, bent or flat; short or wide. All of them have sharp ends.

Diversidad de cuernos de la familia Bovidae. Fuente
Horns’ diversity of Bovidae. Source

All bovids (bulls, goats, sheep, antelopes…) have horns, including the females in many species. However, in general, females have thinner horns while in males they are wider and can withstand more force.

HORN GROWTH

When the horns begin to grow, they do not do it directly from the bone, but from the connective tissue. When growth is complete the horn nucleus ossifies and fuses with the frontal bones of the skull.

Cráneo de cabra en el que se observa el interior óseo del cuerno y la cubierta queratinosa. Fuente
Goat skull showing the bony interior of the horn and the keratinous covering. Source

AN EXCEPTION

The pronghorn has different horns than the bovids: they are branched and the keratinized covers change annually, whereas in bovids are permanent.

Berrendo (Antilocapra americana). Fuente
Pronghorn (Antilocapra americana). Source

WHAT ARE ANTLERS?

Antlers are two bony structures that come out of the frontal bones, but they are seasonal (they change every year) and branched .

Antlers only exist in males of the Cervidae family, except for the caribou or reindeer (Rangifer tarandus), in which both males and most of females have antlers.

GROWTH OF THE ANTLERS

Unlike horns, antlers do grow out of bony structures (pedicle) found on the side of the frontal bones.

Growth begins in spring (April or May in the Northern Hemisphere), due to hormonal changes and the gradual increase in light hours. The growth of the antlers has several phases:

  • Initial phase: antlers are covered with skin and velvet, so they also have blood vessels and nerves.
  • Intermediate phase: the exterior of spongy bone is replaced by compact bone. The interior is filled with spongy laminar bone.
  • Final phase: the velvet dies and it is removed. To help this removing the animals rub against the trunks and vegetation, leaving the antlers polished and brown.

    A, B, C: 1, 15 y 30 días de crecimiento. D, E: 3 y 5 meses después.F: pérdida del terciopelo. Fotos: A-E, Steve Demarais, F, Dave Hewitt.
    A, B, C: 1, 15 y 30 days of growht. D, E: 3 and 5 months later. F: loss of the velvet. Photos: A-E, Steve Demarais, F, Dave Hewitt

After the reproductive period the hormonal levels fall and the photoperiod decrease, which causes the pedicle to lose calcium, it weakens the union between itself and the horn and the horn ends up falling. The cycle will be repeated the following spring, and will appear one more branch, so the most an antler is branched, the older is the individual.

Alce pediendo su terciopleo. Fuente
Reindeer losing its velvet. Source

USES OF HORNS AND ANTLERS

As we know, mainly antlers and horns are used by males during the breeding season to compete for females, in fights and exhibitions. Usually the animals collide their horns/antlers together to demonstrate their body strength. Horns, often sharp, are also used as a defense against predator attacks.

Check out this spectacular dispute between two Canadian mouflons:

There are species with small antlers but highly developed tusks, despite being herbivores. This is because they also use them during fights. In contrast, species with larger antlers do not have these developed tusks.

Siberian musk deer (Moschus moschiferus) - does not belong to the family Cervidae-, Muntjac (Muntiacus sp.) And roe deer (Capreolus capreolus)
Siberian musk deer (Moschus moschiferus) -it does not belong to the family Cervidae-, Muntjac (Muntiacus sp.) and roe deer (Capreolus capreolus). Source

For humans, horns and antlers shouldn’t have significance. Unfortunately, its carriers are objective of hunters, for the mere achievement of their “trophy.” In Spain there are more than one million people with a hunting license. According to Fecaza, the hunting business generates 3.6 billion euros a year in Spain.

Trofeos de caza robados incautados por la Guardia Civil. Su valor pudo ascender a 300.000 euros. Fuente
Stolen hunting trophies seized by the Guardi Civil. Its value could amount to 300,000 euros. Source

Spain is also the second importing country of hunting trophies. Thousands of euros are paid (from 2,000 to 80,000) to make hunting safaris in Africa, for example, where the most valuable animal is the one with the largest horns. This results in the elimination of the best breeding males and in the decrease of specimens in general.

AND THE RHINOCEROS HORN?

Ironically, since their horns have led and are leading to extinction many species, rhinos do not actually have real horns, as they do not have a bony nucleus or a cover. They are an accumulation of corneous fibers, resembling a thick hair, although they are not true hairs. In addition, the horn is placed above the nasal bones, not  in frontal position as in the case of antlers and true horns. Only in species with two horns, the second one rests on the frontal bones.

In females, the horn would help to protect the young, whereas in males to face their rivals.

Sección de un cuerno de rinoceronte cisto bajo lus ultravioleta. Se observa el cartílago nasal, el hueso, la dermis y cómo el cuerno se asienta encima de la dermis. Fuente
Fraction of a rhinoceros horn under ultraviolet light. The nasal cartilage, the bone, the dermis and how the horn settle in above the dermis can be seen. Source

As we have discussed, due to the alleged magical powers of rhinoceros horns in the traditional medicine, we are extinguishing rhinoceroses just like with are doing with the pangolin… for a handful of keratin. On the black market, a kilo of rhinoceros horn can cost from $ 60,000 to $ 100,000, more than gold.

Rinoceronte con el cuerno amputado.
Rhinoceros with its horn amputated. Photo: A. Steirn

HAVE YOU NOTICED GIRAFFE’S HORNS?

As you may assume at this point, no, giraffes do not have true horns, but they also have two structures in the head, males, females and newborns. They are called ossicones. They are permanent, not branched and they are always covered with hair and skin. In fact, they already appear in the fetus as cartilaginous structures and do not merge into the skull until the age of 4, between the frontal and parietal bones.

Female giraffe (Giraffa camelopardalis). Source
Female giraffe (Giraffa camelopardalis). Source

We can tell age and sex of a giraffe by its ossicones: if they are thin and ended up in a tuft of hair they are young ones or females, while males do not usually have hair on its top. Males also have a protrusion in front of the ossicones more sharp than females. At an older age, this protuberance is bigger, since calcium is deposited over time.

Giraffe ossicones are used by males during their confrontations. Surely they played a more important role in its ancestors like the Sivatherium, the largest giraffid that has ever existed. It is possible that they also have some function in thermoregulation.

REFERENCES

MIREIA QUEROL ALL YOU NEED IS BIOLOGY

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