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Re: Phorusrhacids killing large mammals in National Geographic Channel



> You are right in both observations. However, I think temper of the
> carnivore is important. For example, incisors of rodents are very
> dangerous and for sure would inflict great damage, yet mustelids kill
> them anyway, sometimes rodents larger than themselves. I never heard
> of rat-sized rodents killing ermines, for example, although it may
> have happened sometime… (lucky rodent).

Well, mustelids like that have a fairly specialized means of attack,
involving going for the back of the skull and biting into the brain to
achieve a quick kill. AFAIK that's a function of their small size,
which permits great flexibility and thus agility, whereas bigger
mustelids generally kill with a more conventional grasping/biting
method. So that example might not be applicable.

One anteater is known to have
> killed a 19 years old zoo keeper with his claws, and I heard something
> of anteaters even killing a jaguar.

!!!

But most of the times, the
> anteater is the prey. And it is true that modern pilosans are not fast
> reproductively, yet in the Cenozoic they were very abundant, both
> individually and in species number. And for a carnivore with such
> thick jaws as Borhyaena, turtles and small cingulates are other
> options. I am neither so sure all the small South American ungulates
> were as fast as proterotheriids and hegetotheres, not sure how fast
> small toxodonts, and some caviomorphs were.

All good points. Still, the key question here is a dual "were
phorusrhacids mainly predators/were they top predators" one, so if the
sparassodonts were hunting smaller prey, then the birds would still be
essentially unchallenged in that niche.

In addition, mustelids
> hunt prey faster than them, such as rabbits, just by digging, so this
> may be also the case for these marsupial predators.

Perhaps, although I'm not aware of any modern 30 kg predators that
survive mainly by digging for prey (not that they won't - witness
lions dragging warthogs out of aardvark burrows - but that's difficult
and atypical).

> Most aggresive creatures are commonly very stocky, with powerful jaws,
> and resisting much injury,

OK, but look at cause and effect here . . . it strikes me that a
slower carnivore *has* to be more aggressive, because fleeing will
often not be an option. And in order to rely on aggression, it needs
to be backed up by either sheer size (bears) or a stocky, powerful,
durable, and easily defensible build (wolverines, Tasmanian devils,
etc).

Also, aggression seems to me to be mainly concerned with the ability
to either defend in a context where escape is not an option (a burrow,
perhaps), and/or with the ability to take and hold carcasses against
other carnivores - like when wolverines sometimes win against bears or
wolves for control of carrion. Either way, the aggression is *not* an
adaptation for capturing prey, the selective pressures for which
should revolve around some combination of stealth, endurance,
technique, and sometimes social coordination. Being aggressive does
not by itself get you closer to your quarry, make you strong enough to
bring it down, or provide you with a technique to more easily secure
it or finish it off. It can supplement these things to a degree, but I
suspect it's mainly defensive/intraspecific in its evolutionary
origins.

I could be wrong, but that seems to make sense to me.

but that does not explain why the maximal
> prey size of a pack of African wild dogs (adult zebra) is the same
> than that of the much larger and more robust hyaenas.

Don't they have different hunting methods? The dogs use a relay system
that hyenas don't, AFAIK, and - an important obeservation - the hyenas
also scavenge much more frequently and with much greater success.
Zebras may be the largest available prey that isn't too aggressive to
be worth it (i.e. broadly similarly sized Cape buffalo, if we're
assuming that adults are more commonly taken than juveniles to begin
with), but the size and robustness of the hyenas allows them to
successfully compete with lions for carcasses, something the dogs
can't do - against lions *or* hyenas. Since lions and hyenas both get
a substantial fraction of their calories from carrion, but the dogs
don't, it would seem that size and ferocity are important not for
hunting, but for claiming carcasses. And access to calories is the
important consideration here, not only live-prey availability
contraints.

Or why a small
> pack of these dogs, or the Cuon, can kill large prey way faster than
> the more dubitative wolf.

That I'm going to give you, although I guess I don't know the average
size of the prey for either group. I know wolves can take down deer
awfully fast once they're on top of them, and that they of course take
much longer for big dangerous stuff like moose and bison, but I don't
know if *Lycaon* or dholes actually *kill* antelope/deer that much
faster, versus using more coordinated tactics/greater numbers to cut
off escape and thus actually *catch* prey faster. I also don't know
that they *ever* take bison- or moose-sized prey the way wolves can;
I've never heard of adult buffalo being taken by *Lycaon*, although
there are occasional, rather probably exaggerated claims of dholes
taking pretty big stuff - even gaur, IIRC.

 As you say, sociability does not imply large
> pack numbers. So, it would not be rare if the canids facing
> phorusrhacids have more of a wolf-like cautious behaviour, if forming
> small packs. Perhaps, if these carnivores respected the large bird
> when both were active, they may respect them also at night.

Could be true. Heck, since we don't have any modern analogues to a
really big predatory ground bird, it's possible that phorusrhacid
eyesight was better-suited to night hunting than, say, modern raptors,
which rely on specialized long-range eyesight because they hunt either
way up in the air or from a perch where prey may be distant.
Phorusrhacids probably didn't have those restrictions, so their sight
may have been more suited to their grounded nature.

>
> True, but killing smaller or less social carnivores does not imply
> extinction of one of them.

Not when they've evolved together, no. But I suppose the point is moot
since the birds and the northerners managed to coexist reasonably well
for a good million years or so.

Phorusrhacids may have where to hide their
> eggs, or perhaps even themselves, even among bushy vegetation. There
> seems to be some evidence, presented by some Argentinian
> paleontologists, that some large ground sloths may have digged large
> caves, where much other animals may have hided (many owls do so in
> rodent-digged tunnels). Anyway, I do not know many cases of predation
> of sleepy ostriches by mammalian carnivores, even when they would be
> easy to subdue even by a Cape badger because of their thin neck.
> Perhaps it is also matter of the awareness the birds can have.

That's also a good point. I guess I don't even know what kind of sleep
schedule birds typically have, and if it might be shorter or lighter
than mammalian sleep cycles.

>
> The less dominant carnivores are not necessarily doomed. Phorusrhacids
> face some danger similar to ostriches and cheetahs, so that their eggs
> are difficult to protect, as their youngs, they can be killed while
> sleeping, and they only can escape with velocity. In low population
> numbers, they may resemble cheetahs. Yet cheetahs do not go extinct,
> even with everybody robbing their food, killing their youngs, and for
> sure trying to kill asleep adults. After all, small cats live in
> Africa alongside the similarly agile, but larger and stronger,
> caracal. Or more generally speaking, you would have to perform a test
> of how much probable was the encounter between a carnivore and a
> sleepy bird given an area, with which frequency, and taking in account
> the population number of the bird and their predators, to see which
> impact such event will have in the population of the bird. I mean, to
> settle this question we should make many calculations. The same with
> the carnivore-phorusrhacid egg question. That the Iberian lynx can
> kill many other smaller carnivores do not imply these will be
> extinguished.

Right, and again, the point is probably not worth arguing given the
survival of the birds alongside placentals right up to the start of
glaciation.

> Yes, I heard the argument concerning sabertooths, anyway, I also heard
> of a lioness with a broken jaw which lived from locusts she alone
> hunted. Sociability is much restricted in cats, and is less
> parsimonious to infer given the extant outgroups for machairodonts
> (e.g., linsangs and the primitive character state for Felidae).

Interesting note about the lioness, although I can't say whether the
degree of stump-wear in the sabertooth would correspond to such a
behavior. And while sociality is indeed not typical, its roots are
more widespread, having been observed in (IIRC) lynxes, leopards, and
tigers, which are all surprising comfortable being around each other
in some contexts - even wild ones. Moreover, at least some sabertooths
(*Homotherium*, *Smilodon fatalis*) appear to have lived in open
habitats, where competition with such things as hyenas, wolves, lions,
and short-faced bears would have made group hunting far more
profitable and safe than solitary hunting - unless they could bolt to
trees like leopards, but that seems unlikely.

>
> Ok., this was for your assertion that large herbivorous birds were
> folivorous instead of seed-eaters. More for Diatryma than
> Phorusrhacos.

Which is fair, but it's just not a main point on my part. I think we
can readily agree that phorusrhacids were not (predominantly)
herbivorous.

>
> Perhaps you are right, but this requires smaller parrots evolved from
> larger ones (which goes against the general pattern envisaged by
> Cope’s Rule; anyway, this statement has not to be unviolable, I only
> would posit against it that it requires an assumption).

Well yeah, that's why I said "I assume." :p

 This theme of
> the explanation of the appearance of the parrot beak is also
> interesting. Although I do not doubt parrots bite hard, their enhanced
> cranial kinetic system suggests greater dexterity more than sheer
> force. Both strength and dexterity are correlated with avoiding seed
> toxic membranes, so in any case they fit the seed-eating selective
> scenario.

Interesting, and good point.

"Anyway, parrots do not only eat seeds, and they include many
> other fruits also, so it is also an alternative that manipulative
> abilities came first and then were used in very different ways,
> including nut-cracking (which also correlates well with manipulative
> abilities of feet, which are even of use to grasp the same nuts). It
> seems that greater manipulative capacities, along with brains capable
> of imagining how to use these tools, is also a selectively favourable
> trait which does not require specific sizes."

True, although many ducks eat fish despite having originally evolved
complex straining equipment for filtering small organisms; the point
is that an adaptive radiation can encompass behaviors and lifestyles
not orginally involved in selecting for the trait that permitted the
radiation in the first place. A beak that evolves for seeds initially
can, if any direct competition is removed, readily be used for
easier-to-process fruits (or leaves, or meat, depending) later on.

Still, it is of course a truism that traits don't evolve from one
cause in isolation from others, so it would make sense that superior
manipulation and intelligence could arise conjunctively as means of
exploiting an otherwise un(der)tapped resource.


>
> The wider beak suggests resistance to greater lateral forces, so yes,
> it is likely to help coping with relatively larger prey.

Right, but if there's a distinct body-mass correlation with the two
beak types, that would *in itself* constitute possible evidence of
bigger-prey-handling.


>
> As far as I know, from a 1980s paper by Marshall et al. in Science,
> faunal members of both the South and North American realms went on
> extinguishing all along the time the interchange continued. Perhaps
> the stress for the ecosystem as a whole, instead of one-to-one (or
> more) competition between species can explain that.

Hmm . . . general ecological stress coupled with a fairly sudden onset
of continental glaciation/aridity seems like a reasonable explanation.

"That's probably enough; faunal movement south plus climate change,
affecting a species in a dispersed, low-numbers, marginal reproduction
niche."

And that puts it even more precisely in context. Well said.

"But the wild dogs still have to compete in terms of _eating speed_
with the arrival time of the local pride of lions.  This may never
have been true of wolves; we don't know how they handled niche
partitioning when there were sabertooth cats and North American lions
and short-faced bears around to compete with, other than that they
were substantially larger than the extant ones."

Yeeaah . . . but similar pressures in similar lineages should usually
produce similar results. Today we *do* have examples of bear vs wolf
interactions in both North America and northern Asia, so we're not
totally in the dark, and if anything we'd expect to see even more
forceful reactions under a regime of many large predators roaming
about.

I mean, in Eurasia, wolves and their forerunners would have had to
deal with hyenas, lions, and bears at a minimum (with sabertooths and
tigers too, depending on the time and place), while in North America
there would have been some combination of lions, absolutely huge
bone-crunching short-faced bears, sabertooths of at least two
varieties, jaguars, and (perhaps exlcuding them across their range)
dire wolves. Hunting dogs have to deal with just lions and hyenas, and
that's bad enough.

Still, it's been more than ten thousand years, and wolves are pretty
plastic behaviorally, so who knows?

"So trying to extrapolate from the behaviour of extant wolves is very
risky, especially in context of giant ground-running predatory birds,
of which we have no examples."

And that should be taken to heart in general here. Bird behavior is
unlikely to closely mirror mammal behavior, because of anatomical
contraints if nothing else.

"All
these carnivores are timid and tend to run away if facing armed men,
even the wolverine."

*Armed* anything renders aggression pretty much useless, so naturally
any population of behaviorally adaptable critters that's been exposed
to what rifles can do is going to produce specimens which avoid them
at all costs.