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



On 04.03.2016 17:59, Mike Habib wrote:
I would flip this on its head: big cats, as high power precision biters, are 
unusually well adapted to kill large prey. That's why cats do so much more 
often than other living mammalian predators.
Well, I think its obvious I’m with Bakker on this one.

Also I think most mammals could be described as high-power biters, but this is another adaption born out of necessity; they cannot usually afford to lose teeth, so their teeth had to become relatively robust, which in turn means they aren’t effective at filling the roles of


Most varanids, some of which have teeth that are also good matches for 
theropods, are obligate small prey hunters (they cannot cut effectively with 
their teeth). Komodos are the exception, and their ability to carve muscle is 
not so much a matter of their teeth as it is a special form of cranial kinesis 
that allows them to saw with the jaws (see work by Domenic D'Amore).
D’Amore’s works are one of the main sources for the analogy between theropod and komodo dragon dentitions. I think in his dissertation he made it quite clear that he envisions them to have functioned in a similar manner.

Most sharks are also small game hunters. Even large adult great whites mostly 
hunt juvenile pinnipeds that can be consumed in a bite or two.
Yet they still closely follow the trend observed in other animals; Great whites can also take Elephant seals and right whale calves.

The adults are unusual prey
Hayward & Kerley 2005 cite Scheel (1993) as confirming that only 25% of kills in the Serengeti are juveniles, and go on to estimate the preferred prey sizes of African Lions at over 200kg.

Hayward, Matt W., and Graham I. H. Kerley. 2005. Prey preferences of the lion (Panthera leo). Journal of Zoology 267: 309–322. doi:10.1017/S0952836905007508.

Yes, there is enough footage to show that this occurs, but that doesn't mean 
it's common.  And that's for big cats, which as already noted, are unusually 
well adapted to kill large prey. (Much more so than a theropod).
But that’s the point, it also occurs in predators that are not big cats and have none of their peculiarities. Those animals do it by entirely different means and succeed all the same.

That depends on how we measure strength. Tyrannosaur skulls are truly strong in 
the way I think you're referring to.
I’m afraid that’s not the way I’m referring to it. I was specifically referring to the findings of Rayfield et al. 2001. These seem to clearly corroborate Bakker’s earlier hypotheses about _Allosaurus_, even if the details have been subject to some disagreement.

But they don't have a great number of particularly specific reinforcements to 
twisting or even compressive loads along the dorsal margin of the skull.
Because they didn’t need them, the most efficient way to avoid injury from prey is to avoid prolonged physical contact. Cats don’t do it because their teeth aren’t suitable for bite-and-let-go behaviour, but every predator that hunts large prey with teeth that are remotely analogous to carnosaurs does.

The jaws of small prey specialists can actually look a lot like those of 
related large prey capable taxa. Varanids are a good example, as are cats.
You implied that komodo dragon skulls are specifically adapted for flesh-tearing, and I certainly won’t argue with that, in fact I think certain theropods display analogous adaptions, but that is where you disagree. Are the same features present in other varanids and just go completely unused? Otherwise, looks are just deceiving.

Actually, this raises an interesting question for discussion: what do we 
predict that a small prey adapted theropod skull should look like, and what 
should a large prey specialist skull look like? I suspect we have different 
predictions.
Primarily shallower, more gracile, and also proportionately smaller, with additional differences in tooth morphology (often adaptions for handling and restraining small prey, as is present in _Dilophosaurus_). And less optimized for handling loads than _Allosaurus_ or the like, which may or may not be visible, but will surely be detectable using Finite Element Analysis. E.g. Spinosaurs have shallow skulls, inferred to have had relatively less resistance to bending. Their teeth have lost much (Baryonychines) or all (Spinosaurines) of their cutting function. And direct evidence of predatory interactions and diet supports a diet of fish, pterosaurs and juvenile dinosaurs, so they fit the presumed niche of "small-prey specialist" nicely on every account. I am also not aware of any spinosaur bite marks on large dinosaur skeletons, or spinosaur skeletons with peculiar pathologies inferred to have been directly or indirectly caused by a large animal (while what there is are foreign bodies from sawfish stuck in their jaws). Your previously used analogue of a stork is quite fitting here, although I must say I highly disagree with comparing _Allosaurus_ to a stork.

What would be your prediction?

True. But bite marks are often interpreted as carrion feeding traces.
Not if they are healed. The others, sure, but the question is how much rigour is in such statements or whether they just feel like they are making less of a bold statement if they assume scavenging than if they assume predation.

I disagree; living birds often injury each other  during intraspecific combat, 
for a start.
Certainly intraspecific combat is a potential explanation, but if they were so adept at causing injuries to conspecifics, and so willing to engage in risky behaviour, it seems strange they would absolutely avoid killing a similar-sized herbivore.

I'm not sure why that would be difficult.
It’s probably more difficult for a lion to catch a gazelle than it is to catch a buffalo.

Living taxa don't fill every ecology that we can come up with. True niches are 
not all available permutations.
Yes, but the niche I’m referring to isn’t a hypothetical permutation. It is one that seems to be filled in every extant ecosystem.

That's a good point, but since juveniles are still preferred in the modern 
world, I'd consider that to be the dominant trend.
I fully agree that it is a dominant trend, but using a variety of adaptions and techniques (others apart from doing it like a cat) extant top predators are by no means limited to juveniles and small prey as you seem to imply theropods were. Everything from cats, to canids, to bears, to varanids, to extant theropods, to delphinids and lamniforms at least occasionally kills prey its own size or larger. Theropds in general, as well as carnosaurs are among the most successful major predatory taxa ever, and they absolutely dominated terrestrial predatory niches of the mesozoic with very few exceptions. So from a purely parsimonious standpoint, it’s nothing far-fetched that I’m suggesting here (and sure enough it has been suggested quite frequently).

Yours sincerely,

Darius Nau
--
dariusnau@gmx.at
https://urldefense.proofpoint.com/v2/url?u=http-3A__www.paleo.keepfree.de&d=CwIDaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=x82f3Wlkwtmbr1z8IAt9jA&m=fXYcpYTS6-nJ8aa6b2hPesfnS_GoY15DmYdtjX5Ckec&s=on4F68_TS_bDGGcJji2gczv24pxc4N4nW4FifgYU-2Q&e=