I started making this video about horns with a very simple goal: just define what
a horn is and show you some of the other things that are like horns, but not quite.
But it turns out that Life is very hard to classify,
and after studying horns I have more questions than when I started.
So join me on this convoluted journey to define which animal have horns, and which ones do not.
Horns are used by animals for defense against predators, and for fighting other animals of
the same species. Horns can be sharp enough to injure a predator, and they are not vulnerable
to damage. That is why so many different animals have things that look like horns.
But true horns are found in the animals of this one group. Heres.
Bovidae includes animals like bison, yaks, and cows that have interesting horns,
but it also includes some impressive horns like kudu, oryx, mountain goats, and sheep.
The American Heritage Science Dictionary defines a horn as "Either of the bony growths projecting
from the upper part of the head of certain hoofed mammals, such as cattle, sheep, and goats.
The horns of these animals are never shed, and they consist of bone covered by keratin."
That sounds like an unnecessarily complicated definition,
until you start to see how living things make classification more interesting.
Antlers, for example, are found on animals like Moose, White-tailed Deer,
and Caribou. They are made of bone with no keratin cover, and they are shed and regrown
each year. So they have a bone core, but no keratin cover and they are not permanent.
Pronghorns have these interesting horns with a bony core and keratin cover. But they actually
shed the cover each year and just keep the bony core in the other seasons. So they are
like a cross between antlers and horns, because they have horns part of the year and then don't
have horns for the rest of the year. But true horns never shed, so these are something else.
The closest living relative of the Pronghorn are the Giraffe and Okapi, which have these little
things on their heads. They are called ossicones. Ossicones have a bone core surrounded by skin.
Ossicones never shed, and they are used like horns, but they do not have a keratin cover.
Rhinos have one or two big pointy things on their face,
but are they horns? They are permanent and made of keratin,
but they have no bone core. So not truly a horn, even though that is what they are called...
Narwhals have a pointy thing on their faces. That is a giant tooth that grows up to 10 feet long.
They are permanent, but teeth are not bones, and they have no keratin cover.
In the Middle Ages, narwhal tusks were actually traded as unicorn horns
even though they are teeth. Narwhals are awesome, but do not have horns.
While we're at it, Elephant tusks and Walrus tusks are also not horns. Those are also teeth.
Longhorn Cowfish have these pointy things that are mineralized collagen fibers.
Permanent, but no bone core and no keratin cover, so they're not horns.
Horned Screamers have a keratin spine that grows continuously from their heads.
No bone core, does have keratin, is permanent, is not a horn.
Other birds called Horned Guans have a pointy....... thing? on their heads.
It has a bone core, it is permanent, and it s surrounded by skin, so it's not a horn.
Great Horned Owls don't have great horns. They just have some feathers
sticking out. Same thing with Horned Larks, Horned Grebes, Horned Sungems,
and so on. No bone core, no hard keratin cover though technically feathers are made of keratin,
and they are more or less permanent. Still not horns.
Cassowaries, on the other hand, have a bony-cored pointy crest thing that
IS covered by keratin. Is this a horn? It really blurs the edges, because if it's not
pointy it might be called a crest, but then if it IS pointy, does it suddenly become a horn?
Rhinoceros Hornbills also make things more complicated, because they have a permanent
pointy projection on their head that has a bone core
and is covered with keratin. Ironically, the Rhinoceros Hornbill meets more horn criteria
with its beak than an actual Rhinoceros does with its horn.
Actually, now that I'm thinking about it, bird beaks are all permanent bony projections covered
in keratin and on the head. Uhhhh... does every bird have a pair of horns that they use to eat?
And horned lizards also clearly have horns.
These ones are not horns, but these ones meet all the criteria for horns.
We have seen just a selection of the diverse ways that animals have found to use things like horns.
Going back to the scientific definition, we see why it had to be so oddly specific. "Either of
the bony growths [because elephant] projecting from the upper part of the head (because stork)
of certain hoofed mammals, such as cattle, sheep,
and goats [because cassowary crests]. The horns of these animals are never
shed [because pronghorn] , and they consist of bone covered by keratin [because giraffe]."
There's and important lesson in here, which is that there are two different ways to
define what a horn is. There's the scientific definition that we have been using so far.
A permanent, keratin-covered bony projection from the head of certain mammals. Then there's the
plain English definition, which is "something that looks like a horn". By common usage,
all the animals that we have seen today have horns.
Most people just aren't going to check whether all those conditions have been met.
So if you see someone using the wrong word for something like a horn, be kind. That person may
someday experience the thrill of discovery when they learn about the true diversity of Life.
Thanks for learning today! Let me know if there are any other animals that I missed. If you're
a greenhorn on this channel you can subscribe to keep learning. And let me shoehorn in a few other
videos that you might watch. Thanks for stopping by this week to learn what makes Life awesome!