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Horns, Frills, Clubs And Spikes - Show Or Defense?


Tyrannoraptor

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Herbivore dinosaurs are every bit as interesting as the big, scary monsters that were preying on them. While herbivores may have been the more peaceful kind, their variety is what makes them so fascinating - Stegosaurs with large plates on their backs and spiked tails, Ceratopsians with their horns and bony frills, or Ankylosaurs with their impressive armour. It must have all been for defense, right?

Perhaps not. Many scientists now believe that those structures (well, aside from Ankylosaur's thick armour perhaps) have been used primarily as means of display or intimidation. for example, Triceratops mainly used his large frill to attract a mate, possibly with flashy colors, and used its horns in duels with members of its own species. Apparently fighting off a predator was not an option, since the horns were located on its head, creating a possibly dangerous situation, when a mortally injured T. rex could have fallen on the Triceratops, crushing its head in the process, killing them both.

But is this really possible? I mean, in modern times buffalos certainly use their horns against their lion attackers if neccessary. That may not be the primary reason for their horns to evolve, but the fact is that they do use their horns, and can inflict serious injuries to their attackers. We can observe this. Besides, is there any better place to have a weapon as dangerous as the horns of a Triceratops? By having them right above your eyes you can always see your enemy and strike precisely where you want. In my opinion this is not a flaw, but an advantage.

Also, did Pachys really use their thick skull domes only for display? According to J. Horner the dome of Pachycephalosaurus consisted of bone that was not designed to do the job of head-butting and the animal would risk serious injuries doing so. But in modern times other head-butting animals also risk serious injuries, yet they still behave this way.

Your thoughts on these theories?

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The defenses seem to have evolved in lockstep with the threat. The null hypothesis begs the question "why no display apparatus on the giant sauropods?".

"There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant

“Try to learn something about everything and everything about something.” - Thomas Henry Huxley

>Paleontology is an evolving science.

>May your wonders never cease!

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It is my opinion that flight wins over fight. It's like the two guys hiking when approached by a hungry bear, one guy stopped to put tennis shoes on. The other asked why he stopped, as he could never outrun the bear anyway, he replied, "I don't have to outrun the bear, I have to outrun you". The one that stays and does battle is allowing the others to escape. This is not a good way to pass your genes on to the next generation.

However, altruism is a strong selective pressure, it is implicated as the driving force behind eusociality. (Not being political here, but referring to honey bees, ants, naked mole rats, even some shrimp). However, I don't think that is what is going on here.

These species are fighting for hierarchial dominance, which allows them to breed. Being able to kick your competitors rear also has uses when attacked by somebody oggeling a meal.

The whitetail deer male is well equipped to defend itself for about 4 months a year, but it gets along fine the other 8 months. The female gets along fine all 12 months without built in spears.

Display apparatus also may not fossilize, or be recognized.as such. Size is often a criteria when breeding begins.

Ultimately, in vertebrates, it usually comes down to the female. Why do giraffe's have long necks? No, not to allow then to reach higher branches, but because studies have shown that female giraffes select the males with the longest necks to breed with. Size does matter.

Don't think it doesn't happen in humans? Why are males taller then females? I regularly ask my class this, and they scratch their heads. Then I ask the ladies, "Everything being equal, would you marry a guy shorter then you, or taller then you?" Nearly to a person, they will choose taller. When asked why, they don't know.

I am glad I am not a male peacock. Louder and brighter gets you more offspring, but also shortens you lifetime considerably.

Its always the women.

Brent Ashcraft

ashcraft, brent allen

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But what would explain the horns in cows, then? Both bulls and cows have them. Sorry if this is a stupid question.

I agree with your theory, ashcraft, running would be a better tactic than trying to fight. I still think that those horns would become handy if there was no alternative, even if they were meant for intraspecific combat. And that is what happens today, too. I think it's unlikely that a Triceratops wouldn't defend itself if it needed to, just because it had horns on its head and risked getting injured (or killed) in the process. Animals do take risks.

And actually, sauropods had some impressive display structures, too: http://en.wikipedia.org/wiki/Amargasaurus

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The thing about evolution is it doesn't have to choose. Both uses could be at work. I can think of many species where the display item is also useful for obtaining food (giraffe necks) or defense (deer antlers).

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I have the same problem with the horn display theory. If only the males had horns or had significantly larger horns than males then one could argue display (or primarily display) but both sexes having them, defense seems more reasonable. You actually don't have to use the horn as a weapon just display it as a threat. The Tyrannosaur approaches, you turn and face him with your horns and he decides that maybe a hadrosaur might make an easier meal. This doesn't stop you from sparing with another male over a mate as a deer or bison would either.

As for the tail spikes on Stegosaurus, there exists an Allosaurus bone with a nice matching hole for the spike. The spikes are also somewhat small in relationship to the overall size of the animal which probably also small eyes and fairly poor eyesight and is not strategically located for a display item. The back plates on the other hand, large and prominent.

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As far as defense goes deer have the best defense in their hooves. Those things can be deadly and cut up a predator. I believe for example that their antlers are for display and sparing for a mate.

I am far from educated on this so I can only guess though.

Personally I sort of think in the case of dinosaurs that both display and defense were the factors.

It is a very interesting topic none the less.

Robert
Southeast, MO

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I have the same problem with the horn display theory. If only the males had horns or had significantly larger horns than males then one could argue display (or primarily display) but both sexes having them, defense seems more reasonable. You actually don't have to use the horn as a weapon just display it as a threat. The Tyrannosaur approaches, you turn and face him with your horns and he decides that maybe a hadrosaur might make an easier meal. This doesn't stop you from sparing with another male over a mate as a deer or bison would either.

As for the tail spikes on Stegosaurus, there exists an Allosaurus bone with a nice matching hole for the spike. The spikes are also somewhat small in relationship to the overall size of the animal which probably also small eyes and fairly poor eyesight and is not strategically located for a display item. The back plates on the other hand, large and prominent.

In the group "deer", most males grow antlers, and females do not. The only exception is the caribou, where the female is much reduced "hornage". Primitive deer used fangs for sexual display, which seem to have been lost when they evolved antlers, some whitetails still display reduced fangs today. I suspect the antelope females carry horns, because they have to, not because of defense or show, but because the males need them, so for developmental reasons, the females have to have them. Like nipples on a male.

As far as tail spikes being only for defense. It is just as likely that they add size to the overall appearance to a poor sited animal, which makes them more attractive to females.

Brent Ashcraft

ashcraft, brent allen

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