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Re: Tyrannosaur hunting strategies (was Re: How Did HadrosaursSurvive?)



Before reading all this, please keep in mind I am not suggesting that
tyrannosaurs hunted ONLY using one specific strategy. Obviously it is
nigh on impossible to prove behavioural strategies to any degree of
detail in a long extinct species. Since neither one of us can provide
any actual evidence to totally prove or disprove ideas in extinct
behaviour, it merely comes down to whether we individually think
something was possible or not. Hopefully this will be the end of a tired
thread. We could argue for months, with no real evidence used to back up
the ideas.

I shall answers some of the following questions posed to me, although I
have ALREADY answered them. It sometimes pays to actually read a post
thoroughly before commenting... (*ouch!*)

Oh, and I've resisted the urge to put a whole lot of [sic]s in HP
Booth's post. I don't have THAT much time to spare.  :)

Brett Booth wrote:
>
> > Crocs can hunt in groups, and even specialise their tasks. Smaller ones
> > chase mammalian prey into deeper water, while larger individuals wait
> > down stream to finish them off. They usually do this when herds of
> > herbivores cross rivers during annual migrations. I doubt it is true
> > "pack" hunting, but it does the job quite nicely. Even when scavenging,
> > they work together and specialise tasks. Large crocs clamp down on the
> > carcass, while others twist pieces off. They'll even work together to
> > chase lions off a kill. There's not complex communication involved. Just
> > a combination of instinct and experience.
> 
> I've never heard this, everything I know on crocs says that they are highly
> canniblistic and would just as soon eat the young croc as the mammal.

It depends on the species. Salties (C.Porosus) are largely solitary, so
will kill each other on sight if they think they can. Niles
(C.niloticus), on the other hand, regularly live in large groups. I
suspect their cannabilistic leanings are somewhat less.  

> I know
> they will share a kill like komodo Dragons, but from what i know they don't
> hunt coopertively. They hunt and capure an animal and the other crocs in the
> area come over and 'help' eat the food.

They go further than sharing a kill. Niles co-operate to bring large
animals down. There's nothing complex about co-operation, even task
specialisation. Even insects do it. 

> > There are no modern predators that even come close to a Tyrannosaur
> > analogue. Thinking modern may not be the way to go, and may simply limit
> > our ability to postulate new theories (like this one).
> 
> Why not? Just because it was big? It's food was big. 

Because it was a hige bipedal predator. None of those around today.

> I think Lions and
> Tigers, who usually hunt similar sized prey, make a great example. 

Quadrupeds, with flexible backs and large mammalian brains. Verses
bipeds with stiff, birdie skeletons and little ol' archosaur brains.

> At least
> you can make some basic scientific claims and don't need to invent a new
> hunting technique, never seen before, just for T. rex.

Not seen - except in Nile crocs (with their little ol' archosaur
brains). :)

Besides, I think dinosaurs are different enough from modern carnivores
to warrant inventing new theories.

> And what if the juviniles die? Or it's a new mated pair with NO offspring?

Then, as I point out below, DO SOMETHING DIFFERENT. Any predator limited
to just one strategy is too specialised. When ecological trouble
comes-a-knockin', they'll be the first to go.

> 
> And you just don't run into a heard and scatter them, you have to drive them
> to the 'killers.' 

And if the 'killers' are scattered about in strategic places? Or they
didn't actually do this at all? Nothing I've proposed is carved in
stone. It's all conjectural. It works just as well without really young
animals acting as scatterers.

> You're making T. rex out to be MUCH more complex than any modern
> animal. Now I think T. rex was halfway intelegent, but this goes way beyond
> that. You're bassing there entire existance on the young, and that just
> doesn't work for me.

Not ENTIRELY. Please read ALL of a post before commenting. I've never
said they used JUST one strategy.

> It still doesn't explian what happens when the chain of babies is broken.

...which I've ALREADY explained in the post you are relying to. Please
read it ALL.

> Your supposing T. rex lived in large packs, any evidence for this? 

And then you say later...

> It's not a big assumption, they have several T. rex sites with multiple
> animals, they have a site with 12 Albertosaurs, seems like pretty good basic
> evidence to me.

There you go. You answered your own question. Of course a group of
animals need not be a 'pack'.

> why would
> they really need to be that fast? The animals they are hunting aren't
> exactly speedsters. 

I'm guessing a six metre long Tarbosaurus would have no trouble taking
down a six metre long Gallimimus. They were probably just as fast, too.
If tyrannosaurs were largely solitary (at least some species), then 6m
long animals wouldn't have hunted the same prey they could when they
grew to 12m. If they hunted in groups, and only the 12m full adults
hunted, that's an awefully long time to feed offspring!

> But again, if there are no young, how do the big ones eat?

READ THE POST. It's all there!

> Yes, but why risk loosing a kill due to adolesant stupidity? 

Young mammals may be "stupid" (or inexperienced), but then, a lot of
complex mammalian behaviour is learned. Amongst archosaurs, a lot of it
is instinctual. Birds don't have to learn how to make nests, or even
gather food. Many of then are hard-wired for it. Tyrannosaurs weren't
mammals.

> You never see
> young Lions, wolves ect. hunting with the adults. Why? Becasue they screw it
> up, you don't eat and you die. The sub adults might be allowed to watch, but
> not participate until they were were versed in the technique. And why would
> you have the inexperianced sub-adults teach something that the adult were
> much better at?

Exactly. "Experienced". Mammals learn. Archosaurs 'just do it' (as the
footwear slogan goes). Besides, youngsters can learn to hunt just as
well by watching as by actually doing. That is, if they need to learn at
all and it isn't hard-wired from birth.

Also, mammals are born relatively large, and grow fast. Compare the size
of a tyrannosaur egg to the adult. They hatch relatively smaller than
the adults than most mammals do (marsupials excepted, of course). A
sub-adult tyrannosaur (say, 3-6 metres long) may be several years old.
During which time it has managed not to die (not even once!), so must
have been doing something right. Unless the full adults take total care
of their offspring for a length of time comparable to human children
(which seems to be the exception amongst mammals).

> > That's one theory. Based on some modern animals. Besides, I've seen
> > dingos hurl themselves into a flock of magpie geese. The fit animals
> > react quickly and fly off. Sick or injured animals become apparent
> > immediately. I expect that arctic foxes do something similar, since the
> > geese can generally see them coming with not much cover about.
> 
>  But that's not really hunting in a pack is it?

Group hunting and true 'pack' hunting aren't necessarily the same. See
the many posts about 'pack' hunting in the archives.

>  They aren't collectively
> bringing down the birds, they're just running in to see if they can grab a
> few. You don't need a pack for that, any house cat can do this.

What is easy for a mammalian cat might be just the thing for an
archosaur-brained theropod. K.I.S.S. (another abreviation to look up!).
Perhaps a great strategy for a solitary sub-adult tyrannosaur. Sure it's
hit-and-miss, but better than just plain 'miss'.

> > Outside of an established group, sub-adults may be able to breed. A one
> > year old wolf can breed, but doesn't get the chance if the alpha pair
> > are around. Send it out by itself and it gets the chance.
> 
> Not really, MALE wolves might breed at that age, but females take 2 years
> before they have their first heat. But since they are able to breed wouldn't
> that make them adults?

Adults if they DO breed. In a pack structure, only the alpha pair act as
'full adults'. A one year old male will still behave much like a puppie
(especially to the alpha female). Humans reach sexual maturity long
before they are considered adults. Put them in a "Lord of the Flies"
situation, and you could have a next generation of human colonists
sooner than if they were in a Western social context.

> Animals generally don't work like humans in this aspect.

You differentiate between "human" and "animal"? I don't!

> > They pick off smaller prey, until their offspring are old enough to join
> > them. The complex pack-hunting of really large prey is worked up to
> > gradually. Arctic wolves raise young in pairs, hunting mostly rabbits.
> > Other wolves hunt in packs, and can bring down items larger than
> > themselves. Even lone wolves manage to survive. Being a predator means
> > being flexible.
> 
> If they can pick off smaller prey, which is most likey faster and quicker,
> why not just hunt the Big stuff?

Catching something fast and catching something big and more dangerous
are two very different kettles of fish.

> Plus you can't feed the chicks with just
> small stuff, not at that size. 

But I'm suggesting they MAY only have had to resort to small stuff if
there are no 3, 6 or even 9m long sub-adults about. Remember, this whole
thing started when I suggested that 12m tyrannosaurs were probably not
as fast or agile as they were when younger. Hence the use of younger
animals for the leg work.

> They need a big kill to feed everybody.

Not if there is no 'everybody'. You originally asked whether the adults
starved with no younger animals about. I suggested they do something
different, like take on smaller prey. Now you ask how they would have
fed young animals with smaller prey? Has logic put up the "gone fishin'"
sign?

> Arctic wolves will hunt larger prey like moose, it depends on what's in
> their area, I've seen them do it (in fact the male was 14 years old!)

Exactly. They'll hunt large animals if they can. If they're not about,
they do something else. The strategies involved in hunting moose are
quite different from those required to catch Arctic hares. Predators
using more than one strategy? Who'da thunk it!

> Yes, so why would they be so INFLEXABLE as to only hunting the big food
> items with the young? 

Because, as I've said ad nauseum, having a lot of young (but still large
by anyones' standards) animals about means you can take advantage of
both fast runners and plenty of 'fire power'. Some do the chasing.
Others help in dispatching the prey, and defending the carcass from
rivals.

> If they're so adept at hunting fast small animal and
> they have the ability to bring down large prey, why not just hunt the big
> stuff?

Because (*sigh*), if this IS a small group just starting out, they may
not have the numbers or experience to take on really large prey (if they
even need experience).

> > Besides, in social animals (and we're assuming the tyrannosaurs were
> > social - a BIG assumption), it's not just the adults that help feed
> > young. Offspring from previous years also help out. Year-old wolves
> > will regurgitate for the pups.
> 
> It's not a big assumption, they have several T. rex sites with multiple
> animals, they have a site with 12 Albertosaurs, seems like pretty good basic
> evidance to me. 

Back-flip in progress! See above.

> So why wouldn't the sub adults stay home and guard the
> juviniles, like modern animals do.

There we go again. Modern animals again...

Besides, a 6m sub-adult tyrannosaur would have been every bit as lethal
as a 6m adult Indosuchus. A group of 6m beasties is a formidable hunting
force. Throw in a few 9m all-purpose animals, and a smaller number of
12m behemouths, and you've got a lot of different skills to call upon.
Why not take full advantage of said varying skills?

> >> T.rex was as big as most of the food items it hunted.
> >
> > Most? How do we know what tyrannosaurs habitually hunted?
> > There is no rule that says a large predator needs to always hunt
> > large prey (wolves mostly eat things like mice).
> 
> That is a myth, wolves eat whatever food is in the area and what season it
> is. If there are large animals in the area wolves will prefer to hunt them.

Bingo. Flexibility in a predator. They CAN do things more than one
way...

> So what you're saying is that to hunt a large animal T. rex had to have
> juviniles? 

Once again... I've never said that. READ THE POST!! Smaller animals,
with their faster speeds and better agility, would be an asset. Not
essential, but if you've got it, why not use it to its full advantage?

> I'm not bying that, if they only ate small animals what would they
> be, Gallimimus? If they're doing so well on these small food items why
> switch to the larger ones?

For the same reason that modern carnivores do (great - now you've got ME
doing it!). Large prey involves greater risk, but also greater rewards.
If your hunting force is up to the challenge, and you can specialise
tasks and use strategy to lower the risks, then great. If you're not up
to the challenge, you're better off sticking to smaller, less risky
prey. 

Tyrannosaurs could have targeted adult ornithomimosaurs, or juveniles of
larger species (like hadrosaurs, ceratopians, etc). Lions will kill
infant elephants if they are desperate enough. They would NEVER take on
an adult though. Of course, if lions were as large as elephants...

> >> What would the advantage be in having such an extended
> >> family together?
> >
> > Complex pack-hunting of really large prey. Share the risk about.
> 
> Why risk the inexperiance young if hunting is so risky? Not very good
> parenting is it?

Hence why lots of little eggs were layed. Besides, if you are born with
abilities hard-wired, experience isn't as important as it is in many
mammals.

> > You wouldn't, necessaarily. A large group can do things that a smaller
> > group might not be able to, but the smaller group can still get by using
> > other hunting strategies. I'm not suggesting that tyrannosaurs had just
> > one strategy. A successful predator needs to be flexible.
> 
> But you need to look at the food items, would they support large packs?
> Maybe, maybe not. Butwhat evidance we have is more for small family groups.
> One or two T. rexex is plent big enough to kill anything in it's echo
> system, why would you need a large pack?

You don't NEED one. Hell, large tyrannosaur packs may not have even
existed. If you DID have a large pack, and you lived in an area that
could support it, then you can target prey items that a smaller 'pack'
may not have been capable of. I beleive I'm repeating myself again...

> Well, since we have no idea how long they took to gro up, I'm not going to
> speculate on this one;)

Which raises an interesting point: has anyone studied maturation rates
in dinosaurs? I believe someone once estimated that it took around ten
years for a brachiosaur to reach full adult size, but what of
tyrannosaurs? Exactly how long DID it take to reach the magic 12m
length? Enquiring minds need to know.

> >> Who feeds the adults then,
> >
> > Adults simply employ other hunting strategies, if required. Why not
> > scavenge for a while?
> 
> So while waiting for the babies to grow up, say a year and a half, the
> adults scavenged? 

Or targeted smaller, less dangerous prey. Or took the risk on larger
prey, if it was deemed worthwjile.

> Not very likely. They'd have to sit around waiting for
> food to die, plus feed the chicks, scavenging alone just can't support large
> animals.

In MODERN ecosystems. Sauropods are in short supply now-a-days. And they
had to die sometime.

> > If tyrannosaurs had an alpha pair, and they took many years to reach a
> > size capable of challenging them for breeding rights, then they may have
> > remained sub-adults for several years. Amongst mandrils, males only
> > reach sexual maturity if there is no dominant male around. When the
> > alpha male dies, one of the younger males suddenly has a growth spurt,
> > becoming larger and developing his "war paint". It actually happens
> > quite rapidly.
> 
> Yes, but wouldn't the big female rex be his mother? 

Whose mother? The mandril's?

> You still didn't answer
> the queston, who teaches the babies how to hunt if their are no sub adults
> to teach them?

Instinct? Trial and error on their part? Who knows? What am I, a
tyrannosaur hebavioural expert? :)

> > No, because... yep, you guessed it - they can employ other food
> > procuring strategies. Ambush animals along a game trail. Steal from
> > other carnivores. Turn on each other, if need be. There's more than one
> > way to feed a tyrannosaur.
> 
> Why are you so adverse to them hunting down a hadrosaur if they needed too?

I'm not. Sometimes risk is worth taking, if it's try or starve. I'm just
suggesting that having younger animals, 3, 6 or even 9m in length, would
be an advantage while hunting, since I can't see a 12m full adult
running for any length of time (or even running at all!). Not having the
advantage doesn't make hunting of really large prey impossible. Just
harder.

> > They wouldn't depend on them. Just utilise their greater speed and
> > agility. If it's not there to be utilised, then do something else. But
> > if they do happen to have a bunch of spritely sub-adults, why not
> > maximise their hunting strategy by assigning specialised tasks
> > (flushers, chasers, killers, defenders of the carcass).
> 
>  Why risk the young like that, taking say a 20 foot juvinile and placing it
> into a herd of 40 ft hadrosaurs is very dangerous. The juviniles would
> easily get trampled if not VERY careful. Again why risk the young like this?

Why not, if there are plenty or juvies around? Besides, fleet-of-foot 3m
tyrannosaurs may have been quick and agile enough to dance about adult
hadrosaurs with impunity. A 12m animal, with it's reduced
maneouverability, would have to be more careful. An injury to a
predator, no matter how small, can be a serious disadvantage.

> > Most modern carnivores ARE mostly scavengers. Why turn down a free meal
> > if you can get it?
>
> No, they are oppertunists, and they only scavenge when they find an easy
> meal or can't kill it for themselves.

Actually, I'd suggest they only hunt if there's no scavenged vittels to
be had.

> > Or the other way around. They scavenged, or resorted to other food
> > procuring strategies, if they didn't have a group structure that allowed
> > for more complex hunting strategies.
> 
> You can't have the largest predator in an echo system scavange for a living

Not for a living. Just if there is no other way of procuring food (the
"other food procuring strategies" in the above sentence).

> Scavengers are usually small so they can survive off the meager food they
> get.

MODERN scavengers. A VERY different ecosystem than the Mesozoic.

> But what if a desease runs through? All the babies would be very vunerable
> and most would die, then the adults can't eat. Or another animal raids the
> nest and eats all the eggs?

Not "can't eat". Just have to resort to something else, or take a few
more risks.

> It's a theroy that, to me doesn't hold up in a real echo system. 

By "real *ecosystem*" you mean a modern one?

> The
> scavenging thing is a differnt argument all together (hyenas are not
> scavengers anymore than wolves are!)

I'd say they probably scavenge equally. Being a scavenger is not
mutually exclusive with being a hunter.

> 
> > In fact, here's another theory: sub-adults chased prey into one of
> > several waiting adults (which are scattered about in strategic places).
> > The adult grabs the prey (in this case an Edmontosaurus) by the tail,
> > and uses its bulk to hold it steady (or as steady as a terrified
> > hadrosaur can be). The sub-adults arrive. They would have been too small
> > to subdue the prey themselves, but with it held securely by the tail by
> > a heavier adult, the more agile sub-adults can nip in and deliver quick
> > well-aimed bites to kill the animal. The larger adult is able to hold
> > the prey, but may have lacked sufficient manoeuverability to dispatch it
> > safely without being injured (and a badly injured tyrannosaur is in
> > serious trouble). By working together, and utilising the various skills
> > of different tyrannosaur size classes, the predators make a successful
> > kill.
> 
> They'd need arms for that.

What, and hug a large struggling prey item to your chest? A large head
on the end of a long neck puts more distance between the two.

> It's WAY too risky.

Being a hunting carnivore is risky.

> Why risk a kick from a
> edmontosaur, why not just have the adults bite the head off. Much less
> risky.

Could they kick backwards? Can an animal on all fours, with much smaller
forelimbs, risk losing traction by raising a hind leg in this situation?

> > Of course, if the adult was unable to hold the prey long enough for the
> > sub-adults to arrive, then it may have escaped, bearing the scars of its
> > close call. Now if only we could find an Edmontosaur skeleton with a
> > healed bite mark on its tail... :)
> 
> I think that bite mark would be the mark from hell.

Actually, it's the one from the Hell Creek formation :)

-- 
________________________________________________________________

Dann Pigdon                   Australian Dinosaurs:
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://www.alphalink.com.au/~dannj/
________________________________________________________________