Wait ... what?

Basically, this: Most land predators on Earth use their mouths to kill their prey. That is, they have to stick their precious, irreplaceable heads into harm's way every time they want a meal. I speculate that this has an effect on how ... tentative predators can be. Again, wait ... what? I've watched a number of nature videos, and there is often a lot of backing and filling and trying to get behind the prey before making the big rush.

Now imagine a new predator. Think a ravenous kangaroo with a spiked tail. Its attack is to rush up close to the prey then swivel, crashing its cruel spikes into the beast, laming it and causing blood loss. Its head never gets within range of the prey's desperate counter-attacks.

So here's the question. Does it make sense to posit that this (um) "Velocikangaroo" would be more insanely aggressive than your typical mammalian predator, because its attack doesn't risk its head?

Note: I'm ignoring the elephant in the room, ie humans. Humans are not obligate carnivores, and they are psychologically weird anyway, so they don't count for this exercise.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monica Cellio Nov 24 '17 at 21:32

13 Answers 13


Instead of a velocikangaroo, why not go straight with the Velociraptor from the Cretaceous? One of the reasons why the Therapods (the branch of dinosaurs that evolved into birds) were capable of surviving in a flying form was the pronounced development of their breast muscles and the sheer power they could bring to bear on displacing enough air to take flight.

Velociraptors on the other hand used those muscles very differently (according to what we've extrapolated from the fossil record); to grab their prey. Yes, they were ambush predators, but instead of using their heads to strike, they used their arms, then used their heads to make the kill once they had hold of their prey.

That said, I don't think the protection of their heads factored into their style of attack so much as the benefit of being able to see what they were doing with their arms and therefore being more agile; something your velocikangaroo isn't.

Truth is, risk of injury is more a factor in fighting over females, or defending territory against one's own kind. There the match is even, and the risk of damaging yourself and not being able to hunt is too great. On the other hand, if an ambush predator is worried about its head when hunting, it's just more likely to go after smaller or weaker prey. Hunger is more of a factor in hunting aggression than knowledge of one's weaknesses and that means that you're likely to see a wide variety of aggression levels and risk taking even within the one species.

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    $\begingroup$ One reason we might not go for Velociraptors is that we don't actually have any direct knowledge of their psychology... Your description of their attack style is only educated speculation. $\endgroup$ – Harabeck Nov 21 '17 at 17:14
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    $\begingroup$ This is true; evolution is one of those rare times in science where there is a wealth of evidence and no way to prove it experimentally. The speculation above is based on what we know of their physiology from the fossil record. Intererestingly, their psychology may have been more similar to humans than other animals; we know that they were a social animal, that they were reasonably intelligent and despite their razor sharp claws had rudimentary hands that did more than support walking; If the meteor hadn't struck back then, it's possible they would have been the Earth's first intelligent life. $\endgroup$ – Tim B II Nov 21 '17 at 22:07

Not really, no.

Within the scope of hunting prey, predators are doing this not because they like it: they do it as a means of survival. If there were a species which expended almost as much energy obtaining their food as they earned eating it, they would not survive long. With that in mind, it is easy to see why predators typically go for ambush tactics, only engaging in high-intensity chases/ hunts when absolutely necessary.

As such, the lack of "aggression" as you see it in today's predators may not be completely due to a fear of injury, but also to minimize effort. Going all out and smashing your prey to a pulp may sound attractive if you do not risk injury, but you will probably expend a lot of energy doing so - where's the benefit?

If your Velociroopter (you're welcome) became such an advanced killing machine that it were able to kill its prey very efficiently, it is plausible to suggest that it goes on killing for sport/ fun. In this case, perhaps it would display hyper-aggressive behavior on such sport kills.

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    $\begingroup$ +even more for Velociroopter! Beats the tar out of Tyranosauroo Rex... ;D $\endgroup$ – akaioi Nov 21 '17 at 15:48
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    $\begingroup$ If Velociroopter becomes such an advanced killing machine, they are probably going to be killing each other a lot, because they will have to become either cannibalistic or extremely territorial. Or both. Or die out by multiplying too much so there's no food for them. $\endgroup$ – Headcrab Nov 22 '17 at 7:15
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    $\begingroup$ I like the Velociroopter, but also vote for the Kangaraptor... $\endgroup$ – Thern Nov 22 '17 at 10:48

Does it make sense to posit that this (um) "Velocikangaroo" would be more insanely aggressive than your typical mammalian predator, because its attack doesn't risk its head?

I'd say that it depends. If the prey animal defends itself and bites off or maims your Velocikangaroo's tail (or one of its limbs) then the Velocikangaroo will be unable to hunt and die of starvation. In other words, its main hunting weapon is just as essential for survival as its head.

Another animal which attacks with its tail:

enter image description here

It does not do spinning attacks... the tail strikes to the front where the scorpion can see. While its dinner is busy parring its pincers, its tail strikes from above. The pincers are also armored and tough.

I think you would need an animal which can deploy a reusable ranged weapon.

This spider doesn't wait for you to fall into its web. It throws the web at you instead!

The velvet worm shoots glue.

The spitting cobra shoots venom (and it aims for the eyes!)

The Komodo Dragon has armor and a venomous bite (it's pretty vicious)...

You could also have a slightly less peaceful kind of deer which impales you on its horns and then eats you...


enter image description here

Eagles are not especially aggressive.

Also, cats and back-leg kicks: https://www.youtube.com/watch?v=uBBwdtr14rM

Cats are not especially aggressive.

The way to make a predator aggressive is to make it perceive a threat to its territory/mate/offspring/food supply. Boars, mother bears, alligators around its nest, ... hornets!


Animals that can use tail attacks normally do so as a defensive move against an attacker, they also do this while standing side-on so they can also see the attacker's position.

I think crocodiles can use tail attacks but again I think this is a defensive rather than offensive attack pattern for them, but am happy to be corrected on this point if anyone has more experience of crocodiles there aren't a lot of them wandering around my part of the UK. :)

As mentioned by others, a spinning tail attack would require the attacker to lose sight of the prey and have to predict where the prey is going to be for the tail to strike in the intended place.

If the prey changes direction or elevation of the target area, stops, stumbles, jinks, zigs instead of zags, the attack will miss and Velociroopter (I like that name) ends up spinning out of control then flat on its face in the dust with its tail in the air gently waving in the breeze like a flag of disappointment.

However give your Velociroopter the claws common to Velociraptors and the tail as a backup defensive weapon, or perhaps make the tail strike over the head or shoulder akin to a scorpion's sting so that the Velociroopter does not have to lose eye contact with the prey to strike, and you'd have an effective predator.

BTW, is someone going to draw this?

Xenocacia came up with Velociroopter, I reused it as it is epic.

  • $\begingroup$ Gawainuk you get my eternal praise for "Velociroopter" ;D $\endgroup$ – akaioi Nov 21 '17 at 8:17
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    $\begingroup$ @akaioi Actually, looks like that one was Xenocacia's, though Gawainuk used it several more times. $\endgroup$ – user Nov 21 '17 at 8:18

There are reasons why predators attack from the back:

  • head is in the front: you either look where you are going or watch out for your back. You cannot do both at the same time.
  • chasing has the clear advantage of following the prey

Now, imagine I am the dumbest prey in the world: it just takes me a sudden stop or deviation, while this fantastic kangaroo has overtook me and is charging its tail, to avoid the blow. And moreover the kangaroo won't even see me going away until I am more distant from him then I was when he overtook me.

Shortly said, your kangaroo would struggle to survive.

But your question is about the psychology of the animal: chasing a prey is already a considerable effort, overtaking it is with good reasons even a greater struggle. Also, swinging your tail while in movement and keeping balance is not a trivial task (unless you want to fall down and being rolled over by your running prey). Definitely, I don't see any push for this animal to become overly aggressive.

  • $\begingroup$ While I'd love to discuss the tremendous speed of the tail strike (like animal taekwondo!), I'm trying to focus on the effect -- if any -- on the kangaroo's behavior... ;D $\endgroup$ – akaioi Nov 21 '17 at 6:27
  • $\begingroup$ Reason number three: what they really want to do is stick an incisor in between your second and third vertebrae, which is extremely hard from the front. $\endgroup$ – Mazura Nov 21 '17 at 15:27
  • $\begingroup$ ... and the reasons why everybody uses their teeth: my guess would be bite force. Most animals have the ability to not let you go if they don't want to. Try doing that with your thumbs... $\endgroup$ – Mazura Nov 22 '17 at 19:00

But not all ocean predators use their mouths.

As requested, some use their tails.

  • Some groups of orca tail slap the bait ball to stun their prey before picking them off.

  • The thresher shark does something similar, also tail whipping to stun their prey.

There are advantages to doing this in the water over doing it on land, including shockwave propagation due to the incompressibility of water meaning they don't have to be particularly accurate to hit a large number of targets, but your intended principle is there for you to work with.

Given a pack hunting Velociroopter that rounds up the prey as ocean predators do, rather than land predators who tend to run it down, then attacks a target with the tail meaning they less vulnerable to horns or other defences. Perhaps it could be a viable hunting technique on land as well.

As for your primary question: What would be the personality of such an animal?

Controlled, sociable, pack hunting. Probably high intelligence with solid communication. Definitely not a nutter. In fact less aggressive, it's fundamentally a lower risk attack.


The loss of use of an arm/leg/tail means almost certain death for a wild animal, predator or prey, so its not just the head that is precious.

If you use a big spiked arm/leg/tail to attack and that gets disabled then you can no longer hunt and you die because you cannot eat. If you use it for defence then you die as you can no longer defend yourself from predators, who will naturally look for weak or injured prey.


I think that there is no general effect (read: justification for psychotic behaviour) because the issue balances itself in the sense that the head becomes as armoured as needed/possible given the rest (think of a shark's eye protected by a membrane an instant before biting down, thick skulls in headbutting herbivores like pachycephalosaurs and rams): Losing a limb is just as deadly as losing a head (or jaw!) to a lion, the dying just takes a few extra days/weeks. Note also fighting male giraffes striking with their necks(! occasionally breaking them), not those rudimentary horns they have.

But possible adaptations, of which I like the last best:

Shockwaves? You said "land-based" which rules out a whole class of attacks using shockwaves in water, most notably pistol shrimp (micro-cavitation!), "hammer" mantis shrimp, tail-slapping orcas, echo-location-type-to-the-max type bursts in dolphins; and a few electric shocks using the conductivity of water (eels, rays, ... ). I seem to remember a few "How to Train Your Dragon" dragons use shockwaves. And I think some bats do the echolocation equivalent of dolphins, to inhibit their prey.

Pincers This is the obvious thing, in everything from praying mantis (well, kind of a reversed pincer) to already-suggested scorpion (where many have weak venoms and rely on their pincers alone --- it's those with heavy stings and skinny pincers that tend to be dangerously venomous). Also "spearer" mantis shrimps [yeah previous pistol and "smasher" mantis shrimps use adapted forelegs as tool but the use/effect isn't grabbing.]

Projectiles? Some snails shoot a calcium-based arrow into their partners: Being hermaphroditic, they benefit from being "the male" in a copulation because the genetic/offspring benefit is the same (see RA Fisher and sex ratio theory) but the investment is much smaller ('male' means 'having the smaller gametes', i.e., sperm not eggs). So this arrow is full of sex-changing hormones, no reason why your creature couldn't re-grow this arrow faster than a snail (hah!) and cover it in venomous proteins/peptids instead of hormones. These are easier to aim if in the head (looking=aiming) than in the tail (3D measurement/estimation of relative positions and angles of observing head, prey, and aiming tail) or possibly the body. (Note scorpion's sting strikes just in front of its head, no sideways only some small arc of possible strike points low/near to higher/further, so that head is in the 'danger zone'; but that head can thus verify hit/miss.)

Spitting venom in cobras is defensive, not offensive (a running-away or surprised prey isn't facing them, skin is impervious). So similarly your projectile attack will work well on mollusks and amphibians and unprotected humans, but anything scaly (or possibly even excessively hairy) will not be penetrated by the dart: Pangolins and paladins are safe.


The real elephant in the room is that their attack is to rush up close to the prey then swivel (!). Its attack puts it in the position every other predator wants it in. Plausible only if your world lacks felines and other animals with instinctive kill strikes from the rear.

Let's look at a ... (the only ?) large creature that had a tail as a weapon, the Ankylosaurus. A quadruped that used its tail for defense.

enter image description here

Notice that it also had armor throughout, with special attention to the neck plates. It also wields a bludgeoning weapon without spikes that can neither break off nor injure itself with.

enter image description here

The psychological effect of this would be an animal that does not want to use this mechanism unless absolutely necessary due to the high probability of injuring itself, and said creature is unlikely to have evolved, based solely on the lack of precedent in the animal kingdom (no animal has spikes that point at itself). It already has a hard enough time curling up and getting comfortable in bed.

Hunting ass-backwards is.

  • $\begingroup$ Ok sure, there's other dinosaurs with spikes, too. But none them were carnivorous afaik. They were always defensive weapons. He who kills with his tail has forgotten the face of their father. $\endgroup$ – Mazura Nov 22 '17 at 18:37

I'd like to offer an additional insight into why heads typically contain the weapon of choice, and maybe some alternatives that fit what we're familiar with.

First, evolution tends to favor efficient energy expenditure and low complexity. You don't see too many body parts exposed to wear and tear that are also complex. It's the same mentality engineers use all the time: The more a piece gets used, the more chances it has to break, and the harder it is to fix it. Most carnivores require some sort of appendage to tear apart food, and a jaw is a wonderfully simple way to concentrate a lot of force on a small area to do just that. Well if you've already got that much power in one spot, what's the benefit to developing more power in a second spot? All you need to do is restrain your prey (with those same limbs that are already great for travel) and then the jaw can do all the work. Multitasking!

Second, there are plenty of carnivores out there that don't rely on their jaw/head for the kill. Some snakes strangle their prey. Many predatory birds kill with the impact of a dive. Lots of sea creatures hunt with tentacles or stingers. They've all adapted these methods because in their particular cases, there is some kind of advantage. For example an octopus pries open mollusks with its tentacles, because even a strong jaw isn't powerful enough to defeat them otherwise. A falcon kills with outstretched talons so its eyes can keep the target perfectly in view during its 120Mph dive.

But to your original question, does this affect their psychology? Long story short, there's no good way to answer that. They certainly aren't more or less aggressive on the whole, because they only risk their necks as often as they need to for food, the same as everything else. Could they? Sure, probably. But they'd have nothing to gain from it, other than social status, which isn't a thing for most animals outside of mating.

Now there are plenty of creatures which are hyper-aggressive for various reasons. It just happens to have little or nothing to do with their preferred method of killing; As others have mentioned, it's usually to do with mating or territory. So invent whatever reason you see fit to make this velociroopter (lol) aggressive. Features that might help shoehorn that trait in would be things like having the mouth separate from the head, or making it have to consume/digest its prey slowly. The process of eating might make it vulnerable somehow, so it has to be able to scare off or intimidate potential threats first.

TL;DR Body type has no direct correlation with psychology, in the world as we know it. The practical advice is, don't go too crazy designing an aggressive creature, just design a creature and then describe why its environment requires that it be aggressive. Remember that even the most safely-built creatures don't stick their neck out more often than needed for food, mates, and territory.


One serious limitation to the velocikangaroo is that it cannot be looking while it strikes. It literally must flail blindly to make its killing blow. Meanwhile, the prey can see what they're doing. It would be quite difficult to land a good blow on any nimble prey.

Using jaws allows you to use simple guidance algorithms all the way into the point where you're close enough to need to close your eyes to protect them. Remember, when we try to catch a baseball, we don't move to the optimal spot right away. We move in a way which keeps the angular motion of the ball linear with respect to our own eye. It makes the guidance algorithms easier, so you can have faster processing.

If you really wanted to hunt this way, you'd have to do two things. The first is you'd need to make your weapon expendable. A predator that can't hunt prey is as doomed as a predator whose face got hurt in an attack. The second thing is you're going to need an attack which doesn't require you to look away from the enemy.

I suggest a bioweapon akin to the Chinese dart:

Chinese dart

Wielded properly, this operates like your spiked tail, only one strives to maintain both energy and angular momentum at all times, so it's much more effective if you miss. It's quite a sight to behold. It's also a cheap enough structure that a predator might be able to afford to lose one or two without breaking the energy budget that a predator needs to stay alive.

  • $\begingroup$ +1 for mention of energy budget vs disposable weaps. That's an important consideration! $\endgroup$ – akaioi Nov 23 '17 at 5:54

Think baseball

I speculate that this has an effect on how ... tentative predators can be. Again, wait ... what? I've watched a number of nature videos, and there is often a lot of backing and filling and trying to get behind the prey before making the big rush.

Your instinct to think about humans was the right one even though you don't want to consider humans particularly.

What do humans have that only a handful of other animals do?

  1. Ranged weapons like bows and arrows, slings and rocks, and atlatl to throw spears.

  2. Tool use.

The answer, I think, comes from baseball and not zoology, as I explain below.


@Peufeu notes several animals that use bio-projectiles (spit or glue or spider silk), and another class of bio-projectiles could be numerous disposable spores or spines that could be hurled at prey.

Another bio-projectile would be poisonous feces dropped by a bird (or better yet a whole flock of birds since birds in flocks tend to poop in unison at roughly the same target) from the air on you. Poisonous or caustic or acidic poop from a whole flock of carnivorous killer pigeons at once is something you have to take seriously. It would be the moral equivalent of napalm.

Tool use

The other option is tool use.

Quite a few animals use tools (a few even turn other animals into zombies to do their bidding for them), rather than actually attacking with parts of their bodies.

Tool users, especially those that attack at range, can afford to be psychologically much less tentative because they aren't putting themselves at risk.

Is this far fetched for a much more primitive animal than man?


For example, have you ever had a squirrel throw acorns at you? If you haven't, I absolute assure you that the do it, ruthlessly, with impunity, from high in a tree where you can't get them. They do it to dogs too (something I rather admire them for doing).

Suppose that your velocikangaroo, rather than using his tail like a mace, used its tail which had a sling-like pouch at the end of it, like a baseball pitcher to throw medium sized rocks at prey at 200 miles per hour at distances of 100 feet with deadly accuracy. Now that is a predator who might not be timid at all, and that predator, unlike those who used bio-projectiles, wouldn't have to pay much of a biological/energy supply/healing cost to gather up unmodified medium sized rocks to stack up and throw at prey. Thus, the velocikangaroo could be a tool user simply by throwing ordinary, easy to find rocks, without being a tool maker, which is a much more sophisticated thing.

You'd also want to give your velocikangaroo kean, stereo hearing to locate threats and prey before they go to close and accurately aim at them, and keen binocular eyes to aim with, and a good sense of smell (again to prevent ambush attacks). Color vision might be unnecessary for an obligate carnivore since color vision can actually make it harder to see camouflage and the purpose color vision evolve for (distinguishing ripe from not ripe or rotten fruit) isn't important to a carnivore.

Finally, he'd still have to be pretty fast because if he ran out of ammo he'd probably want to run like hell.


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