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Re: Phorusrhacids killing large mammals in National Geographic Channel

True, Tommy, but I think these birds you mention, which take
relatively large prey, are birds with enlarged talons. As far as I
know, predatory birds which do not have enlarged talons do not kill
prey so large, and I suppose that the feet of phorusrhacids did not
function like that of raptorial birds, so the larger phorusrhacids
would not stab with talons hitting at high velocities (I think I heard
someone saying some phorusrhacids may have had raptorial feet, do you
know if something have been published on that?). However, if they were
able to outrun rheas, I suppose it would be easy to kill one of these
which is the same size of the phorusrhacid, because of their light
built. Against a more massive mammal of the same volume, things would
be more difficult to me.

In favor of the possibilities of phorusrhacids is that the beak seems
to be proportionally larger than in any Recent predatory bird, with
the possible exception of the shoebill. I suppose the enlarged beak
with pointed tips directed towards the prey would replace the stabbing
grasp produced by the feet in raptorial birds. Otherwise, the tip of
the upper jaw points downwards, while the tip of the lower jaw points
more anteriorly (and upwards). This reminds me of the orientation of
the incisors in rodents, some mammalian "insectivores", parrots and
rhynchosaurs. With the last of these the phorusrhacids share the
presence of a notch in the upper jaw to give place for the tip of the
lower jaw. The majority of these are not carnivorous, so... may this
suggest a not so entirely carnivorous diet for phorusrhacids?

2009/7/22 Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>:
> While it is true that most birds do not habitually kill prey heavier
> than about half their weight there are plenty of exceptions. Golden
> Eagles regularly kill adult foxes which are about the same weight as an
> eagle. Merlins frequently kill birds of nearly their own weight. Pygmy
> Owls at least occasionally kill prey considerably heavier than
> themselves (e. g. Mistlethrush). These are just examples I can think of
> right away, there are undoubtedly many more.
> I think an important factor in prey size is that birds frequently have
> to be able to lift and transport the prey. It is certainly quite
> possible to train birds to kill much larger prey than they normally do
> in the wild. Falconers for example have trained Golden Eagles to kill
> wolves, Peregrines and Goshawks to hunt cranes and herons and merlins to
> hunt pigeons.
> For a large flightless predator like a phorusrhacid I should think
> killing prey their own weight would be fairly easy.
> Tommy Tyrberg
> -----Ursprungligt meddelande-----
> Från: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] För Augusto
> Haro
> Skickat: den 21 juli 2009 20:21
> Till: lor@fibertel.com.ar
> Kopia: dinosaur
> Ämne: Re: Phorusrhacids killing large mammals in National Geographic
> Channel
> It seems to be that the claws of some phorusrhacids are laterally
> compressed instead of wide and blunt as in Ratites, so they are
> supposed to use their legs to kick small prey. As far as I know, the
> beak is tall and laterally compressed in at least some phorusrhacids.
> I suppose perhaps the pointed tip was used more as a canine to kill
> with a bite, which would serve for itself against small prey, but not
> with prey closer to their size. Unless phorusrhacids shake their heads
> to the sides like crocs and dogs, then they may easily kill animals
> half their size, but I do not know of birds which do so. Also, the
> long pointing tip of the upper jaw and the dorsoventrally tall beak
> seems to better suggest resistance to orthal (biting) forces than to
> lateral (shaking) forces (the wider snout of crocodylians better
> resist lateral forces).
> It seems that if the head was used as in the secretary bird or
> seriemas, the proportionally larger size of the head and beak in
> phorusrhacids suggest they killed proportionally larger prey when
> compared to the Recent birds previously mentioned.