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Re: Phorusrhacids killing large mammals in National Geographic Channel



> 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.

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.
-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. 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. 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.
-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.

> 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.

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?

> 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).

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.

> 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.

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. 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.
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. 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.

> 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.

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

> 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.

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

> it's possible that phorusrhacid
> eyesight was better-suited to night hunting than, say, modern raptors,

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

>> True, but killing smaller or less social carnivores does not imply
>> extinction of one of them.
>
> Not when they've evolved together, no.

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

> 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.

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.

> 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.

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.

>> 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

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. 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. 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.