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Re: Phorusrhacids killing large mammals in National Geographic Channel



> May be true, but I have to objections:
> -I cannot mind of any placental carnivoran which does not try to go
> for the neck or nape first when attacking an animal about their size.

I can think of a fair number . . . bears, for instance, which (when
they hunt) are just as likely to kill with the forepaws as by biting.
I'm not sure about polar bears, given their specialized existence. I
don't think dogs and hyenas do either, at least not strictly; they
certainly will in some cases, but in others - mainly in groups - just
pulling prey down is sufficient to then rip open the abdomen and
finish it off by eating it.

Also, the fact that most small carnivorans (badgers, raccoons,
wildcats, foxes, etc) generally do not hunt prey as large or larger
than themselves, while small mustelids do, means that we have to be
careful in considering that the latter may be highly specialized for
their technique - and therefore that we shouldn't really consider
their behavior in a vacuum independent of morphology. Behavior has to
be enabled by morphology, but the reverse is not necessarily true.

> -small cats also bite the nape and are agile yet they leave even
> smaller prey more commonly when they put some defense, as most other 
> carnivores do.

Right, again returning to my point that small cats (and most critters
in their size range) are not specialized in the way that small weasely
mustelids are. Mustelids in that weasel/ferret size range have a
number of biological advantages in that role, including the fact that
they are extremely flexible and can twist or yank themselves out of
disadvantageous positions quickly, and that as quite small mammals
they have a high metabolism and can therefore support the higher
reflexes needed to safely engage in potentially very risky behaviors.
Mongooses are similar in these respects, and they can effectively take
down highly venomous snakes, which is something most larger
carnivorans won't usually risk (I know they can in some instances -
I've seen footage of coyotes taking on rattlesnakes - but the behavior
is pretty commonplace in mongooses and not in most other carnivorans).

My point is that these animals, especially weasels, clearly have a
suite of specializations lacking in other carnivorans. That gives them
a distinctly different set of physical capabilities, and we have to
look at their behavior relative to what those capabilities will permit
in a natural selective context. I.e., their behaviors may well be
different from those of larger predators because the behaviors are
allowed/enabled/backed up by other pertinent traits lacking in other
creatures. Aggression alone is not responsible for their success.

Further, cougars and tigers can also individually kill prey much
larger than themselves (elk/guar, respectively), yet are not known for
being notably more aggressive than other big cats. Aggression can
complement morphological adaptations for taking on comparatively large
prey, but it cannot compensate for a lack of physical ability. As an
example, a hyper-aggressive cheetah will never take down a halfway
healthy Cape buffalo; clearly the physical limitations of the predator
are more crucial than the behavioral aspects at some threshold.

 In other size, jaguars are at least as agile as a
> peccari, and bites too hard at the back of the skull, yet it will
> leave prey putting some good defense.

It would be interesting to know if ice-age jaguars in the temperate
north were as cautious as those in tropical environments, given that
the risk of infection to prey-inflicted wounds is much higher in a
rainforest than in a temperate woodland. But I digress. The more
important point, as I see it, is that the jaguar's mass scales
differently and does not allow it to maneuver against prey as
effectively as a small mustelid. Reflexes matter, too, although I
can't quantify that.

 I never knew of a mustelid
> giving up a prey. Anyway, why can't a cat of the size of a domestic
> one kill an adult rabbit and an ermine can, even when the cat has
> stronger jaw muscles and canines, related to the absolutely larger
> head, and even when the cat also uses the same bite at the nape? I
> think they are bold.

As far as I'm aware, housecats *can* kill adult rabbits, but usually
prefer easier prey. Also, stoats have the advantage of being able to
tunnel after the rabbits, whereas cats would have to run them down
(which is impractical for the cat, at best).

> -killing prey fast is not contradictory with greater aggressivity and
> boldness. In fact, dubitative and cautious behaviour against prey
> which defends tend to prolongate the time of a confrontation between
> prey and predator in some cases.

Oh no, no, I'm not saying its contradictory or mutually exclusive or
anything like that. I'm just saying that boldness needs to be backed
up by ability. Being bold and then constantly dashing into situations
that get you injured or killed because you're not physically prepared
to handle them is not adaptive behavior. If you're bold *and* capable,
well all right then, but if you're bold and incompetent then your
courageous zeal becomes mere overconfidence, which in the wild will
limit your reproductive output right quick. Likewise if you're
generally but not superlatively capable, then it pays to be cautious.

>
> That Borhyaena hunted small prey does not mean it cannot also messed
> up with the largers. Many carnivores have a large range of size of
> their prey items, and the same may be true of phorusrhacids. I think
> Borhyaena it has some edge against larger animals, overall if they are
> rather slow, and if the borhyaenid was "brave"; at least its skull is
> strongly built to do so. After all, gluttons also mess with much
> larger prey, as caribou, so why would not a beast of slightly larger
> size and with a head roughly the size of a bear not mess with prey of
> at least similar size?

I think it may be fair to say that *Borhyaena* was adapted to kill
prey larger than most predators of its size normally could. It is
stocky (i.e. well-muscled with good leverage) and well-armed, via the
jaws. So it seems reasonable to suggest that perhaps it could subdue
prey that another 30-kg predator, say a dhole or a lynx, could not.
But if we're talking about direct competition with phorusrhacids and
whether they were more effective at killing the large mammals of the
time, I just don't think there's a comparison. We've got a 30-kg
mammal up against 100-kg birds; I'd say those aren't good odds.

About wolverines taking (adult) caribou - don't they have to attack
very weak individuals or ones that are trapped in snow? I've heard
tell of them even killing moose, if the moose is floundering in a
snowbank and can't flee or retaliate. But then again, lynx can take
large elk under similar circumstances, even though they can't
normally.

>
> Because lions and large canids are not so good digging for prey as
> mustelids. There were large fossil mustelids before, which may have
> had a similar habits to the digging larger terrestrial mustelids of
> our days. Gluttons largely excavate for frozen carrion. Also, bars
> unearth small rodents from time to time, but most bears are
> omnivorous. Polar bears, which are very carnivorous, in a different
> context, excavates for phocids.

First question is, then, were animals like *Borhyena* specialized for
digging? I wouldn't know, honestly, but I've never heard anything
about their limb structure indicating a burrowing habit on par with
badgers or other truly burrowing mustelids. (I'm also not sure how
weasels stack up against badgers, or either of those against dogs,
which themselves are really pretty effective diggers). I assume their
leverage would have made them fairly effective, but do we even know
what kinds of prey animals would have been inhabiting the burrows
there and then? More importantly, would phorusrhacids have been
seeking out such prey themselves? If not, then the mammal was
specialized on prey that the birds didn't rely on.

As to large (I'm presuming ~30+ kg) fossil mustelids, the only one I
can name - *Ekorus* - is notable for having a distinctly
*non*-burrowing limb structure, more akin to the upright cursorial-ish
stance of a leopard than the sprawling stance of a ratel. I know there
were some large wolverine relatives back in the Miocene, some of which
were the size of small bears, but I have no idea if they were
organized for burrowing.

Do the wolverines you mention dig through soil for that carrion, or
through snow? Packed snow can be hard, but it's still generally an
easier medium to get through than the average plot of dirt. Just
wondering.

Yeah, bears do quite a bit of digging, but as you implied, that's
mostly an extension of predominantly herbivorous/generalized foraging
habits. As for polar bears, their method is rather specialized, since
it involves that rearing-and-slamming action to punch through the snow
and take the seal by surprise. Obviously that may not be applicable
here . . .

>
> Although aggressivity helps defense from predators or competitors, it
> also helps dealing with aggresive prey which is not fast at running.
> Many prey items, because of not being fast, do not run and have a
> strategy of fighting back. So, a carnivore which is not fast (as a
> mustelid) may have a "niche" preying upon these slow prey, and if you
> have to fight your prey, it is better to be a good fighter.

That is a good point, but it has to be taken as relative to the size
of the animal (*Borhyaena*) itself. We also need to look at *relative*
speed: most of the South American herbivores of that time were slowish
by modern standards, but were probably still a fair bit faster than a
flat-footed, short-legged marsupial wanna-be. (Or much more heavily
armored/armed.) I don't doubt that *Borhyaena* was an effective
predator within its prey-size range, or that its prey-size range could
have been larger than usual for a predator of its mass, but I do doubt
whether that range extended up into any substantial overlap with that
of the larger phorusrhacids.

Gluttons
> attack beavers, which in one occasion are said to have killed the
> glutton (in an old Reader's Digest number). Cape badgers eat pythons,
> monitors and mongooses, all creatures capable of inflicting damage.

To be fair, ratels are completely psychotic. ;p

But they can (and do) back it up.


> Fighting in tunnels would occur mostly against prey, for mustelids are
> the biggest natural predators in the tunnels. And their main prey
> there are the rodents, which can be large and inflict nasty wounds.

And for this analogy to work in the sense of evolutionarily convergent
behavior, *Borhyaena* needs to be specialized for tunnel-fighting to a
comparable degree. I don't know that it is (seems unlikely, though).
Wolverines and Tasmanian devils seem like better comparisons to me.

 To
> deal with these animals, being good fighters is useful, either killing
> fast or being tenacious. Most animals at some time get dubitative,
> when facing an aggressive adversary, between the adaptive responses of
> fighting against it and trying to escape. I think the boldness of the
> mustelid may be useful to kill the animals which doubts this way,
> which in a moment of conflict,
> is not adaptive.

That's possible, I suppose, but I'm not sure it applies readily to
animals with much greater mass and therefore much different locomotor
traits. There are, of course, very good reasons why we don't see
200-kg weasel-shaped predators running around anywhere.

We also know that solitary predators in general usually prefer to take
prey smaller than themselves, or roughly their own size at most, and
there's no evidence of cooperative hunting in *Borhyaena*.


> I do not understand the relation of the relay system of the African
> wild dogs with their maximal prey size being the same of that of
> hyaenas.

That was to suggest that their hunting technique may be relevant -
although whether as an advantage (wearing out prey more efficiently)
or disadvantage (not working well against buffalo, which often cluster
tightly or turn to gang up on predators), I can't say exactly. But I
can say that zebras are pretty much the largest herbivores on the
savanna that aren't either hyper-aggressive, brawny, and well-armed
(like buffalo) or just obviously too large to hunt (like rhinos and
giraffes). So maximum prey size here may be more a factor of pragmatic
availability than physical limitations. I have little doubt that a
clan of 30 spotted hyenas could take down an animal with the mass of a
black rhino, but black rhinos have tough hide and horns to back up
their belligerence, making them too risky to hunt (regularly).

 If you have that hyaenas are stronger and better armed than
> the dogs, and with better chances of defending a prey against larger
> carnivores, then in principle they would have to be capable of killing
> larger prey and defending it in a greater measure than the dogs can.

Well, I think I agree; I do believe that hyenas should be capable of
taking larger prey than painted dogs. I think it's even been observed
to be true, IIRC. Hyenas are bigger (almost twice the size, in
females), they're proportionately more robust, and they hunt in bigger
groups. But the prey continuum on the savanna is not smooth; there's
nothing, or at least nothing common*, filling the gap between 250-kg
zebra and 1000-kg black rhinos - except for 750-kg Cape buffalo that
are extremely aggressive, have dangerous horns, and are known for
wheeling around and attacking predators en masse if the element of
surprise is lost on the part of the hunters. It's hypothetical,
admittedly, but I suspect that hyenas *would* take larger prey more
frequently than wild dogs do *if* there routinely were better options
than super-cantankerous buffalo and rhinos. I think we have to
consider the other attributes, and not only mass, of the prey
available when making pronouncements of "maximum" prey size.

*Eland are about the same size as buffalo, but IIRC they're not common
and often prefer different habitats than do painted dogs. Also, both
they and buffalo *are* occasionally hunted by painted dogs, so
"maximum prey size" and "habitual maximum prey size" are clearly
different.  (http://en.wikipedia.org/wiki/African_Wild_Dog). And, in
fact, this is also true for hyenas: they have been known to take adult
buffalo and even black rhinos, despite the fact that they focus on
midsized prey. (http://en.wikipedia.org/wiki/Spotted_Hyena#Hunting_and_diet)

We have to consider the efficiency of preferring smaller prey when
talking about prey size, since smaller prey is more common and
provides more calories ingested per calories expended. Whether or not
it is *possible* to kill larger prey is less relevant than the
energetics of the animals in question.

> Unless they are not so good in competing with lions (as when male
> lions appear). I do not think hyaenas are bolder or more ferocious
> than African wild dogs, so I cannot avail in this case the correlation
> between ferocity and carrion-eating.

I do. Hyenas are bigger and tougher than painted dogs and will
challenge other predators more readily. They are also smarter, so
perhaps they have a better sense of when to flee and when to press
their advantage, but my understanding is that the dogs rarely
challenge lions, -even when the pack is big enough to take on a small
number of the big cats. Hyenas, on the other hand, habitually do so,
and steal a sizable fraction of lion kills in some areas (the dogs do
not, anywhere, AFAIK). Spotted hyenas seem almost specialized,
behaviorally, for engaging lions in contests over carcasses. They
deliberately exclude each other in a way that neither does with other
predators.

And yet the greater cooperation of the dogs allows them to resist
hyenas more effectively than one would expect. In this case, a more
complex behavior than simple high aggression is at work, although in
this case it's made effective through greater precision rather than
through greater intensity.


Similarly, buzzards are driven
> off from carrion by raptorial birds, and jackals are far from
> ferocious at kill sites when there are larger carrion eaters.

Yes . . . *because they have nothing to back it up.* That's my point.
These animals cannot *afford* to be aggressive in those situations
because they have no proficiency in actually *winning.* The scavengers
that are best at holding kills are at least somewhat specialized to do
so, and high aggression is typically one of those specializations.
Wolverines are roughly the size of the larger jackals, and yet are
capable of intimidating much larger predators not simply because they
are more aggressive, but because they are much stronger and more
potently armed than jackals. (Including their spray.)

So my point about aggression is that it's primarily (IMO) about
defense, whether due to not being able to flee (slow, or trapped in a
burrow) or to holding kills. Jackals do not attempt to hold kills
against bigger predators because that's not their primary lifestyle
(which is hunting for small game), so naturally they have no
adaptations for it. For wolverines, it is a more significant part of
their lifestyle - especially in winter - and their adaptations make it
work. And this, in turn, makes it hard to generalize about higher
aggression leading to superior hunting capability. If that were just
broadly true, we'd expect to see predators off all stripes exhibiting
that feature, but we only see it in a smaller subset of the continuum.
I guess I'm looking for adaptive evolutionary explanations for why
some do and some don't show high aggression, since it must be
advantageous in many cases to *not* be hyperaggressive. That's just
the observed pattern.

 Even a
> lone cheetah may keep a hyaena at bay.

. . . Rarely. Lone hyenas have been known to steal kills from
leopards, which hypothetically are much better equipped to defend
themselves than cheetahs.


 For sure, juvenile buffalo is
> taken by hyaenas, and juveniles are generally more predated upon in
> most cases, but my case is about the maximal prey carnivorans hunt and
> the time in which they do so.

Right, and I think I've elaborated enough on the complexities of prey
selection for our purposes. Apparent limits on prey size are not
necessarily actual limits, nor is aggression a prime determinant of
hunting success.

>
>> Or why a small
>>> pack of these dogs, or the Cuon, can kill large prey way faster than
>>> the more dubitative wolf.
> Several wolves can spend hours killing a caribou, and many times will
> fail. 5 Lycaon open the gut of a similarly sized zebra and kill it
> almost at the moment they reach them. The same goes for Cuon, although
> in this case I do not know the maximal prey size. I was talking more
> about time of killing than maximal prey size in this point.

Actually, the Wikipedia article provides some possible reasons, as
well as a validation of the earlier argument about painted dogs
needing to eat faster than wolves: One, the dogs have the highest
bite-force-to-mass ratio of any living carnivoran, so they're actually
better at getting into prey than wolves are, at least for their size.
So that balances out against their lower mass. Also, they and a few
other canids, including the dholes we were discussing, have
specialized teeth which enable them to shear meat more efficiently and
thereby eat faster. It would indeed seem that competition with other
predators has driven an evolutionary response in these canids, one not
obeserved in wolves.

In any case, greater boldness seems at best to be secondary to
morphological (and cooperative behavioral) aspects.


 Wolves may
> kill fast once they are on top of some deer, but there can have passed
> some time of the confrontation before the wolf is on top. There is a
> report of a long struggle between a wolf and a Capreolus (which at the
> end, the deer won).

I was talking about group hunting there, not one-on-one. I can see a
lone wolf struggling with a healthy roe deer.


 Lycaon kills gazelles when it reaches it. Also,
> take into account Lycaon and Cuon are about half the size of northern
> timber wolves.

Yep, note again the proportionately stronger jaws and more tightly
knit cooperation of the painted dogs versus the wolves.

> May be, but most parsimonius is to think they were diurnal, as are
> their outgroups.

Oh I agree - I never tried to claim they were truly *nocturnal.* I
just meant that they could perhaps handle themselves better in
twilight or at night than can other raptors that are diurnal by
necessity, and that they could even have been crepuscular,
hypothetically. I guess we can't really tell that by brain endocasts .
. . oh well.

>
> And I do not see reason why extinction would be implied when they
> first met after evolving separately either.

Um . . . because of competitive exclusion or predation between
creatures with parallel niches? That's the implication, anyway. When
an invasive species arrives in a new habitat, it can expand at the
expense of its competitors because it lacks certain limitations in the
new environment. If it's not invasive, then it can get crushed by
entrenched natives that prevent it from getting a foothold. Only if
its preferred ecospace is not occupied in the new home will it blend
in without incident. The GAInterchange was a *colossal* episode of
species invading new territories and getting sorted out into new
ecosystems, with many invasive immigrants succeeding and non-invasive
immigrants getting repelled by well-established residents.

But the implication that phorusrhacids were victims of superior
"invady" forms is, again, moot. No good evidence for it. General
habitat alterations leading to stress on their populations and then
giving way to even more radical changes at the start of the
Pleistocene seems reasonable though.

>
> May be, but greagariousness at some moment of your life does not mean
> forming packs which act in a conjunct way. Bears aggregate at rivers,
> but I do not think that indicates they are social animals. This goes
> with respect to wether the bird may have been able to kill asleep
> placental carnivores, I supposed a large pack of wolves or lions would
> kill the bird if it killed one member of the pack when they were
> sleeping. But if they are just aggregated, they will not try to
> conjoinedly hunt the predator, in the same way most cats do not help
> each other bringing down the same prey individual.

All I meant there was that it may be a basal condition for cats to
have some degree of (potential for) sociality, which can be readily
acted upon to produce group hunting tactics under the right conditions
- i.e. open plains, lots of competitors.

>
> I once had the hypothesis that, as most carnivorous mammals use
> canine-baring as an intimidation means, and are thus able to get
> intimidated by some specimen with larger canines, that perhaps a saber
> tooth woud be able to intimidate most other carnivores because of the
> size of their canines, even perhaps the largest bears, which also use
> that signal. In such a case, even if solitary, a sabertooth would
> intimidate most carnivores. After all, a glutton may intimidate a pack
> of wolves. And even the largest of bears or the largest groups of
> lions and wolves would avoid getting into confrontation with an animal
> that not only bares large teeth, but can stab with them.

Actually, the sabers would have been *less* effective at defense than
conical canines, since they would have had to swing the jaws wider and
come in with the head at a more restricted angle - and that's without
considering the fragility of the sabers. They were much too brittle to
make good stabbing weapons; they were probably used for a specialized,
risky, but highly lethal throat bite.

>
> The problem with making assumptions is that the interpretations of the
> reality derive in a lesser degree from nature and more from ad hoc
> suppositions. Sometimes you have to make assumptions, but the less you
> make it is better. That's the reason for using parsimony, for example
> in phylogenetics, and not the idea that evolution occurs
> parsimoniously.

:P

OK, c'mon, I *made sure* to say "I assume" so that you and others
would know that I wasn't making a serious claim. It was a throwaway
comment based on intuition, and what I wrote was an attempt to
acknowledge that. I'm well aware of the basic scientific principle of
parsimony (gimme a little credit here), which is why I tried to be
clear that I wasn't making a real claim - because had that been the
case, I would have made the claim in ignorance, and that would be
either dumb or intellectually dishonest. But I can apply logical
inference to make a suggestion, which I did, as long as I note that's
what I'm doing, which I did.

Take it easy. : )


Thus, if we have that the beak can be used for general
> manipulation in most parrots, and for Brazilian nut-eating in large
> parrots, it requires less supositions the first choice, because the
> general manipulation can appear at any size and does not need a
> further supposition on the size of the original parrot. Also, on
> itself, general manipulation implies the beak will be used with almost
> anything the bird will handle.

OK . . . but what's the advantage? Finches eat small seeds, have no
problem with manipulating and de-husking them, and have in fact
evolved a mechanically and developmentally much simpler solution to
their situation than a parrot-like beak would be. If manipulation is
therefore not a problem for small seeds, but no bird with a finch-like
beak habitually cracks large nuts, then I think we have to consider
the simple volumetric scaling differences between large and small
seeds as being very relevant. And this implies that there *is* some
kind of evolutionary correlation between size and beak shape. Right?
If there are no finch-beaked birds cracking open two-centimeter palm
nuts, then it's more *parsimonious* to presume, at the very least,
that parrot-beaks are much better for this and allow their owners to
dominate that niche, correct?

Or not, just showing how the reasoning flows at that stage of analysis.

But from there we can make another parsimonious inference - that for
processing smaller seeds, a simpler solution would normally be favored
selectively (i.e. the straight but thickened finch beak, very popular
with small granivorous birds), and therefore that small-seed-eating
birds with what seems to be a needlessly complex solution (i.e. parrot
beaks, common but not to the same degree) probably have a more complex
history that involved other forces earlier in their evolution. In this
case, whether power or manipulation was more important doesn't matter,
so long as either is correlated with processing bigger seeds (which
demands bigger jaws, which demands a bigger bird, etc).

It was a quick assumption on my part, yes, and, indeed, it remains
untested - but as you can see, it wasn't a totally uniformed or
unreasonable one. ; )

 The originally nut-cracking devise will
> not be much different in structure than the hypothesis that the curved
> beak was originally meant to climb better or carry larger
> branches/pieces of food, and then being secondarily used in other
> ways.

True, although again it's probably something that evolved under
pressure from multiple forces, not just one or another. And of course
distinguishing between them is probably well nigh impossible at this
point.


By the way, don't feel too pressured to keep responding. This is
something I'm doing for fun in my spare time, so you don't have to
spend masses of effort on it if you have other things to do. ;p