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RE: Theropod bluff & hunting (was re Dilophosaurus Forelimb Bone Maladies



On 04.03.2016 08:02, Mike Habib wrote:
But the problem is not the ability to do damage so much as avoid receiving it.
A lion has enough weaponry to kill a mature cape buffalo if it strikes in the just the right 
way. The reason that lions almost never do this appears to be that there is a very good 
chance that the buffalo does lethal damage in the process. The would-be brontophage 
can’t just be capable of dealing wounds - to be a regular predator of giant prey, it 
must have a reliable way of avoiding severe injury (reliable enough that the behavior can be 
used regularly with only a very small chance of mishap). The head and neck mechanics work you 
cited (especially the work by Eric Snively) applies just as well to a case where an allosaur 
bites something 500-800 kg in mass, for example. That’s still relatively large prey 
for a 2 ton animal. Certainly large enough for the head-depression carving to be useful.

For a lion, this involves grappling the buffalo and applying pressure to its trachea until it asphyxiates. Its bite isn’t sufficiently damaging to reliably bring down something that large by other means.

A carnosaur (or a komodo dragon, or shark) would have had no such restriction, and consequently no need for much precision or getting into a direct strength contest with its prey. Their jaws are proportionately larger, and more importantly, are filled with serrated teeth that would cause proportionately much larger wounds and greater blood loss that are dangerous to even a very large prey item all by themselves (demonstrated by extant animals with this tooth morphology).

Yet in some regions Cape Buffalo are the preferred prey species of African Lions, such as Hwange where in males and females respectively they represent 56% and 33% of all prey items by count of kill sites. I don’t think that qualifies as "almost never".
https://urldefense.proofpoint.com/v2/url?u=http-3A__&d=CwID-g&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=x82f3Wlkwtmbr1z8IAt9jA&m=g7QBr42OmN1F5IUL0TNuUu4kChkAf1IAXWWgxYEY0eE&s=azoNeklNUYTPEBz99PJOsikRji9mYZruhmK35pX2f2M&e=
  journals.plos.org/plosone/article?id=10.1371/journal.pone.0055182
Other large animals are also a common part of their diet, we can potentially extend the same arguments to several other large mammals; Giraffes, Young Elephants, Wildebeest, Zebra and Greater Kudu, which are all at least similar in size to an adult lion. None of these animals is particularly unusual prey.

Now of course its tempting to attribute this to the lions only taking juveniles of those species, but (with the exception of elephants, whose newborns are already larger than adult lions anyway) that isn’t the case. There is enough footage demonstrating that they hunt and kill adult cape buffalo, despite the risk. Tigers accomplish similar feats, in their case to gaur. This is not counting the occasional report of either cat killing an adult elephant, which are what I would classify as "very rare".

The capacity for rapid neck motions noted by Snively et al. also fits what we 
would predict to see from a small prey specialist.
Yes, but not exclusively. What does not fit what we would predict to see from a small prey specialist though is that the skull is also tremendously strong, and most small-prey specialists don’t have jaws that could easily be mistaken to be adapted for brontophagy.

Now it is obvious we have different views regarding the relative macrophagous capabilities of a large theropod, but that some were very well-adapted for taking large prey is not exclusively my view, and would certainly provide a consistent explanation for a fair number of trace fossils (numerous bite marks, the paluxy track-site…) and pathological evidence of interactions (thagomizer pathology, healed bite marks on ceratopsians…).

Another point, this _Dilophosaurus_ is obviously not the only known theropod to have sustained serious trauma (think BHI 3033, FMNH PR 2081, SMA 0005, MOR 693…). Another thing that would be hard to explain if all theropods were the ecological equivalent of overgrown storks, but very easy to bring into accord with predation on large and dangerous prey. It’s also noteworthy that such injuries seem more common in large, presumed apex predatory theropods, but that could be an artifact of study or sampling bias.

Why would something run past the piles of 50 kg animals to attack the two ton 
one?
With inter- and intraspecific competition for prey (as well as the difficulty of a multi-ton predator to catch 50kg animals) it would be strange if predators didn’t tend to evolve to fill every available niche. In the extant world there may be fewer juveniles, but they undoubtedly exist, and yet there are a variety of predators for which killing large and dangerous adults seems to be worthwhile.

Yours sincerely,

Darius Nau
--
dariusnau@gmx.at
https://urldefense.proofpoint.com/v2/url?u=http-3A__www.paleo.keepfree.de&d=CwID-g&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=x82f3Wlkwtmbr1z8IAt9jA&m=g7QBr42OmN1F5IUL0TNuUu4kChkAf1IAXWWgxYEY0eE&s=0OqcOURvsFD05BDH0f4w8GJJQ8tPzeVuXmPcXUP9rTg&e=